package com.vibevault.service;

import com.vibevault.dto.PlaylistDTO;
import com.vibevault.dto.SongCreateDTO;
import com.vibevault.dto.SongDTO;
import com.vibevault.exception.ResourceNotFoundException;
import com.vibevault.exception.UnauthorizedException;
import com.vibevault.model.Playlist;
import com.vibevault.model.Song;
import com.vibevault.model.User;
import com.vibevault.repository.PlaylistRepository;
import com.vibevault.repository.UserRepository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

/**
 * 歌单服务实现
 * 
 * 需要实现：
 * - 所有 PlaylistService 接口中定义的方法
 * - 将实体转换为 DTO 返回给调用者
 * - 资源不存在时抛出 ResourceNotFoundException
 * - [Challenge] 检查用户是否有权限操作歌单（所有权检查）
 */
@Service
public class PlaylistServiceImpl implements PlaylistService {

    private final PlaylistRepository playlistRepository;
    private final UserRepository userRepository;

    public PlaylistServiceImpl(PlaylistRepository playlistRepository, UserRepository userRepository) {
        this.playlistRepository = playlistRepository;
        this.userRepository = userRepository;
    }

    @Override
    public List<PlaylistDTO> getAllPlaylists() {
        return playlistRepository.findAll()
                .stream()
                .map(this::toDTO)
                .toList();
    }

    @Override
    public PlaylistDTO getPlaylistById(Long id) {
        Playlist playlist = playlistRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Playlist not found with id: " + id));
        return toDTO(playlist);
    }

    @Override
    @Transactional
    public PlaylistDTO createPlaylist(String name, String ownerUsername) {
        User owner = userRepository.findByUsername(ownerUsername)
                .orElseThrow(() -> new ResourceNotFoundException("User not found: " + ownerUsername));
        
        Playlist playlist = new Playlist(name, owner);
        Playlist savedPlaylist = playlistRepository.save(playlist);
        
        return toDTO(savedPlaylist);
    }

    @Override
    @Transactional
    public PlaylistDTO addSongToPlaylist(Long playlistId, SongCreateDTO song, String username) {
        Playlist playlist = playlistRepository.findById(playlistId)
                .orElseThrow(() -> new ResourceNotFoundException("Playlist not found with id: " + playlistId));
        
        // [Challenge] 检查用户是否有权限操作此歌单
        checkPermission(playlist, username);
        
        Song newSong = new Song(song.title(), song.artist(), song.durationInSeconds());
        playlist.addSong(newSong);
        
        Playlist updatedPlaylist = playlistRepository.save(playlist);
        return toDTO(updatedPlaylist);
    }

    @Override
    @Transactional
    public void removeSongFromPlaylist(Long playlistId, Long songId, String username) {
        Playlist playlist = playlistRepository.findById(playlistId)
                .orElseThrow(() -> new ResourceNotFoundException("Playlist not found with id: " + playlistId));
        
        // [Challenge] 检查用户是否有权限操作此歌单
        checkPermission(playlist, username);
        
        Song song = playlist.getSongs().stream()
                .filter(s -> s.getId().equals(songId))
                .findFirst()
                .orElseThrow(() -> new ResourceNotFoundException("Song not found with id: " + songId));
        
        playlist.removeSong(song);
        playlistRepository.save(playlist);
    }

    @Override
    @Transactional
    public void deletePlaylist(Long playlistId, String username) {
        Playlist playlist = playlistRepository.findById(playlistId)
                .orElseThrow(() -> new ResourceNotFoundException("Playlist not found with id: " + playlistId));
        
        // [Challenge] 检查用户是否有权限操作此歌单
        checkPermission(playlist, username);
        
        playlistRepository.delete(playlist);
    }

    // ========== Advanced 方法 ==========



    @Override
    @Transactional(readOnly = true)
    public List<PlaylistDTO> searchPlaylists(String keyword) {
        return playlistRepository.findByNameContainingIgnoreCase(keyword)
                .stream()
                .map(this::toDTO)
                .toList();
    }

    @Override
    @Transactional
    public PlaylistDTO copyPlaylist(Long playlistId, String newName, String username) {
        // 获取要复制的歌单
        Playlist originalPlaylist = playlistRepository.findById(playlistId)
                .orElseThrow(() -> new ResourceNotFoundException("Playlist not found with id: " + playlistId));
        
        // 获取当前用户（新歌单的所有者）
        User currentUser = userRepository.findByUsername(username)
                .orElseThrow(() -> new ResourceNotFoundException("User not found: " + username));
        
        // 创建新歌单
        Playlist copiedPlaylist = new Playlist(newName, currentUser);
        
        // 复制原歌单中的所有歌曲
        originalPlaylist.getSongs().forEach(originalSong -> {
            Song copiedSong = new Song(
                    originalSong.getTitle(),
                    originalSong.getArtist(),
                    originalSong.getDurationInSeconds()
            );
            copiedPlaylist.addSong(copiedSong);
        });
        
        // 保存新歌单
        Playlist savedPlaylist = playlistRepository.save(copiedPlaylist);
        
        return toDTO(savedPlaylist);
    }

    // ========== 辅助方法 ==========

    /**
     * 将 Playlist 实体转换为 DTO
     */
    private PlaylistDTO toDTO(Playlist playlist) {
        List<SongDTO> songDTOs = playlist.getSongs()
                .stream()
                .map(this::toSongDTO)
                .toList();
        
        return new PlaylistDTO(
                playlist.getId(),
                playlist.getName(),
                playlist.getOwner().getUsername(),
                songDTOs
        );
    }

    /**
     * 将 Song 实体转换为 DTO
     */
    private SongDTO toSongDTO(Song song) {
        return new SongDTO(
                song.getId(),
                song.getTitle(),
                song.getArtist(),
                song.getDurationInSeconds()
        );
    }

    /**
     * [Challenge] 检查用户是否有权限操作指定歌单
     * 规则：歌单所有者或管理员可以操作
     */
    private void checkPermission(Playlist playlist, String username) {
        User currentUser = userRepository.findByUsername(username)
                .orElseThrow(() -> new ResourceNotFoundException("User not found: " + username));
        
        // 检查是否是歌单所有者或管理员
        if (!playlist.getOwner().getUsername().equals(username) && !currentUser.getRole().equals("ROLE_ADMIN")) {
            throw new UnauthorizedException("You don't have permission to modify this playlist");
        }
    }
}