//! The remembered peer copy of every streamed track — on disk, where a
//! process with no WebView can read it.
//!
//! The phone's resolver remembers which peer file it last played for a
//! catalog track (`src/lib/sources.js`, `soulstream.streamSources.v1`), and
//! that memory is what lets a track play again from the stream cache with no
//! search at all. It lived in the WebView's localStorage, which meant it
//! existed only while a WebView did: Android Auto starting the app cold —
//! no Activity, no page — could see the cache files sitting in
//! `stream-cache/` and had no way to tell which playlist row any of them
//! belonged to. Every streamed row was "needs the app", even the ones whose
//! bytes were all there.
//!
//! This is the same memory, mirrored to `<data_dir>/stream-sources.json` by
//! the page every time it remembers a source, and read back here by the
//! headless browse tree and the cold player. The page stays the writer of
//! record for its own store; this file is a second copy that the Rust side
//! owns, and the two are keyed identically so a row found by either agrees
//! with the other.
//!
//! Also the home of `keep`: a source fetched because its playlist is kept
//! offline is marked, and `playback::prune_cache` leaves that file alone
//! however old it gets. Without it the retention window (thirty days
//! unplayed, two gigabytes) would quietly undo an offline playlist.

use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::path::{Path, PathBuf};

/// One remembered peer file. `size` is the peer-stated size, which is also
/// how a byte-complete cache file is recognised.
#[derive(Debug, Clone, Serialize, Deserialize, Default, PartialEq)]
pub struct StreamSource {
    pub username: String,
    pub path: String,
    pub size: u64,
    #[serde(default)]
    pub duration: Option<f64>,
    /// Pinned by an offline playlist; the cache pruner skips it.
    #[serde(default)]
    pub keep: bool,
}

/// What the page sends when it remembers (or re-sends) a source.
#[derive(Debug, Clone, Deserialize)]
pub struct RememberArg {
    pub track_id: Option<String>,
    pub artist: Option<String>,
    pub title: Option<String>,
    pub username: String,
    pub path: String,
    pub size: u64,
    #[serde(default)]
    pub duration: Option<f64>,
    /// `None` leaves an existing pin as it was; `Some` sets it.
    #[serde(default)]
    pub keep: Option<bool>,
}

/// More than the page keeps (400): this file also holds the offline pins,
/// and a pinned source must never be the one an unpinned one pushes out.
const CAP: usize = 1200;

pub fn file(data_dir: &Path) -> PathBuf {
    data_dir.join("stream-sources.json")
}

/// The lookup keys for a track, the page's own rule (`streamSourceKeys`):
/// the catalog id when there is one, and the lowercased `artist|title`.
pub fn keys(track_id: Option<&str>, artist: Option<&str>, title: Option<&str>) -> Vec<String> {
    let mut out = Vec::with_capacity(2);
    if let Some(t) = track_id.map(str::trim).filter(|t| !t.is_empty()) {
        out.push(format!("t:{t}"));
    }
    if let (Some(a), Some(t)) = (artist, title) {
        if !a.is_empty() && !t.is_empty() {
            out.push(format!("n:{a}|{t}").to_lowercase());
        }
    }
    out
}

/// Insertion-ordered so the cap can drop the oldest memory first — a
/// BTreeMap would forget which was old.
pub fn load(data_dir: &Path) -> Vec<(String, StreamSource)> {
    std::fs::read_to_string(file(data_dir))
        .ok()
        .and_then(|s| serde_json::from_str::<Vec<(String, StreamSource)>>(&s).ok())
        .unwrap_or_default()
}

fn save(data_dir: &Path, entries: &[(String, StreamSource)]) {
    let path = file(data_dir);
    if let Ok(json) = serde_json::to_string(entries) {
        // Written beside and renamed over: a cold browse may be reading the
        // file at this exact moment, and it must see the old whole file or
        // the new whole file, never half of one.
        let tmp = path.with_extension("json.tmp");
        if std::fs::write(&tmp, json).is_ok() {
            let _ = std::fs::rename(&tmp, &path);
        }
    }
}

/// Remember these sources. Every key of an entry maps to the same record;
/// an existing key is moved to the end (newest), and `keep` is carried
/// forward from the old record unless the argument sets it.
pub fn remember(data_dir: &Path, args: &[RememberArg]) {
    if args.is_empty() {
        return;
    }
    let mut entries = load(data_dir);
    for a in args {
        if a.username.is_empty() || a.path.is_empty() || a.size == 0 {
            continue;
        }
        for key in keys(a.track_id.as_deref(), a.artist.as_deref(), a.title.as_deref()) {
            let old_keep = entries
                .iter()
                .position(|(k, _)| *k == key)
                .map(|i| entries.remove(i).1.keep)
                .unwrap_or(false);
            entries.push((
                key,
                StreamSource {
                    username: a.username.clone(),
                    path: a.path.clone(),
                    size: a.size,
                    duration: a.duration,
                    keep: a.keep.unwrap_or(old_keep),
                },
            ));
        }
    }
    if entries.len() > CAP {
        // Drop the oldest UNPINNED memories first; a pin outlives the cap.
        let over = entries.len() - CAP;
        let mut dropped = 0;
        entries.retain(|(_, s)| {
            if dropped < over && !s.keep {
                dropped += 1;
                false
            } else {
                true
            }
        });
    }
    save(data_dir, &entries);
}

/// Pin or unpin the source remembered for a track.
pub fn set_keep(data_dir: &Path, track_id: Option<&str>, artist: Option<&str>, title: Option<&str>, keep: bool) {
    let wanted = keys(track_id, artist, title);
    if wanted.is_empty() {
        return;
    }
    let mut entries = load(data_dir);
    let mut changed = false;
    for (k, s) in entries.iter_mut() {
        if wanted.contains(k) && s.keep != keep {
            s.keep = keep;
            changed = true;
        }
    }
    if changed {
        save(data_dir, &entries);
    }
}

/// The remembered source for a track, catalog id first.
pub fn lookup(data_dir: &Path, track_id: Option<&str>, artist: Option<&str>, title: Option<&str>) -> Option<StreamSource> {
    let wanted = keys(track_id, artist, title);
    if wanted.is_empty() {
        return None;
    }
    let entries = load(data_dir);
    for key in &wanted {
        if let Some((_, s)) = entries.iter().find(|(k, _)| k == key) {
            return Some(s.clone());
        }
    }
    None
}

/// The cache file this source would land in, if its bytes are all there.
/// `None` for a missing file or a mid-transfer prefix — a prefix is not
/// the track, and a car that started one would stop mid-song.
pub fn cached_file(data_dir: &Path, src: &StreamSource) -> Option<PathBuf> {
    let file = crate::playback::cache_file_in(&crate::playback::cache_dir_in(data_dir), &src.username, &src.path);
    match std::fs::metadata(&file) {
        Ok(md) if src.size > 0 && md.len() == src.size => Some(file),
        _ => None,
    }
}

/// Every cache file a pinned source names — the pruner's exemption list.
pub fn kept_cache_files(data_dir: &Path) -> HashSet<PathBuf> {
    let dir = crate::playback::cache_dir_in(data_dir);
    load(data_dir)
        .into_iter()
        .filter(|(_, s)| s.keep)
        .map(|(_, s)| crate::playback::cache_file_in(&dir, &s.username, &s.path))
        .collect()
}

/// Where this instance keeps its data — the same directory the config and
/// the stream cache live in, which on Android is also the `dataDir` the
/// media service hands to the cold browse.
fn data_dir(app: &tauri::AppHandle) -> Result<PathBuf, String> {
    crate::paths::app_data(app)
}

/// The page remembering a source (one), or re-sending its whole store at
/// boot so memories made before this file existed reach the cold side.
#[tauri::command]
pub fn stream_source_remember(app: tauri::AppHandle, entries: Vec<RememberArg>) -> Result<(), String> {
    let dir = data_dir(&app)?;
    tauri::async_runtime::spawn_blocking(move || remember(&dir, &entries));
    Ok(())
}

/// Pin or unpin a track's remembered source for the cache pruner.
#[tauri::command]
pub fn stream_source_keep(
    app: tauri::AppHandle,
    track_id: Option<String>,
    artist: Option<String>,
    title: Option<String>,
    keep: bool,
) -> Result<(), String> {
    let dir = data_dir(&app)?;
    tauri::async_runtime::spawn_blocking(move || {
        set_keep(&dir, track_id.as_deref(), artist.as_deref(), title.as_deref(), keep)
    });
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    fn tmp() -> PathBuf {
        let d = std::env::temp_dir().join(format!("ss-stream-sources-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&d);
        std::fs::create_dir_all(&d).unwrap();
        d
    }

    #[test]
    fn keys_follow_the_page() {
        assert_eq!(
            keys(Some("42"), Some("Hermeth"), Some("Once Again")),
            vec!["t:42".to_string(), "n:hermeth|once again".to_string()]
        );
        assert_eq!(keys(None, Some("A"), None), Vec::<String>::new());
    }

    #[test]
    fn remember_then_lookup_by_either_key_and_keep_survives() {
        let d = tmp();
        remember(
            &d,
            &[RememberArg {
                track_id: Some("7".into()),
                artist: Some("Hermeth".into()),
                title: Some("Strictly Acid".into()),
                username: "peer".into(),
                path: "a\\b.flac".into(),
                size: 10,
                duration: Some(280.0),
                keep: None,
            }],
        );
        assert_eq!(lookup(&d, Some("7"), None, None).unwrap().path, "a\\b.flac");
        assert_eq!(lookup(&d, None, Some("hermeth"), Some("STRICTLY ACID")).unwrap().size, 10);
        set_keep(&d, Some("7"), None, None, true);
        // a re-remember without `keep` carries the pin forward
        remember(
            &d,
            &[RememberArg {
                track_id: Some("7".into()),
                artist: None,
                title: None,
                username: "peer2".into(),
                path: "c\\d.flac".into(),
                size: 11,
                duration: None,
                keep: None,
            }],
        );
        let s = lookup(&d, Some("7"), None, None).unwrap();
        assert_eq!(s.username, "peer2");
        assert!(s.keep);
        assert_eq!(kept_cache_files(&d).len(), 1);
    }

    #[test]
    fn cached_file_wants_the_whole_track() {
        let d = tmp();
        let src = StreamSource { username: "u".into(), path: "x\\y.mp3".into(), size: 3, duration: None, keep: false };
        assert!(cached_file(&d, &src).is_none());
        let f = crate::playback::cache_file_in(&crate::playback::cache_dir_in(&d), "u", "x\\y.mp3");
        std::fs::create_dir_all(f.parent().unwrap()).unwrap();
        std::fs::write(&f, b"ab").unwrap();
        assert!(cached_file(&d, &src).is_none(), "a prefix is not the track");
        std::fs::write(&f, b"abc").unwrap();
        assert_eq!(cached_file(&d, &src), Some(f));
    }
}