-- 051_stats_views.sql
-- Database Views for Common Queries (BE-DB-013: Add database views for common queries)
-- Create views for user_stats, track_stats, playlist_stats

-- === USER_STATS VIEW ===
-- View for user statistics aggregating data from multiple tables
CREATE OR REPLACE VIEW public.user_stats AS
SELECT
    u.id AS user_id,
    u.username,
    u.email,
    u.created_at AS user_created_at,
    
    -- Track statistics
    COUNT(DISTINCT t.id) AS tracks_count,
    COALESCE(SUM(t.play_count), 0) AS total_track_plays,
    COALESCE(SUM(t.like_count), 0) AS total_track_likes,
    COALESCE(SUM(t.download_count), 0) AS total_track_downloads,
    
    -- Playlist statistics
    COUNT(DISTINCT p.id) AS playlists_count,
    COALESCE(SUM(p.track_count), 0) AS total_playlist_tracks,
    COALESCE(SUM(p.follower_count), 0) AS total_playlist_followers,
    
    -- Social statistics
    COUNT(DISTINCT f1.id) AS followers_count,
    COUNT(DISTINCT f2.id) AS following_count,
    
    -- Playback statistics
    COUNT(DISTINCT tp.track_id) AS unique_tracks_played,
    COUNT(tp.id) AS total_plays,
    COALESCE(SUM(tp.duration), 0) AS total_play_duration,
    CASE 
        WHEN COUNT(tp.id) > 0 THEN COALESCE(SUM(tp.duration), 0)::FLOAT / COUNT(tp.id)
        ELSE 0
    END AS average_play_duration,
    
    -- Like statistics
    COUNT(DISTINCT tl.track_id) AS liked_tracks_count,
    
    -- Comment statistics
    COUNT(DISTINCT tc.id) AS comments_count
    
FROM public.users u
LEFT JOIN public.tracks t ON t.creator_id = u.id AND t.deleted_at IS NULL
LEFT JOIN public.playlists p ON p.user_id = u.id AND p.deleted_at IS NULL
LEFT JOIN public.follows f1 ON f1.followed_id = u.id
LEFT JOIN public.follows f2 ON f2.follower_id = u.id
LEFT JOIN public.track_plays tp ON tp.user_id = u.id
LEFT JOIN public.track_likes tl ON tl.user_id = u.id
LEFT JOIN public.track_comments tc ON tc.user_id = u.id AND tc.deleted_at IS NULL
WHERE u.deleted_at IS NULL
GROUP BY u.id, u.username, u.email, u.created_at;

COMMENT ON VIEW public.user_stats IS 'Aggregated user statistics view including tracks, playlists, social, and playback metrics';

-- === TRACK_STATS VIEW ===
-- View for track statistics aggregating plays, likes, comments, and downloads
CREATE OR REPLACE VIEW public.track_stats AS
SELECT
    t.id AS track_id,
    t.title,
    t.artist,
    t.creator_id,
    t.created_at AS track_created_at,
    t.published_at,
    
    -- Denormalized counts from tracks table
    t.play_count AS views,
    t.like_count AS likes,
    t.comment_count AS comments,
    t.download_count AS downloads,
    
    -- Playback statistics
    COUNT(DISTINCT tp.user_id) AS unique_listeners,
    COUNT(tp.id) AS total_plays,
    COALESCE(SUM(tp.duration), 0) AS total_play_time,
    CASE 
        WHEN COUNT(tp.id) > 0 THEN COALESCE(SUM(tp.duration), 0)::FLOAT / COUNT(tp.id)
        ELSE 0
    END AS average_duration,
    
    -- Share statistics
    COUNT(DISTINCT ts.id) AS share_links_count,
    COALESCE(SUM(ts.access_count), 0) AS total_share_accesses
    
FROM public.tracks t
LEFT JOIN public.track_plays tp ON tp.track_id = t.id
LEFT JOIN public.track_shares ts ON ts.track_id = t.id AND ts.deleted_at IS NULL
WHERE t.deleted_at IS NULL
GROUP BY t.id, t.title, t.artist, t.creator_id, t.created_at, t.published_at, 
         t.play_count, t.like_count, t.comment_count, t.download_count;

COMMENT ON VIEW public.track_stats IS 'Aggregated track statistics view including plays, likes, comments, and downloads';

-- === PLAYLIST_STATS VIEW ===
-- View for playlist statistics aggregating tracks, followers, and plays
CREATE OR REPLACE VIEW public.playlist_stats AS
SELECT
    p.id AS playlist_id,
    p.name AS playlist_name,
    p.user_id AS creator_id,
    p.created_at AS playlist_created_at,
    p.updated_at AS playlist_updated_at,
    
    -- Denormalized counts from playlists table
    p.track_count AS tracks_count,
    p.follower_count AS followers_count,
    
    -- Track statistics (aggregated from playlist_tracks)
    COUNT(DISTINCT pt.track_id) AS actual_track_count,
    COALESCE(SUM(t.play_count), 0) AS total_track_plays,
    COALESCE(SUM(t.like_count), 0) AS total_track_likes,
    COALESCE(AVG(t.duration), 0) AS average_track_duration,
    COALESCE(SUM(t.duration), 0) AS total_playlist_duration,
    
    -- Collaboration statistics
    COUNT(DISTINCT pc.user_id) AS collaborators_count,
    
    -- Share statistics
    COUNT(DISTINCT psl.id) AS share_links_count,
    COALESCE(SUM(psl.access_count), 0) AS total_share_accesses
    
FROM public.playlists p
LEFT JOIN public.playlist_tracks pt ON pt.playlist_id = p.id
LEFT JOIN public.tracks t ON t.id = pt.track_id AND t.deleted_at IS NULL
LEFT JOIN public.playlist_collaborators pc ON pc.playlist_id = p.id AND pc.deleted_at IS NULL
LEFT JOIN public.playlist_share_links psl ON psl.playlist_id = p.id AND psl.deleted_at IS NULL
WHERE p.deleted_at IS NULL
GROUP BY p.id, p.name, p.user_id, p.created_at, p.updated_at, 
         p.track_count, p.follower_count;

COMMENT ON VIEW public.playlist_stats IS 'Aggregated playlist statistics view including tracks, followers, plays, and collaboration metrics';

-- Indexes for better query performance (if needed)
-- Note: Views don't support indexes directly, but indexes on underlying tables will help