-- Multi-assignee support for activities (implicit many-to-many)
CREATE TABLE IF NOT EXISTS "_ActivityAssignees" (
    "A" TEXT NOT NULL,
    "B" TEXT NOT NULL
);

CREATE UNIQUE INDEX IF NOT EXISTS "_ActivityAssignees_AB_unique" ON "_ActivityAssignees"("A", "B");
CREATE INDEX IF NOT EXISTS "_ActivityAssignees_B_index" ON "_ActivityAssignees"("B");

DO $$
BEGIN
  IF NOT EXISTS (
    SELECT 1 FROM pg_constraint WHERE conname = '_ActivityAssignees_A_fkey'
  ) THEN
    ALTER TABLE "_ActivityAssignees"
      ADD CONSTRAINT "_ActivityAssignees_A_fkey"
      FOREIGN KEY ("A") REFERENCES "Activity"("id")
      ON DELETE CASCADE ON UPDATE CASCADE;
  END IF;
  IF NOT EXISTS (
    SELECT 1 FROM pg_constraint WHERE conname = '_ActivityAssignees_B_fkey'
  ) THEN
    ALTER TABLE "_ActivityAssignees"
      ADD CONSTRAINT "_ActivityAssignees_B_fkey"
      FOREIGN KEY ("B") REFERENCES "User"("id")
      ON DELETE CASCADE ON UPDATE CASCADE;
  END IF;
END $$;

-- Backfill from legacy single assigneeId
INSERT INTO "_ActivityAssignees" ("A", "B")
SELECT a."id", a."assigneeId"
FROM "Activity" a
WHERE a."assigneeId" IS NOT NULL
ON CONFLICT DO NOTHING;