package apis

import (
	"context"
	"crypto/tls"
	"datamanager/backend/core"
	"github.com/fatih/color"
	"github.com/labstack/echo/v5"
	"github.com/labstack/echo/v5/middleware"
	"github.com/pocketbase/pocketbase/tools/list"
	"golang.org/x/crypto/acme"
	"log"
	"log/slog"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"
)

// ServeConfig defines a configuration struct for apis.Serve().
type ServeConfig struct {
	// ShowStartBanner indicates whether to show or hide the server start console message.
	ShowStartBanner bool

	// HttpAddr is the TCP address to listen for the HTTP server (eg. `127.0.0.1:80`).
	HttpAddr string

	// HttpsAddr is the TCP address to listen for the HTTPS server (eg. `127.0.0.1:443`).
	HttpsAddr string

	// Optional domains list to use when issuing the TLS certificate.
	//
	// If not set, the host from the bound server address will be used.
	//
	// For convenience, for each "non-www" domain a "www" entry and
	// redirect will be automatically added.
	CertificateDomains []string

	// AllowedOrigins is an optional list of CORS origins (default to "*").
	AllowedOrigins []string
}

func Serve(app core.App, config ServeConfig) (*http.Server, error) {
	if len(config.AllowedOrigins) == 0 {
		config.AllowedOrigins = []string{"*"}
	}

	router, err := InitApi(app)
	if err != nil {
		return nil, err
	}

	// configure cors
	router.Use(middleware.CORSWithConfig(middleware.CORSConfig{
		Skipper:      middleware.DefaultSkipper,
		AllowOrigins: config.AllowedOrigins,
		AllowMethods: []string{http.MethodGet, http.MethodHead, http.MethodPut, http.MethodPatch, http.MethodPost, http.MethodDelete},
	}))

	// start http server
	// ---
	mainAddr := config.HttpAddr
	if config.HttpsAddr != "" {
		mainAddr = config.HttpsAddr
	}

	var wwwRedirects []string

	// extract the host names for the certificate host policy
	hostNames := config.CertificateDomains
	if len(hostNames) == 0 {
		host, _, _ := net.SplitHostPort(mainAddr)
		hostNames = append(hostNames, host)
	}
	for _, host := range hostNames {
		if strings.HasPrefix(host, "www.") {
			continue // explicitly set www host
		}

		wwwHost := "www." + host
		if !list.ExistInSlice(wwwHost, hostNames) {
			hostNames = append(hostNames, wwwHost)
			wwwRedirects = append(wwwRedirects, wwwHost)
		}
	}

	// implicit www->non-www redirect(s)
	if len(wwwRedirects) > 0 {
		router.Pre(func(next echo.HandlerFunc) echo.HandlerFunc {
			return func(c echo.Context) error {
				host := c.Request().Host

				if strings.HasPrefix(host, "www.") && list.ExistInSlice(host, wwwRedirects) {
					return c.Redirect(
						http.StatusTemporaryRedirect,
						c.Scheme()+"://"+host[4:]+c.Request().RequestURI,
					)
				}

				return next(c)
			}
		})
	}

	// base request context used for cancelling long running requests
	// like the SSE connections
	baseCtx, cancelBaseCtx := context.WithCancel(context.Background())
	defer cancelBaseCtx()

	server := &http.Server{
		TLSConfig: &tls.Config{
			MinVersion: tls.VersionTLS12,
			NextProtos: []string{acme.ALPNProto},
		},
		ReadTimeout:       10 * time.Minute,
		ReadHeaderTimeout: 30 * time.Second,
		// WriteTimeout: 60 * time.Second, // breaks sse!
		Handler: router,
		Addr:    mainAddr,
		BaseContext: func(l net.Listener) context.Context {
			return baseCtx
		},
	}

	if config.ShowStartBanner {
		schema := "http"
		addr := server.Addr

		if config.HttpsAddr != "" {
			schema = "https"

			if len(config.CertificateDomains) > 0 {
				addr = config.CertificateDomains[0]
			}
		}

		date := new(strings.Builder)
		log.New(date, "", log.LstdFlags).Print()

		bold := color.New(color.Bold).Add(color.FgGreen)
		_, _ = bold.Printf(
			"%s Server started at %s\n",
			strings.TrimSpace(date.String()),
			color.CyanString("%s://%s", schema, addr),
		)
	}

	// WaitGroup to block until server.ShutDown() returns because Serve and similar methods exit immediately.
	// Note that the WaitGroup would not do anything if the app.OnTerminate() hook isn't triggered.
	var wg sync.WaitGroup

	// wait for the graceful shutdown to complete before exit
	defer wg.Wait()

	// ---
	// @todo consider removing the server return value because it is
	// not really useful when combined with the blocking serve calls
	// ---

	// start HTTPS server
	if config.HttpsAddr != "" {
		// if httpAddr is set, start an HTTP server to redirect the traffic to the HTTPS version
		if config.HttpAddr != "" {
			go func() {
				err := http.ListenAndServe(config.HttpAddr, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
					http.Redirect(w, r, "https://"+r.Host+r.RequestURI, http.StatusMovedPermanently)
				}))
				if err != nil {
					slog.Error("Failed to start HTTP server for redirect: %v", err)
				}
			}()
		}

		return server, server.ListenAndServeTLS("", "")
	}

	// OR start HTTP server
	return server, server.ListenAndServe()
}