use prometeu_hal::app_mode::AppMode;
use prometeu_hal::cartridge::CartridgeManifest;
use std::fs;
use std::path::{Path, PathBuf};
use std::time::SystemTime;

#[derive(Debug, Clone)]
pub struct GameLibraryEntry {
    pub manifest: CartridgeManifest,
    pub title: String,
    pub app_id: u32,
    pub app_version: String,
    pub path: PathBuf,
    pub discovered_at: SystemTime,
}

impl GameLibraryEntry {
    fn new(path: PathBuf, manifest: CartridgeManifest, discovered_at: SystemTime) -> Self {
        Self {
            title: manifest.title.clone(),
            app_id: manifest.app_id,
            app_version: manifest.app_version.clone(),
            manifest,
            path,
            discovered_at,
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct GameLibraryDiagnostic {
    pub path: PathBuf,
    pub reason: GameLibraryDiagnosticReason,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum GameLibraryDiagnosticReason {
    RootNotDirectory,
    CandidateReadFailed,
    MissingManifest,
    InvalidManifest,
    UnsupportedVersion,
    MissingProgram,
    NonGameAppMode,
}

#[derive(Debug, Clone, Default)]
pub struct GameLibrary {
    entries: Vec<GameLibraryEntry>,
    diagnostics: Vec<GameLibraryDiagnostic>,
}

impl GameLibrary {
    pub fn empty() -> Self {
        Self::default()
    }

    pub fn entries(&self) -> &[GameLibraryEntry] {
        &self.entries
    }

    pub fn diagnostics(&self) -> &[GameLibraryDiagnostic] {
        &self.diagnostics
    }

    pub fn is_empty(&self) -> bool {
        self.entries.is_empty()
    }
}

pub fn discover_games_root(root: impl AsRef<Path>) -> GameLibrary {
    let root = root.as_ref();
    let discovered_at = SystemTime::now();

    if !root.is_dir() {
        return GameLibrary {
            entries: Vec::new(),
            diagnostics: vec![GameLibraryDiagnostic {
                path: root.to_path_buf(),
                reason: GameLibraryDiagnosticReason::RootNotDirectory,
            }],
        };
    }

    let read_dir = match fs::read_dir(root) {
        Ok(read_dir) => read_dir,
        Err(_) => {
            return GameLibrary {
                entries: Vec::new(),
                diagnostics: vec![GameLibraryDiagnostic {
                    path: root.to_path_buf(),
                    reason: GameLibraryDiagnosticReason::CandidateReadFailed,
                }],
            };
        }
    };

    let mut entries = Vec::new();
    let mut diagnostics = Vec::new();

    for item in read_dir {
        let Ok(item) = item else {
            diagnostics.push(GameLibraryDiagnostic {
                path: root.to_path_buf(),
                reason: GameLibraryDiagnosticReason::CandidateReadFailed,
            });
            continue;
        };

        let path = item.path();
        if !path.is_dir() {
            continue;
        }

        match discover_candidate(&path, discovered_at) {
            Ok(entry) => entries.push(entry),
            Err(reason) => diagnostics.push(GameLibraryDiagnostic { path, reason }),
        }
    }

    entries.sort_by(|left, right| {
        left.title
            .cmp(&right.title)
            .then_with(|| left.app_id.cmp(&right.app_id))
            .then_with(|| left.path.cmp(&right.path))
    });

    GameLibrary { entries, diagnostics }
}

fn discover_candidate(
    path: &Path,
    discovered_at: SystemTime,
) -> Result<GameLibraryEntry, GameLibraryDiagnosticReason> {
    let manifest_path = path.join("manifest.json");
    if !manifest_path.exists() {
        return Err(GameLibraryDiagnosticReason::MissingManifest);
    }

    let manifest_content = fs::read_to_string(manifest_path)
        .map_err(|_| GameLibraryDiagnosticReason::InvalidManifest)?;
    let manifest: CartridgeManifest = serde_json::from_str(&manifest_content)
        .map_err(|_| GameLibraryDiagnosticReason::InvalidManifest)?;

    if manifest.magic != "PMTU" {
        return Err(GameLibraryDiagnosticReason::InvalidManifest);
    }
    if manifest.cartridge_version != 1 {
        return Err(GameLibraryDiagnosticReason::UnsupportedVersion);
    }
    if manifest.app_mode != AppMode::Game {
        return Err(GameLibraryDiagnosticReason::NonGameAppMode);
    }
    if !path.join("program.pbx").exists() {
        return Err(GameLibraryDiagnosticReason::MissingProgram);
    }

    Ok(GameLibraryEntry::new(path.to_path_buf(), manifest, discovered_at))
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;
    use std::sync::atomic::{AtomicU64, Ordering};
    use std::time::UNIX_EPOCH;

    static TEST_DIR_COUNTER: AtomicU64 = AtomicU64::new(0);

    struct TestRoot {
        path: PathBuf,
    }

    impl TestRoot {
        fn new() -> Self {
            let unique = TEST_DIR_COUNTER.fetch_add(1, Ordering::Relaxed);
            let path = std::env::temp_dir().join(format!(
                "prometeu-game-library-test-{}-{}",
                std::process::id(),
                unique
            ));
            fs::create_dir_all(&path).expect("test root should be created");
            Self { path }
        }

        fn add_candidate(&self, name: &str, manifest: serde_json::Value, with_program: bool) {
            let candidate = self.path.join(name);
            fs::create_dir_all(&candidate).expect("candidate should be created");
            fs::write(candidate.join("manifest.json"), manifest.to_string())
                .expect("manifest should be written");
            if with_program {
                fs::write(candidate.join("program.pbx"), [0_u8])
                    .expect("program should be written");
            }
        }
    }

    impl Drop for TestRoot {
        fn drop(&mut self) {
            let _ = fs::remove_dir_all(&self.path);
        }
    }

    fn manifest(title: &str, app_id: u32, app_mode: &str) -> serde_json::Value {
        json!({
            "magic": "PMTU",
            "cartridge_version": 1,
            "app_id": app_id,
            "title": title,
            "app_version": "1.0.0",
            "app_mode": app_mode
        })
    }

    #[test]
    fn discovery_returns_only_immediate_valid_game_directories() {
        let root = TestRoot::new();
        root.add_candidate("zeta", manifest("Zeta", 2, "Game"), true);
        root.add_candidate("alpha", manifest("Alpha", 1, "Game"), true);
        root.add_candidate("shell", manifest("Shell", 3, "Shell"), true);
        root.add_candidate("missing-program", manifest("Missing Program", 4, "Game"), false);
        fs::write(root.path.join("loose-file.txt"), "ignored").expect("file should be written");

        let nested_parent = root.path.join("nested-parent");
        fs::create_dir_all(nested_parent.join("nested-game")).expect("nested dir should exist");
        fs::write(
            nested_parent.join("nested-game").join("manifest.json"),
            manifest("Nested", 5, "Game").to_string(),
        )
        .expect("nested manifest should be written");
        fs::write(nested_parent.join("nested-game").join("program.pbx"), [0_u8])
            .expect("nested program should be written");

        let library = discover_games_root(&root.path);

        assert_eq!(library.entries().len(), 2);
        assert_eq!(library.entries()[0].title, "Alpha");
        assert_eq!(library.entries()[0].app_id, 1);
        assert_eq!(library.entries()[0].app_version, "1.0.0");
        assert_eq!(library.entries()[0].manifest.app_mode, AppMode::Game);
        assert!(library.entries()[0].path.ends_with("alpha"));
        assert!(library.entries()[0].discovered_at >= UNIX_EPOCH);
        assert_eq!(library.entries()[1].title, "Zeta");

        assert!(library.diagnostics().iter().any(|diagnostic| {
            diagnostic.path.ends_with("shell")
                && diagnostic.reason == GameLibraryDiagnosticReason::NonGameAppMode
        }));
        assert!(library.diagnostics().iter().any(|diagnostic| {
            diagnostic.path.ends_with("missing-program")
                && diagnostic.reason == GameLibraryDiagnosticReason::MissingProgram
        }));
        assert!(library.diagnostics().iter().any(|diagnostic| {
            diagnostic.path.ends_with("nested-parent")
                && diagnostic.reason == GameLibraryDiagnosticReason::MissingManifest
        }));
    }

    #[test]
    fn missing_root_returns_diagnostic_and_no_entries() {
        let root = TestRoot::new();
        let missing = root.path.join("missing");

        let library = discover_games_root(&missing);

        assert!(library.is_empty());
        assert_eq!(library.diagnostics().len(), 1);
        assert_eq!(library.diagnostics()[0].reason, GameLibraryDiagnosticReason::RootNotDirectory);
    }
}