// Package server provides the HTTP server and lifecycle management.
package server

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"time"

	"github.com/getsentry/sentry-go"
	"github.com/go-chi/chi/v5"
	"go.uber.org/fx"
	"sneak.berlin/go/pixa/internal/config"
	"sneak.berlin/go/pixa/internal/globals"
	"sneak.berlin/go/pixa/internal/handlers"
	"sneak.berlin/go/pixa/internal/logger"
	"sneak.berlin/go/pixa/internal/middleware"
)

// Shutdown configuration constants.
const (
	ShutdownTimeout    = 5 * time.Second
	SentryFlushTimeout = 2 * time.Second
)

// errStillProcessing is returned by the server's stop hook when images are
// still being processed once ShutdownTimeout has passed.
var errStillProcessing = errors.New("images still being processed at shutdown")

// Params defines dependencies for Server.
type Params struct {
	fx.In

	Logger     *logger.Logger
	Globals    *globals.Globals
	Config     *config.Config
	Middleware *middleware.Middleware
	Handlers   *handlers.Handlers
	Shutdowner fx.Shutdowner
}

// Server is the main HTTP server.
type Server struct {
	log           *slog.Logger
	config        *config.Config
	globals       *globals.Globals
	mw            *middleware.Middleware
	h             *handlers.Handlers
	shutdowner    fx.Shutdowner
	startupTime   time.Time
	sentryEnabled bool
	httpServer    *http.Server
	router        *chi.Mux
}

// New creates a new Server instance. Its start hook starts Sentry and the
// HTTP server; its stop hook, which fx runs on SIGINT, SIGTERM or a
// shutdown request, shuts them down.
func New(lc fx.Lifecycle, params Params) (*Server, error) {
	s := &Server{
		log:        params.Logger.Get(),
		config:     params.Config,
		globals:    params.Globals,
		mw:         params.Middleware,
		h:          params.Handlers,
		shutdowner: params.Shutdowner,
	}

	lc.Append(fx.Hook{
		OnStart: func(_ context.Context) error {
			s.startupTime = time.Now()

			err := s.enableSentry()
			if err != nil {
				return err
			}

			s.SetupRoutes()
			s.httpServer = s.newHTTPServer()

			go s.serveUntilShutdown()

			return nil
		},
		OnStop: s.cleanShutdown,
	})

	return s, nil
}

// MaintenanceMode returns whether maintenance mode is enabled.
func (s *Server) MaintenanceMode() bool {
	return s.config.MaintenanceMode
}

func (s *Server) enableSentry() error {
	s.sentryEnabled = false

	if s.config.SentryDSN == "" {
		return nil
	}

	err := sentry.Init(sentry.ClientOptions{
		Dsn:     s.config.SentryDSN,
		Release: fmt.Sprintf("%s-%s", s.globals.Appname, s.globals.Version),
	})
	if err != nil {
		return fmt.Errorf("sentry init failure: %w", err)
	}

	s.log.Info("sentry error reporting activated")
	s.sentryEnabled = true

	return nil
}

// cleanShutdown stops the HTTP server, waits for the images still being
// processed, then flushes Sentry. The first two share ShutdownTimeout. It
// returns errStillProcessing when images are still being processed after
// that, as their work is abandoned.
func (s *Server) cleanShutdown(ctx context.Context) error {
	s.log.Info("shutting down")

	ctxShutdown, shutdownCancel := context.WithTimeout(ctx, ShutdownTimeout)
	defer shutdownCancel()

	err := s.httpServer.Shutdown(ctxShutdown)
	if err != nil {
		s.log.Error("server clean shutdown failed", "error", err)
	}

	stillProcessing := s.h.WaitForProcessing(ctxShutdown)

	if s.sentryEnabled {
		sentry.Flush(SentryFlushTimeout)
	}

	if stillProcessing > 0 {
		s.log.Error("images still being processed at shutdown",
			"count", stillProcessing)

		return errStillProcessing
	}

	return nil
}