package app

import (
	"context"
	"errors"
	"net"
	"net/http"
	"os"
	"os/signal"
	"sync"
	"syscall"
	"time"

	"git.yuntuo.hk/k2safe/go-omni/config"
	apierrors "git.yuntuo.hk/k2safe/go-omni/errors"
	"git.yuntuo.hk/k2safe/go-omni/httpx"
	"git.yuntuo.hk/k2safe/go-omni/middleware"
	netrouter "git.yuntuo.hk/k2safe/go-omni/transport/nethttp"
)

// App is the top-level GoOmni application. Its public behavior depends on
// httpx.Router, leaving the network implementation replaceable.
type App struct {
	router      httpx.Router
	config      config.Config
	middlewares []httpx.Middleware
	closers     []func() error
	closeOnce   sync.Once
	closeErr    error
}

// New creates an application using GoOmni's standard-library router.
func New(options ...config.Option) *App {
	settings := configure(options...)
	return newApp(netrouter.New(), settings)
}

// NewWithRouter creates an application with a custom network layer. A custom
// router only needs to implement httpx.Router; handlers and business code stay
// unchanged when the transport changes.
func NewWithRouter(router httpx.Router, options ...config.Option) *App {
	if router == nil {
		panic("go-omni: nil router")
	}
	return newApp(router, configure(options...))
}

func configure(options ...config.Option) config.Config {
	settings := config.Default()
	for _, option := range options {
		if option != nil {
			option(&settings)
		}
	}
	return settings
}

func newApp(router httpx.Router, settings config.Config) *App {
	middlewares := []httpx.Middleware{middleware.RequestID(settings.RequestIDHeader)}
	if settings.EnableLogger {
		middlewares = append(middlewares, middleware.AccessLog())
	}
	middlewares = append(middlewares, middleware.Recovery())
	return &App{router: router, config: settings, middlewares: middlewares}
}

// Router returns the transport contract used by this application.
func (a *App) Router() httpx.Router { return a.router }

// Engine is kept as a compatibility name for the old API. It returns a
// standard http.Handler, so callers do not depend on a router type.
func (a *App) Engine() http.Handler { return a.router }

// ServeHTTP implements http.Handler for standard servers and HTTP tests.
func (a *App) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
	a.router.ServeHTTP(writer, request)
}

// Config returns the effective application configuration.
func (a *App) Config() config.Config { return a.config }

// Use adds middleware to routes registered after this call.
func (a *App) Use(middleware ...httpx.Middleware) *App {
	a.middlewares = append(a.middlewares, middleware...)
	return a
}

// OnShutdown registers a cleanup function owned by the application. Cleanup
// functions run in reverse registration order when Close or RunContext ends.
// This keeps omni.New as the only public startup entry point while allowing
// projects to attach databases, loggers and other resources to its lifecycle.
func (a *App) OnShutdown(cleanup func() error) *App {
	if cleanup != nil {
		a.closers = append(a.closers, cleanup)
	}
	return a
}

// Close releases application resources. It is safe to call more than once.
func (a *App) Close() error {
	a.closeOnce.Do(func() {
		for index := len(a.closers) - 1; index >= 0; index-- {
			if err := a.closers[index](); err != nil {
				a.closeErr = errors.Join(a.closeErr, err)
			}
		}
	})
	return a.closeErr
}

// Run starts the HTTP server and handles SIGINT/SIGTERM. Use RunContext when
// the caller owns cancellation. The default address is :8080.
func (a *App) Run(address ...string) error {
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()
	return a.RunContext(ctx, address...)
}

// NewServer creates a standard HTTP server around the application.
func (a *App) NewServer(address string) *http.Server {
	if address == "" {
		address = a.config.Address
		if address == "" {
			address = ":8080"
		}
	}
	return &http.Server{Addr: address, Handler: a.router}
}

// RunContext serves until the context is canceled, then performs a graceful shutdown.
func (a *App) RunContext(ctx context.Context, address ...string) error {
	if ctx == nil {
		ctx = context.Background()
	}
	if ctx.Err() != nil {
		return a.Close()
	}
	listenOn := a.config.Address
	if listenOn == "" {
		listenOn = ":8080"
	}
	if len(address) > 0 && address[0] != "" {
		listenOn = address[0]
	}
	server := a.NewServer(listenOn)
	listener, err := net.Listen("tcp", server.Addr)
	if err != nil {
		return errors.Join(err, a.Close())
	}
	return a.serveContext(ctx, server, listener)
}

func (a *App) serveContext(ctx context.Context, server *http.Server, listener net.Listener) error {
	serveErr := make(chan error, 1)
	go func() { serveErr <- server.Serve(listener) }()

	select {
	case err := <-serveErr:
		closeErr := a.Close()
		if err == http.ErrServerClosed {
			return closeErr
		}
		return errors.Join(err, closeErr)
	case <-ctx.Done():
		shutdownTimeout := a.config.ShutdownTimeout
		if shutdownTimeout <= 0 {
			shutdownTimeout = 10 * time.Second
		}
		shutdownCtx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
		defer cancel()
		shutdownErr := server.Shutdown(shutdownCtx)
		if shutdownErr != nil {
			// Shutdown leaves active connections open on timeout. Close them so
			// request contexts are canceled before releasing shared resources.
			shutdownErr = errors.Join(shutdownErr, server.Close())
		}
		if err := <-serveErr; err != nil && err != http.ErrServerClosed {
			shutdownErr = errors.Join(shutdownErr, err)
		}
		return errors.Join(shutdownErr, a.Close())
	}
}

func (a *App) writeError(ctx *httpx.Context, err error) {
	if err == nil || ctx.Responded() {
		return
	}
	ctx.WriteError(apierrors.From(err))
}