"""FastAPI application for the autoscaler daemon."""

from __future__ import annotations

import logging
import uuid
from collections.abc import Callable
from datetime import datetime
from typing import TYPE_CHECKING, NoReturn

from fastapi import FastAPI, HTTPException, Request, Response
from fastapi.responses import JSONResponse
from pydantic import BaseModel

from .models import (
    CapacityHint,
    CapacityPolicy,
    EffectiveConfigResponse,
    ErrorDetail,
    ErrorResponse,
    HealthResponse,
    ReservationPhase,
    ReservationRequest,
    ReservationResponse,
    SchedulerPolicy,
    SlotInfo,
    SlotState,
    StateSummary,
)

if TYPE_CHECKING:
    from .config import AppConfig
    from .metrics import MetricsRegistry
    from .providers.clock import Clock
    from .providers.haproxy import HAProxyRuntime
    from .runtime.base import RuntimeAdapter
    from .state_db import StateDB

log = logging.getLogger(__name__)


class SlotAdminRequest(BaseModel):
    """Admin action request that targets a slot."""

    slot_id: str


def _parse_required_dt(value: str) -> datetime:
    return datetime.fromisoformat(value)


def _parse_optional_dt(value: str | None) -> datetime | None:
    if value is None:
        return None
    return datetime.fromisoformat(value)


def _resv_to_response(resv: dict) -> ReservationResponse:
    return ReservationResponse(
        reservation_id=str(resv["reservation_id"]),
        phase=ReservationPhase(str(resv["phase"])),
        slot=resv.get("slot_id"),
        instance_id=resv.get("instance_id"),
        system=str(resv["system"]),
        created_at=_parse_required_dt(str(resv["created_at"])),
        updated_at=_parse_required_dt(str(resv["updated_at"])),
        expires_at=_parse_required_dt(str(resv["expires_at"])),
        released_at=_parse_optional_dt(resv.get("released_at")),
    )


def _slot_to_info(slot: dict) -> SlotInfo:
    return SlotInfo(
        slot_id=str(slot["slot_id"]),
        system=str(slot["system"]),
        state=SlotState(str(slot["state"])),
        instance_id=slot.get("instance_id"),
        instance_ip=slot.get("instance_ip"),
        lease_count=int(slot["lease_count"]),
        last_state_change=_parse_required_dt(str(slot["last_state_change"])),
    )


def _error_response(
    request: Request,
    status_code: int,
    code: str,
    message: str,
    retryable: bool = False,
) -> NoReturn:
    request_id = getattr(request.state, "request_id", str(uuid.uuid4()))
    payload = ErrorResponse(
        error=ErrorDetail(code=code, message=message, retryable=retryable),
        request_id=request_id,
    )
    raise HTTPException(status_code=status_code, detail=payload.model_dump(mode="json"))


def create_app(
    db: StateDB,
    config: AppConfig,
    clock: Clock,
    metrics: MetricsRegistry,
    runtime: RuntimeAdapter | None = None,
    haproxy: HAProxyRuntime | None = None,
    scheduler_running: Callable[[], bool] | None = None,
    reconciler_running: Callable[[], bool] | None = None,
    ready_check: Callable[[], bool] | None = None,
    reconcile_now: Callable[[], dict[str, object] | None] | None = None,
) -> FastAPI:
    """Create the FastAPI application."""
    app = FastAPI(title="nix-builder-autoscaler", version="0.1.0")

    app.state.db = db
    app.state.config = config
    app.state.clock = clock
    app.state.metrics = metrics
    app.state.runtime = runtime
    app.state.haproxy = haproxy

    @app.middleware("http")
    async def request_id_middleware(request: Request, call_next: Callable) -> Response:
        request.state.request_id = str(uuid.uuid4())
        response = await call_next(request)
        response.headers["x-request-id"] = request.state.request_id
        return response

    @app.exception_handler(HTTPException)
    async def http_exception_handler(request: Request, exc: HTTPException) -> JSONResponse:
        detail = exc.detail
        if isinstance(detail, dict) and "error" in detail and "request_id" in detail:
            return JSONResponse(status_code=exc.status_code, content=detail)

        request_id = getattr(request.state, "request_id", str(uuid.uuid4()))
        payload = ErrorResponse(
            error=ErrorDetail(
                code="http_error",
                message=str(detail) if detail else "Request failed",
                retryable=False,
            ),
            request_id=request_id,
        )
        return JSONResponse(status_code=exc.status_code, content=payload.model_dump(mode="json"))

    @app.post("/v1/reservations", response_model=ReservationResponse)
    def create_reservation(body: ReservationRequest) -> ReservationResponse:
        resv = db.create_reservation(
            body.system,
            body.reason,
            body.build_id,
            config.capacity.reservation_ttl_seconds,
        )
        return _resv_to_response(resv)

    @app.get("/v1/reservations/{reservation_id}", response_model=ReservationResponse)
    def get_reservation(reservation_id: str, request: Request) -> ReservationResponse:
        resv = db.get_reservation(reservation_id)
        if resv is None:
            _error_response(request, 404, "not_found", "Reservation not found")
        return _resv_to_response(resv)

    @app.post("/v1/reservations/{reservation_id}/release", response_model=ReservationResponse)
    def release_reservation(reservation_id: str, request: Request) -> ReservationResponse:
        resv = db.release_reservation(reservation_id)
        if resv is None:
            _error_response(request, 404, "not_found", "Reservation not found")
        return _resv_to_response(resv)

    @app.get("/v1/reservations", response_model=list[ReservationResponse])
    def list_reservations(
        phase: ReservationPhase | None = None,
    ) -> list[ReservationResponse]:
        reservations = db.list_reservations(phase)
        return [_resv_to_response(resv) for resv in reservations]

    @app.get("/v1/slots", response_model=list[SlotInfo])
    def list_slots() -> list[SlotInfo]:
        slots = db.list_slots()
        return [_slot_to_info(slot) for slot in slots]

    @app.get("/v1/state/summary", response_model=StateSummary)
    def state_summary() -> StateSummary:
        summary = db.get_state_summary()
        return StateSummary.model_validate(summary)

    @app.get("/v1/config/effective", response_model=EffectiveConfigResponse)
    def effective_config() -> EffectiveConfigResponse:
        return EffectiveConfigResponse(
            capacity=CapacityPolicy(
                min_slots=config.capacity.min_slots,
                max_slots=config.capacity.max_slots,
                target_warm_slots=config.capacity.target_warm_slots,
                max_leases_per_slot=config.capacity.max_leases_per_slot,
                idle_scale_down_seconds=config.capacity.idle_scale_down_seconds,
                drain_timeout_seconds=config.capacity.drain_timeout_seconds,
                launch_timeout_seconds=config.capacity.launch_timeout_seconds,
                boot_timeout_seconds=config.capacity.boot_timeout_seconds,
                binding_timeout_seconds=config.capacity.binding_timeout_seconds,
                terminating_timeout_seconds=config.capacity.terminating_timeout_seconds,
                termination_cooldown_seconds=config.capacity.termination_cooldown_seconds,
            ),
            scheduler=SchedulerPolicy(
                tick_seconds=config.scheduler.tick_seconds,
                reconcile_seconds=config.scheduler.reconcile_seconds,
            ),
        )

    @app.post("/v1/hints/capacity")
    def capacity_hint(hint: CapacityHint) -> dict[str, str]:
        log.info(
            "capacity_hint",
            extra={
                "builder": hint.builder,
                "queued": hint.queued,
                "running": hint.running,
                "system": hint.system,
                "timestamp": hint.timestamp.isoformat(),
            },
        )
        return {"status": "accepted"}

    @app.get("/health/live", response_model=HealthResponse)
    def health_live() -> HealthResponse:
        return HealthResponse(status="ok")

    @app.get("/health/ready", response_model=HealthResponse)
    def health_ready() -> HealthResponse:
        if ready_check is not None and not ready_check():
            return JSONResponse(  # type: ignore[return-value]
                status_code=503,
                content=HealthResponse(status="degraded").model_dump(mode="json"),
            )
        if scheduler_running is not None and not scheduler_running():
            return JSONResponse(  # type: ignore[return-value]
                status_code=503,
                content=HealthResponse(status="degraded").model_dump(mode="json"),
            )
        if reconciler_running is not None and not reconciler_running():
            return JSONResponse(  # type: ignore[return-value]
                status_code=503,
                content=HealthResponse(status="degraded").model_dump(mode="json"),
            )
        return HealthResponse(status="ok")

    @app.get("/metrics")
    def metrics_endpoint() -> Response:
        return Response(content=metrics.render(), media_type="text/plain")

    @app.post("/v1/admin/drain")
    def admin_drain(body: SlotAdminRequest, request: Request) -> dict[str, str]:
        slot = db.get_slot(body.slot_id)
        if slot is None:
            _error_response(request, 404, "not_found", "Slot not found")
        state = str(slot["state"])
        if state == SlotState.DRAINING.value or state == SlotState.TERMINATING.value:
            return {"status": "accepted", "slot_id": body.slot_id, "state": state}

        allowed_states = {
            SlotState.READY.value,
            SlotState.BINDING.value,
            SlotState.BOOTING.value,
            SlotState.LAUNCHING.value,
        }
        if state not in allowed_states:
            _error_response(
                request,
                409,
                "invalid_state",
                f"Cannot drain slot from state {state}",
            )
        db.update_slot_state(body.slot_id, SlotState.DRAINING, interruption_pending=0)
        return {"status": "accepted", "slot_id": body.slot_id, "state": SlotState.DRAINING.value}

    @app.post("/v1/admin/unquarantine")
    def admin_unquarantine(body: SlotAdminRequest, request: Request) -> dict[str, str]:
        slot = db.get_slot(body.slot_id)
        if slot is None:
            _error_response(request, 404, "not_found", "Slot not found")

        state = str(slot["state"])
        if state != SlotState.ERROR.value:
            _error_response(
                request,
                409,
                "invalid_state",
                f"Cannot unquarantine slot from state {state}",
            )

        db.update_slot_state(
            body.slot_id,
            SlotState.EMPTY,
            instance_id=None,
            instance_ip=None,
            instance_launch_time=None,
            lease_count=0,
            cooldown_until=None,
            interruption_pending=0,
        )
        return {"status": "accepted", "slot_id": body.slot_id, "state": SlotState.EMPTY.value}

    @app.post("/v1/admin/reconcile-now")
    def admin_reconcile_now(request: Request) -> dict[str, object]:
        if reconcile_now is None:
            _error_response(
                request,
                503,
                "not_configured",
                "Reconcile trigger not configured",
                retryable=True,
            )
        try:
            result = reconcile_now()
        except Exception:
            log.exception("admin_reconcile_now_failed")
            _error_response(
                request,
                500,
                "reconcile_failed",
                "Reconcile tick failed",
                retryable=True,
            )

        payload: dict[str, object] = {"status": "accepted"}
        if isinstance(result, dict):
            payload.update(result)
        return payload

    return app