const { logger } = require('@nexusai/shared');

// Forward-only schema migrations. Entry i takes the database from user_version i
// to i+1, so migrations[0] is the v0→v1 step, migrations[1] the v1→v2 step, etc.
//
// schema.js already holds the COMPLETE current shape, so a fresh database is
// created whole and stamped straight to LATEST_VERSION — these run only to carry
// an OLDER database forward. Add a new schema change by appending a function here
// (which bumps LATEST_VERSION by one); never edit an existing entry once shipped,
// since databases already stamped past it will not re-run it.
//
// Each migration receives the better-sqlite3 db handle and runs inside a
// transaction together with its version bump, so a failure rolls back cleanly.
const migrations = [
  // v0 → v1: baseline. The historical ALTER TABLE / CREATE INDEX statements that
  // used to run (wrapped in try/catch) on every boot are folded into schema.js.
  // Nothing to do here — this entry exists to mark v1 as the consolidated baseline.
  (_db) => {},
];

const LATEST_VERSION = migrations.length;

// Applies any migrations newer than the database's current user_version, one at a
// time, each with its version bump, inside a transaction. Returns the resulting
// version. A no-op when the database is already current. The migrations list and
// target version are injectable for testing; production callers pass just `db`.
function migrate(db, migs = migrations, latest = migs.length) {
  const current = db.pragma('user_version', { simple: true });
  if (current >= latest) return current;

  for (let v = current; v < latest; v++) {
    const step = db.transaction(() => {
      migs[v](db);
      db.pragma(`user_version = ${v + 1}`);
    });
    step();
  }

  logger.info(`[db] schema migrated ${current} -> ${latest}`);
  return latest;
}

module.exports = { migrate, migrations, LATEST_VERSION };