//! C4 — `TombstoneReconciler` (spec §6.7).
//!
//! Streams a chunk of local track ids, hits `getSong` per id, and
//! marks `track.deleted = 1` for every `SubsonicError::NotFound`
//! (error code 70). Designed for two callers:
//!
//! - **Mode A (manual integrity check):** Settings → "Verify library
//!   integrity" loops `reconcile_chunk(N)` until it returns
//!   `checked == 0`.
//! - **Mode B (auto, threshold-triggered):** the delta scheduler
//!   tests `should_auto_reconcile` against the count drop, then loops
//!   `reconcile_chunk(budget)` once per delta tick until the gap
//!   closes.
//!
//! Streaming so memory stays bounded at 500k: `LIMIT N ORDER BY
//! synced_at ASC` picks the next chunk; PR-3c keeps the loop entirely
//! caller-driven so cancellation is checked between chunks.

use std::sync::atomic::Ordering;
use std::sync::Arc;
use std::time::Duration;

use psysonic_integration::subsonic::{SubsonicClient, SubsonicError};

use super::backoff::{jitter_salt, with_jitter, Backoff};
use super::error::SyncError;
use crate::store::LibraryStore;

const MAX_ATTEMPTS_PER_BATCH: u32 = 5;

#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct TombstoneReport {
    pub checked: u32,
    pub deleted: u32,
}

pub struct TombstoneReconciler<'a> {
    store: &'a LibraryStore,
    subsonic: &'a SubsonicClient,
    server_id: String,
    cancel: Option<Arc<std::sync::atomic::AtomicBool>>,
    sleep_enabled: bool,
}

impl<'a> TombstoneReconciler<'a> {
    pub fn new(
        store: &'a LibraryStore,
        subsonic: &'a SubsonicClient,
        server_id: impl Into<String>,
    ) -> Self {
        Self {
            store,
            subsonic,
            server_id: server_id.into(),
            cancel: None,
            sleep_enabled: true,
        }
    }

    pub fn with_cancellation(mut self, flag: Arc<std::sync::atomic::AtomicBool>) -> Self {
        self.cancel = Some(flag);
        self
    }

    pub fn with_sleep_disabled(mut self) -> Self {
        self.sleep_enabled = false;
        self
    }

    /// Process up to `budget` not-yet-checked tracks. Returns counts
    /// for this call only — caller loops until `checked == 0` to
    /// complete a Mode A pass, or stops at any budget for Mode B
    /// sampled passes. Order: oldest `synced_at` first so the most
    /// stale rows get re-validated soonest.
    pub async fn reconcile_chunk(&self, budget: u32) -> Result<TombstoneReport, SyncError> {
        if budget == 0 {
            return Ok(TombstoneReport::default());
        }
        let ids = self.next_candidates(budget)?;
        let mut report = TombstoneReport::default();
        for id in ids {
            self.check_cancellation()?;
            report.checked = report.checked.saturating_add(1);
            let outcome = retry_with_backoff(
                self,
                || self.subsonic.get_song(&id),
                |e: SubsonicError| -> SyncError { e.into() },
            )
            .await;
            match outcome {
                Ok(_) => {
                    // Still present — stamp `synced_at` so it goes to
                    // the back of the queue and we don't re-probe it
                    // again on the next chunk.
                    self.mark_synced(&id)?;
                }
                Err(SyncError::NotFound) => {
                    self.mark_deleted(&id)?;
                    report.deleted = report.deleted.saturating_add(1);
                }
                Err(other) => return Err(other),
            }
        }
        Ok(report)
    }

    fn check_cancellation(&self) -> Result<(), SyncError> {
        if let Some(flag) = &self.cancel {
            if flag.load(Ordering::SeqCst) {
                return Err(SyncError::Cancelled);
            }
        }
        Ok(())
    }

    fn next_candidates(&self, budget: u32) -> Result<Vec<String>, SyncError> {
        self.store
            .with_conn("tombstone.next_candidates", |c| {
                let mut stmt = c.prepare(
                    "SELECT id FROM track \
                     WHERE server_id = ?1 AND deleted = 0 \
                     ORDER BY synced_at ASC LIMIT ?2",
                )?;
                let rows: rusqlite::Result<Vec<String>> = stmt
                    .query_map(rusqlite::params![self.server_id, budget as i64], |r| {
                        r.get::<_, String>(0)
                    })?
                    .collect();
                rows
            })
            .map_err(SyncError::Storage)
    }

    fn mark_deleted(&self, id: &str) -> Result<(), SyncError> {
        self.store
            .with_conn("tombstone.mark_deleted", |c| {
                c.execute(
                    "UPDATE track SET deleted = 1, synced_at = ?3 \
                     WHERE server_id = ?1 AND id = ?2",
                    rusqlite::params![self.server_id, id, now_unix_ms()],
                )?;
                Ok(())
            })
            .map_err(SyncError::Storage)
    }

    fn mark_synced(&self, id: &str) -> Result<(), SyncError> {
        self.store
            .with_conn("tombstone.mark_synced", |c| {
                c.execute(
                    "UPDATE track SET synced_at = ?3 \
                     WHERE server_id = ?1 AND id = ?2",
                    rusqlite::params![self.server_id, id, now_unix_ms()],
                )?;
                Ok(())
            })
            .map_err(SyncError::Storage)
    }

    async fn sleep(&self, d: Duration) {
        if self.sleep_enabled && !d.is_zero() {
            tokio::time::sleep(d).await;
        }
    }
}

/// §6.7 Mode B threshold check — returns `true` when the local /
/// server count gap exceeds the configured percentage. `server_count
/// == 0` is treated as "no signal" → `false` (no spurious reconcile
/// on a fresh server response).
pub fn should_auto_reconcile(local_count: u32, server_count: u32, threshold_pct: u32) -> bool {
    if server_count == 0 {
        return false;
    }
    let gap = local_count.saturating_sub(server_count);
    let ratio_x100 = gap.saturating_mul(100) / server_count;
    ratio_x100 > threshold_pct
}

fn now_unix_ms() -> i64 {
    use std::time::{SystemTime, UNIX_EPOCH};
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|d| d.as_millis().min(i64::MAX as u128) as i64)
        .unwrap_or(0)
}

async fn retry_with_backoff<'a, F, FFut, T, E>(
    reconciler: &TombstoneReconciler<'a>,
    mut build: F,
    map_err: impl Fn(E) -> SyncError,
) -> Result<T, SyncError>
where
    F: FnMut() -> FFut,
    FFut: std::future::Future<Output = Result<T, E>>,
{
    let mut backoff = Backoff::default();
    let mut attempt = 0u32;
    loop {
        reconciler.check_cancellation()?;
        attempt += 1;
        match build().await {
            Ok(v) => return Ok(v),
            Err(e) => {
                let mapped = map_err(e);
                if !is_retryable(&mapped) || attempt >= MAX_ATTEMPTS_PER_BATCH {
                    return Err(mapped);
                }
                let delay = backoff.next_delay();
                let jittered = with_jitter(delay, jitter_salt(attempt));
                reconciler.sleep(jittered).await;
            }
        }
    }
}

fn is_retryable(e: &SyncError) -> bool {
    matches!(e, SyncError::Transport(_) | SyncError::Navidrome(_))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::repos::{TrackRepository, TrackRow};
    use psysonic_integration::subsonic::{SubsonicClient, SubsonicCredentials};
    use serde_json::json;
    use wiremock::matchers::{method as wm_method, path as wm_path, query_param};
    use wiremock::{Mock, MockServer, ResponseTemplate};

    fn test_subsonic(uri: &str) -> SubsonicClient {
        SubsonicClient::with_static_credentials(
            uri,
            SubsonicCredentials::with_static("user", "tok", "salt"),
            reqwest::Client::new(),
        )
    }

    fn seed_track(store: &LibraryStore, id: &str, synced_at: i64) {
        TrackRepository::new(store)
            .upsert_batch(&[TrackRow {
                server_id: "s1".into(),
                id: id.into(),
                title: id.into(),
                title_sort: None,
                artist: None,
                artist_id: None,
                album: String::new(),
                album_id: None,
                album_artist: None,
                duration_sec: 0,
                track_number: None,
                disc_number: None,
                year: None,
                genre: None,
                suffix: None,
                bit_rate: None,
                size_bytes: None,
                cover_art_id: None,
                starred_at: None,
                user_rating: None,
                play_count: None,
                played_at: None,
                server_path: None,
                library_id: None,
                isrc: None,
                mbid_recording: None,
                bpm: None,
                replay_gain_track_db: None,
                replay_gain_album_db: None,
                content_hash: None,
                server_updated_at: None,
                server_created_at: None,
                deleted: false,
                synced_at,
                raw_json: "{}".into(),
            }])
            .unwrap();
    }

    // ── should_auto_reconcile threshold predicate ─────────────────────

    #[test]
    fn threshold_fires_when_local_outpaces_server_above_pct() {
        // 110 local vs 100 server → 10% gap > 5% threshold.
        assert!(should_auto_reconcile(110, 100, 5));
    }

    #[test]
    fn threshold_stays_silent_within_tolerance() {
        // 102 local vs 100 server → 2% gap, threshold 5%.
        assert!(!should_auto_reconcile(102, 100, 5));
    }

    #[test]
    fn threshold_silent_when_local_is_below_or_equal_server() {
        assert!(!should_auto_reconcile(100, 100, 0));
        assert!(!should_auto_reconcile(50, 100, 5));
    }

    #[test]
    fn threshold_silent_when_server_count_is_zero() {
        // No signal — never reconcile on a server that's still scanning.
        assert!(!should_auto_reconcile(1000, 0, 5));
    }

    // ── reconcile_chunk marks deleted on code 70 ─────────────────────

    #[tokio::test(flavor = "multi_thread")]
    async fn reconcile_chunk_marks_deleted_for_code_70() {
        let server = MockServer::start().await;
        // tr_a → still present, tr_b → 404 via code 70.
        Mock::given(wm_method("GET"))
            .and(wm_path("/rest/getSong.view"))
            .and(query_param("id", "tr_a"))
            .respond_with(ResponseTemplate::new(200).set_body_json(json!({
                "subsonic-response": {
                    "status": "ok",
                    "song": { "id": "tr_a", "title": "Still here" }
                }
            })))
            .mount(&server)
            .await;
        Mock::given(wm_method("GET"))
            .and(wm_path("/rest/getSong.view"))
            .and(query_param("id", "tr_b"))
            .respond_with(ResponseTemplate::new(200).set_body_json(json!({
                "subsonic-response": {
                    "status": "failed",
                    "error": { "code": 70, "message": "Song not found" }
                }
            })))
            .mount(&server)
            .await;

        let store = LibraryStore::open_in_memory();
        seed_track(&store, "tr_a", 1);
        seed_track(&store, "tr_b", 2);

        let subsonic = test_subsonic(&server.uri());
        let report = TombstoneReconciler::new(&store, &subsonic, "s1")
            .with_sleep_disabled()
            .reconcile_chunk(10)
            .await
            .unwrap();

        assert_eq!(report.checked, 2);
        assert_eq!(report.deleted, 1);

        // tr_b is marked deleted; tr_a stays live but its synced_at is
        // refreshed (so it doesn't get re-picked immediately).
        let (a_deleted, b_deleted): (i64, i64) = store
            .with_conn("misc", |c| {
                let a: i64 = c.query_row(
                    "SELECT deleted FROM track WHERE id='tr_a'",
                    [],
                    |r| r.get(0),
                )?;
                let b: i64 = c.query_row(
                    "SELECT deleted FROM track WHERE id='tr_b'",
                    [],
                    |r| r.get(0),
                )?;
                Ok((a, b))
            })
            .unwrap();
        assert_eq!(a_deleted, 0);
        assert_eq!(b_deleted, 1);
    }

    // ── reconcile_chunk respects budget and ordering ─────────────────

    #[tokio::test(flavor = "multi_thread")]
    async fn reconcile_chunk_processes_oldest_first_up_to_budget() {
        let server = MockServer::start().await;
        // Any id → ok envelope.
        Mock::given(wm_method("GET"))
            .and(wm_path("/rest/getSong.view"))
            .respond_with(ResponseTemplate::new(200).set_body_json(json!({
                "subsonic-response": {
                    "status": "ok",
                    "song": { "id": "any", "title": "t" }
                }
            })))
            .mount(&server)
            .await;

        let store = LibraryStore::open_in_memory();
        // Seed three tracks with distinct synced_at values; oldest first.
        seed_track(&store, "tr_oldest", 100);
        seed_track(&store, "tr_middle", 200);
        seed_track(&store, "tr_newest", 300);

        let subsonic = test_subsonic(&server.uri());
        let report = TombstoneReconciler::new(&store, &subsonic, "s1")
            .with_sleep_disabled()
            .reconcile_chunk(2)
            .await
            .unwrap();
        assert_eq!(report.checked, 2);

        // After the chunk: the two checked rows have a refreshed
        // synced_at; the un-checked tr_newest still sits at 300.
        let untouched: i64 = store
            .with_conn("misc", |c| c.query_row(
                "SELECT synced_at FROM track WHERE id='tr_newest'",
                [],
                |r| r.get(0),
            ))
            .unwrap();
        assert_eq!(untouched, 300, "tr_newest must not be probed within budget=2");
    }

    // ── reconcile_chunk: empty store ───────────────────────────────────

    #[tokio::test(flavor = "multi_thread")]
    async fn reconcile_chunk_returns_zero_counts_on_empty_store() {
        let server = MockServer::start().await;
        let store = LibraryStore::open_in_memory();
        let subsonic = test_subsonic(&server.uri());
        let report = TombstoneReconciler::new(&store, &subsonic, "s1")
            .with_sleep_disabled()
            .reconcile_chunk(50)
            .await
            .unwrap();
        assert_eq!(report.checked, 0);
        assert_eq!(report.deleted, 0);
    }

    // ── reconcile_chunk: cancellation ─────────────────────────────────

    #[tokio::test(flavor = "multi_thread")]
    async fn reconcile_chunk_returns_cancelled_when_flag_tripped() {
        let server = MockServer::start().await;
        let store = LibraryStore::open_in_memory();
        seed_track(&store, "tr_x", 1);

        let flag = Arc::new(std::sync::atomic::AtomicBool::new(true));
        let subsonic = test_subsonic(&server.uri());
        let err = TombstoneReconciler::new(&store, &subsonic, "s1")
            .with_cancellation(flag)
            .with_sleep_disabled()
            .reconcile_chunk(10)
            .await
            .unwrap_err();
        assert!(matches!(err, SyncError::Cancelled));
    }
}