package watchlist

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"

	"github.com/google/uuid"

	"mal/integrations/jikan"
	"mal/internal/db"
)

type Service struct {
	db          db.Querier
	sqlDB       *sql.DB
	jikanClient *jikan.Client
}

var (
	ErrInvalidAnimeID = errors.New("invalid anime ID")
	ErrInvalidStatus  = errors.New("invalid watchlist status")
)

var validStatuses = map[string]struct{}{
	"watching":      {},
	"completed":     {},
	"dropped":       {},
	"plan_to_watch": {},
	"on_hold":       {},
}

func NewService(db db.Querier, sqlDB *sql.DB, jikanClient *jikan.Client) *Service {
	return &Service{db: db, sqlDB: sqlDB, jikanClient: jikanClient}
}

// ensureAnimeExists checks if anime exists in db, fetches from jikan if not, then upserts.
func (s *Service) ensureAnimeExists(ctx context.Context, animeID int64) error {
	_, err := s.db.GetAnime(ctx, animeID)
	if err == nil {
		return nil // already exists
	}

	// fetch from jikan and store locally
	anime, err := s.jikanClient.GetAnimeByID(ctx, int(animeID))
	if err != nil {
		return fmt.Errorf("failed to fetch anime from jikan: %w", err)
	}

	_, err = s.db.UpsertAnime(ctx, db.UpsertAnimeParams{
		ID:            int64(anime.MalID),
		TitleOriginal: anime.Title,
		TitleEnglish:  sql.NullString{String: anime.TitleEnglish, Valid: anime.TitleEnglish != ""},
		TitleJapanese: sql.NullString{String: anime.TitleJapanese, Valid: anime.TitleJapanese != ""},
		ImageUrl:      anime.Images.Jpg.LargeImageURL,
		Airing:        sql.NullBool{Bool: anime.Airing, Valid: true},
	})
	if err != nil {
		return fmt.Errorf("failed to save anime: %w", err)
	}

	return nil
}

type AddRequest struct {
	AnimeID       int64
	TitleOriginal string
	TitleEnglish  string
	TitleJapanese string
	ImageURL      string
	Status        string
	Airing        bool
}

// AddToWatchlist adds or updates an anime entry in user's watchlist.
func (s *Service) AddToWatchlist(ctx context.Context, userID string, animeID int64, status string) error {
	if animeID <= 0 {
		return ErrInvalidAnimeID
	}

	if _, ok := validStatuses[status]; !ok {
		return ErrInvalidStatus
	}

	// ensure anime exists in local db before linking
	if err := s.ensureAnimeExists(ctx, animeID); err != nil {
		return err
	}

	entryID := uuid.New().String()
	_, err := s.db.UpsertWatchListEntry(ctx, db.UpsertWatchListEntryParams{
		ID:                 entryID,
		UserID:             userID,
		AnimeID:            animeID,
		Status:             status,
		CurrentEpisode:     sql.NullInt64{Valid: false},
		CurrentTimeSeconds: 0,
	})
	if err != nil {
		return fmt.Errorf("failed to update watchlist: %w", err)
	}

	return nil
}

// RemoveEntry deletes a watchlist entry and returns the anime for potential use.
func (s *Service) RemoveEntry(ctx context.Context, userID string, animeID int64) (db.Anime, error) {
	if animeID <= 0 {
		return db.Anime{}, ErrInvalidAnimeID
	}

	anime, err := s.db.GetAnime(ctx, animeID)
	if err != nil {
		return db.Anime{}, fmt.Errorf("anime not found: %w", err)
	}

	err = s.db.DeleteWatchListEntry(ctx, db.DeleteWatchListEntryParams{
		UserID:  userID,
		AnimeID: animeID,
	})
	if err != nil {
		return db.Anime{}, fmt.Errorf("failed to delete from watchlist: %w", err)
	}

	return anime, nil
}

// GetUserWatchlist retrieves all watchlist entries for a user.
func (s *Service) GetUserWatchlist(ctx context.Context, userID string) ([]db.GetUserWatchListRow, error) {
	entries, err := s.db.GetUserWatchList(ctx, userID)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch watchlist: %w", err)
	}
	return entries, nil
}

// DeleteContinueWatching removes entry and clears associated watch progress.
// uses transaction when sqlDB is available.
func (s *Service) DeleteContinueWatching(ctx context.Context, userID string, animeID int64) error {
	if strings.TrimSpace(userID) == "" {
		return errors.New("invalid user id")
	}

	if animeID <= 0 {
		return ErrInvalidAnimeID
	}

	params := db.DeleteContinueWatchingEntryParams{
		UserID:  userID,
		AnimeID: animeID,
	}

	clearProgress := db.SaveWatchProgressParams{
		CurrentEpisode:     sql.NullInt64{Valid: false},
		CurrentTimeSeconds: 0,
		UserID:             userID,
		AnimeID:            animeID,
	}

	// use transaction when sqlDB available for consistency
	if s.sqlDB == nil {
		if err := s.db.DeleteContinueWatchingEntry(ctx, params); err != nil {
			return fmt.Errorf("failed to delete continue watching entry: %w", err)
		}
		return s.db.SaveWatchProgress(ctx, clearProgress)
	}

	txQueries, tx, err := db.BeginTx(ctx, s.sqlDB)
	if err != nil {
		return fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	if err := txQueries.DeleteContinueWatchingEntry(ctx, params); err != nil {
		return fmt.Errorf("failed to delete continue watching entry: %w", err)
	}
	if err := txQueries.SaveWatchProgress(ctx, clearProgress); err != nil {
		return fmt.Errorf("failed to clear watchlist progress: %w", err)
	}

	return tx.Commit()
}