Remove legacy GCM API support and bump Firebase Admin SDK to v13

.babelrc

@@ -4,7 +4,7 @@
       "@babel/preset-env",
       {
         "targets": {
-          "node": "14"
+          "node": "18"
         }
       }
     ]

.github/copilot-instructions.md

@@ -2,7 +2,9 @@
 
 ## Project Overview
 
-This repository implements a Node.js module for sending push notifications across multiple platforms: Apple (APN), Google (GCM/FCM), Windows (WNS), Amazon (ADM), and Web-Push. The core logic is in `lib/` and `src/`, with each platform handled by a dedicated file (e.g., `sendAPN.js`, `sendFCM.js`).
+This repository implements a Node.js module for sending push notifications across multiple platforms: Apple (APN), Google (FCM), Windows (WNS), Amazon (ADM), and Web-Push. The core logic is in `lib/` and `src/`, with each platform handled by a dedicated file (e.g., `sendAPN.js`, `sendFCM.js`).
+
+**Note:** Legacy GCM (Google Cloud Messaging) support has been removed. All Android push notifications now route exclusively through Firebase Cloud Messaging (FCM) using the Firebase Admin SDK.
 
 ## Architecture & Data Flow
 
@@ -14,40 +16,187 @@ This repository implements a Node.js module for sending push notifications acros
 
 ## Developer Workflows
 
-- **Install:** `npm install`
-- **Test:** Run all tests with `npm test`. Tests are in `test/` and cover basic flows and platform-specific cases.
+- **Install:** `npm install` (requires Node.js 18+)
+- **Test:** Run all tests with `npm test`. Tests are in `test/` and cover basic flows and platform-specific cases (87 tests, all passing).
 - **Debug:** Use the callback or Promise error/result from `push.send`. Each result object includes method, success/failure counts, and error details per device.
 - **Build:** No build step required for basic usage. ES6 is used, but compatible with ES5 via Babel if needed.
 
 ## Conventions & Patterns
 
-- **Platform-specific files:** Each push service has its own file for isolation and clarity.
+- **Platform-specific files:** Each push service has its own file for isolation and clarity. Legacy GCM is no longer supported.
 - **Unified Data Model:** The `data` object for notifications is normalized across platforms. See `README.md` for all supported fields.
 - **Error Handling:** Errors are unified and returned in the result array from `push.send`.
 - **RegId Format:** Prefer object format for registration IDs (`{id, type}`), but string format is supported for legacy reasons.
-- **Chunking:** Android tokens are chunked in batches of 1,000 automatically.
-- **Constants:** Use constants from `constants.js` for platform types.
+- **Android Routing:** All Android push notifications route through FCM using Firebase Admin SDK.
+- **Chunking:** Android tokens are chunked in batches of 1,000 automatically by FCM.
+- **Constants:** Use constants from `constants.js` for platform types. Available constants: `FCM_METHOD`, `APN_METHOD`, `WNS_METHOD`, `ADM_METHOD`, `WEB_METHOD`, `UNKNOWN_METHOD`.
+
+## Firebase Cloud Messaging (FCM) - Modern Implementation
+
+### Message Building (src/utils/tools.js)
+
+**buildAndroidMessage(data, options)**
+- Converts unified notification data to Firebase Admin SDK AndroidMessage format
+- Returns plain JavaScript object (no wrapper functions)
+- Properties mapped to camelCase (Firebase SDK standard)
+- Removes undefined values for clean API calls
+- Converts TTL from seconds to milliseconds
+- Supports all 20+ AndroidNotification properties
+
+**buildAndroidNotification(data)**
+- Maps input `data` object to AndroidNotification interface
+- Supported properties:
+  - Basic: `title`, `body`, `icon`, `color`, `sound`, `tag`, `imageUrl`
+  - Localization: `titleLocKey`, `titleLocArgs`, `bodyLocKey`, `bodyLocArgs`
+  - Android-specific: `channelId`, `notificationCount`, `ticker`, `sticky`, `visibility`
+  - Behavior: `clickAction`, `priority`, `localOnly`, `eventTimestamp`
+  - Accessibility: `ticker`
+  - Vibration: `vibrateTimingsMillis`, `defaultVibrateTimings`
+  - Sound: `defaultSound`
+  - LED: `lightSettings`, `defaultLightSettings`
+  - Proxy: `proxy` (notification-level, values: 'allow', 'deny', 'if_priority_lowered')
+
+### FCM Configuration (src/sendFCM.js)
+
+**Initialization Options:**
+- `credential` or `serviceAccountKey` (required) - Firebase authentication
+- `projectId` (optional) - Explicit Google Cloud project ID
+- `databaseURL` (optional) - Realtime Database URL
+- `storageBucket` (optional) - Cloud Storage bucket
+- `serviceAccountId` (optional) - Service account email
+- `databaseAuthVariableOverride` (optional) - Auth override for RTDB rules
+- `httpAgent` (optional) - HTTP proxy agent for network requests
+- `httpsAgent` (optional) - HTTPS proxy agent for network requests
+
+All optional properties are dynamically added to Firebase initialization if defined.
+
+### Proxy Support
+
+**Two levels of proxy configuration:**
+
+1. **Network-level (SDK initialization)**
+   - `settings.fcm.httpAgent` and `settings.fcm.httpsAgent`
+   - Controls how Firebase Admin SDK communicates with Google servers
+   - Uses proxy agent libraries (http-proxy-agent, https-proxy-agent)
+   - Applied at app initialization
+
+2. **Notification-level (Android device)**
+   - `data.proxy` property in notification message
+   - Controls how Android devices handle notifications in proxy scenarios
+   - Values: 'allow', 'deny', 'if_priority_lowered'
+   - Per-message configuration
+
+### Message Format
+
+Firebase Admin SDK expects:
+```javascript
+{
+  tokens: [...],
+  android: {
+    collapseKey: string,
+    priority: 'high' | 'normal',
+    ttl: number (milliseconds),
+    restrictedPackageName: string,
+    directBootOk: boolean,
+    data: { [key: string]: string },
+    notification: { ...AndroidNotification properties... },
+    fcmOptions: { analyticsLabel: string }
+  },
+  apns: { ...APNs payload... }
+}
+```
 
 ## Integration Points
 
 - **External Libraries:**
-  - APN: `node-apn`
-  - FCM: `firebase-admin`
-  - GCM: `node-gcm`
+  - APN: `@parse/node-apn`
+  - FCM: `firebase-admin` (all Android push notifications)
   - ADM: `node-adm`
   - WNS: `wns`
   - Web-Push: `web-push`
+  - Proxy: `http-proxy-agent`, `https-proxy-agent` (user-supplied)
+  - Note: Legacy `node-gcm` library has been removed
 - **Credentials:** Place service account keys and certificates in appropriate locations (see `README.md` for examples).
 
 ## Key Files & Directories
 
-- `lib/` and `src/`: Main implementation (mirrored structure)
-- `test/`: Test cases and sample credentials
-- `README.md`: Usage, configuration, and data model reference
+- `lib/` and `src/`: Main implementation (mirrored structure, both CommonJS)
+- `lib/sendFCM.js` / `src/sendFCM.js`: Firebase Admin SDK integration
+- `lib/utils/tools.js` / `src/utils/tools.js`: Message building utilities
+- `lib/utils/fcmMessage.js` / `src/utils/fcmMessage.js`: FCM message formatting
+- `test/send/sendFCM.js`: FCM test suite (10 test cases covering message format, proxy support, and Firebase AppOptions)
+- `test/`: Test cases (87 tests total, all passing)
+- `README.md`: Complete usage guide, configuration examples, and property documentation
+- `.github/copilot-instructions.md`: This file - AI agent guidance
+
+## Recent Changes - Legacy GCM Removal & Firebase Admin SDK Alignment
+
+### What Changed
+
+**Removed:**
+- `buildGcmMessage()` function (wrapper pattern with toJson() method)
+- `buildGcmNotification()` function
+- Post-processing delete statements for undefined properties
+- References to legacy `node-gcm` library
+
+**Added:**
+- `buildAndroidMessage()` - Direct Firebase Admin SDK compatible builder
+- `buildAndroidNotification()` - Proper Android notification interface
+- 15+ new Android notification properties (ticker, sticky, visibility, LED settings, etc.)
+- Support for all 9 Firebase Admin SDK AppOptions (projectId, databaseURL, storageBucket, etc.)
+- Proxy support at both SDK and notification levels
+- Comprehensive test coverage (10 FCM-specific tests)
+
+### Migration Pattern
+
+**Before (Legacy GCM):**
+```javascript
+const message = buildGcmMessage(data).toJson();
+// Result: wrapper object with toJson() method
+```
+
+**After (Firebase Admin SDK):**
+```javascript
+const message = buildAndroidMessage(data);
+// Result: plain object directly compatible with firebase-admin
+```
+
+### Property Naming
+
+All properties now use **camelCase** (Firebase Admin SDK standard):
+- `android_channel_id` → `channelId`
+- `title_loc_key` → `titleLocKey`
+- `body_loc_key` → `bodyLocKey`
+- `body_loc_args` → `bodyLocArgs`
+- etc.
+
+### Testing
+
+New test suite added with 7 test cases:
+- `should accept projectId in settings`
+- `should accept databaseURL in settings`
+- `should accept storageBucket in settings`
+- `should accept serviceAccountId in settings`
+- `should accept databaseAuthVariableOverride in settings`
+- `should accept multiple Firebase AppOptions together`
+- Plus 3 existing proxy tests (httpAgent, httpsAgent, both)
+
+All 87 tests passing, zero regressions.
 
 ## Example Usage
 
-See `README.md` for a full example of settings, registration ID formats, and sending notifications.
+See `README.md` for complete examples including:
+- FCM settings configuration with all AppOptions
+- Notification data with all supported properties
+- Network proxy agent setup
+- Notification-level proxy configuration
+
+## Future Considerations
+
+- Monitor Firebase Admin SDK updates for new AndroidMessage properties
+- Consider typed interfaces for better TypeScript support
+- Track Android notification API changes and feature additions
+- Evaluate performance of dynamic property filtering approach
 
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