-- Migration: Add id column to song table and change PK from composite to single column
-- This prepares the song table for eventual UUID migration

-- Step 1: Add new id column (nullable initially)
ALTER TABLE song ADD COLUMN id serial4;

-- Step 2: Create unique constraint on id (allows backfilling)
ALTER TABLE song ADD CONSTRAINT song_id_unique UNIQUE (id);

-- Step 3: Backfill existing rows with sequential IDs
-- Use DEFAULT which pulls from the sequence
UPDATE song SET id = DEFAULT WHERE id IS NULL;

-- Step 4: Verify all rows have an id
-- If this returns 0, backfill worked
-- SELECT COUNT(*) FROM song WHERE id IS NULL;

-- Step 5: Drop the composite primary key (soundtrack_id, path)
ALTER TABLE song DROP CONSTRAINT song_pkey;

-- Step 6: Add new primary key on id column
ALTER TABLE song ADD CONSTRAINT song_pkey PRIMARY KEY (id);

-- Step 7: Ensure soundtrack_id remains a foreign key to soundtrack
-- First drop existing FK if it exists (from the rename migration)
ALTER TABLE song DROP CONSTRAINT IF EXISTS song_soundtrack_id_fkey;

-- Then recreate it
ALTER TABLE song ADD CONSTRAINT song_soundtrack_id_fkey 
    FOREIGN KEY (soundtrack_id) REFERENCES soundtrack(id);

-- Step 8: Create index on soundtrack_id for query performance
CREATE INDEX IF NOT EXISTS idx_song_soundtrack_id ON song(soundtrack_id);

-- Step 9: Create index on path for lookups (previously part of PK)
CREATE INDEX IF NOT EXISTS idx_song_path ON song(path);