package library

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"log/slog"
	"os"
	"path/filepath"
	"syscall"

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

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

// ErrTrackNotFound is returned when DeleteTrackFile is called with an id
// that has no row in tracks.
var ErrTrackNotFound = errors.New("library: track not found")

// removeFile is os.Remove behind a variable so a test can make removal fail the
// way a read-only mount or a wrongly-owned directory does. A chmod-based test
// cannot stand in for that: root ignores permission bits, so in a CI container
// running as root it would pass without ever exercising the failure.
var removeFile = os.Remove

// FileRemoveError reports that a track's file exists but could not be removed.
// When DeleteTrackFile returns one, NOTHING was deleted: the row, its likes, its
// play history and its playlist memberships are all intact.
type FileRemoveError struct {
	Path string
	// UID and GID are the identity the server process runs as — the half of a
	// permission problem the operator cannot see from the host side.
	UID, GID int
	Err      error
}

func (e *FileRemoveError) Error() string { return fmt.Sprintf("remove track file: %v", e.Err) }

func (e *FileRemoveError) Unwrap() error { return e.Err }

// Dir is the directory removal needs write access to. Unlinking a file writes to
// its PARENT, so a world-writable file inside a read-only directory still cannot
// be removed — naming the file's own permissions would send the operator to the
// wrong place.
func (e *FileRemoveError) Dir() string { return filepath.Dir(e.Path) }

// NotWritable reports whether the library is unwritable for this process — a
// read-only mount or a permission denial — rather than an I/O fault. It is the
// case the operator can fix, so callers answer it differently.
func (e *FileRemoveError) NotWritable() bool {
	return errors.Is(e.Err, fs.ErrPermission) || errors.Is(e.Err, syscall.EROFS)
}

// Reason is the underlying cause without the path os.Remove already wrapped
// around it, for messages that name the directory themselves.
func (e *FileRemoveError) Reason() string {
	var pathErr *fs.PathError
	if errors.As(e.Err, &pathErr) {
		return pathErr.Err.Error()
	}
	return e.Err.Error()
}

// DeletedTrack reports what a delete tidied away beyond the track itself.
type DeletedTrack struct {
	// AlbumID is set when the track was its album's last, so the album went too.
	AlbumID *pgtype.UUID
	// ArtistID is set when that album was its artist's last, so the artist went too.
	ArtistID *pgtype.UUID
}

// DeleteTrackFile removes a track's file from disk and then its row, tidying
// away an album or artist the delete leaves empty. It is the ONLY path that
// deletes a track file: the admin remove-track endpoint and quarantine's Delete
// file both come through here (#3918).
//
// Order is the whole contract. The file goes first, and if it cannot go — a
// read-only mount, a permission denial, an I/O error — nothing else happens and
// a *FileRemoveError comes back. Proceeding past that failure is how #3918 lost
// history: tracks CASCADEs to play_events, general_likes, contextual_likes,
// playlist_tracks, track_tags and playback_errors, so the row and everything
// hanging off it were destroyed while the file survived, and the next scan
// re-imported it as a brand-new track with none of it.
//
// A file that is already gone (fs.ErrNotExist) is not a failure; the row is
// removed as asked.
//
// This is NOT the missing-file path. That lifecycle is deliberately
// non-destructive: reconcile stamps missing_since (#2523), selection paths
// filter on it, and a returning file is un-marked or adopted (#2528). This is the
// explicit, irreversible "remove this recording", never the way to tidy up a row
// whose file merely went away.
//
// dataDir, when set, also clears the cached art of an artist the delete removed.
// logger may be nil.
func DeleteTrackFile(
	ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger, dataDir string, trackID pgtype.UUID,
) (DeletedTrack, error) {
	if logger == nil {
		logger = slog.Default()
	}
	q := dbq.New(pool)
	track, err := q.GetTrackByID(ctx, trackID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return DeletedTrack{}, ErrTrackNotFound
		}
		return DeletedTrack{}, fmt.Errorf("get track: %w", err)
	}

	if err := removeFile(track.FilePath); err != nil && !errors.Is(err, fs.ErrNotExist) {
		return DeletedTrack{}, &FileRemoveError{
			Path: track.FilePath, UID: os.Getuid(), GID: os.Getgid(), Err: err,
		}
	}

	// The row and any album or artist it empties go together, so a failure
	// partway cannot leave a deleted track with a ghost album behind it.
	tx, err := pool.Begin(ctx)
	if err != nil {
		return DeletedTrack{}, fmt.Errorf("begin tx: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()
	tq := dbq.New(tx)

	deleted, err := tq.DeleteTrack(ctx, trackID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			// Removed by someone else between the lookup and here.
			return DeletedTrack{}, ErrTrackNotFound
		}
		return DeletedTrack{}, fmt.Errorf("delete track: %w", err)
	}

	var out DeletedTrack
	album, err := tq.DeleteAlbumIfEmpty(ctx, deleted.AlbumID)
	switch {
	case err == nil:
		albumID := album.ID
		out.AlbumID = &albumID
		artistID, aerr := tq.DeleteArtistIfEmpty(ctx, album.ArtistID)
		switch {
		case aerr == nil:
			out.ArtistID = &artistID
		case errors.Is(aerr, pgx.ErrNoRows):
			// The artist still has other albums or stray tracks.
		default:
			return DeletedTrack{}, fmt.Errorf("delete artist if empty: %w", aerr)
		}
	case errors.Is(err, pgx.ErrNoRows):
		// The album still has other tracks.
	default:
		return DeletedTrack{}, fmt.Errorf("delete album if empty: %w", err)
	}

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

	// Both of these run after the delete has committed, so neither may fail
	// it: the recording is gone either way. An unlogged change leaves the track
	// in offline clients' caches until the next scan touches its album; a
	// leftover art directory is only disk.
	if err := syncpkg.LogChange(ctx, pool, syncpkg.EntityTrack,
		syncpkg.FormatUUID(trackID), syncpkg.OpDelete); err != nil {
		logger.Warn("track delete: LogChange failed", "track_id", syncpkg.FormatUUID(trackID), "err", err)
	}
	if out.ArtistID != nil && dataDir != "" {
		if err := coverart.CleanupArtistArt(dataDir, *out.ArtistID); err != nil {
			logger.Warn("track delete: artist-art cleanup failed",
				"artist_id", syncpkg.FormatUUID(*out.ArtistID), "err", err)
		}
	}
	return out, nil
}