-- Art-movement predecessor → successor edges for timeline / Tree of Art.
-- Curators manage these with a required proof URL (literature or web essay).

CREATE TABLE IF NOT EXISTS movement_lineage_links (
  id SERIAL PRIMARY KEY,
  source_movement_id INTEGER NOT NULL REFERENCES art_movements(id) ON DELETE CASCADE,
  target_movement_id INTEGER NOT NULL REFERENCES art_movements(id) ON DELETE CASCADE,
  link_year_approx INTEGER,
  proof_url TEXT NOT NULL,
  proof_label TEXT,
  notes TEXT,
  created_by INTEGER REFERENCES users(id) ON DELETE SET NULL,
  created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
  CONSTRAINT movement_lineage_links_distinct CHECK (source_movement_id <> target_movement_id),
  CONSTRAINT movement_lineage_links_unique UNIQUE (source_movement_id, target_movement_id)
);

CREATE INDEX IF NOT EXISTS movement_lineage_links_source_idx
  ON movement_lineage_links (source_movement_id);
CREATE INDEX IF NOT EXISTS movement_lineage_links_target_idx
  ON movement_lineage_links (target_movement_id);
CREATE INDEX IF NOT EXISTS movement_lineage_links_year_idx
  ON movement_lineage_links (link_year_approx);

CREATE OR REPLACE FUNCTION movement_lineage_links_touch_updated_at()
RETURNS TRIGGER AS $$
BEGIN
  NEW.updated_at = now();
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;

DROP TRIGGER IF EXISTS movement_lineage_links_updated_at ON movement_lineage_links;
CREATE TRIGGER movement_lineage_links_updated_at
  BEFORE UPDATE ON movement_lineage_links
  FOR EACH ROW EXECUTE PROCEDURE movement_lineage_links_touch_updated_at();