-- Migration: Fix deduplication constraints and clean up duplicate rows

-- 1. Deduplicate attachments
DELETE FROM attachment a
USING attachment b
WHERE a.announcement_id = b.announcement_id
  AND a.url = b.url
  AND a.id > b.id;

-- 2. Unique constraint for attachment idempotency
DO $$
BEGIN
    IF NOT EXISTS (
        SELECT 1 FROM pg_constraint WHERE conname = 'uq_attachment_announcement_url'
    ) THEN
        ALTER TABLE attachment ADD CONSTRAINT uq_attachment_announcement_url UNIQUE (announcement_id, url);
    END IF;
END $$;

-- 3. Fix invalid self-referencing canonical_id
UPDATE announcement SET canonical_id = NULL WHERE canonical_id = id;

-- 4. Clean duplicate positions and add unique index
DELETE FROM position a
USING position b
WHERE a.announcement_id = b.announcement_id
  AND a.post_name = b.post_name
  AND COALESCE(a.dept, '') = COALESCE(b.dept, '')
  AND a.id > b.id;

CREATE UNIQUE INDEX IF NOT EXISTS uq_position_announcement_post_dept 
ON position (announcement_id, post_name, COALESCE(dept, ''));