app/core/settings_loader.py

"""
Settings loader with 3-layer fallback: Redis cache → MongoDB → .env defaults.
Loads booking allocation settings from scm_merchant_settings (merchant_type='company').
"""
import json
import logging

import redis.asyncio as redis

from app.core.config import settings

logger = logging.getLogger(__name__)

SETTINGS_CACHE_KEY = "merchant_settings:company"
SETTINGS_CACHE_TTL = 86400  # 24 hours

DEFAULTS = {
    "allocation_lead_time_minutes": settings.ALLOCATION_LEAD_TIME_MINUTES,
    "scheduler_window_buffer_minutes": settings.SCHEDULER_WINDOW_BUFFER_MINUTES,
    "scheduler_poll_interval_seconds": settings.SCHEDULER_POLL_INTERVAL_SECONDS,
    "offer_expiry_seconds": settings.OFFER_EXPIRY_SECONDS,
    "reschedule_cutoff_minutes": 180,
    "queue_alert_threshold": settings.QUEUE_ALERT_THRESHOLD,
    "max_offer_retries": settings.MAX_OFFER_RETRIES,
    "max_partner_distance_km": 50,
    "scoring_weights": {
        "distance": 0.40,
        "rating": 0.30,
        "load": 0.20,
        "experience": 0.10,
    },
}


async def get_allocation_settings(redis_client: redis.Redis, mongo_db=None) -> dict:
    """
    Load allocation settings with 3-layer fallback.

    Layer 1: Redis cache (24hr TTL)
    Layer 2: MongoDB scm_merchant_settings
    Layer 3: .env defaults — never crash
    """
    # Layer 1: Redis cache
    try:
        cached = await redis_client.get(SETTINGS_CACHE_KEY)
        if cached:
            return json.loads(cached)
    except Exception as e:
        logger.warning("Redis cache read failed", extra={"error": str(e)})

    # Layer 2: MongoDB
    allocation_settings = None
    if mongo_db is not None:
        try:
            doc = await mongo_db["scm_merchant_settings"].find_one(
                {"merchant_type": "company", "is_active": True},
                {"booking_allocation": 1, "_id": 0},
            )
            if doc and "booking_allocation" in doc:
                allocation_settings = {**DEFAULTS, **doc["booking_allocation"]}
        except Exception as e:
            logger.warning("MongoDB settings fetch failed — using defaults", extra={"error": str(e)})

    if allocation_settings is None:
        # Layer 3: .env defaults
        allocation_settings = DEFAULTS.copy()

    # Cache in Redis for next call
    try:
        await redis_client.set(
            SETTINGS_CACHE_KEY,
            json.dumps(allocation_settings),
            ex=SETTINGS_CACHE_TTL,
        )
    except Exception as e:
        logger.warning("Redis cache write failed", extra={"error": str(e)})

    return allocation_settings