// Package tracks owns the track-level admin actions exposed by the
// M7 #372 track-actions menu. Today that's RemoveTrack: the destructive
// part is always handled directly by Minstrel (os.Remove + DB delete +
// cascade); when the operator opts in via `unmonitor=true` the service
// also tells Lidarr to flip the track's monitored flag off so Lidarr
// doesn't search for a replacement.
//
// History: an earlier shape (commit 50a231f, since rewritten) routed
// Lidarr-managed tracks through lidarrquarantine.DeleteViaLidarr — but
// that primitive deletes the entire **album** in Lidarr (Lidarr is
// album-granular and has no per-track delete API), which would silently
// drop sibling tracks the operator didn't ask to remove. The current
// shape per spec revision 723eee9 is "always direct delete; opt-in
// Lidarr unmonitor for replacement-suppression."
package tracks

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"os"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgtype"
	"github.com/jackc/pgx/v5/pgxpool"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/coverart"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
)

// ErrNotFound is returned when the track id doesn't resolve. Aliased
// to apierror.ErrNotFound so handlers can errors.Is against the shared
// sentinel; existing tracks.ErrNotFound callsites still resolve to the
// same pointer.
var ErrNotFound = apierror.ErrNotFound

// LidarrUnmonitorer is the subset of *lidarr.Client RemoveTrack uses.
// Defined as an interface so tests can stub without spinning up a Lidarr
// httptest server. UnmonitorTrack failures are non-fatal at the service
// layer — the file + DB are already gone — so any error returned here
// surfaces as a `lidarr_unmonitor_failed` flag in the response, not as
// a hard error.
type LidarrUnmonitorer interface {
	UnmonitorTrack(ctx context.Context, trackMbid, albumMbid string) error
}

// Service owns RemoveTrack. lidarr may be nil — when it is, the
// unmonitor branch is skipped entirely (with `lidarrUnmonitorFailed`
// remaining false) regardless of the unmonitor query param. This is
// the right fallback when Lidarr isn't configured: file + DB delete
// still happen.
type Service struct {
	pool    *pgxpool.Pool
	logger  *slog.Logger
	lidarr  LidarrUnmonitorer
	dataDir string
}

// NewService constructs a Service. logger may be nil (defaults to
// slog.Default). lidarr may be nil to disable the unmonitor branch.
// dataDir is the on-disk root for cached artifacts; used to clean up
// artist-art on artist delete. Empty string disables the cleanup.
func NewService(pool *pgxpool.Pool, logger *slog.Logger, lidarr LidarrUnmonitorer, dataDir string) *Service {
	if logger == nil {
		logger = slog.Default()
	}
	return &Service{pool: pool, logger: logger, lidarr: lidarr, dataDir: dataDir}
}

// RemoveTrack deletes the file from disk and the DB rows, runs the
// album-empty / artist-empty cascade tidy-up, and (when unmonitor is
// true and the track is Lidarr-managed) tells Lidarr to flip the track's
// monitored flag off so it won't search for a replacement.
//
// Returns:
//   - deletedAlbumID: non-nil when removing the track left the album
//     empty and the album row was deleted.
//   - deletedArtistID: non-nil when both album AND artist were left
//     empty (only set if deletedAlbumID is also set).
//   - lidarrUnmonitorFailed: true when the operator requested unmonitor
//     and the Lidarr call failed; the file + DB delete still succeeded.
//   - err: only for failures *before* the destructive part completes.
//     A failed os.Remove is logged and tolerated. A failed Lidarr
//     unmonitor is reflected in the bool flag, not the error.
//
// adminID is currently unused — the cascade audit-log line that would
// reference it isn't wired in this slice. It's threaded through the
// signature so the upcoming admin_tracks handler doesn't have to
// re-plumb when audit logging lands.
func (s *Service) RemoveTrack(
	ctx context.Context,
	trackID, adminID pgtype.UUID, //nolint:revive // adminID reserved for audit-log wiring in a follow-up
	unmonitor bool,
) (deletedAlbumID *pgtype.UUID, deletedArtistID *pgtype.UUID, lidarrUnmonitorFailed bool, err error) {
	q := dbq.New(s.pool)

	track, err := q.GetTrackByID(ctx, trackID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil, false, ErrNotFound
		}
		return nil, nil, false, fmt.Errorf("get track: %w", err)
	}

	// Capture the album's mbid *before* the cascade-delete transaction.
	// If removing this track empties the album, DeleteAlbumIfEmpty
	// removes the row and a post-commit GetAlbumByID would return
	// pgx.ErrNoRows — leaving the unmonitor walk with no album mbid.
	var albumMbid string
	if track.Mbid != nil && *track.Mbid != "" && unmonitor && s.lidarr != nil {
		alb, alerr := q.GetAlbumByID(ctx, track.AlbumID)
		if alerr == nil && alb.Mbid != nil {
			albumMbid = *alb.Mbid
		}
		// Lookup failure is tolerated — handled below as
		// "no albumMbid → can't unmonitor → flag failure."
	}

	// Always: remove the file. Tolerate already-missing.
	if track.FilePath != "" {
		if rerr := os.Remove(track.FilePath); rerr != nil && !errors.Is(rerr, os.ErrNotExist) {
			s.logger.Warn("track delete: file remove failed",
				"path", track.FilePath, "track_id", trackID, "err", rerr)
			// Proceed: DB consistency is the priority.
		}
	}

	// DB cleanup in a transaction so a midway failure leaves things consistent.
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return nil, nil, false, fmt.Errorf("begin tx: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	tq := dbq.New(tx)

	deleted, err := tq.DeleteTrack(ctx, trackID)
	if err != nil {
		return nil, nil, false, fmt.Errorf("delete track: %w", err)
	}

	albumRow, aerr := tq.DeleteAlbumIfEmpty(ctx, deleted.AlbumID)
	switch {
	case aerr == nil:
		albumID := albumRow.ID
		deletedAlbumID = &albumID
		artistID, arerr := tq.DeleteArtistIfEmpty(ctx, albumRow.ArtistID)
		switch {
		case arerr == nil:
			id := artistID
			deletedArtistID = &id
		case errors.Is(arerr, pgx.ErrNoRows):
			// Artist still has other albums or stray tracks. OK.
		default:
			return nil, nil, false, fmt.Errorf("delete artist if empty: %w", arerr)
		}
	case errors.Is(aerr, pgx.ErrNoRows):
		// Album still has other tracks. OK.
	default:
		return nil, nil, false, fmt.Errorf("delete album if empty: %w", aerr)
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, nil, false, fmt.Errorf("commit: %w", err)
	}

	// Cleanup artist-art filesystem cache if the delete cascade orphaned
	// an artist. Non-fatal — the destructive part is done; we just want
	// to keep the dataDir tidy.
	if deletedArtistID != nil && s.dataDir != "" {
		if err := coverart.CleanupArtistArt(s.dataDir, *deletedArtistID); err != nil {
			s.logger.Warn("track delete: artist-art cleanup failed",
				"artist_id", *deletedArtistID, "err", err)
		}
	}

	// Lidarr unmonitor — non-fatal. The destructive part is done; any
	// failure here is informational so the operator can retry manually.
	if unmonitor && track.Mbid != nil && *track.Mbid != "" && s.lidarr != nil {
		if albumMbid == "" {
			// Couldn't capture the album mbid (album row had nil mbid
			// or was missing somehow). The Lidarr walk needs it; mark
			// failure rather than calling with an empty string.
			s.logger.Warn("track delete: lidarr unmonitor skipped — no album mbid",
				"track_id", trackID, "track_mbid", *track.Mbid)
			lidarrUnmonitorFailed = true
		} else if uerr := s.lidarr.UnmonitorTrack(ctx, *track.Mbid, albumMbid); uerr != nil {
			s.logger.Warn("track delete: lidarr unmonitor failed",
				"track_id", trackID, "track_mbid", *track.Mbid, "err", uerr)
			lidarrUnmonitorFailed = true
		}
	}

	return deletedAlbumID, deletedArtistID, lidarrUnmonitorFailed, nil
}