-- Phase 1.1: 会话级单调递增 seq，用于消息排序、去重与断线补拉
ALTER TABLE "ImConversation" ADD COLUMN IF NOT EXISTS "nextSeq" INTEGER NOT NULL DEFAULT 1;

ALTER TABLE "ImMessage" ADD COLUMN IF NOT EXISTS "seq" INTEGER NOT NULL DEFAULT 0;

ALTER TABLE "ImReadCursor" ADD COLUMN IF NOT EXISTS "lastReadSeq" INTEGER NOT NULL DEFAULT 0;

-- 按 createdAt 回填历史 seq
WITH ranked AS (
  SELECT id, ROW_NUMBER() OVER (PARTITION BY "conversationId" ORDER BY "createdAt", id) AS rn
  FROM "ImMessage"
)
UPDATE "ImMessage" m SET seq = ranked.rn FROM ranked WHERE m.id = ranked.id;

UPDATE "ImConversation" c
SET "nextSeq" = COALESCE((
  SELECT MAX(seq) + 1 FROM "ImMessage" WHERE "conversationId" = c.id
), 1);

UPDATE "ImReadCursor" rc
SET "lastReadSeq" = COALESCE((
  SELECT MAX(seq) FROM "ImMessage" m
  WHERE m."conversationId" = rc."conversationId" AND m."createdAt" <= rc."lastReadAt"
), 0);

CREATE INDEX IF NOT EXISTS "ImMessage_conversationId_seq_idx" ON "ImMessage"("conversationId", "seq");