/**
 * Chat unread state lives on the server so it survives reloads and agrees
 * across tabs and devices: `users.chat_read_at` is the created_at of the newest
 * message the user has seen. Existing users start caught up (now) rather than
 * with the whole history unread; new users fall back to their own created_at.
 *
 * The history cursor now pages on (created_at, id) so two messages sharing a
 * millisecond can't be skipped at a page boundary; the index follows suit.
 *
 * Idempotent: also runs against fresh databases created from schema.sql, where
 * the column and index already exist.
 *
 * @module
 */

import type { DatabaseSync } from "node:sqlite";

/** Applies this migration to `db`. */
export function up(db: DatabaseSync): void {
  const cols = db.prepare(`PRAGMA table_info(users);`).all() as {
    name: string;
  }[];
  if (!cols.some((c) => c.name === "chat_read_at")) {
    db.exec(`ALTER TABLE users ADD COLUMN chat_read_at TEXT;`);
    db.prepare(`UPDATE users SET chat_read_at = ?;`).run(
      new Date().toISOString(),
    );
  }

  db.exec(`DROP INDEX IF EXISTS idx_chat_messages_created;`);
  db.exec(
    `CREATE INDEX IF NOT EXISTS idx_chat_messages_created_id ON chat_messages(created_at, id);`,
  );
}