from __future__ import annotations

from importlib import import_module
from pathlib import Path
from tempfile import NamedTemporaryFile

from alembic.config import Config
from alembic.script import ScriptDirectory
from fastapi import APIRouter, Response, status
from sqlalchemy import text

from app.core.config import get_settings
from app.db.session import get_engine
from app.providers.registry import list_provider_capabilities
from app.schemas.health import (
    HealthResponse,
    SystemCapabilities,
    SystemCapabilitiesEnvelope,
)
from app.services.model_registry_service import ModelRegistryService

router = APIRouter()


def _dependency_enabled(module: str) -> bool:
    try:
        import_module(module)
        return True
    except Exception:
        return False


def _expected_migration_heads() -> list[str]:
    backend_root = Path(__file__).resolve().parents[3]
    config = Config(str(backend_root / "alembic.ini"))
    config.set_main_option("script_location", str(backend_root / "alembic"))
    return list(ScriptDirectory.from_config(config).get_heads())


def _database_checks() -> dict[str, str]:
    checks = {
        "database": "degraded",
        "postgis": "degraded",
        "migration": "degraded",
    }
    try:
        with get_engine().connect() as connection:
            connection.execute(text("SELECT 1"))
            checks["database"] = "ok"
            connection.execute(
                text("SELECT PostGIS_Version()")
            ).scalar_one()
            checks["postgis"] = "ok"
            database_head = connection.execute(
                text("SELECT version_num FROM alembic_version")
            ).scalar_one()
            expected_heads = _expected_migration_heads()
            if len(expected_heads) == 1 and database_head == expected_heads[0]:
                checks["migration"] = "ok"
            else:
                checks["migration"] = "degraded"
    except Exception:
        return checks
    return checks


def _storage_check(storage_root: str) -> str:
    root = Path(storage_root).expanduser()
    try:
        root.mkdir(parents=True, exist_ok=True)
        with NamedTemporaryFile(
            prefix=".geointel-readiness-",
            dir=root,
            delete=True,
        ) as handle:
            handle.write(b"ok")
            handle.flush()
        return "ok"
    except OSError:
        return "degraded"


def _readiness_payload() -> HealthResponse:
    settings = get_settings()
    checks = _database_checks()
    checks["storage"] = _storage_check(settings.storage_root)
    ready = all(
        value == "ok" or value.startswith("ok:")
        for value in checks.values()
    )
    return HealthResponse(
        status="ok" if ready else "degraded",
        service="geointel-backend",
        version="public",
        database=checks["database"],
        postgis=checks["postgis"],
        migration=checks["migration"],
        storage=checks["storage"],
        checks=checks,
    )


@router.get("/health/live", response_model=HealthResponse)
def liveness() -> HealthResponse:
    return HealthResponse(
        status="ok",
        service="geointel-backend",
        version="public",
    )


def _readiness_response(response: Response) -> HealthResponse:
    payload = _readiness_payload()
    if payload.status != "ok":
        response.status_code = status.HTTP_503_SERVICE_UNAVAILABLE
    return payload


@router.get("/health", response_model=HealthResponse)
def readiness(response: Response) -> HealthResponse:
    return _readiness_response(response)


@router.get("/health/ready", response_model=HealthResponse)
def readiness_explicit(response: Response) -> HealthResponse:
    return _readiness_response(response)


@router.get(
    "/api/v1/system/capabilities",
    response_model=SystemCapabilitiesEnvelope,
)
def capabilities() -> SystemCapabilitiesEnvelope:
    settings = get_settings()
    providers = [item.to_dict() for item in list_provider_capabilities()]
    configured_yolo = ModelRegistryService.get_model_capability(
        settings.yolo_model_id,
        settings=settings,
    )
    yolo_configured = bool(configured_yolo and configured_yolo.configured)
    yolo_status = configured_yolo.status if configured_yolo else "not_configured"
    configured_sam = ModelRegistryService.get_model_capability(
        settings.sam_model_id,
        settings=settings,
        task_type="segmentation",
    )
    postgis_ready = _database_checks()["postgis"].startswith("ok:")
    return SystemCapabilitiesEnvelope(
        data=SystemCapabilities(
            postgis=postgis_ready,
            rasterio=_dependency_enabled("rasterio"),
            geopandas=_dependency_enabled("geopandas"),
            yolo=yolo_configured,
            yolo_status=yolo_status,
            sam=bool(configured_sam and configured_sam.configured),
            grb="bounded",
            sentinel="planned",
            version=settings.app_version,
            build_sha=settings.build_sha,
            providers=providers,
        )
    )