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Duc Nguyen
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fission-python/template/examples/example_webhook.py
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296
fission-python/template/examples/example_webhook.py
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"""
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Example: Webhook receiver pattern.
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This demonstrates:
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- Processing external service callbacks
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- Signature verification
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- Event type handling
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- Idempotency checks
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- Async processing patterns
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"""
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import hashlib
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import hmac
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from flask import request
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from helpers import init_db_connection, get_secret
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from exceptions import ValidationError, DatabaseError
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# For signed webhooks, you'll need a secret
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WEBHOOK_SECRET = get_secret("WEBHOOK_SECRET", "")
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def verify_signature(payload: bytes, signature: str) -> bool:
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"""
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Verify HMAC-SHA256 webhook signature.
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Args:
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payload: Raw request body bytes
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signature: Signature header value (format: "sha256=<hex>")
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Returns:
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True if signature is valid, False otherwise
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"""
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if not WEBHOOK_SECRET:
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return True # Skip verification if no secret configured (for dev)
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expected = hmac.new(
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WEBHOOK_SECRET.encode(),
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payload,
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hashlib.sha256
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).hexdigest()
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# Signature header format: "sha256=abcdef..."
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received = signature.split("=", 1)[1] if "=" in signature else signature
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return hmac.compare_digest(expected, received)
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def webhook_receiver(event, context):
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"""
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```fission
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{
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"name": "webhook-receiver",
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"http_triggers": {
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"webhook": {
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"url": "/webhooks/external-service",
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"methods": ["POST"]
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}
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}
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}
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```
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Receive and process webhook from external service.
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**Request:**
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- Raw JSON payload in body
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- Signature header: `X-Webhook-Signature: sha256=<hmac>`
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**Response:**
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- 200: Webhook accepted for processing
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- 400: Invalid signature or payload
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- 500: Processing error
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**Idempotency:**
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This function is idempotent - duplicate webhooks with same
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event ID will not be processed twice.
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"""
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# Get raw body for signature verification
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payload = request.get_data()
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signature = request.headers.get("X-Webhook-Signature", "")
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# Verify signature
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if not verify_signature(payload, signature):
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raise ValidationError("Invalid webhook signature")
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# Parse payload
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try:
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data = request.get_json()
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except Exception as e:
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raise ValidationError(f"Invalid JSON payload: {str(e)}")
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# Validate required fields
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event_id = data.get("event_id") or data.get("id")
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event_type = data.get("event_type") or data.get("type")
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if not event_id:
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raise ValidationError("Missing event_id in webhook payload")
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if not event_type:
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raise ValidationError("Missing event_type in webhook payload")
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# Idempotency check: have we already processed this event?
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conn = None
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try:
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conn = init_db_connection()
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cursor = conn.cursor()
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# Check if event already processed
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cursor.execute(
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"SELECT id FROM webhook_events WHERE event_id = %s",
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(event_id,)
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)
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if cursor.fetchone():
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# Already processed - return success (idempotent)
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return {"status": "already_processed", "event_id": event_id}
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# Record webhook event (for idempotency)
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cursor.execute(
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"""
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INSERT INTO webhook_events (event_id, event_type, payload, received_at)
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VALUES (%s, %s, %s, NOW())
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""",
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(event_id, event_type, payload.decode('utf-8'))
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)
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# Process based on event type
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result = process_event(cursor, event_type, data)
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conn.commit()
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return {"status": "processed", "event_id": event_id, "result": result}
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except Exception as e:
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if conn:
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conn.rollback()
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raise DatabaseError(f"Failed to process webhook: {str(e)}")
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finally:
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if conn:
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conn.close()
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def process_event(cursor, event_type: str, data: dict):
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"""
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Route event to appropriate handler.
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Args:
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cursor: Database cursor
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event_type: Type of event (e.g., "user.created", "order.updated")
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data: Event payload
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Returns:
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Handler result
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"""
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handlers = {
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"user.created": handle_user_created,
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"user.updated": handle_user_updated,
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"user.deleted": handle_user_deleted,
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"order.created": handle_order_created,
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"order.paid": handle_order_paid,
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"order.shipped": handle_order_shipped,
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}
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handler = handlers.get(event_type)
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if not handler:
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# Log unknown event type but don't fail
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logger = get_logger()
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logger.warning(f"Unhandled webhook event type: {event_type}")
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return {"skipped": True, "reason": "unknown_event_type"}
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return handler(cursor, data)
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def handle_user_created(cursor, data: dict):
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"""Handle user creation event."""
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user_id = data.get("user_id") or data.get("id")
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email = data.get("email")
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name = data.get("name")
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# Create user record
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cursor.execute(
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"""
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INSERT INTO users (id, email, name, created_at)
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VALUES (%s, %s, %s, NOW())
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ON CONFLICT (id) DO UPDATE SET
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email = EXCLUDED.email,
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name = EXCLUDED.name,
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updated_at = NOW()
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""",
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(user_id, email, name)
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)
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# Send welcome email (async via message queue, etc.)
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# enqueue_welcome_email(user_id, email)
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return {"action": "user_created", "user_id": user_id}
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def handle_user_updated(cursor, data: dict):
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"""Handle user update event."""
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user_id = data.get("user_id") or data.get("id")
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updates = data.get("updates", {})
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# Build dynamic update
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set_clauses = []
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params = []
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for key, value in updates.items():
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set_clauses.append(f"{key} = %s")
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params.append(value)
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params.append(user_id)
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cursor.execute(
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f"UPDATE users SET {', '.join(set_clauses)}, updated_at = NOW() WHERE id = %s",
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params
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)
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return {"action": "user_updated", "user_id": user_id}
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def handle_user_deleted(cursor, data: dict):
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"""Handle user deletion event."""
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user_id = data.get("user_id") or data.get("id")
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# Soft delete (mark as inactive)
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cursor.execute(
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"UPDATE users SET status = 'deleted', deleted_at = NOW() WHERE id = %s",
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(user_id,)
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)
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return {"action": "user_deleted", "user_id": user_id}
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def handle_order_created(cursor, data: dict):
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"""Handle order creation event."""
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order_id = data.get("order_id") or data.get("id")
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user_id = data.get("user_id")
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total = data.get("total")
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cursor.execute(
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"""
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INSERT INTO orders (id, user_id, total, status, created_at)
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VALUES (%s, %s, %s, 'pending', NOW())
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""",
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(order_id, user_id, total)
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)
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return {"action": "order_created", "order_id": order_id}
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def handle_order_paid(cursor, data: dict):
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"""Handle order payment event."""
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order_id = data.get("order_id") or data.get("id")
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payment_id = data.get("payment_id")
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amount = data.get("amount")
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cursor.execute(
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"""
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UPDATE orders
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SET status = 'paid',
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paid_amount = %s,
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payment_id = %s,
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paid_at = NOW()
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WHERE id = %s
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""",
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(amount, payment_id, order_id)
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)
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# Trigger fulfillment
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# enqueue_fulfillment(order_id)
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return {"action": "order_paid", "order_id": order_id}
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def handle_order_shipped(cursor, data: dict):
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"""Handle order shipment event."""
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order_id = data.get("order_id") or data.get("id")
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tracking_number = data.get("tracking_number")
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carrier = data.get("carrier")
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cursor.execute(
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"""
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UPDATE orders
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SET status = 'shipped',
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tracking_number = %s,
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carrier = %s,
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shipped_at = NOW()
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WHERE id = %s
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""",
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(tracking_number, carrier, order_id)
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)
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# Send shipping notification
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# send_shipping_email(order_id)
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return {"action": "order_shipped", "order_id": order_id}
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def get_logger():
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"""Get logger instance."""
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import logging
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return logging.getLogger(__name__)
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