path: root/lib/xixanta/src/assembler.rs

use crate::errors::{Error, EvalError};
use crate::mapping::Mapping;
use crate::node::{ControlType, NodeType, PNode, PString};
pub use crate::object::{Bundle, Context, Object, ObjectType};
use crate::opcodes::{AddressingMode, INSTRUCTIONS};
use crate::parser::Parser;
use std::cmp::Ordering;
use std::collections::HashMap;
use std::io::Read;
use std::ops::Range;

/// The mode in which a literal is expressed.
#[derive(Clone, PartialEq)]
pub enum LiteralMode {
    /// An 8/16 bit hexadecimal value.
    Hexadecimal,

    /// A byte expressed in binary format.
    Binary,

    /// A byte expressed in plain decimal format.
    Plain,
}

/// The different stages that the assembler goes through and which are relevant
/// for the process.
#[derive(PartialEq)]
pub enum Stage {
    /// The context is still building up (i.e. we don't have all the variable
    /// values, labels and their addresses yet).
    Context,

    /// An initial context is there, and we can already consume most bundles. We
    /// only need to leave some of them as pending if they require a value that
    /// is relative to the end size of segments.
    Bundling,

    /// We have most bundles, and we already know the size for all segments.
    /// Hence, we can resolve (crunch) the nodes that were pending to be
    /// bundled.
    Crunching,
}

#[derive(Clone, Debug)]
pub struct Macro {
    nodes: Range<usize>,
    args: Vec<PString>,
}

#[derive(Clone, Debug)]
pub struct PendingNode {
    mapping: usize,
    segment: usize,
    context: String,
    bundle_index: usize,
    node: PNode,
    labels_seen: usize,
}

pub struct Assembler {
    context: Context,
    literal_mode: Option<LiteralMode>,
    stage: Stage,
    macros: HashMap<String, Macro>,
    can_bundle: bool,
    mappings: Vec<Mapping>,
    current_mapping: usize,
    current_segment: usize,
    pending: Vec<PendingNode>,
    labels_seen: usize,
}

impl Assembler {
    pub fn new(mappings: Vec<Mapping>) -> Self {
        crate::mapping::assert(&mappings);

        Self {
            context: Context::new(),
            literal_mode: None,
            stage: Stage::Context,
            macros: HashMap::new(),
            can_bundle: true,
            mappings,
            current_mapping: 0,
            current_segment: 0,
            pending: vec![],
            labels_seen: 0,
        }
    }

    pub fn assemble(&mut self, reader: impl Read) -> Result<Vec<Bundle>, Vec<Error>> {
        // First of all, parse the input so we get a list of nodes we can work
        // with.
        let mut parser = Parser::default();
        if let Err(errors) = parser.parse(reader) {
            return Err(errors.iter().map(|e| Error::Parse(e.clone())).collect());
        }

        // Build the context by iterating over the parsed nodes and checking
        // where scopes start/end, evaluating values for variables, labels, etc.
        self.eval_context(&parser.nodes)?;

        // Finally convert the relevant nodes into binary bundles which can be
        // used by the caller.
        self.stage = Stage::Bundling;
        self.bundle(&parser.nodes)?;

        self.stage = Stage::Crunching;
        self.crunch_and_resolve_pending()
    }

    pub fn eval_context(&mut self, nodes: &[PNode]) -> Result<(), Vec<Error>> {
        let mut errors = Vec::new();
        let mut current_macro = None;

        for (idx, node) in nodes.iter().enumerate() {
            match &node.node_type {
                NodeType::Label => {
                    if !node.value.is_empty() {
                        if let Err(err) = self.context.set_variable(
                            &node.value,
                            &Object::new(
                                self.current_mapping,
                                self.current_segment,
                                ObjectType::Address,
                            ),
                            false,
                        ) {
                            errors.push(Error::Context(err));
                        }
                    }
                }
                NodeType::Assignment => {
                    // TODO: in fact, we cannot have assignments in many places.
                    if current_macro.is_some() {
                        errors.push(Error::Eval(EvalError {
                            message: "cannot have assignments inside of macro definitions"
                                .to_string(),
                            line: node.value.line,
                            global: false,
                        }));
                        continue;
                    }
                    match self.evaluate_node(node.left.as_ref().unwrap()) {
                        Ok(value) => {
                            if let Err(err) = self.context.set_variable(
                                &node.value,
                                &Object {
                                    bundle: value,
                                    mapping: self.current_mapping,
                                    segment: self.current_segment,
                                    object_type: ObjectType::Value,
                                },
                                false,
                            ) {
                                errors.push(Error::Context(err));
                            }
                        }
                        Err(e) => errors.push(Error::Eval(e)),
                    }
                }
                NodeType::Control(control_type) => {
                    // TODO: prevent nesting of control statements depending on
                    // a definition (e.g. .macro's cannot be nested inside of
                    // another control statement, but .if yes).

                    match control_type {
                        ControlType::StartMacro => {
                            // TODO: macros are only on the global scope.
                            //
                            // TODO: boy this is ugly. In fact, this stupid shit if
                            // current_macro might not be relevant anymore.
                            current_macro = Some(&node.left.as_ref().unwrap().value);
                            // TODO: watch out for weird shit on the name of arguments.
                            self.macros
                                .entry(node.left.as_ref().unwrap().value.value.clone())
                                .or_insert(Macro {
                                    nodes: Range {
                                        start: idx + 1,
                                        end: idx + 1,
                                    },
                                    args: node
                                        .args
                                        .clone()
                                        .unwrap_or_default()
                                        .into_iter()
                                        .map(|a| a.value)
                                        .collect::<Vec<_>>(),
                                });
                        }
                        ControlType::EndMacro => {
                            // TODO: if m.nodes.start < idx - 1 => empty macro

                            if let Some(name) = current_macro {
                                self.macros
                                    .entry(name.value.clone())
                                    .and_modify(|m| m.nodes.end = idx - 1);
                            }
                            current_macro = None;
                        }
                        _ => {}
                    }
                    if let Err(err) = self.context.change_context(node) {
                        // TODO: forbid if inside_macro
                        errors.push(Error::Context(err));
                    }
                }
                _ => {}
            }
        }

        if errors.is_empty() {
            Ok(())
        } else {
            Err(errors)
        }
    }

    pub fn bundle(&mut self, nodes: &Vec<PNode>) -> Result<(), Vec<Error>> {
        let mut errors = Vec::new();

        for node in nodes {
            match node.node_type {
                NodeType::Label => {
                    let segment =
                        &self.mappings[self.current_mapping].segments[self.current_segment];
                    let value = segment.offset.to_le_bytes();
                    let object = Object {
                        bundle: Bundle {
                            bytes: [value[0], value[1], value[2]],
                            size: 2,
                            address: 0,
                            cycles: 0,
                            affected_on_page: false,
                            resolved: false,
                        },
                        mapping: self.current_mapping,
                        segment: self.current_segment,
                        object_type: ObjectType::Address,
                    };

                    if !node.value.is_empty() {
                        if let Err(err) = self.context.set_variable(&node.value, &object, true) {
                            errors.push(Error::Context(err));
                        }
                    }
                    self.context.add_label(&object);
                }
                NodeType::Instruction => {
                    if self.can_bundle {
                        self.literal_mode = None;
                        match self.evaluate_node(node) {
                            Ok(bundle) => {
                                if let Err(e) = self.push_bundle(bundle, node) {
                                    errors.push(Error::Eval(e));
                                }
                            }
                            Err(e) => errors.push(Error::Eval(e)),
                        }
                    }
                }
                NodeType::Control(_) => {
                    if let Err(e) = self.evaluate_control_statement(node) {
                        errors.push(Error::Eval(e));
                    }
                }
                NodeType::Value | NodeType::Call => {
                    if let Err(e) = self.bundle_call(node, nodes) {
                        errors.push(Error::Eval(e));
                    }
                }

                _ => {}
            }
        }

        if errors.is_empty() {
            Ok(())
        } else {
            Err(errors)
        }
    }

    // TODO: maybe split?
    pub fn crunch_and_resolve_pending(&mut self) -> Result<Vec<Bundle>, Vec<Error>> {
        let mut errors = vec![];

        for pn in self.pending.clone() {
            self.labels_seen = pn.labels_seen;
            self.context.force_context_switch(&pn.context);

            match self.evaluate_node(&pn.node) {
                Ok(mut bundle) => {
                    let current = &self.mappings[pn.mapping].segments[pn.segment];
                    bundle.address = current.bundles[pn.bundle_index].address;

                    if pn.node.is_branch() {
                        bundle.resolved = true;
                        if let Err(e) = self.to_relative_address(&pn.node, &mut bundle) {
                            errors.push(Error::Eval(e));
                        }
                    }

                    let current_mut = &mut self.mappings[pn.mapping].segments[pn.segment];
                    current_mut.bundles[pn.bundle_index].bytes = bundle.bytes;
                }
                Err(e) => errors.push(Error::Eval(e)),
            }

            self.context.force_context_pop();
        }

        // Validate the mappings that have been evaluated before spitting it
        // out.
        if let Err(e) = crate::mapping::validate(&self.mappings) {
            return Err(vec![Error::Eval(e)]);
        }

        let mut res = vec![];

        for mapping in &mut self.mappings {
            for segment in mapping.segments.iter_mut() {
                // TODO: return a warning instead.
                if segment.is_empty() {
                    return Err(vec![Error::Eval(EvalError {
                        line: 0,
                        message: format!("segment '{}' is empty", segment.name),
                        global: true,
                    })]);
                }
                res.append(&mut segment.bundles);
            }

            let mut diff = mapping.size as isize - mapping.offset as isize;
            if diff < 0 {
                errors.push(Error::Eval(EvalError{
                        line: 0,
                        message: format!(
                            "exceeding segment size for '{}'; expecting {} bytes and {} bytes have already been seen",
                            mapping.name, mapping.size, mapping.offset,
                        ),
                        global: false,
                }));
            }

            if let Some(fill) = mapping.fill {
                while diff > 0 {
                    res.push(Bundle::fill(fill));
                    diff -= 1;
                }
            }
        }

        if errors.is_empty() {
            Ok(res)
        } else {
            Err(errors)
        }
    }

    fn bundle_call(&mut self, node: &PNode, nodes: &[PNode]) -> Result<(), EvalError> {
        // Get the macro object for the given identifier.
        let mcr = self
            .macros
            .get(&node.value.value)
            .ok_or(EvalError {
                line: node.value.line,
                message: format!(
                    "could not find a macro with the name '{}'",
                    node.value.value
                ),
                global: false,
            })?
            .clone();

        // Detect missmatches between the number of arguments provided and the
        // ones defined by the macro.
        let args = node.args.as_ref();
        let nargs = match args {
            Some(v) => v.len(),
            None => 0,
        };
        if mcr.args.len() != nargs {
            return Err(EvalError {
                line: node.value.line,
                message: format!(
                    "wrong number of arguments for '{}': {} required but {} given",
                    node.value.value,
                    mcr.args.len(),
                    nargs
                ),
                global: false,
            });
        }

        // If there are arguments defined by the macro, set their values now.
        if nargs > 0 {
            let mut margs = mcr.args.iter();

            for arg in args.unwrap().iter() {
                let obj = Object {
                    bundle: self.evaluate_node(arg)?,
                    mapping: self.current_mapping,
                    segment: self.current_segment,
                    object_type: ObjectType::Value,
                };
                self.context
                    .set_variable(margs.next().unwrap(), &obj, false)?;
            }
        }

        // And now replicate the nodes as contained inside of the macro
        // definition.
        for node in nodes
            .get(mcr.nodes.start..=mcr.nodes.end)
            .unwrap_or_default()
        {
            let bundle = self.evaluate_node(node)?;
            self.push_bundle(bundle, node)?;
        }

        Ok(())
    }

    fn push_bundle(&mut self, mut bundle: Bundle, node: &PNode) -> Result<(), EvalError> {
        let current = &mut self.mappings[self.current_mapping];
        bundle.address = current.start as usize + current.offset;
        current.offset += bundle.size as usize;
        current.segments[self.current_segment].offset += bundle.size as usize;

        if !bundle.resolved {
            self.pending.push(PendingNode {
                mapping: self.current_mapping,
                segment: self.current_segment,
                context: self.context.name().to_string(),
                bundle_index: current.segments[self.current_segment].bundles.len(),
                node: node.to_owned(),
                labels_seen: self.context.labels_seen(),
            });
        }
        current.segments[self.current_segment].bundles.push(bundle);

        Ok(())
    }

    fn evaluate_node(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        match node.node_type {
            NodeType::Instruction => Ok(self.evaluate_instruction(node)?),
            NodeType::Literal => Ok(self.evaluate_literal(node)?),
            NodeType::Control(_) => Ok(self.evaluate_control_expression(node)?),
            NodeType::Value => match self.literal_mode {
                Some(LiteralMode::Hexadecimal) => Ok(self.evaluate_hexadecimal(node)?),
                Some(LiteralMode::Binary) => Ok(self.evaluate_binary(node)?),
                Some(LiteralMode::Plain) => Ok(self.evaluate_decimal(node)?),
                None => {
                    if self.stage == Stage::Context {
                        // If we are just evaluating the context (e.g. parsing a
                        // variable), we'll assume that non-prefixed literals are
                        // just decimal values.
                        Ok(self.evaluate_decimal(node)?)
                    } else if node.value.is_anonymous_relative_reference() {
                        Ok(self.evaluate_anonymous_relative_reference(node)?)
                    } else if node.value.is_valid_identifier(true).is_err() {
                        // If this is not a valid identifier, just error out.
                        Err(EvalError {
                            message: "no prefix was given to operand".to_string(),
                            line: node.value.line,
                            global: false,
                        })
                    } else {
                        // This is actually a valid identifier! Try to fetch the
                        // variable.
                        match self.evaluate_variable(&node.value) {
                            Ok(v) => {
                                self.literal_mode = Some(LiteralMode::Hexadecimal);
                                Ok(v)
                            }
                            Err(err) => Err(EvalError {
                                message: format!(
                                    "no prefix was given to operand and {} either",
                                    err.message
                                ),
                                line: node.value.line,
                                global: false,
                            }),
                        }
                    }
                }
            },
            _ => Err(EvalError {
                message: format!("unexpected '{}' expression type", node.node_type),
                line: node.value.line,
                global: false,
            }),
        }
    }

    fn evaluate_anonymous_relative_reference(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        self.literal_mode = Some(LiteralMode::Plain);

        match &self.stage {
            Stage::Bundling => Ok(Bundle {
                bytes: [0, 0, 0],
                size: 2,
                address: 0,
                cycles: 0,
                affected_on_page: false,
                resolved: false,
            }),
            Stage::Crunching => {
                match self.context.get_relative_label(
                    node.value.to_isize(),
                    self.labels_seen,
                    &self.mappings,
                ) {
                    Ok(object) => Ok(object.bundle),
                    Err(e) => Err(EvalError {
                        line: node.value.line,
                        message: e.message,
                        global: false,
                    }),
                }
            }
            _ => panic!("unexpected evaluation of relative reference"),
        }
    }

    fn evaluate_hexadecimal(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        let mut chars = node.value.value.chars();
        let mut bytes = [0, 0, 0];
        let size: u8;

        match node.value.value.len() {
            1 => {
                bytes[0] = self.char_to_hex(chars.next(), node)?;
                size = 1;
            }
            2 => {
                bytes[0] = self.char_to_hex(chars.next(), node)? * 16;
                bytes[0] += self.char_to_hex(chars.next(), node)?;
                size = 1;
            }
            3 => {
                bytes[1] = self.char_to_hex(chars.next(), node)?;
                bytes[0] = self.char_to_hex(chars.next(), node)? * 16;
                bytes[0] += self.char_to_hex(chars.next(), node)?;
                size = 2;
            }
            4 => {
                bytes[1] = self.char_to_hex(chars.next(), node)? * 16;
                bytes[1] += self.char_to_hex(chars.next(), node)?;
                bytes[0] = self.char_to_hex(chars.next(), node)? * 16;
                bytes[0] += self.char_to_hex(chars.next(), node)?;
                size = 2;
            }
            _ => {
                if self.evaluate_variable(&node.value).is_ok() {
                    return Err(EvalError {
                        message: format!(
                            "you cannot use variables like '{}' in hexadecimal literals",
                            node.value.value
                        ),
                        line: node.value.line,
                        global: false,
                    });
                }
                return Err(EvalError {
                    message: "expecting a number of 1 to 4 hexadecimal digits".to_string(),
                    line: node.value.line,
                    global: false,
                });
            }
        }

        Ok(Bundle {
            bytes,
            size,
            address: 0,
            cycles: 0,
            affected_on_page: false,
            resolved: true,
        })
    }

    fn evaluate_binary(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        let string = node.value.value.as_str();
        let mut value = 0;
        let mut shift = 0;

        for c in string.chars().rev() {
            if c == '1' {
                let val = 1 << shift;
                value += val;
            } else if c != '0' {
                if self.evaluate_variable(&node.value).is_ok() {
                    return Err(EvalError {
                        message: format!(
                            "you cannot use variables like '{}' in binary literals",
                            string
                        ),
                        line: node.value.line,
                        global: false,
                    });
                }
                return Err(EvalError {
                    message: format!("bad binary format for '{}'", string),
                    line: node.value.line,
                    global: false,
                });
            }

            shift += 1;
        }

        match shift.cmp(&8) {
            Ordering::Less => Err(EvalError {
                message: "missing binary digits to get a full byte".to_string(),
                line: node.value.line,
                global: false,
            }),
            Ordering::Greater => Err(EvalError {
                message: "too many binary digits for a single byte".to_string(),
                line: node.value.line,
                global: false,
            }),
            Ordering::Equal => Ok(Bundle {
                bytes: [value as u8, 0, 0],
                size: 1,
                address: 0,
                cycles: 0,
                affected_on_page: false,
                resolved: true,
            }),
        }
    }

    fn evaluate_decimal(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        let string = node.value.value.as_str();
        if string.is_empty() {
            return Err(EvalError {
                message: "empty decimal literal".to_string(),
                line: node.value.line,
                global: false,
            });
        }

        let mut value = 0;
        let mut shift = 1;

        for c in string.chars().rev() {
            if shift > 100 {
                return Err(EvalError {
                    message: "decimal value is too big".to_string(),
                    line: node.value.line,
                    global: false,
                });
            }
            if c != '0' {
                match c.to_digit(10) {
                    Some(digit) => {
                        value += digit * shift;
                    }
                    None => {
                        if self.stage == Stage::Context {
                            return Err(EvalError {
                                message: format!(
                                    "variables must come from a constant expression, \
                                                  you cannot use other variables such as '{}' \
                                                  in variable definitions",
                                    string
                                ),
                                line: node.value.line,
                                global: false,
                            });
                        }
                        match self.evaluate_variable(&node.value) {
                            Ok(v) => return Ok(v),
                            Err(err) => {
                                return Err(EvalError {
                                    message: format!(
                                        "'{}' is not a decimal value and {} either",
                                        c, err.message
                                    ),
                                    line: node.value.line,
                                    global: false,
                                })
                            }
                        }
                    }
                }
            }

            shift *= 10;
        }
        if value > 255 {
            return Err(EvalError {
                message: "decimal value is too big".to_string(),
                line: node.value.line,
                global: false,
            });
        }

        Ok(Bundle {
            bytes: [value as u8, 0, 0],
            size: 1,
            address: 0,
            cycles: 0,
            affected_on_page: false,
            resolved: true,
        })
    }

    fn evaluate_literal(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        // The value of the literal is guaranteed to not be empty by the parser.
        // If that's not the case, then it's a bug.
        let val = node.value.value.as_str();
        assert!(!val.is_empty(), "the value for the literal was empty!");

        // Pick up the left node, which is the node to be further evaluated, and
        // determine the literal mode to be used.
        let left = node.left.as_ref().unwrap();

        let lm;
        if val.starts_with('$') {
            lm = Some(LiteralMode::Hexadecimal);
            if left.node_type == NodeType::Literal {
                return Err(EvalError {
                    message: "literal cannot embed another literal".to_string(),
                    line: node.value.line,
                    global: false,
                });
            }
        } else if val.starts_with('%') {
            lm = Some(LiteralMode::Binary);
            if left.node_type == NodeType::Literal {
                return Err(EvalError {
                    message: "literal cannot embed another literal".to_string(),
                    line: node.value.line,
                    global: false,
                });
            }
        } else {
            lm = Some(LiteralMode::Plain);
        }

        // And evaluate the left node.
        self.literal_mode = lm.clone();
        let expr = self.evaluate_node(left)?;
        self.literal_mode = lm;

        Ok(expr)
    }

    fn char_to_hex(&mut self, oc: Option<char>, source: &PNode) -> Result<u8, EvalError> {
        match oc {
            Some(c) => match c.to_digit(16) {
                Some(c) => Ok(c as u8),
                None => {
                    if (c.is_alphabetic() || c == '_')
                        && self.evaluate_variable(&source.value).is_ok()
                    {
                        return Err(EvalError {
                            message: format!(
                                "you cannot use variables like '{}' in hexadecimal literals",
                                source.value.value
                            ),
                            line: source.value.line,
                            global: false,
                        });
                    }
                    Err(EvalError {
                        message: "could not convert digit to hexadecimal".to_string(),
                        line: source.value.line,
                        global: false,
                    })
                }
            },
            None => Err(EvalError {
                message: "digit out of bounds".to_string(),
                line: source.value.line,
                global: false,
            }),
        }
    }

    fn evaluate_control_statement(&mut self, node: &PNode) -> Result<(), EvalError> {
        let changed;

        // This might just be a statement that changes the context (e.g.
        // ".macro", ".proc", etc.). In this case change the context and leave
        // early.
        (changed, self.can_bundle) = self.context.change_context(node)?;
        if changed {
            return Ok(());
        }

        // Otherwise, check the function that could act as a statement that
        // produces bundles.
        match node.node_type {
            NodeType::Control(ControlType::Byte) => self.push_evaluated_arguments(node, 1),
            NodeType::Control(ControlType::Addr) | NodeType::Control(ControlType::Word) => {
                self.push_evaluated_arguments(node, 2)
            }
            NodeType::Control(ControlType::Segment) => self.switch_to_segment(node),
            _ => Err(EvalError {
                line: node.value.line,
                message: format!(
                    "cannot handle control statement '{}' in this context",
                    node.value.value
                ),
                global: false,
            }),
        }
    }

    fn evaluate_control_expression(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        match node.node_type {
            NodeType::Control(ControlType::Hibyte) => self.evaluate_byte(node, true),
            NodeType::Control(ControlType::Lobyte) => self.evaluate_byte(node, false),
            _ => Err(EvalError {
                line: node.value.line,
                message: format!(
                    "cannot handle control statement '{}' as an expression in this context",
                    node.value.value
                ),
                global: false,
            }),
        }
    }

    fn evaluate_byte(&mut self, node: &PNode, high: bool) -> Result<Bundle, EvalError> {
        // The parser actually guarantees that the ".hibyte" and ".lobyte"
        // functions have exactly one argument. Hence, if this is not the case,
        // it's fine to let "unwrap" panic: it's a sign that's something is
        // wrong elsewhere.
        let arg = node.args.as_ref().unwrap().first().unwrap();

        // Get the bundle from the argument
        let mut bundle = self.evaluate_node(arg)?;

        // The bundle we got is going to be shuffled if we wanted the high byte.
        // After that, just zero out the rest (not mandatory but let's do it out
        // of consistency) and set the size to just one byte.
        if high {
            bundle.bytes[0] = bundle.bytes[1];
        }
        bundle.bytes[1] = 0x00;
        bundle.bytes[2] = 0x00;
        bundle.size = 1;

        Ok(bundle)
    }

    fn push_evaluated_arguments(&mut self, node: &PNode, nbytes: u8) -> Result<(), EvalError> {
        match &node.args {
            Some(args) => {
                for arg in args {
                    // Evaluate the argument as a node.
                    let mut bundle = self.evaluate_node(arg)?;

                    // If there is a missmatch between the expected number of
                    // bytes and what we got, we might be able to resolve it if
                    // we expected two bytes and only one was received: extend
                    // it by leading zeroes. Otherwise we have to error out:
                    // it's up to the programmer to either call `.hibyte` or
                    // something similar if that's whay they intended.
                    if bundle.size != nbytes {
                        match nbytes {
                            1 => {
                                return Err(EvalError {
                                    line: arg.value.line,
                                    message: "expecting an argument that fits into a byte"
                                        .to_string(),
                                    global: false,
                                })
                            }
                            2 => {
                                bundle.size = 2;
                                bundle.bytes[1] = 0x00;
                                bundle.bytes[2] = 0x00;
                            }
                            _ => panic!("bad argument when evaluating arguments"),
                        }
                    }
                    self.push_bundle(bundle, node)?;
                }
            }
            None => {
                return Err(EvalError {
                    line: node.value.line,
                    message: format!(
                        "expecting at least one argument for '{}'",
                        node.value.value.as_str(),
                    ),
                    global: false,
                })
            }
        }

        Ok(())
    }

    fn switch_to_segment(&mut self, node: &PNode) -> Result<(), EvalError> {
        // First of all, fetch the argument for the ".segment" statement and
        // validate that it has some basic format. Note that the existence of
        // exactly one argument is guaranteed by the parser and, thus,
        // `unwrap()` calls are not dangerous in this context.
        let arg = &node.args.as_ref().unwrap().first().unwrap();
        let val = &arg.value.value;
        if val.len() < 3 || !val.starts_with('"') || !val.ends_with('"') {
            return Err(EvalError {
                line: node.value.line,
                message: format!(
                    "segment declaration has to be written inside of double quotes ('{}' given instead)",
                    val,
                ),
                            global: false,
            });
        }

        // Validate the segment name.
        let name = &val[1..val.len() - 1];
        if name
            .chars()
            .any(|ch| !(ch.is_ascii_alphanumeric() || ch == '_' || ch == '-'))
        {
            return Err(EvalError {
                line: node.value.line,
                message: "segment name contains bad characters".to_string(),
                global: false,
            });
        }

        // You cannot change the segment if you are not in the global context.
        if !self.context.is_global() {
            return Err(EvalError {
                line: node.value.line,
                message: format!(
                    "cannot switch to segment '{}' if we are still inside of a scope ('{}')",
                    name,
                    self.context.name()
                ),
                global: false,
            });
        }

        // Find the segment being referenced and update the
        // `self.current_segment` accordingly.
        let mut found = false;
        for (mapping_idx, mapping) in self.mappings.iter().enumerate() {
            for (segment_idx, segment) in mapping.segments.iter().enumerate() {
                if segment.name == name {
                    self.current_mapping = mapping_idx;
                    self.current_segment = segment_idx;
                    found = true;
                    break;
                }
            }
        }
        if !found {
            return Err(EvalError {
                line: node.value.line,
                message: format!("unknown segment '{}'", name),
                global: false,
            });
        }
        Ok(())
    }

    fn evaluate_variable(&mut self, id: &PString) -> Result<Bundle, EvalError> {
        match self.context.get_variable(id, &self.mappings) {
            Ok(value) => Ok(value.bundle),
            Err(e) => Err(EvalError {
                message: e.message,
                line: id.line,
                global: false,
            }),
        }
    }

    fn evaluate_instruction(&mut self, node: &PNode) -> Result<Bundle, EvalError> {
        self.literal_mode = None;

        let (mode, mut bundle) = match &node.left {
            Some(_) => self.get_addressing_mode_and_bytes(node)?,
            None => (AddressingMode::Implied, Bundle::new(true)),
        };

        let mnemonic = node.value.value.to_lowercase();
        match INSTRUCTIONS.get(&mnemonic) {
            Some(entries) => match entries.get(&mode) {
                Some(values) => {
                    bundle.cycles = values.cycles;
                    bundle.size = values.size;
                    bundle.affected_on_page = values.affected_on_page;
                    bundle.bytes[2] = bundle.bytes[1];
                    bundle.bytes[1] = bundle.bytes[0];
                    bundle.bytes[0] = values.opcode.to_le_bytes()[0];
                }
                None => {
                    return Err(EvalError {
                        message: format!(
                            "cannot use {} addressing mode for the instruction '{}'",
                            mode, mnemonic
                        ),
                        line: node.value.line,
                        global: false,
                    })
                }
            },
            None => {
                return Err(EvalError {
                    message: format!("unknown instruction {}", mnemonic),
                    line: node.value.line,
                    global: false,
                });
            }
        }
        Ok(bundle)
    }

    fn get_addressing_mode_and_bytes(
        &mut self,
        node: &PNode,
    ) -> Result<(AddressingMode, Bundle), EvalError> {
        let left = &node.left;

        if left.as_ref().unwrap().node_type == NodeType::Indirection {
            self.get_from_indirect(node)
        } else if node.right.is_some() {
            self.get_from_indexed(node)
        } else {
            self.get_from_left(node, left.as_ref().unwrap())
        }
    }

    fn get_from_indirect(&mut self, node: &PNode) -> Result<(AddressingMode, Bundle), EvalError> {
        let left = node.left.as_ref().unwrap();

        match node.right.as_ref() {
            Some(right) => {
                if right.value.value.trim().to_lowercase() == "y" {
                    if left.right.is_some() {
                        return Err(EvalError {
                            message:
                                "it has to be either X addressing or Y addressing, not all at once"
                                    .to_string(),
                            line: node.value.line,
                            global: false,
                        });
                    }

                    let val = self.evaluate_node(left.left.as_ref().unwrap())?;
                    if val.size != 1 {
                        return Err(EvalError {
                            message: "address can only be one byte long on indirect Y addressing"
                                .to_string(),
                            line: node.value.line,
                            global: false,
                        });
                    }
                    return Ok((AddressingMode::IndirectY, val));
                }
                Err(EvalError {
                    message: "only the Y index is allowed on indirect Y addressing".to_string(),
                    line: node.value.line,
                    global: false,
                })
            }
            None => match left.right.as_ref() {
                Some(right) => {
                    if right.value.value.trim().to_lowercase() == "x" {
                        let val = self.evaluate_node(left.left.as_ref().unwrap())?;
                        if val.size != 1 {
                            return Err(EvalError {
                                message:
                                    "address can only be one byte long on indirect X addressing"
                                        .to_string(),
                                line: node.value.line,
                                global: false,
                            });
                        }
                        return Ok((AddressingMode::IndirectX, val));
                    }
                    Err(EvalError {
                        message: "only the X index is allowed on indirect X addressing".to_string(),
                        line: node.value.line,
                        global: false,
                    })
                }
                None => {
                    let val = self.evaluate_node(left.left.as_ref().unwrap())?;
                    if val.size != 2 {
                        return Err(EvalError {
                            message: "expecting a full 16-bit address".to_string(),
                            line: node.value.line,
                            global: false,
                        });
                    }
                    Ok((AddressingMode::Indirect, val))
                }
            },
        }
    }

    fn get_from_indexed(&mut self, node: &PNode) -> Result<(AddressingMode, Bundle), EvalError> {
        // Evaluate the left arm of the instruction.
        let left = node.left.as_ref().unwrap();
        let val = self.evaluate_node(left)?;

        // Ensure that the literal mode for the left arm ensures an address
        // instead of some bogus number.
        if let Some(lm) = &self.literal_mode {
            if *lm != LiteralMode::Hexadecimal {
                return Err(EvalError {
                    message: "indexed addressing only works with addresses".to_string(),
                    line: node.value.line,
                    global: false,
                });
            }
        }

        // Check the right arm to know the index being used.
        let right = node.right.as_ref().unwrap();
        match right.value.value.to_lowercase().trim() {
            "x" => {
                if val.size == 1 {
                    Ok((AddressingMode::ZeropageIndexedX, val))
                } else {
                    Ok((AddressingMode::IndexedX, val))
                }
            }
            "y" => {
                if val.size == 1 {
                    Ok((AddressingMode::ZeropageIndexedY, val))
                } else {
                    Ok((AddressingMode::IndexedY, val))
                }
            }
            _ => Err(EvalError {
                message: "can only use X and Y as indices".to_string(),
                line: node.value.line,
                global: false,
            }),
        }
    }

    fn get_from_left(
        &mut self,
        base: &PNode,
        left_arm: &PNode,
    ) -> Result<(AddressingMode, Bundle), EvalError> {
        if left_arm.value.value.to_lowercase().trim() == "a" {
            return Ok((AddressingMode::Implied, Bundle::new(true)));
        }

        let val = self.evaluate_node(left_arm)?;
        match self.literal_mode {
            Some(LiteralMode::Hexadecimal) => {
                if base.is_branch() || val.size == 1 {
                    Ok((AddressingMode::RelativeOrZeropage, val))
                } else {
                    Ok((AddressingMode::Absolute, val))
                }
            }
            Some(LiteralMode::Plain) => {
                if base.is_branch() {
                    Ok((AddressingMode::RelativeOrZeropage, val))
                } else if val.size > 1 {
                    match base.value.value.as_str() {
                        "jmp" | "jsr" => Ok((AddressingMode::Absolute, val)),
                        _ => Err(EvalError {
                            message: "immediate is too big".to_string(),
                            line: left_arm.value.line,
                            global: false,
                        }),
                    }
                } else {
                    Ok((AddressingMode::Immediate, val))
                }
            }
            _ => Err(EvalError {
                message: "left arm of instruction is neither an address nor an immediate"
                    .to_string(),
                line: left_arm.value.line,
                global: false,
            }),
        }
    }

    fn to_relative_address(&self, node: &PNode, bundle: &mut Bundle) -> Result<(), EvalError> {
        if !bundle.resolved {
            return Ok(());
        }

        let next = (bundle.address + 2) as u16;
        let target = u16::from_le_bytes([bundle.bytes[1], bundle.bytes[2]]);

        let byte = if target < next {
            let diff = target as i16 - next as i16;
            if diff < -128 {
                return Err(EvalError {
                    line: node.value.line,
                    message: "you cannot branch to this location: it's too far away".to_string(),
                    global: false,
                });
            }
            diff.to_le_bytes()[0]
        } else {
            let diff = target - next;
            if diff > 127 {
                return Err(EvalError {
                    line: node.value.line,
                    message: "you cannot branch to this location: it's too far away".to_string(),
                    global: false,
                });
            }
            diff.to_le_bytes()[0]
        };

        bundle.bytes[1] = byte;
        bundle.bytes[2] = 0;
        bundle.size = 2;

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::mapping::{SectionType, Segment, EMPTY};

    fn one_two() -> Vec<Mapping> {
        vec![
            Mapping {
                name: String::from("HEADER"),
                start: 0x0000,
                size: 0x0010,
                offset: 0,
                fill: Some(0x00),
                section_type: SectionType::Header,
                segments: vec![Segment {
                    name: String::from("HEADER"),
                    len: 0,
                    offset: 0,
                    bundles: vec![],
                }],
            },
            Mapping {
                name: String::from("ROM0"),
                start: 0x8000,
                size: 0x8000,
                offset: 0,
                fill: None,
                section_type: SectionType::PrgRom,
                segments: vec![
                    Segment {
                        name: String::from("ONE"),
                        len: 0,
                        offset: 0,
                        bundles: vec![],
                    },
                    Segment {
                        name: String::from("TWO"),
                        len: 0,
                        offset: 0,
                        bundles: vec![],
                    },
                ],
            },
        ]
    }

    fn minimal_header() -> Vec<Bundle> {
        vec![
            Bundle::fill(0x4E), // N
            Bundle::fill(0x45), // E
            Bundle::fill(0x53), // S
            Bundle::fill(0x1A), // MS-DOS \0
            Bundle::fill(0x01), // 1 * 8KB of PRG ROM
            Bundle::fill(0x00), // No CHR ROM
        ]
    }

    fn assert_instruction(line: &str, hex: &[u8]) {
        // Set up the empty mapper, but we have to push a minimal header
        // (otherwise an early assertion will fail), and we need to point to the
        // "CODE" segment (which is in the mapping indexed by 1).
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;

        // Grab the result passed the initial header.
        let res = &asm.assemble(line.as_bytes()).unwrap()[0x10..];

        assert_eq!(res.len(), 1);

        for i in 0..res[0].size {
            assert_eq!(hex[i as usize], res[0].bytes[i as usize]);
        }
    }

    fn assert_error(line: &str, id: &str, line_num: usize, global: bool, message: &str) {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;

        assert_error_with_assembler(&mut asm, line, id, line_num, global, message);
    }

    fn assert_error_with_assembler(
        asm: &mut Assembler,
        line: &str,
        id: &str,
        line_num: usize,
        global: bool,
        message: &str,
    ) {
        let res = asm.assemble(line.as_bytes());
        let msg = if global {
            format!("{} error: {}.", id, message)
        } else {
            format!("{} error (line {}): {}.", id, line_num, message)
        };
        assert_eq!(res.unwrap_err().first().unwrap().to_string().as_str(), msg);
    }

    fn assert_eval_error(line: &str, message: &str) {
        assert_error(line, "Evaluation", 1, false, message);
    }

    fn assert_context_error(line: &str, message: &str, line_num: usize) {
        assert_error(line, "Context", line_num, false, message);
    }

    // Empty

    #[test]
    fn empty_line() {
        for line in vec!["", "  ", ";; Comment", "  ;; Comment"].into_iter() {
            assert_error(line, "Evaluation", 1, true, "segment 'CODE' is empty");
        }
    }

    // Literal modes

    #[test]
    fn parse_binary() {
        assert_eval_error("adc #%0001", "missing binary digits to get a full byte");
        assert_eval_error("adc #%0001000", "missing binary digits to get a full byte");
        assert_eval_error(
            "adc #%000100001",
            "too many binary digits for a single byte",
        );
        assert_error(
            r#"
Variable = 42
adc %Variable
"#,
            "Evaluation",
            3,
            false,
            "you cannot use variables like 'Variable' in binary literals",
        );
        assert_instruction("adc #%10100010", &[0x69, 0xA2]);
    }

    #[test]
    fn parse_hexadecimal() {
        assert_eval_error(
            "adc #$12345",
            "expecting a number of 1 to 4 hexadecimal digits",
        );
        assert_eval_error("adc $AW", "could not convert digit to hexadecimal");
        assert_error(
            r#"
Variable = 42
adc $Variable
"#,
            "Evaluation",
            3,
            false,
            "you cannot use variables like 'Variable' in hexadecimal literals",
        );
        assert_error(
            r#"
Four = 4
adc $Four
"#,
            "Evaluation",
            3,
            false,
            "you cannot use variables like 'Four' in hexadecimal literals",
        );
        assert_instruction("adc $AA", &[0x65, 0xAA]);
        assert_instruction("adc $10", &[0x65, 0x10]);
        assert_instruction("adc $10AB", &[0x6D, 0xAB, 0x10]);
    }

    #[test]
    fn parse_decimal() {
        assert_eval_error("adc #256", "decimal value is too big");
        assert_eval_error("adc #2000", "decimal value is too big");
        assert_eval_error(
            "adc #2A",
            "'A' is not a decimal value and could not find variable '2A' in the global scope either",
        );
        assert_instruction("adc #1", &[0x69, 0x01]);
    }

    // Variables

    #[test]
    fn scoped_variable() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
.scope One   ; This is a comment
  adc #Variable

  Variable = $20
.endscope

.scope Another
  Variable = $40
.endscope

Variable = $30
adc #Variable

adc #One::Variable
adc #Another::Variable
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 4);
        let instrs: Vec<[u8; 2]> = vec![[0x69, 0x20], [0x69, 0x30], [0x69, 0x20], [0x69, 0x40]];

        for i in 0..4 {
            assert_eq!(res[i].size, 2);
            assert_eq!(res[i].bytes[0], instrs[i][0]);
            assert_eq!(res[i].bytes[1], instrs[i][1]);
        }
    }

    #[test]
    fn bare_variables() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
Variable = 4
adc Variable
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 1);

        let instr = res.first().unwrap();
        assert_eq!(instr.size, 2);
        assert_eq!(instr.bytes[0], 0x65);
        assert_eq!(instr.bytes[1], 0x04);
    }

    #[test]
    fn bad_variable_but_valid_identifier_in_instruction() {
        assert_eval_error(
            "adc Variable",
            "no prefix was given to operand and could not find variable 'Variable' in the global scope either",
        );
        assert_eval_error(
            "adc Scoped::Variable",
            "no prefix was given to operand and did not find scope 'Scoped' either",
        );
    }

    #[test]
    fn redefined_variable() {
        assert_context_error(
            r#"
.scope One
  Variable = 1
.endscope

Variable = 1
Yet = 3
Yet = 4
"#,
            "'Yet' already defined in the global scope: you cannot re-assign variables",
            8,
        );
    }

    #[test]
    fn unknown_variables() {
        assert_eval_error(
            "lda #Variable",
            "'e' is not a decimal value and could not find variable \
                      'Variable' in the global scope either",
        );
        assert_eval_error(
            "lda #Scope::Variable",
            "'e' is not a decimal value and did not find scope 'Scope' either",
        );
        assert_error(
            r#"
.scope Scope
.endscope
lda #Scope::Variable
"#,
            "Evaluation",
            4,
            false,
            "'e' is not a decimal value and could not find variable 'Variable' in 'Scope' either",
        );
    }

    // Regular instructions

    #[test]
    fn bad_addressing() {
        assert_eval_error(
            "unknown #$20",
            "could not find a macro with the name 'unknown'",
        );
        assert_eval_error(
            "adc ($2002, x)",
            "address can only be one byte long on indirect X addressing",
        );
        assert_eval_error(
            "adc ($2002), y",
            "address can only be one byte long on indirect Y addressing",
        );
        assert_eval_error(
            "adc ($20, y)",
            "only the X index is allowed on indirect X addressing",
        );
        assert_eval_error(
            "adc ($20), x",
            "only the Y index is allowed on indirect Y addressing",
        );
        assert_eval_error("jmp ($20)", "expecting a full 16-bit address");
        assert_eval_error("adc $20, z", "can only use X and Y as indices");
        assert_eval_error(
            "adc ($2000)",
            "cannot use indirect addressing mode for the instruction 'adc'",
        );
        assert_eval_error("lda 12", "no prefix was given to operand")
    }

    #[test]
    fn adc() {
        assert_instruction("adc #20", &[0x69, 0x14]);
        assert_instruction("adc #$20", &[0x69, 0x20]);
        assert_instruction("adc $2002", &[0x6D, 0x02, 0x20]);
        assert_instruction("adc $20", &[0x65, 0x20]);
        assert_instruction("adc $20, x", &[0x75, 0x20]);
        assert_instruction("adc $2002, x", &[0x7D, 0x02, 0x20]);
        assert_instruction("adc $2002, y", &[0x79, 0x02, 0x20]);
        assert_instruction("adc ($20, x)", &[0x61, 0x20]);
        assert_instruction("adc ($20), y", &[0x71, 0x20]);
    }

    #[test]
    fn sbc() {
        assert_instruction("sbc #$20", &[0xE9, 0x20]);
        assert_instruction("sbc $2002", &[0xED, 0x02, 0x20]);
        assert_instruction("sbc $20", &[0xE5, 0x20]);
        assert_instruction("sbc $20, x", &[0xF5, 0x20]);
        assert_instruction("sbc $2002, x", &[0xFD, 0x02, 0x20]);
        assert_instruction("sbc $2002, y", &[0xF9, 0x02, 0x20]);
        assert_instruction("sbc ($20, x)", &[0xE1, 0x20]);
        assert_instruction("sbc ($20), y", &[0xF1, 0x20]);
    }

    #[test]
    fn shift() {
        // asl
        assert_instruction("asl", &[0x0A]);
        assert_instruction("asl a", &[0x0A]);
        assert_instruction("asl $20", &[0x06, 0x20]);
        assert_instruction("asl $20, x", &[0x16, 0x20]);
        assert_instruction("asl $2002", &[0x0E, 0x02, 0x20]);
        assert_instruction("asl $2002, x", &[0x1E, 0x02, 0x20]);

        // lsr
        assert_instruction("lsr", &[0x4A]);
        assert_instruction("lsr a", &[0x4A]);
        assert_instruction("lsr $20", &[0x46, 0x20]);
        assert_instruction("lsr $20, x", &[0x56, 0x20]);
        assert_instruction("lsr $2002", &[0x4E, 0x02, 0x20]);
        assert_instruction("lsr $2002, x", &[0x5E, 0x02, 0x20]);
    }

    #[test]
    fn rotate() {
        // rol
        assert_instruction("rol", &[0x2A]);
        assert_instruction("rol a", &[0x2A]);
        assert_instruction("rol $20", &[0x26, 0x20]);
        assert_instruction("rol $20, x", &[0x36, 0x20]);
        assert_instruction("rol $2002", &[0x2E, 0x02, 0x20]);
        assert_instruction("rol $2002, x", &[0x3E, 0x02, 0x20]);

        // ror
        assert_instruction("ror", &[0x6A]);
        assert_instruction("ror a", &[0x6A]);
        assert_instruction("ror $20", &[0x66, 0x20]);
        assert_instruction("ror $20, x", &[0x76, 0x20]);
        assert_instruction("ror $2002", &[0x6E, 0x02, 0x20]);
        assert_instruction("ror $2002, x", &[0x7E, 0x02, 0x20]);
    }

    #[test]
    fn and() {
        assert_instruction("and #$20", &[0x29, 0x20]);
        assert_instruction("and $2002", &[0x2D, 0x02, 0x20]);
        assert_instruction("and $20", &[0x25, 0x20]);
        assert_instruction("and $20, x", &[0x35, 0x20]);
        assert_instruction("and $2002, x", &[0x3D, 0x02, 0x20]);
        assert_instruction("and $2002, y", &[0x39, 0x02, 0x20]);
        assert_instruction("and ($20, x)", &[0x21, 0x20]);
        assert_instruction("and ($20), y", &[0x31, 0x20]);
    }

    #[test]
    fn or() {
        // eor
        assert_instruction("eor #$20", &[0x49, 0x20]);
        assert_instruction("eor $20", &[0x45, 0x20]);
        assert_instruction("eor $20, x", &[0x55, 0x20]);
        assert_instruction("eor $2002", &[0x4D, 0x02, 0x20]);
        assert_instruction("eor $2002, x", &[0x5D, 0x02, 0x20]);
        assert_instruction("eor $2002, y", &[0x59, 0x02, 0x20]);
        assert_instruction("eor ($20, x)", &[0x41, 0x20]);
        assert_instruction("eor ($20), y", &[0x51, 0x20]);

        // ora
        assert_instruction("ora #$20", &[0x09, 0x20]);
        assert_instruction("ora $20", &[0x05, 0x20]);
        assert_instruction("ora $20, x", &[0x15, 0x20]);
        assert_instruction("ora $2002", &[0x0D, 0x02, 0x20]);
        assert_instruction("ora $2002, x", &[0x1D, 0x02, 0x20]);
        assert_instruction("ora $2002, y", &[0x19, 0x02, 0x20]);
        assert_instruction("ora ($20, x)", &[0x01, 0x20]);
        assert_instruction("ora ($20), y", &[0x11, 0x20]);
    }

    #[test]
    fn load() {
        // lda
        assert_instruction("lda #$20", &[0xA9, 0x20]);
        assert_instruction("lda $20", &[0xA5, 0x20]);
        assert_instruction("lda $20, x", &[0xB5, 0x20]);
        assert_instruction("lda $2002", &[0xAD, 0x02, 0x20]);
        assert_instruction("lda $2002, x", &[0xBD, 0x02, 0x20]);
        assert_instruction("lda $2002, y", &[0xB9, 0x02, 0x20]);
        assert_instruction("lda ($20, x)", &[0xA1, 0x20]);
        assert_instruction("lda ($20), y", &[0xB1, 0x20]);

        // ldx
        assert_instruction("ldx #$20", &[0xA2, 0x20]);
        assert_instruction("ldx $20", &[0xA6, 0x20]);
        assert_instruction("ldx $20, y", &[0xB6, 0x20]);
        assert_instruction("ldx $2002", &[0xAE, 0x02, 0x20]);
        assert_instruction("ldx $2002, y", &[0xBE, 0x02, 0x20]);

        // ldy
        assert_instruction("ldy #$20", &[0xA0, 0x20]);
        assert_instruction("ldy $20", &[0xA4, 0x20]);
        assert_instruction("ldy $20, x", &[0xB4, 0x20]);
        assert_instruction("ldy $2002", &[0xAC, 0x02, 0x20]);
        assert_instruction("ldy $2002, x", &[0xBC, 0x02, 0x20]);
    }

    #[test]
    fn jump() {
        assert_instruction("jsr $2002", &[0x20, 0x02, 0x20]);

        assert_instruction("jmp $2002", &[0x4C, 0x02, 0x20]);
        assert_instruction("jmp ($2002)", &[0x6C, 0x02, 0x20]);
    }

    #[test]
    fn inc_dec_instructions() {
        // inc
        assert_instruction("inc $10", &[0xE6, 0x10]);
        assert_instruction("inc $1000", &[0xEE, 0x00, 0x10]);
        assert_instruction("inc $10, x", &[0xF6, 0x10]);
        assert_instruction("inc $1000, x", &[0xFE, 0x00, 0x10]);

        assert_instruction("inx", &[0xE8]);

        assert_instruction("iny", &[0xC8]);

        // dec
        assert_instruction("dec $10", &[0xC6, 0x10]);
        assert_instruction("dec $1000", &[0xCE, 0x00, 0x10]);
        assert_instruction("dec $10, x", &[0xD6, 0x10]);
        assert_instruction("dec $1000, x", &[0xDE, 0x00, 0x10]);

        assert_instruction("dex", &[0xCA]);

        assert_instruction("dey", &[0x88]);
    }

    #[test]
    fn transfer_instructions() {
        assert_instruction("tax", &[0xAA]);
        assert_instruction("tay", &[0xA8]);
        assert_instruction("tsx", &[0xBA]);
        assert_instruction("txa", &[0x8A]);
        assert_instruction("txs", &[0x9A]);
        assert_instruction("tya", &[0x98]);
    }

    #[test]
    fn return_instructions() {
        assert_instruction("rti", &[0x40]);
        assert_instruction("rts", &[0x60]);
    }

    #[test]
    fn set_clear_instructions() {
        assert_instruction("clc", &[0x18]);
        assert_instruction("cld", &[0xD8]);
        assert_instruction("cli", &[0x58]);
        assert_instruction("clv", &[0xB8]);

        assert_instruction("sec", &[0x38]);
        assert_instruction("sed", &[0xF8]);
        assert_instruction("sei", &[0x78]);
    }

    #[test]
    fn push_pull_instructions() {
        assert_instruction("pha", &[0x48]);
        assert_instruction("php", &[0x08]);
        assert_instruction("pla", &[0x68]);
        assert_instruction("plp", &[0x28]);
    }

    #[test]
    fn nop_brk() {
        assert_instruction("nop", &[0xEA]);
        assert_instruction("brk", &[0x00]);
    }

    #[test]
    fn cmp() {
        // cmp
        assert_instruction("cmp #$20", &[0xC9, 0x20]);
        assert_instruction("cmp $2002", &[0xCD, 0x02, 0x20]);
        assert_instruction("cmp $20", &[0xC5, 0x20]);
        assert_instruction("cmp $20, x", &[0xD5, 0x20]);
        assert_instruction("cmp $2002, x", &[0xDD, 0x02, 0x20]);
        assert_instruction("cmp $2002, y", &[0xD9, 0x02, 0x20]);
        assert_instruction("cmp ($20, x)", &[0xC1, 0x20]);
        assert_instruction("cmp ($20), y", &[0xD1, 0x20]);

        // cpx
        assert_instruction("cpx #$20", &[0xE0, 0x20]);
        assert_instruction("cpx $2002", &[0xEC, 0x02, 0x20]);
        assert_instruction("cpx $20", &[0xE4, 0x20]);

        // cpy
        assert_instruction("cpy #$20", &[0xC0, 0x20]);
        assert_instruction("cpy $2002", &[0xCC, 0x02, 0x20]);
        assert_instruction("cpy $20", &[0xC4, 0x20]);
    }

    #[test]
    fn store_instructions() {
        //sta
        assert_instruction("sta $20", &[0x85, 0x20]);
        assert_instruction("sta $20, x", &[0x95, 0x20]);
        assert_instruction("sta $2002", &[0x8D, 0x02, 0x20]);
        assert_instruction("sta $2002, x", &[0x9D, 0x02, 0x20]);
        assert_instruction("sta $2002, y", &[0x99, 0x02, 0x20]);
        assert_instruction("sta ($20, x)", &[0x81, 0x20]);
        assert_instruction("sta ($20), y", &[0x91, 0x20]);

        // stx
        assert_instruction("stx $20", &[0x86, 0x20]);
        assert_instruction("stx $20, y", &[0x96, 0x20]);
        assert_instruction("stx $2002", &[0x8E, 0x02, 0x20]);

        // sty
        assert_instruction("sty $20", &[0x84, 0x20]);
        assert_instruction("sty $20, x", &[0x94, 0x20]);
        assert_instruction("sty $2002", &[0x8C, 0x02, 0x20]);
    }

    #[test]
    fn bit() {
        assert_instruction("bit $10", &[0x24, 0x10]);
        assert_instruction("bit $1001", &[0x2C, 0x01, 0x10]);
    }

    // Labels & branching

    #[test]
    fn same_segment_labels() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
nop
@hello:
    jmp @hello
    jmp @end
@end:
    nop
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 4);

        // jmp @hello
        assert_eq!(res[1].size, 3);
        assert_eq!(res[1].bytes[0], 0x4C);
        assert_eq!(res[1].bytes[1], 0x01);
        assert_eq!(res[1].bytes[2], 0x80);

        // jmp @end
        assert_eq!(res[2].size, 3);
        assert_eq!(res[2].bytes[0], 0x4C);
        assert_eq!(res[2].bytes[1], 0x07);
        assert_eq!(res[2].bytes[2], 0x80);
    }

    #[test]
    fn anonymous_relative_jumps() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
nop
:
    nop
@hello:
    jmp :--
    jmp :+
    jmp @hello
    jmp :+++
@end:
    nop
:
    nop
: nop
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 9);

        // First two nop's
        assert_eq!(res[0].size, 1);
        assert_eq!(res[0].bytes[0], 0xEA);
        assert_eq!(res[1].size, 1);
        assert_eq!(res[1].bytes[0], 0xEA);

        // jmp :--
        assert_eq!(res[2].size, 3);
        assert_eq!(res[2].bytes[0], 0x4C);
        assert_eq!(res[2].bytes[1], 0x01);
        assert_eq!(res[2].bytes[2], 0x80);

        // jmp :+
        assert_eq!(res[3].size, 3);
        assert_eq!(res[3].bytes[0], 0x4C);
        assert_eq!(res[3].bytes[1], 0x0E);
        assert_eq!(res[3].bytes[2], 0x80);

        // jmp @hello
        assert_eq!(res[4].size, 3);
        assert_eq!(res[4].bytes[0], 0x4C);
        assert_eq!(res[4].bytes[1], 0x02);
        assert_eq!(res[4].bytes[2], 0x80);

        // jmp :+++
        assert_eq!(res[5].size, 3);
        assert_eq!(res[5].bytes[0], 0x4C);
        assert_eq!(res[5].bytes[1], 0x10);
        assert_eq!(res[5].bytes[2], 0x80);

        // Three last nop's.
        assert_eq!(res[6].size, 1);
        assert_eq!(res[6].bytes[0], 0xEA);
        assert_eq!(res[7].size, 1);
        assert_eq!(res[7].bytes[0], 0xEA);
        assert_eq!(res[8].size, 1);
        assert_eq!(res[8].bytes[0], 0xEA);
    }

    #[test]
    fn anonymous_relative_branches() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
nop
:
    nop
@hello:
    beq :--
    beq :+
    beq @hello
    beq :+++
@end:
    nop
:
    nop
: nop
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 9);

        // First two nop's
        assert_eq!(res[0].size, 1);
        assert_eq!(res[0].bytes[0], 0xEA);
        assert_eq!(res[1].size, 1);
        assert_eq!(res[1].bytes[0], 0xEA);

        // beq :--
        assert_eq!(res[2].size, 2);
        assert_eq!(res[2].bytes[0], 0xF0);
        assert_eq!(res[2].bytes[1], 0xFD);

        // beq :+
        assert_eq!(res[3].size, 2);
        assert_eq!(res[3].bytes[0], 0xF0);
        assert_eq!(res[3].bytes[1], 0x04);

        // beq @hello
        assert_eq!(res[4].size, 2);
        assert_eq!(res[4].bytes[0], 0xF0);
        assert_eq!(res[4].bytes[1], 0xFA);

        // beq :+++
        assert_eq!(res[5].size, 2);
        assert_eq!(res[5].bytes[0], 0xF0);
        assert_eq!(res[5].bytes[1], 0x02);

        // Three last nop's.
        assert_eq!(res[6].size, 1);
        assert_eq!(res[6].bytes[0], 0xEA);
        assert_eq!(res[7].size, 1);
        assert_eq!(res[7].bytes[0], 0xEA);
        assert_eq!(res[8].size, 1);
        assert_eq!(res[8].bytes[0], 0xEA);
    }

    #[test]
    fn conditional_branch_to_labels() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
nop
@hello:
    beq @hello
    beq @end
@end:
    nop
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 4);

        // beq @hello
        assert_eq!(res[1].size, 2);
        assert_eq!(res[1].bytes[0], 0xF0);
        assert_eq!(res[1].bytes[1], 0xFE);

        // beq @end
        assert_eq!(res[2].size, 2);
        assert_eq!(res[2].bytes[0], 0xF0);
        assert_eq!(res[2].bytes[1], 0x00);
    }

    // TODO: function calls
    // TODO: labels and jumps inside of proc's, macros, etc.

    // Control statements

    #[test]
    fn byte_literals() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
.scope Vars
    Variable = 4
.endscope

.byte #Vars::Variable
.dw $2001, $02
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 3);

        // .byte
        assert_eq!(res[0].bytes[0], 0x04);
        assert_eq!(res[0].bytes[1], 0x00);
        assert_eq!(res[0].size, 1);

        // First .dw argument.
        assert_eq!(res[1].bytes[0], 0x01);
        assert_eq!(res[1].bytes[1], 0x20);
        assert_eq!(res[1].size, 2);

        // Second .dw argument.
        assert_eq!(res[2].bytes[0], 0x02);
        assert_eq!(res[2].bytes[1], 0x00);
        assert_eq!(res[2].size, 2);
    }

    #[test]
    fn hi_lo_byte() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
Var = $2002
lda #.lobyte(Var)
lda #.hibyte(Var)
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 2);
        let instrs: Vec<[u8; 2]> = vec![[0xA9, 0x02], [0xA9, 0x20]];

        for i in 0..2 {
            assert_eq!(res[i].size, 2);
            assert_eq!(res[i].bytes[0], instrs[i][0]);
            assert_eq!(res[i].bytes[1], instrs[i][1]);
        }
    }

    // Macros

    #[test]
    fn macro_no_arguments() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
lda #42

.macro MACRO
    lda #2
.endmacro

lda #1
MACRO
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 3);
        let instrs: Vec<[u8; 2]> = vec![[0xA9, 0x2A], [0xA9, 0x01], [0xA9, 0x02]];

        for i in 0..3 {
            assert_eq!(res[i].size, 2);
            assert_eq!(res[i].bytes[0], instrs[i][0]);
            assert_eq!(res[i].bytes[1], instrs[i][1]);
        }
    }

    #[test]
    fn macro_not_enough_arguments() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = asm
            .assemble(
                r#"
lda #42

.macro MACRO(Var)
    lda #Var
.endmacro

lda #1
MACRO
"#
                .as_bytes(),
            )
            .unwrap_err();

        assert_eq!(
            res.first().unwrap().to_string(),
            "Evaluation error (line 9): wrong number of arguments for 'MACRO': 1 required but 0 given."
        );
    }

    #[test]
    fn macro_too_many_arguments() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = asm
            .assemble(
                r#"
lda #42

.macro MACRO(Var)
    lda #Var
.endmacro

lda #1
MACRO(1, 2)
"#
                .as_bytes(),
            )
            .unwrap_err();

        assert_eq!(
            res.first().unwrap().to_string(),
            "Evaluation error (line 9): wrong number of arguments for 'MACRO': 1 required but 2 given."
        );
    }

    #[test]
    fn macro_with_one_argument() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
lda #42

.macro MACRO(Var)
    lda #Var
.endmacro

lda #1
MACRO(2)
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 3);
        let instrs: Vec<[u8; 2]> = vec![[0xA9, 0x2A], [0xA9, 0x01], [0xA9, 0x02]];

        for i in 0..3 {
            assert_eq!(res[i].size, 2);
            assert_eq!(res[i].bytes[0], instrs[i][0]);
            assert_eq!(res[i].bytes[1], instrs[i][1]);
        }
    }

    #[test]
    fn macro_unknown_arguments() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = asm
            .assemble(
                r#"
lda #42

.macro MACRO(Var)
    lda #Va
.endmacro

lda #1
MACRO(1)
"#
                .as_bytes(),
            )
            .unwrap_err();

        assert_eq!(
            res.first().unwrap().to_string(),
            "Evaluation error (line 5): 'a' is not a decimal value and \
             could not find variable 'Va' in the global scope either."
        );
    }

    #[test]
    fn macro_shadow_argument() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = asm
            .assemble(
                r#"
Var = 3
lda #42

.macro MACRO(Var)
    lda #Va
.endmacro

lda #1
MACRO(1)
"#
                .as_bytes(),
            )
            .unwrap_err();

        assert_eq!(
            res.first().unwrap().to_string(),
            "Evaluation error (line 5): 'Var' already defined in the global scope: \
             you cannot re-assign variables."
        );
    }

    #[test]
    fn macro_multiple_arguments() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
.macro WRITE_PPU_DATA address, value
    bit $2002                   ; PPUSTATUS
    lda #.HIBYTE(address)
    sta $2006                   ; PPUADDR
    lda #.LOBYTE(address)
    sta $2006                   ; PPUADDR
    lda #value
    sta $2007                   ; PPUDATA
.endmacro

WRITE_PPU_DATA $20B9, $04
"#
                .as_bytes(),
            )
            .unwrap()[0x10..];

        assert_eq!(res.len(), 7);

        // bit $2002
        assert_eq!(res[0].size, 3);
        assert_eq!(res[0].bytes[0], 0x2C);
        assert_eq!(res[0].bytes[1], 0x02);
        assert_eq!(res[0].bytes[2], 0x20);

        // lda #.HIBYTE(address)
        assert_eq!(res[1].size, 2);
        assert_eq!(res[1].bytes[0], 0xA9);
        assert_eq!(res[1].bytes[1], 0x20);

        // sta $2006
        assert_eq!(res[2].size, 3);
        assert_eq!(res[2].bytes[0], 0x8D);
        assert_eq!(res[2].bytes[1], 0x06);
        assert_eq!(res[2].bytes[2], 0x20);

        // lda #.LOBYTE(address)
        assert_eq!(res[3].size, 2);
        assert_eq!(res[3].bytes[0], 0xA9);
        assert_eq!(res[3].bytes[1], 0xB9);

        // sta $2006
        assert_eq!(res[4].size, 3);
        assert_eq!(res[4].bytes[0], 0x8D);
        assert_eq!(res[4].bytes[1], 0x06);
        assert_eq!(res[4].bytes[2], 0x20);

        // lda #value
        assert_eq!(res[5].size, 2);
        assert_eq!(res[5].bytes[0], 0xA9);
        assert_eq!(res[5].bytes[1], 0x04);

        // sta $2007
        assert_eq!(res[6].size, 3);
        assert_eq!(res[6].bytes[0], 0x8D);
        assert_eq!(res[6].bytes[1], 0x07);
        assert_eq!(res[6].bytes[2], 0x20);
    }

    // Segments

    #[test]
    fn error_on_unknown_segment() {
        let mut asm = Assembler::new(one_two().to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;

        let line = r#"
.segment "THREE"

.segment "TWO"
nop
"#;
        assert_error_with_assembler(
            &mut asm,
            line,
            "Evaluation",
            2,
            false,
            "unknown segment 'THREE'",
        )
    }

    #[test]
    fn error_on_empty_segment() {
        let mut asm = Assembler::new(one_two().to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        let line = r#"
.segment "ONE"

.segment "TWO"
nop
"#;
        assert_error_with_assembler(
            &mut asm,
            line,
            "Evaluation",
            1,
            true,
            "segment 'ONE' is empty",
        )
    }

    #[test]
    fn jmp_and_beq_inside_segment() {
        let mut asm = Assembler::new(one_two().to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        let bundles = &asm
            .assemble(
                r#"
.segment "ONE"
nop

.segment "TWO"
nop
:
    nop
@hello:
    beq :--
    beq :+
    jmp @hello
    beq @hello
    beq :+++
    beq @end
@end:
    nop
:
    nop
: nop
"#
                .as_bytes(),
            )
            .unwrap()[0x11..]; // Ignoring HEADER + nop from ONE

        // First two nop's
        assert_eq!(bundles[0].size, 1);
        assert_eq!(bundles[0].bytes[0], 0xEA);
        assert_eq!(bundles[1].size, 1);
        assert_eq!(bundles[1].bytes[0], 0xEA);

        // beq :--
        assert_eq!(bundles[2].size, 2);
        assert_eq!(bundles[2].bytes[0], 0xF0);
        assert_eq!(bundles[2].bytes[1], 0xFD);

        // beq :+
        assert_eq!(bundles[3].size, 2);
        assert_eq!(bundles[3].bytes[0], 0xF0);
        assert_eq!(bundles[3].bytes[1], 0x09);

        // jmp @hello
        assert_eq!(bundles[4].size, 3);
        assert_eq!(bundles[4].bytes[0], 0x4C);
        assert_eq!(bundles[4].bytes[1], 0x03);
        assert_eq!(bundles[4].bytes[2], 0x80);

        // beq @hello
        assert_eq!(bundles[5].size, 2);
        assert_eq!(bundles[5].bytes[0], 0xF0);
        assert_eq!(bundles[5].bytes[1], 0xF7);

        // beq :+++
        assert_eq!(bundles[6].size, 2);
        assert_eq!(bundles[6].bytes[0], 0xF0);
        assert_eq!(bundles[6].bytes[1], 0x04);

        // beq @end
        assert_eq!(bundles[7].size, 2);
        assert_eq!(bundles[7].bytes[0], 0xF0);
        assert_eq!(bundles[7].bytes[1], 0x00);

        // Three last nop's.
        assert_eq!(bundles[8].size, 1);
        assert_eq!(bundles[8].bytes[0], 0xEA);
        assert_eq!(bundles[9].size, 1);
        assert_eq!(bundles[9].bytes[0], 0xEA);
        assert_eq!(bundles[10].size, 1);
        assert_eq!(bundles[10].bytes[0], 0xEA);
    }

    #[test]
    fn jmp_on_different_segments_intertwined() {
        let mut asm = Assembler::new(one_two().to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        let bundles = &asm
            .assemble(
                r#"
.segment "ONE"
lala:
    rts

.segment "TWO"
code:
    jsr lala
    jsr code
    rts

.segment "ONE"
    jsr code
"#
                .as_bytes(),
            )
            .unwrap()[0x11..]; // Ignoring HEADER + rts from ONE

        // "jsr code" from ONE (notice that it's intertwined!)
        assert_eq!(bundles[0].size, 3);
        assert_eq!(bundles[0].bytes[0], 0x20);
        assert_eq!(bundles[0].bytes[1], 0x04);
        assert_eq!(bundles[0].bytes[2], 0x80);

        // "jsr lala" from TWO
        assert_eq!(bundles[1].size, 3);
        assert_eq!(bundles[1].bytes[0], 0x20);
        assert_eq!(bundles[1].bytes[1], 0x00);
        assert_eq!(bundles[1].bytes[2], 0x80);

        // "jsr code" from TWO (again, notice that it's intertwined)
        assert_eq!(bundles[2].size, 3);
        assert_eq!(bundles[2].bytes[0], 0x20);
        assert_eq!(bundles[2].bytes[1], 0x04);
        assert_eq!(bundles[2].bytes[2], 0x80);
    }

    #[test]
    fn cannot_switch_to_segment_inside_of_scope() {
        let mut asm = Assembler::new(EMPTY.to_vec());
        asm.mappings[0].segments[0].bundles = minimal_header();
        asm.mappings[0].offset = 6;
        asm.current_mapping = 1;
        let res = &asm
            .assemble(
                r#"
.scope Vars
.segment "CODE"
  nop
.endscope
"#
                .as_bytes(),
            )
            .unwrap_err();

        assert_eq!(
            res.first().unwrap().to_string(),
            "Evaluation error (line 3): cannot switch to segment 'CODE' \
             if we are still inside of a scope ('Vars')."
        );
    }

    // TODO: jmp/beq outside of allocated PRG ROM
}