package playback

import (
	"context"
	"errors"
	"strings"
	"unicode/utf8"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"

	"pipu/api/internal/api/gen"
	"pipu/api/internal/platform/apperr"
)

func validatePlaylist(name, description string, ids []uuid.UUID) error {
	if n := utf8.RuneCountInString(strings.TrimSpace(name)); n < 1 || n > 120 {
		return apperr.Validation("name", "playlist.invalid_name", "name must contain 1–120 characters", nil)
	}
	if utf8.RuneCountInString(description) > 2000 || len(ids) > 2000 {
		return apperr.Validation("playlist", "playlist.too_large", "maximum 2000 description characters and tracks", nil)
	}
	seen := map[uuid.UUID]bool{}
	for _, id := range ids {
		if id == uuid.Nil || seen[id] {
			return apperr.Validation("track_ids", "playlist.invalid_tracks", "track IDs must be unique and nonzero", nil)
		}
		seen[id] = true
	}
	return nil
}

const playlistSelect = `SELECT p.id, p.name, p.description, p.revision, p.created_at, p.updated_at,
 (SELECT count(*) FROM playlist_tracks pt WHERE pt.playlist_id=p.id),
 COALESCE((SELECT sum(t.duration_ms) FROM playlist_tracks pt JOIN tracks t ON t.id=pt.track_id WHERE pt.playlist_id=p.id),0)
 FROM playlists p`

func scanPlaylist(row pgx.Row) (gen.PlaylistSummary, error) {
	var p gen.PlaylistSummary
	err := row.Scan(&p.Id, &p.Name, &p.Description, &p.Revision, &p.CreatedAt, &p.UpdatedAt, &p.TrackCount, &p.DurationMs)
	if errors.Is(err, pgx.ErrNoRows) {
		return p, apperr.NotFound("playlist.not_found", "playlist not found")
	}
	return p, err
}

func (h *Handler) ListPlaylists(ctx context.Context, _ gen.ListPlaylistsRequestObject) (gen.ListPlaylistsResponseObject, error) {
	user, err := principal(ctx)
	if err != nil {
		return nil, err
	}
	rows, err := h.store.pool.Query(ctx, playlistSelect+` WHERE p.user_id=$1 ORDER BY p.updated_at DESC, p.id`, user.UserID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := gen.PlaylistList{Items: []gen.PlaylistSummary{}}
	for rows.Next() {
		p, err := scanPlaylist(rows)
		if err != nil {
			return nil, err
		}
		out.Items = append(out.Items, p)
	}
	return gen.ListPlaylists200JSONResponse(out), rows.Err()
}

func (h *Handler) playlist(ctx context.Context, user, id uuid.UUID) (gen.Playlist, error) {
	var out gen.Playlist
	tx, err := h.store.pool.BeginTx(ctx, pgx.TxOptions{IsoLevel: pgx.RepeatableRead, AccessMode: pgx.ReadOnly})
	if err != nil {
		return out, err
	}
	defer tx.Rollback(ctx)
	p, err := scanPlaylist(tx.QueryRow(ctx, playlistSelect+` WHERE p.user_id=$1 AND p.id=$2`, user, id))
	if err != nil {
		return out, err
	}
	rows, err := tx.Query(ctx, `SELECT track_id FROM playlist_tracks WHERE playlist_id=$1 ORDER BY position`, id)
	if err != nil {
		return out, err
	}
	ids, err := pgx.CollectRows(rows, pgx.RowTo[uuid.UUID])
	if err != nil {
		return out, err
	}
	if err = tx.Commit(ctx); err != nil {
		return out, err
	}
	tracks, err := h.catalog.TracksByIDs(ctx, ids)
	if err != nil {
		return out, err
	}
	dtos, err := h.dto.Tracks(ctx, tracks)
	if err != nil {
		return out, err
	}
	if dtos == nil {
		dtos = []gen.Track{}
	}
	out = gen.Playlist{Id: p.Id, Name: p.Name, Description: p.Description, Revision: p.Revision, CreatedAt: p.CreatedAt, UpdatedAt: p.UpdatedAt, TrackCount: len(dtos), Tracks: dtos}
	for _, t := range dtos {
		out.DurationMs += int64(t.DurationMs)
	}
	return out, nil
}

func (h *Handler) GetPlaylist(ctx context.Context, req gen.GetPlaylistRequestObject) (gen.GetPlaylistResponseObject, error) {
	user, err := principal(ctx)
	if err != nil {
		return nil, err
	}
	p, err := h.playlist(ctx, user.UserID, req.Id)
	if err != nil {
		return nil, err
	}
	return gen.GetPlaylist200JSONResponse(p), nil
}

// A row lock plus revision check prevents stale clients from overwriting each other.
// Replacing ordered membership is atomic, including validation of all foreign keys.
func (st *Store) savePlaylist(ctx context.Context, user, id uuid.UUID, name, description string, ids []uuid.UUID, revision int, create bool) error {
	if err := validatePlaylist(name, description, ids); err != nil {
		return err
	}
	tx, err := st.pool.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(ctx)
	if create {
		_, err = tx.Exec(ctx, `INSERT INTO playlists(id,user_id,name,description) VALUES($1,$2,$3,$4)`, id, user, strings.TrimSpace(name), description)
	} else {
		var current int
		err = tx.QueryRow(ctx, `SELECT revision FROM playlists WHERE id=$1 AND user_id=$2 FOR UPDATE`, id, user).Scan(&current)
		if errors.Is(err, pgx.ErrNoRows) {
			return apperr.NotFound("playlist.not_found", "playlist not found")
		}
		if err != nil {
			return err
		}
		if current != revision {
			return apperr.Conflict("playlist.conflict", "playlist changed; reload before editing")
		}
		_, err = tx.Exec(ctx, `UPDATE playlists SET name=$3, description=$4, revision=revision+1, updated_at=now() WHERE id=$1 AND user_id=$2`, id, user, strings.TrimSpace(name), description)
	}
	if err != nil {
		return err
	}
	if _, err = tx.Exec(ctx, `DELETE FROM playlist_tracks WHERE playlist_id=$1`, id); err != nil {
		return err
	}
	if len(ids) > 0 {
		_, err = tx.Exec(ctx, `INSERT INTO playlist_tracks(playlist_id,track_id,position) SELECT $1, id, ord-1 FROM unnest($2::uuid[]) WITH ORDINALITY AS x(id,ord)`, id, ids)
		if err != nil {
			var pgerr *pgconn.PgError
			if errors.As(err, &pgerr) && pgerr.Code == "23503" {
				return apperr.Validation("track_ids", "playlist.invalid_tracks", "track no longer exists", nil)
			}
			return err
		}
	}
	return tx.Commit(ctx)
}

func (h *Handler) CreatePlaylist(ctx context.Context, req gen.CreatePlaylistRequestObject) (gen.CreatePlaylistResponseObject, error) {
	user, err := principal(ctx)
	if err != nil {
		return nil, err
	}
	if req.Body == nil {
		return nil, apperr.Validation("body", "playlist.invalid_name", "body required", nil)
	}
	id := uuid.New()
	b := req.Body
	if err = h.store.savePlaylist(ctx, user.UserID, id, b.Name, b.Description, b.TrackIds, 0, true); err != nil {
		return nil, err
	}
	p, err := h.playlist(ctx, user.UserID, id)
	if err != nil {
		return nil, err
	}
	return gen.CreatePlaylist201JSONResponse(p), nil
}

func (h *Handler) UpdatePlaylist(ctx context.Context, req gen.UpdatePlaylistRequestObject) (gen.UpdatePlaylistResponseObject, error) {
	user, err := principal(ctx)
	if err != nil {
		return nil, err
	}
	if req.Body == nil {
		return nil, apperr.Validation("body", "playlist.invalid_name", "body required", nil)
	}
	b := req.Body
	if err = h.store.savePlaylist(ctx, user.UserID, req.Id, b.Name, b.Description, b.TrackIds, b.Revision, false); err != nil {
		return nil, err
	}
	p, err := h.playlist(ctx, user.UserID, req.Id)
	if err != nil {
		return nil, err
	}
	return gen.UpdatePlaylist200JSONResponse(p), nil
}

func (h *Handler) DeletePlaylist(ctx context.Context, req gen.DeletePlaylistRequestObject) (gen.DeletePlaylistResponseObject, error) {
	user, err := principal(ctx)
	if err != nil {
		return nil, err
	}
	result, err := h.store.pool.Exec(ctx, `DELETE FROM playlists WHERE id=$1 AND user_id=$2`, req.Id, user.UserID)
	if err != nil {
		return nil, err
	}
	if result.RowsAffected() == 0 {
		return nil, apperr.NotFound("playlist.not_found", "playlist not found")
	}
	return gen.DeletePlaylist204Response{}, nil
}