"""FastAPI application entry point.

Wires up:
- CORS middleware (whitelist, NO wildcard)
- Security headers middleware (CSP, X-Frame-Options, X-Content-Type-Options, HSTS in prod)
- Global exception handlers (HTTPException, RequestValidationError, SQLAlchemyError)
- Startup/shutdown events (DB connection check, log level)
- Versioned API router mounts under /api/v1
- Root-level /health endpoint for Coolify healthcheck
"""

from __future__ import annotations

import logging
from contextlib import asynccontextmanager

from fastapi import FastAPI, Request, status
from fastapi.exceptions import RequestValidationError
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse
from sqlalchemy import text
from sqlalchemy.exc import SQLAlchemyError
from starlette.exceptions import HTTPException as StarletteHTTPException

from app import __version__
from app.api.v1 import (
    accounts,
    activities,
    auth,
    contacts,
    dashboard,
    deals,
    health,
    notes,
    tags,
    users,
)
from app.core.config import get_settings
from app.core.db import AsyncSessionLocal, dispose_engine

logger = logging.getLogger(__name__)


# === Lifespan ===


@asynccontextmanager
async def lifespan(app: FastAPI):
    """Application lifespan: startup and shutdown hooks."""
    settings = get_settings()
    logging.basicConfig(level=settings.LOG_LEVEL)
    logger.info(
        "Starting CRM System v%s in %s mode",
        __version__,
        settings.ENVIRONMENT,
    )

    # Verify DB connection on startup
    try:
        async with AsyncSessionLocal() as session:
            await session.execute(text("SELECT 1"))
        logger.info("Database connection OK (%s)", settings.DATABASE_URL.split("://", 1)[0])
    except Exception as e:
        logger.error("Database connection FAILED on startup: %s", e)
        # Don't crash — let /health report the issue so Coolify can restart

    yield

    # Shutdown
    logger.info("Shutting down CRM System")
    await dispose_engine()


# === App ===


def create_app() -> FastAPI:
    """Application factory (allows easy testing override)."""
    settings = get_settings()

    app = FastAPI(
        title="CRM System",
        version=__version__,
        docs_url="/docs",
        redoc_url="/redoc",
        openapi_url="/openapi.json",
        lifespan=lifespan,
    )

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

    # === Security Headers ===
    @app.middleware("http")
    async def security_headers_middleware(request: Request, call_next):
        """Inject CSP, X-Frame-Options, X-Content-Type-Options, and HSTS headers."""
        response = await call_next(request)
        settings_local = get_settings()

        if settings_local.is_production:
            # Prod: strict CSP (no unsafe-inline for scripts; TODO v1.1 add nonce)
            csp = (
                "default-src 'self'; "
                "script-src 'self' https://cdn.tailwindcss.com; "
                "style-src 'self' 'unsafe-inline'; "
                "img-src 'self' data:; "
                "object-src 'none';"
            )
        else:
            # Dev: allow inline scripts for fast iteration (Alpine.js x-data blocks)
            csp = (
                "default-src 'self'; "
                "script-src 'self' 'unsafe-inline' https://cdn.tailwindcss.com; "
                "style-src 'self' 'unsafe-inline'; "
                "img-src 'self' data:; "
                "object-src 'none';"
            )

        response.headers["Content-Security-Policy"] = csp
        response.headers["X-Content-Type-Options"] = "nosniff"
        response.headers["X-Frame-Options"] = "DENY"
        if settings_local.is_production:
            response.headers["Strict-Transport-Security"] = (
                "max-age=31536000; includeSubDomains"
            )
        return response

    # === Exception Handlers ===

    @app.exception_handler(StarletteHTTPException)
    async def http_exception_handler(
        request: Request, exc: StarletteHTTPException
    ) -> JSONResponse:
        """Format HTTPException responses consistently."""
        # Distinguish token-expired for FR-1.7 acceptance criterion
        if exc.status_code == 401:
            detail = exc.detail
            if detail == "Could not validate credentials":
                # Token invalid or expired — callers can detect this
                return JSONResponse(
                    status_code=exc.status_code,
                    content={"detail": "token_expired_or_invalid"},
                    headers=exc.headers,
                )
        return JSONResponse(
            status_code=exc.status_code,
            content={"detail": exc.detail},
            headers=exc.headers,
        )

    @app.exception_handler(RequestValidationError)
    async def validation_exception_handler(
        request: Request, exc: RequestValidationError
    ) -> JSONResponse:
        """Format Pydantic validation errors consistently."""
        from fastapi.encoders import jsonable_encoder
        return JSONResponse(
            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
            content={"detail": jsonable_encoder(exc.errors())},
        )

    @app.exception_handler(SQLAlchemyError)
    async def sqlalchemy_exception_handler(
        request: Request, exc: SQLAlchemyError
    ) -> JSONResponse:
        """Log DB errors and return a 500 without leaking internals."""
        logger.exception("Database error on %s %s", request.method, request.url)
        return JSONResponse(
            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
            content={"detail": "Database error"},
        )

    # === Routers ===
    # Health is mounted at both /health (root) and /api/v1/health (versioned)
    app.include_router(health.router)
    app.include_router(auth.router, prefix="/api/v1")
    app.include_router(users.router, prefix="/api/v1")
    # Phase 4b business routers
    app.include_router(accounts.router, prefix="/api/v1")
    app.include_router(contacts.router, prefix="/api/v1")
    app.include_router(deals.router, prefix="/api/v1")
    app.include_router(activities.router, prefix="/api/v1")
    app.include_router(notes.router, prefix="/api/v1")
    app.include_router(tags.router, prefix="/api/v1")
    app.include_router(dashboard.router, prefix="/api/v1")

    return app


app = create_app()