"""
interface/api/app.py
─────────────────────
FastAPI application factory.

Usage:
    # Direct (dev)
    uvicorn src.interface.api.app:create_app --factory --port 7860 --reload

    # Docker / HF Spaces
    CMD ["uvicorn", "src.interface.api.app:create_app", "--factory", ...]

Design decisions:
  • Factory function (not module-level app) so tests can create isolated instances.
  • Lifespan context manager handles startup/shutdown cleanly.
  • Global exception handlers registered via error_handlers.register_exception_handlers().
  • CORS is wide-open by default — restrict in production via settings.
"""
from __future__ import annotations

from contextlib import asynccontextmanager
from typing import Annotated, AsyncGenerator

from fastapi import Depends, FastAPI
from fastapi.middleware.cors import CORSMiddleware

from src.infrastructure.database.connection import (
    create_all_tables,
    dispose_engine,
    ping_database,
)
from src.interface.api.dependencies import get_broker, get_model_service
from src.interface.api.error_handlers import register_exception_handlers
from src.interface.api.routes import ppg_routes, prediction_routes
from src.shared.config import get_settings
from src.shared.constants import API_V1_PREFIX
from src.shared.logger import get_logger

logger = get_logger(__name__)


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    """
    Application lifespan handler.

    Startup:
        1. Validate database connectivity (ping).
        2. Create DB tables (dev/SQLite only — Supabase uses Alembic).
        3. Connect to RabbitMQ.
        4. Pre-load AI model.

    Shutdown:
        1. Disconnect from RabbitMQ.
        2. Dispose the DB engine (returns all pooled connections).
    """
    settings = get_settings()
    logger.info("=" * 60)
    logger.info("BP Monitoring Pipeline — Starting up")
    logger.info("Database  : %s", settings.database_url.split("@")[-1] if "@" in settings.database_url else settings.database_url)
    logger.info("Supabase  : %s", "yes" if settings.is_supabase else "no")
    logger.info("Pooler    : %s", "yes (port 6543)" if settings.uses_pooler else "no")
    logger.info("Broker    : %s", settings.rabbitmq_url.split("@")[-1] if "@" in settings.rabbitmq_url else settings.rabbitmq_url)
    logger.info("Mock Model: %s", settings.use_mock_model)
    logger.info("=" * 60)

    # ── 1. Validate database connection ───────────────────────────────────────
    db_ok = await ping_database()
    if db_ok:
        logger.info("✓ Database connection verified.")
    else:
        logger.warning(
            "✗ Database ping failed — check DATABASE_URL. "
            "The API will start but DB operations will fail."
        )

    # ── 2. Create tables (dev/SQLite only) ────────────────────────────────────
    if settings.debug or settings.is_sqlite:
        logger.info("Auto-creating DB tables (dev/SQLite mode)…")
        await create_all_tables()

    # ── 3. Connect broker (best-effort on startup) ────────────────────────────
    broker_provider = app.dependency_overrides.get(get_broker, get_broker)
    broker = broker_provider()
    try:
        await broker.connect()
        logger.info("✓ RabbitMQ broker connected.")
    except Exception as exc:
        logger.warning(
            "✗ Could not connect to RabbitMQ on startup (will retry on first publish): %s", exc
        )

    # ── 4. Pre-load AI model (best-effort) ────────────────────────────────────
    model_provider = app.dependency_overrides.get(get_model_service, get_model_service)
    model_service = model_provider()
    try:
        await model_service.load_model()
        logger.info("✓ Model service ready: %s", model_service.model_version)
    except Exception as exc:
        logger.warning("✗ Could not pre-load model on startup: %s", exc)

    logger.info("Startup complete. API is ready to serve requests.")
    yield

    # ── Shutdown ──────────────────────────────────────────────────────────────
    logger.info("Shutting down…")
    try:
        await broker.disconnect()
    except Exception:
        pass
    await dispose_engine()
    logger.info("Shutdown complete.")


def create_app() -> FastAPI:
    """
    FastAPI application factory.

    Returns a fully configured FastAPI instance with:
        • Lifespan hooks (startup/shutdown)
        • Global domain exception handlers
        • CORS middleware
        • API v1 routes
        • Health check endpoint
        • Swagger UI / ReDoc
    """
    settings = get_settings()

    app = FastAPI(
        title="BP Monitoring Pipeline API",
        description=(
            "REST API for the **Blood Pressure Monitoring Pipeline**.\n\n"
            "Receives PPG signals from IoT devices (ETL #1) and serves "
            "AI-predicted blood pressure results to the frontend.\n\n"
            "**Error Response Format** (all errors):\n"
            "```json\n"
            '{"error": "not_found", "message": "...", "context": {}, "timestamp": "..."}\n'
            "```"
        ),
        version="1.0.0",
        docs_url="/docs",
        redoc_url="/redoc",
        openapi_url="/openapi.json",
        lifespan=lifespan,
    )

    # ── Global Exception Handlers ─────────────────────────────────────────────
    # Registered BEFORE routes so handlers are available for all endpoints.
    register_exception_handlers(app)

    # ── CORS ──────────────────────────────────────────────────────────────────
    app.add_middleware(
        CORSMiddleware,
        allow_origins=["*"],       
        allow_credentials=True,
        allow_methods=["*"],
        allow_headers=["*"],
    )

    # ── Routes ────────────────────────────────────────────────────────────────
    app.include_router(ppg_routes.router, prefix=API_V1_PREFIX)
    app.include_router(prediction_routes.router, prefix=API_V1_PREFIX)

    # ── Health Check ──────────────────────────────────────────────────────────
    @app.get(
        "/health",
        tags=["Health"],
        summary="Health Check",
        responses={
            200: {"description": "Service is healthy."},
            503: {"description": "One or more dependencies are unavailable."},
        },
    )
    async def health(
        broker = Depends(get_broker)
    ) -> dict:
        """
        Returns service health status including database and broker connectivity.
        Used by Docker HEALTHCHECK and HF Spaces monitoring.
        """
        from src.domain.interfaces.services.message_broker import MessageBroker
        
        db_healthy = await ping_database()
        broker_connected = await broker.is_connected()
        model_service = get_model_service()

        all_healthy = db_healthy and broker_connected

        return {
            "status": "ok" if all_healthy else "degraded",
            "database": "ok" if db_healthy else "unavailable",
            "broker_connected": broker_connected,
            "model_loaded": model_service.is_loaded(),
            "model_version": model_service.model_version,
        }

    @app.get("/", tags=["Health"], include_in_schema=False)
    async def root() -> dict:
        return {
            "service": "BP Monitoring Pipeline API",
            "version": "1.0.0",
            "docs": "/docs",
        }

    logger.info("FastAPI application created.")
    return app