README.md

@@ -1,61 +1,75 @@
 # Baïkal Calendar Sync
 
-A Dockerized Python service that periodically synchronizes an external Outlook ICS calendar to a local Baïkal CalDAV server.
+An incremental CalDAV sync service that keeps your Baïkal calendar in sync with an Outlook ICS feed — with zero downtime and near-instant sync times.
 
 ## Features
-- **Automatic Sync**: Runs periodically (default: every 5 minutes).
+
-- **Environment Configurable**: All credentials and URLs are set via environment variables.
+- **Incremental Delta Sync**: Only adds, updates, or deletes events that actually changed
-- **Docker Ready**: Includes `Dockerfile` and `docker-compose.yml` for easy deployment.
+- **Zero Downtime**: Adds/updates events before deleting removed ones — calendar never goes empty
+- **Smart Change Detection**: ETag check first, SHA-256 fallback. Skips sync when nothing changed
+- **Stable Event Hashing**: Ignores volatile fields (DTSTAMP, LAST-MODIFIED) to avoid false updates
+- **Automatic Backoff**: Exponential retry on failures (1m, 2m, 4m... max 30m)
+- **Health Endpoint**: Built-in `/health` and `/metrics` (Prometheus-compatible) on port 8081
+- **Graceful Shutdown**: SIGTERM/SIGINT handlers finish current sync before exiting
+- **Docker Ready**: Includes `Dockerfile`, `docker-compose.yml`, and HEALTHCHECK
 
 ## Prerequisites
-- Docker & Docker Compose installed.
+
-- An existing Baïkal instance.
+- Docker & Docker Compose installed
-- An Outlook ICS link.
+- An existing Baïkal instance
+- An Outlook ICS link
 
 ## Configuration (Environment Variables)
 
 | Variable | Description | Default |
 | :--- | :--- | :--- |
 | `ICS_URL` | The public ICS URL of your Outlook calendar. | **Required** |
-| `BAIKAL_URL` | The URL to your Baïkal calendar (e.g., `http://baikal/dav.php/calendars/user/id/`). | **Required** |
+| `BAIKAL_URL` | The URL to your Baïkal calendar. | **Required** |
 | `BAIKAL_USER` | Your Baïkal username. | **Required** |
 | `BAIKAL_PASS` | Your Baïkal password. | **Required** |
 | `SYNC_FREQUENCY` | How often to sync **in minutes**. | `5` |
+| `CALENDAR_ID` | Optional calendar ID to match against. | — |
 
-## Quick Start with Docker Compose
+## Quick Start
 
-1.  **Clone or download** this repository.
+1. **Clone or download** this repository.
-2.  **Create a `.env` file** (optional but recommended) or export variables:
+2. **Create a `.env` file** (optional but recommended):
 
     ```bash
-    ICS_URL="https://outlook.office365.com/..."
+    ICS_URL="https://outlook.office365.com/owa/calendar/your-calendar.ics"
-    BAIKAL_URL="http://localhost:8080/dav.php/calendars/Lago/default/"
+    BAIKAL_URL="https://your-baikal.com/dav.php/calendars/user/calendar-id/"
-    BAIKAL_USER="Lago"
+    BAIKAL_USER="your-username"
-    BAIKAL_PASS="secret"
+    BAIKAL_PASS="your-password"
     SYNC_FREQUENCY=5
     ```
 
-3.  **Run with Docker Compose**:
+3. **Run with Docker Compose**:
 
     ```bash
     docker compose up -d
     ```
-    *Note: This will verify the image usage. If you need to rebuild locally, run `docker compose up -d --build`.*
 
-4.  **Check Logs**:
+4. **Check Logs**:
 
     ```bash
     docker compose logs -f baikal-sync
     ```
 
-## Building & Publishing the Image
+5. **Check Health**:
 
-1.  **Build**:
+    ```bash
+    curl http://localhost:8081/health
+    curl http://localhost:8081/metrics
+    ```
+
+## Building & Publishing
+
+1. **Build**:
     ```bash
     docker build -t lagortinez/baikal-sync:latest .
     ```
 
-2.  **Push** (requires `docker login`):
+2. **Push**:
     ```bash
     docker push lagortinez/baikal-sync:latest
     ```