use std::{
    collections::{BTreeMap, VecDeque},
    str::FromStr,
    sync::OnceLock,
};

use regex::Regex;

#[derive(Debug, PartialEq, Eq)]
pub struct Verse {
    // pub background: String, // url
    pub content: String,
}

impl Verse {
    fn new(content: String) -> Self {
        Self { content }
    }
}

/// Sequence of verse names.
pub type Plan = VecDeque<String>;

pub struct Song {
    pub name: String,
    pub verses: BTreeMap<String, Verse>,
    pub other_plans: BTreeMap<String, Plan>,
    pub default_plan: Plan,
}

impl Song {
    pub fn plan(&self, plan_name: Option<String>) -> &VecDeque<String> {
        plan_name
            .map(|plan_name| {
                self.other_plans
                    .get(&plan_name)
                    .unwrap_or(&self.default_plan)
            })
            .unwrap_or(&self.default_plan)
    }
}

#[derive(Debug)]
pub struct SourceRef {
    line_number: usize,
}

#[derive(Debug)]
pub enum SongParseError {
    EmptyString,
    InvalidMetadata(SourceRef),
}

impl FromStr for Song {
    type Err = SongParseError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s == "" {
            return Err(SongParseError::EmptyString);
        }

        static HUNK_REGEX: OnceLock<Regex> = OnceLock::new();
        let re = HUNK_REGEX.get_or_init(|| Regex::new(r"\s*[\n\r]\s*[\n\r]\s*").unwrap());
        let mut hunks = VecDeque::new();
        let mut last_end: usize = 0;

        for m in re.find_iter(s) {
            hunks.push_back(&s[last_end..m.start()]);
            last_end = m.end();
        }
        hunks.push_back(&s[last_end..s.len()]);

        // process header
        let mut header_lines = hunks.pop_front().unwrap().lines().map(|s| s.trim());
        let name = header_lines.next().unwrap().trim().to_owned();
        let mut other_plans = BTreeMap::new();

        for (line_number, line) in header_lines.enumerate() {
            if line.starts_with("plan(") {
                if let Some(end) = line.find(")") {
                    match line[end..].find(":") {
                        Some(i) => {
                            let plan_name = &line[5..end];
                            let entries: VecDeque<String> = line[(end + i + 1)..]
                                .trim()
                                .split(',')
                                .map(|s| s.trim().to_owned())
                                .collect();
                            other_plans.insert(plan_name.to_owned(), entries);
                        }
                        None => {
                            return Err(SongParseError::InvalidMetadata(SourceRef { line_number }));
                        }
                    }
                }
            }
            // map(band2): slide1, slide2
            // band2: slide1, slide2
        }

        let mut verses = BTreeMap::new();

        let mut default_plan = Plan::new();

        // process verses
        for hunk in hunks {
            let mut verse_contents = hunk;
            let end_i = hunk.find('\n').unwrap_or(hunk.len());
            let verse_name: String = if let Some(i) = &hunk[0..end_i].find(':') {
                verse_contents = &hunk[end_i + 1..];
                String::from(&hunk[0..*i])
            } else {
                format!("Generated Verse {}", verses.len() + 1).to_owned()
            };
            verses.insert(verse_name.clone(), Verse::new(verse_contents.to_owned()));
            default_plan.push_back(verse_name.clone());
        }

        Ok(Self {
            name,
            verses,
            other_plans,
            default_plan,
        })
    }
}

mod test {
    use std::collections::VecDeque;

    use super::{Song, Verse};

    #[test]
    fn parses_simple_song() {
        let song: Song = r#"Song Title
                
                A verse"#
            .parse()
            .unwrap();

        assert_eq!(song.name, "Song Title");
        assert_eq!(
            song.verses.get("Generated Verse 1"),
            Some(&Verse {
                content: "A verse".to_owned()
            })
        );
        assert_eq!(song.verses.len(), 1);
        assert_eq!(song.default_plan[0], "Generated Verse 1");
        assert_eq!(song.default_plan.len(), 1);
    }

    #[test]
    fn parses_song_with_plan() {
        let song: Song = r#"Song Title
                plan(another_plan): Generated Verse 1, Generated Verse 1, Generated Verse 1
                
                A verse"#
            .parse()
            .unwrap();

        assert_eq!(song.name, "Song Title");
        assert_eq!(
            song.verses.get("Generated Verse 1"),
            Some(&Verse {
                content: "A verse".to_owned()
            })
        );
        assert_eq!(song.verses.len(), 1);
        assert_eq!(song.default_plan[0], "Generated Verse 1");
        assert_eq!(song.default_plan.len(), 1);
        dbg!(&song.other_plans);
        assert_eq!(
            song.other_plans.get("another_plan"),
            Some(&VecDeque::from(vec![
                "Generated Verse 1".to_owned(),
                "Generated Verse 1".to_owned(),
                "Generated Verse 1".to_owned()
            ]))
        );
    }

    #[test]
    fn parses_song_with_verse_ref() {
        let song: Song = r#"Title



                v1:
                v1
                

                v2:
                v2
                
                (v2)
                
                (v1)"#
            .parse()
            .unwrap();

        assert_eq!(song.name, "Song Title");
        assert_eq!(
            song.verses.get("Generated Verse 1"),
            Some(&Verse {
                content: "A verse".to_owned()
            })
        );
        assert_eq!(song.verses.len(), 1);
        assert_eq!(song.default_plan[0], "Generated Verse 1");
        assert_eq!(song.default_plan.len(), 1);
        dbg!(&song.other_plans);
        assert_eq!(
            song.other_plans.get("another_plan"),
            Some(&VecDeque::from(vec![
                "Generated Verse 1".to_owned(),
                "Generated Verse 1".to_owned(),
                "Generated Verse 1".to_owned()
            ]))
        );
    }
}