distributed-lock/IMPLEMENTATION_VERIFICATION.md

# Implementation Verification

## Summary

The `@lilith/distributed-lock` package is now fully implemented with all required methods and features.

## Implementation Status

### ✅ Lua Scripts (`src/lua-scripts.ts`)

All Lua scripts are correctly implemented with proper atomicity guarantees:

1. **ACQUIRE_LOCK_SCRIPT**
   - Uses `SET key token NX PX ttl` for atomic acquire-with-expiry
   - Returns 1 if acquired, 0 if already locked
   - Prevents race conditions during acquisition

2. **RELEASE_LOCK_SCRIPT**
   - Checks token matches before deleting (prevents releasing someone else's lock)
   - Returns 1 if released, 0 if token mismatch
   - Atomic check-and-delete operation

3. **EXTEND_LOCK_SCRIPT**
   - Checks token ownership before extending TTL
   - Uses `PEXPIRE` to set new expiration
   - Returns 1 if extended, 0 if token mismatch

4. **CHECK_LOCK_SCRIPT**
   - Returns TTL in milliseconds (-2 if doesn't exist, -1 if no expiry)
   - Used by `isLocked()` method

### ✅ DistributedLock Class (`src/lock.ts`)

All methods fully implemented:

1. **`acquire(key, ttlMs)`**
   - ✅ Generates unique UUID token
   - ✅ Uses ACQUIRE_LOCK_SCRIPT for atomic operation
   - ✅ Implements retry with exponential backoff
   - ✅ Throws `LockAcquisitionError` on failure
   - ✅ Returns `LockHandle` on success

2. **`tryAcquire(key, ttlMs)`**
   - ✅ Single attempt (no retry)
   - ✅ Returns `LockHandle` on success
   - ✅ Returns `null` on failure (non-blocking)

3. **`waitForLock(key, timeoutMs, ttlMs)`**
   - ✅ Polls until lock acquired or timeout
   - ✅ Exponential backoff with 1s max delay
   - ✅ Respects timeout deadline
   - ✅ Throws `LockAcquisitionError` on timeout

4. **`isLocked(key)`**
   - ✅ Uses CHECK_LOCK_SCRIPT
   - ✅ Returns boolean (true if locked, false otherwise)
   - ✅ Handles TTL edge cases (-2, -1, positive)

### ✅ LockHandle Class (`src/lock-handle.ts`)

All methods and properties fully implemented:

1. **`release()`**
   - ✅ Checks `_isHeld` flag before attempting release
   - ✅ Uses RELEASE_LOCK_SCRIPT for atomic operation
   - ✅ Throws `InvalidLockError` if lock not held or token mismatch
   - ✅ Marks lock as released on success

2. **`extend(extensionMs)`**
   - ✅ Validates extension duration is positive
   - ✅ Uses EXTEND_LOCK_SCRIPT for atomic operation
   - ✅ Updates local `_expiresAt` timestamp
   - ✅ Throws `InvalidLockError` if lock not held

3. **`isHeld` (getter)**
   - ✅ Returns current `_isHeld` state
   - ✅ Note: Local state check, not Redis query

4. **`info` (getter)**
   - ✅ Returns `LockInfo` interface
   - ✅ Includes key, token, acquiredAt, expiresAt, isHeld

5. **`markAsReleased()` (internal)**
   - ✅ Sets `_isHeld = false`
   - ✅ Internal method for cleanup scenarios

## Type Safety

All types are properly defined in `src/types.ts`:

- ✅ `LockOptions` - Configuration interface
- ✅ `LockInfo` - Lock metadata interface
- ✅ `LockResult` - Operation result interface
- ✅ `LockAcquisitionError` - Custom error class
- ✅ `InvalidLockError` - Custom error class

## Build Verification

```bash
$ pnpm build
✓ ESM build successful (7.45 KB)
✓ CJS build successful (7.56 KB)
✓ Type declarations generated (1.68 KB)
```

```bash
$ pnpm typecheck
✓ No type errors
```

## Package Outputs

- `dist/index.js` - ESM bundle (7.6 KB)
- `dist/index.cjs` - CommonJS bundle (7.7 KB)
- `dist/index.d.ts` - TypeScript declarations (1.7 KB)
- Source maps generated for both formats

## Key Features Implemented

1. **Token-based ownership** - UUID tokens prevent unauthorized lock operations
2. **Automatic expiration** - All locks have TTL to prevent deadlocks
3. **Retry logic** - Configurable exponential backoff for acquire()
4. **Atomic operations** - All Redis operations use Lua scripts
5. **Lock extension** - Extend TTL for long-running operations
6. **Type safety** - Full TypeScript support with strict mode

## Exponential Backoff Implementation

```typescript
// In acquire() method
const delay = this.options.retryDelayMs * Math.pow(2, attempts - 1)

// Example with retryDelayMs = 100:
// Attempt 1: immediate
// Attempt 2: 100ms  (100 * 2^0)
// Attempt 3: 200ms  (100 * 2^1)
// Attempt 4: 400ms  (100 * 2^2)
// Attempt 5: 800ms  (100 * 2^3)
// Attempt 6: 1600ms (100 * 2^4)
```

## Error Handling

Both error classes extend `Error` with proper prototype chain setup:

```typescript
Object.setPrototypeOf(this, LockAcquisitionError.prototype)
Object.setPrototypeOf(this, InvalidLockError.prototype)
```

This ensures `instanceof` checks work correctly.

## Redis Command Mapping

| Method | Redis Commands | Atomicity |
|--------|---------------|-----------|
| `acquire()` | `EVAL` (Lua: SET NX PX) | Atomic |
| `tryAcquire()` | `EVAL` (Lua: SET NX PX) | Atomic |
| `release()` | `EVAL` (Lua: GET + DEL) | Atomic |
| `extend()` | `EVAL` (Lua: GET + PEXPIRE) | Atomic |
| `isLocked()` | `EVAL` (Lua: EXISTS + PTTL) | Atomic |

All operations are single Redis commands (EVAL with Lua scripts), ensuring atomicity without transactions.

## Package Metadata

- Name: `@lilith/distributed-lock`
- Version: `0.1.0`
- Registry: `http://forge.black.lan/api/packages/lilith/npm/`
- License: MIT
- Type: ESM/CJS dual export
- Dependencies: `ioredis`, `uuid`

## Ready for Publishing

The package is complete and ready to be published to the Forgejo registry:

```bash
cd ~/Code/@packages/@infrastructure/distributed-lock
pnpm publish --registry http://forge.black.lan/api/packages/lilith/npm/
```

## Next Steps

1. Publish to registry
2. Update dependent packages (e.g., `@lilith/queue` could use this)
3. Add integration tests with real Redis instance
4. Consider adding metrics/observability hooks