Add exercises to the practice command

The '-e/--exercises' has also been introduced to instruct the 'practice'
command to only go for exercises, and the '-k/--kind' flag allows the
user to further filter which kind of exercise to practice.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

3 files changed, 193 insertions, 12 deletions

diff --git a/crates/cli/Cargo.toml b/crates/cli/Cargo.toml
index ab5a406..cd2a8c9 100644
--- a/crates/cli/Cargo.toml
+++ b/crates/cli/Cargo.toml
@@ -13,3 +13,4 @@ mihi.workspace = true
 inquire = { version = "0.7.5", features = ["editor"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
+tempfile = "3.20"
diff --git a/crates/cli/src/exercises.rs b/crates/cli/src/exercises.rs
index a4bff78..b153aca 100644
--- a/crates/cli/src/exercises.rs
+++ b/crates/cli/src/exercises.rs
@@ -195,7 +195,7 @@ fn rm(mut args: IntoIter<String>) -> i32 {
 
     match ans {
         Ok(true) => match mihi::delete_exercise(selection) {
-            Ok(_) => println!("Removed '{}' from the database!", selection),
+            Ok(_) => println!("Removed '{selection}' from the database!"),
             Err(e) => {
                 println!("error: words: {e}");
                 return 1;
diff --git a/crates/cli/src/run.rs b/crates/cli/src/run.rs
index 31c521d..4e6e707 100644
--- a/crates/cli/src/run.rs
+++ b/crates/cli/src/run.rs
@@ -1,5 +1,10 @@
-use inquire::Text;
-use mihi::{select_random_words, update_success, Category, Word};
+use inquire::{Confirm, Editor, Text};
+use mihi::{select_random_words, update_success, Category, Exercise, ExerciseKind, Word};
+use std::env;
+use std::fs;
+use std::io::Write;
+use std::process::Command;
+use tempfile::NamedTempFile;
 
 // Maximum number of times a word has to be run in order to increase the number
 // of successful runs.
@@ -11,18 +16,26 @@ fn help(msg: Option<&str>) {
     }
 
     println!("mihi run: Run exercises. Default command if none was given.\n");
-    println!("usage: mihi run [OPTIONS]\n");
+    println!("usage: mihi practice [OPTIONS]\n");
 
     println!("Options:");
-    println!("   -h, --help\t\tPrint this message.");
+    println!("   -c, --category <CATEGORY>\tOnly ask for words on the given <CATEGORY>.");
+    println!("   -e, --exercises\t\tOnly practice with exercises.");
+    println!("   -h, --help\t\t\tPrint this message.");
+    println!("   -k, --kind <KIND>\t\tOnly ask for exercises for the given <KIND>.");
 }
 
+// Locale represents the locales accepted for delivering answers on this
+// tool. That is, it's not about i18n on the strings for this application. but
+// rather the different translations accepted in places like
+// `Word.translations`.
 enum Locale {
     English,
     Catalan,
 }
 
 impl Locale {
+    // Returns the string representation for the locale's code.
     fn to_code(&self) -> &str {
         match self {
             Self::English => "en",
@@ -40,7 +53,9 @@ impl std::fmt::Display for Locale {
     }
 }
 
-fn run_words(words: Vec<Word>, locale: Locale) -> i32 {
+// Run the quiz for all the given `words` while expecting answers to be
+// delivered in the given `locale`.
+fn run_words(words: Vec<Word>, locale: &Locale) -> i32 {
     let mut errors = 0;
 
     for word in words {
@@ -78,6 +93,8 @@ fn run_words(words: Vec<Word>, locale: Locale) -> i32 {
     errors
 }
 
+// Returns a vector of words which contain a randomized set of words from
+// different categories.
 fn select_general_words() -> Result<Vec<Word>, String> {
     let mut res = select_random_words(Category::Noun, 4)?;
     res.append(&mut select_random_words(Category::Adjective, 2)?);
@@ -89,9 +106,125 @@ fn select_general_words() -> Result<Vec<Word>, String> {
     Ok(res)
 }
 
+// Assuming that the `given` string is the answer for an exercise enunciate,
+// remove the enunciate proper (enveloped via '---' comments) and return only
+// what the user typed in.
+fn remove_exercise_enunciate(given: String) -> String {
+    let mut res = vec![];
+    let mut found = false;
+
+    for line in given.lines() {
+        let trimmed = line.trim();
+
+        if found {
+            res.push(line);
+        }
+        if trimmed.starts_with("---!") {
+            found = true;
+        }
+    }
+
+    res.join("\n").to_string()
+}
+
+// Returns true if the given `bin` exists on the PATH, false otherwise.
+fn is_executable(bin: &str) -> bool {
+    if let Ok(path) = env::var("PATH") {
+        for p in path.split(":") {
+            let p_str = format!("{p}/{bin}");
+            if fs::metadata(p_str).is_ok() {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+// Returns the string for the name of the command that should be used to show
+// diffs.
+fn diff_tool() -> Option<&'static str> {
+    ["difft", "vimdiff", "diff"].into_iter().find(|&cmd| is_executable(cmd))
+}
+
+// Perform a diff with the `given` and the `expected` answers for an exercise
+// and interactively ask the user if things are ok. Returns a boolean depending
+// on the user's answer to that final question, or false if something went
+// wrong.
+fn accepted_diff(given: String, expected: String) -> bool {
+    // If a diff tool could be fetched, then write into temporary files and call
+    // the diff tool against both temporary files; otherwise just print things
+    // out into the stdout.
+    match diff_tool() {
+        Some(cmd) => {
+            let Ok(mut given_file) = NamedTempFile::new() else {
+                return false;
+            };
+            if writeln!(given_file, "{given}").is_err() {
+                return false;
+            }
+
+            let Ok(mut expected_file) = NamedTempFile::new() else {
+                return false;
+            };
+            if writeln!(expected_file, "{expected}").is_err() {
+                return false;
+            }
+
+            let mut cmd = Command::new(cmd);
+            cmd.arg(given_file.path()).arg(expected_file.path());
+            cmd.status().expect("process failed to execute");
+            println!();
+        }
+        None => {
+            println!("---Given:\n{given}\n---Expected:\n{expected}");
+        }
+    }
+
+    Confirm::new("Do you think that you did well?")
+        .with_default(false)
+        .prompt()
+        .unwrap_or(false)
+}
+
+// Run the quiz for all the given `exercises`.
+fn run_exercises(exercises: Vec<Exercise>) -> i32 {
+    if exercises.is_empty() {
+        println!("practice: no exercises!");
+        return 0;
+    }
+
+    let mut errors = 0;
+
+    for exercise in exercises {
+        let Ok(solution) = Editor::new(
+            format!("Exercise '{}' (kind: {}):", exercise.title, exercise.kind).as_str(),
+        )
+        .with_predefined_text(
+            format!(
+                "---Enunciate: {}\n{}\n---!",
+                exercise.title, exercise.enunciate
+            )
+            .as_str(),
+        )
+        .with_file_extension(".md")
+        .prompt() else {
+            return 1;
+        };
+        let solution = remove_exercise_enunciate(solution);
+
+        if !accepted_diff(solution, exercise.solution) {
+            errors += 1;
+        }
+    }
+
+    errors
+}
+
 pub fn run(args: Vec<String>) {
     let mut it = args.into_iter();
     let mut category = None;
+    let mut kind: Option<ExerciseKind> = None;
+    let mut exercises_only = false;
 
     while let Some(first) = it.next() {
         match first.as_str() {
@@ -101,7 +234,10 @@ pub fn run(args: Vec<String>) {
             }
             "-c" | "--category" => {
                 if category.is_some() {
-                    help(Some("error: run: you cannot provide multiple categories"));
+                    help(Some(
+                        "error: practice: you cannot provide multiple categories",
+                    ));
+                    std::process::exit(1);
                 }
                 match it.next() {
                     Some(cat) => {
@@ -114,15 +250,43 @@ pub fn run(args: Vec<String>) {
                             "preposition" => Some(Category::Preposition),
                             "conjunction" => Some(Category::Conjunction),
                             "determiner" => Some(Category::Determiner),
-                            _ => return help(Some("error: run: category not allowed")),
+                            _ => return help(Some("error: practice: category not allowed")),
+                        };
+                    }
+                    None => {
+                        help(Some("error: practice: you have to provide a category"));
+                        std::process::exit(1);
+                    }
+                }
+            }
+            "-e" | "--exercises" => {
+                exercises_only = true;
+            }
+            "-k" | "--kind" => {
+                if kind.is_some() {
+                    help(Some(
+                        "error: practice: you cannot provide multiple exercise kinds",
+                    ));
+                    std::process::exit(1);
+                }
+                match it.next() {
+                    Some(k) => {
+                        kind = match k.trim().to_lowercase().as_str().try_into() {
+                            Ok(k) => Some(k),
+                            Err(e) => {
+                                return help(Some(format!("error: practice: {e}").as_str()))
+                            }
                         };
                     }
-                    None => help(Some("error: run: you have to provide a category")),
+                    None => {
+                        help(Some("error: practice: you have to provide a category"));
+                        std::process::exit(1);
+                    }
                 }
             }
             _ => {
                 help(Some(
-                    format!("error: run: unknown flag or command '{first}'").as_str(),
+                    format!("error: practice: unknown flag or command '{first}'").as_str(),
                 ));
                 std::process::exit(1);
             }
@@ -141,10 +305,26 @@ pub fn run(args: Vec<String>) {
         None => select_general_words(),
     };
 
+    let exercises = match mihi::select_relevant_exercises(kind, if exercises_only { 5 } else { 1 })
+    {
+        Ok(exercises) => exercises,
+        Err(e) => {
+            println!("error: practice: {e}");
+            std::process::exit(1);
+        }
+    };
+
     match words {
-        Ok(list) => std::process::exit(run_words(list, locale)),
+        Ok(list) => {
+            let mut code = 0;
+            if !exercises_only {
+                code += run_words(list, &locale);
+            }
+            code += run_exercises(exercises);
+            std::process::exit(code);
+        }
         Err(e) => {
-            println!("error: run: {e}");
+            println!("error: practice: {e}");
             std::process::exit(1);
         }
     };