import type {
  ISmartMigrationLedgerData,
} from '../interfaces.js';

/**
 * Abstract ledger interface — both MongoLedger and S3Ledger implement this.
 *
 * Lifecycle:
 *   1. `init()` — open the underlying store, create empty document if needed
 *   2. `read()` — return the current ledger data
 *   3. `write(data)` — overwrite the ledger with the given data
 *   4. `acquireLock(holderId, ttlMs)` — best-effort lock; returns true on success
 *   5. `releaseLock(holderId)` — clear the lock if we still hold it
 *   6. `close()` — release any resources
 *
 * The ledger data is a single self-contained JSON-serializable object.
 * Both backends store it as a single document (mongo via EasyStore, s3 via
 * a single sidecar object).
 */
export abstract class Ledger {
  public abstract init(): Promise<void>;
  public abstract read(): Promise<ISmartMigrationLedgerData>;
  public abstract write(data: ISmartMigrationLedgerData): Promise<void>;
  public abstract acquireLock(holderId: string, ttlMs: number): Promise<boolean>;
  public abstract releaseLock(holderId: string): Promise<void>;
  public abstract close(): Promise<void>;
}

/** Build a fresh, empty ledger document. */
export function emptyLedgerData(): ISmartMigrationLedgerData {
  return {
    currentVersion: null,
    steps: {},
    lock: {
      holder: null,
      acquiredAt: null,
      expiresAt: null,
    },
    checkpoints: {},
  };
}