Add push notification functionality with tests and digest scheduler

- Implemented push subscription API with tests for subscribing and unsubscribing users.
- Created web push notification tests triggered by child actions.
- Added digest scheduler to send email digests to users at 9 PM local time.
- Developed utility functions for creating and validating digest action tokens.
- Integrated web push sender to handle sending notifications to users.
- Added service worker for handling push notifications in the frontend.
- Created a push opt-in component for user notification preferences.
- Implemented tests for the push opt-in component to ensure correct behavior.
- Updated frontend services to manage push subscriptions and permissions.

backend/utils/digest_token.py

@@ -0,0 +1,141 @@
+import hashlib
+import hmac
+import json
+import os
+import time
+import uuid
+from datetime import datetime, timedelta, timezone
+
+from db.digest_action_tokens import insert_token, get_token_by_id, mark_token_used
+from models.digest_action_token import DigestActionToken
+
+
+def _get_secret() -> bytes:
+    secret = os.environ.get('DIGEST_TOKEN_SECRET')
+    if not secret:
+        raise RuntimeError('DIGEST_TOKEN_SECRET environment variable is not set.')
+    return secret.encode('utf-8')
+
+
+def _sign(payload: dict) -> str:
+    """Return HMAC-SHA256 hex digest of the canonical JSON payload."""
+    canonical = json.dumps(payload, sort_keys=True, separators=(',', ':'))
+    return hmac.new(_get_secret(), canonical.encode('utf-8'), hashlib.sha256).hexdigest()
+
+
+def create_action_token(
+    user_id: str,
+    child_id: str,
+    entity_id: str,
+    entity_type: str,
+    action: str,
+    expiry_hours: int = 24,
+) -> DigestActionToken:
+    """Create and persist a signed action token. Returns the saved token."""
+    token_id = str(uuid.uuid4())
+    expires_at = (datetime.now(timezone.utc) + timedelta(hours=expiry_hours)).isoformat()
+
+    payload = {
+        'id': token_id,
+        'user_id': user_id,
+        'child_id': child_id,
+        'entity_id': entity_id,
+        'entity_type': entity_type,
+        'action': action,
+        'expires_at': expires_at,
+    }
+    signature = _sign(payload)
+
+    token = DigestActionToken(
+        id=token_id,
+        user_id=user_id,
+        child_id=child_id,
+        entity_id=entity_id,
+        entity_type=entity_type,
+        action=action,
+        expires_at=expires_at,
+        used=False,
+        signature=signature,
+    )
+    insert_token(token)
+    return token
+
+
+def validate_and_consume_token(token_id: str) -> DigestActionToken | None:
+    """
+    Validate a token. Returns the token if valid and marks it as used.
+    Returns None if token is missing, expired, used, or has an invalid signature.
+    """
+    token = get_token_by_id(token_id)
+    if not token:
+        return None
+
+    if token.used:
+        return None
+
+    # Check expiry
+    try:
+        expires_at = datetime.fromisoformat(token.expires_at)
+        if expires_at.tzinfo is None:
+            expires_at = expires_at.replace(tzinfo=timezone.utc)
+        if datetime.now(timezone.utc) > expires_at:
+            return None
+    except (ValueError, TypeError):
+        return None
+
+    # Verify HMAC signature
+    payload = {
+        'id': token.id,
+        'user_id': token.user_id,
+        'child_id': token.child_id,
+        'entity_id': token.entity_id,
+        'entity_type': token.entity_type,
+        'action': token.action,
+        'expires_at': token.expires_at,
+    }
+    expected_sig = _sign(payload)
+    if not hmac.compare_digest(token.signature, expected_sig):
+        return None
+
+    mark_token_used(token_id)
+    return token
+
+
+def create_unsubscribe_token(user_id: str) -> str:
+    """
+    Create a simple signed unsubscribe token string (not persisted in DB).
+    Format: '<user_id>.<expiry_ts>.<signature>'
+    """
+    expiry_ts = int(time.time()) + 30 * 24 * 3600  # 30 days
+    payload_str = f"{user_id}:{expiry_ts}"
+    sig = hmac.new(_get_secret(), payload_str.encode('utf-8'), hashlib.sha256).hexdigest()
+    import base64
+    token = base64.urlsafe_b64encode(f"{payload_str}:{sig}".encode()).decode()
+    return token
+
+
+def validate_unsubscribe_token(token: str) -> str | None:
+    """
+    Validate an unsubscribe token.
+    Returns user_id if valid, None otherwise.
+    """
+    import base64
+    try:
+        decoded = base64.urlsafe_b64decode(token.encode()).decode()
+        parts = decoded.rsplit(':', 1)
+        if len(parts) != 2:
+            return None
+        payload_str, sig = parts
+        expected_sig = hmac.new(_get_secret(), payload_str.encode('utf-8'), hashlib.sha256).hexdigest()
+        if not hmac.compare_digest(sig, expected_sig):
+            return None
+        sub_parts = payload_str.split(':', 1)
+        if len(sub_parts) != 2:
+            return None
+        user_id, expiry_str = sub_parts
+        expiry_ts = int(expiry_str)
+        if time.time() > expiry_ts:
+            return None
+        return user_id
+    except Exception:
+        return None