// piupiu: grab tweets and put them into RSS feeds.
// Copyright (C) 2026-Ω Miquel Sabaté Solà <mssola@mssola.com>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package main

import (
	"encoding/json"
	"encoding/xml"
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type Tweet struct {
	ID        string `json:"id"`
	Text      string `json:"text"`
	CreatedAt string `json:"created_at"`
}

type TweetResponse struct {
	Data []Tweet `json:"data"`
}

type RSS struct {
	XMLName xml.Name   `xml:"rss"`
	Version string     `xml:"version,attr"`
	Channel RSSChannel `xml:"channel"`
}

type RSSChannel struct {
	Title       string    `xml:"title"`
	Link        string    `xml:"link"`
	Description string    `xml:"description"`
	Items       []RSSItem `xml:"item"`
}

type RSSItem struct {
	Title       string `xml:"title"`
	Link        string `xml:"link"`
	Description string `xml:"description"`
	PubDate     string `xml:"pubDate"`
	GUID        string `xml:"guid"`
}

// Given the directory 'path' and the 'username', create a
// '<path>/<username>.xml' file with the 'tweets' in RSS format.
func tweetsToRss(username, path string, tweets []Tweet) error {
	// XML definition of this whole thing.
	rss := RSS{
		Version: "2.0",
		Channel: RSSChannel{
			Title:       fmt.Sprintf("piu piu: @%s", username),
			Link:        fmt.Sprintf("https://x.com/%s", username),
			Description: fmt.Sprintf("@%s", username),
			Items:       make([]RSSItem, 0),
		},
	}

	// Now iterate on the given tweets and transform them into RSSItem's.
	for _, tweet := range tweets {
		tweetURL := fmt.Sprintf("https://x.com/%s/status/%s", username, tweet.ID)

		// Remember how the X API required a specific timestamp format? Well,
		// RSS wants another one. Because timestamp ISO's are how programmers
		// become (even) more cynical.
		t, err := time.Parse(time.RFC3339, tweet.CreatedAt)
		pubDate := tweet.CreatedAt
		if err == nil {
			pubDate = t.Format(time.RFC1123Z)
		}

		// Use the first few words or characters as the RSS item title.
		title := tweet.Text
		if len(title) > 50 {
			title = title[:47] + "..."
		}

		// Voila!
		rss.Channel.Items = append(rss.Channel.Items, RSSItem{
			Title:       title,
			Link:        tweetURL,
			Description: tweet.Text,
			PubDate:     pubDate,
			GUID:        tweetURL,
		})
	}

	// Marshal into XML with a standard header.
	output, err := xml.MarshalIndent(rss, "", "  ")
	if err != nil {
		return err
	}
	fullXML := []byte(xml.Header + string(output))

	// And write the damn thing.
	filename := fmt.Sprintf("%s.xml", username)
	filePath := filepath.Join(path, filename)
	return os.WriteFile(filePath, fullXML, 0644)
}

// Given a user 'id' and the API 'token', fetch all the tweets from the last 24
// hours.
func fetch(id, token string) ([]Tweet, error) {
	apiURL := fmt.Sprintf("https://api.x.com/2/users/%v/tweets", id)
	u, err := url.Parse(apiURL)
	if err != nil {
		return nil, err
	}

	q := u.Query()
	startTime := time.Now().UTC().Add(-24 * time.Hour).Format(time.RFC3339)
	q.Set("start_time", startTime)
	q.Set("tweet.fields", "created_at,text")
	q.Set("exclude", "replies")
	u.RawQuery = q.Encode()

	req, err := http.NewRequest("GET", u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Authorization", "Bearer "+token)

	client := &http.Client{Timeout: 10 * time.Second}
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("API error: %v (%v)", resp.Status, resp.StatusCode)
	}

	var object TweetResponse
	if err := json.NewDecoder(resp.Body).Decode(&object); err != nil {
		return nil, err
	}
	return object.Data, nil
}

func main() {
	// First of all, enforce the stupid ass API token.
	token := os.Getenv("PIUPIU_TOKEN")
	if token == "" {
		fmt.Println("error: you need to provide a token via the 'PIUPIU_TOKEN' environment variable.")
		os.Exit(1)
	}

	// Behold, argument parsing!
	query := flag.String("q", "", "Comma-separated list of '<@user_name>:<user_id>' values.")
	output := flag.String("o", ".", "Directory where RSS files will be dropped")
	flag.Parse()

	// This is cursed in unholy ways, as path sanitization shenanigans have
	// proved since the existence of the concept of a path in operating
	// systems. That being said, I'm the sole user of this, so whatever...
	if *output != "." {
		if err := os.MkdirAll(*output, 0755); err != nil {
			fmt.Printf("error: cannot create directory: %w", err)
			os.Exit(1)
		}
	}

	ids := strings.Split(*query, ",")
	exit := 0
	for _, id := range ids {
		// I could've gone with something friendlier, but this was faster, and I
		// just didn't care. If you don't recall the format, just RTFM (in this
		// case just -h, as manuals are for people who actually want to make a
		// living out of ones and zeroes :P).
		vals := strings.Split(id, ":")
		if len(vals) != 2 {
			fmt.Printf("error: bad argument format\n\n")
			flag.PrintDefaults()
			os.Exit(1)
		}

		// Fetch the tweet data from the API.
		name := strings.TrimSpace(vals[0])
		id = strings.TrimSpace(vals[1])
		tweets, err := fetch(id, token)
		if err != nil {
			fmt.Printf("error: %v\n", err)
			exit = 2
			continue
		}

		// Generate the RSS file for this user.
		err = tweetsToRss(name, *output, tweets)
		if err != nil {
			fmt.Printf("error: %v\n", err)
			exit = 2
		}
	}

	os.Exit(exit)
}