-- Polymorphic influence sources: painting, artist, or movement → a painting
CREATE TABLE IF NOT EXISTS painting_influence_sources (
  id SERIAL PRIMARY KEY,
  painting_id INTEGER NOT NULL REFERENCES paintings(id) ON DELETE CASCADE,
  source_type VARCHAR(20) NOT NULL CHECK (source_type IN ('painting', 'artist', 'movement')),
  source_painting_id INTEGER REFERENCES paintings(id) ON DELETE CASCADE,
  source_artist_id INTEGER REFERENCES artists(id) ON DELETE CASCADE,
  source_movement_id INTEGER REFERENCES art_movements(id) ON DELETE CASCADE,
  period_note VARCHAR(240),
  period_start_year INTEGER,
  period_end_year INTEGER,
  notes TEXT,
  source VARCHAR(500),
  aspects TEXT,
  quote TEXT,
  source_author VARCHAR(200),
  source_url VARCHAR(500),
  discovered_via VARCHAR(120),
  confidence VARCHAR(20) NOT NULL DEFAULT 'curated',
  CONSTRAINT painting_influence_sources_source_shape CHECK (
    (source_type = 'painting' AND source_painting_id IS NOT NULL AND source_artist_id IS NULL AND source_movement_id IS NULL)
    OR (source_type = 'artist' AND source_artist_id IS NOT NULL AND source_painting_id IS NULL AND source_movement_id IS NULL)
    OR (source_type = 'movement' AND source_movement_id IS NOT NULL AND source_painting_id IS NULL AND source_artist_id IS NULL)
  )
);

CREATE UNIQUE INDEX IF NOT EXISTS painting_influence_sources_unique
  ON painting_influence_sources (
    painting_id,
    source_type,
    COALESCE(source_painting_id, 0),
    COALESCE(source_artist_id, 0),
    COALESCE(source_movement_id, 0)
  );

CREATE INDEX IF NOT EXISTS painting_influence_sources_painting_idx
  ON painting_influence_sources (painting_id);

CREATE INDEX IF NOT EXISTS painting_influence_sources_artist_idx
  ON painting_influence_sources (source_artist_id);

CREATE INDEX IF NOT EXISTS painting_influence_sources_movement_idx
  ON painting_influence_sources (source_movement_id);

-- Backfill legacy painting-to-painting edges
INSERT INTO painting_influence_sources (
  painting_id,
  source_type,
  source_painting_id,
  notes,
  source,
  aspects,
  quote,
  source_author,
  source_url,
  confidence
)
SELECT
  pi.painting_id,
  'painting',
  pi.influenced_by_painting_id,
  pi.notes,
  pi.source,
  pi.aspects,
  pi.quote,
  pi.source_author,
  pi.source_url,
  'curated'
FROM painting_influences pi
ON CONFLICT DO NOTHING;