package main

import (
	"log"
	"net/http"
	"strings"

	"github.com/grpc-ecosystem/grpc-gateway/runtime"
	"golang.org/x/net/context"
	"google.golang.org/grpc"
	gw "src.dualinventive.com/go/devsim"
)

func listenAndServeGRPCGateway(httpEndpoint, grpcEndpoint string) error {
	ctx := context.Background()
	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	mux := runtime.NewServeMux()
	opts := []grpc.DialOption{grpc.WithInsecure()}
	err := gw.RegisterRepositoryServiceHandlerFromEndpoint(ctx, mux, grpcEndpoint, opts)
	if err != nil {
		return err
	}

	err = gw.RegisterSimulatorServiceHandlerFromEndpoint(ctx, mux, grpcEndpoint, opts)
	if err != nil {
		return err
	}

	s := &http.Server{
		Addr:    httpEndpoint,
		Handler: allowCORS(mux),
	}

	log.Println("Listening devsimd-gateway on", httpEndpoint, "proxy to", grpcEndpoint)
	return s.ListenAndServe()
}

// allowCORS allows Cross Origin Resoruce Sharing from any origin.
// Don't do this without consideration in production systems.
func allowCORS(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if origin := r.Header.Get("Origin"); origin != "" {
			w.Header().Set("Access-Control-Allow-Origin", origin)
			if r.Method == "OPTIONS" && r.Header.Get("Access-Control-Request-Method") != "" {
				preflightHandler(w, r)
				return
			}
		}
		h.ServeHTTP(w, r)
	})
}

func preflightHandler(w http.ResponseWriter, r *http.Request) {
	headers := []string{"Content-Type", "Accept", "X-User-Agent", "X-Grpc-Web"}
	w.Header().Set("Access-Control-Allow-Headers", strings.Join(headers, ","))
	methods := []string{"GET", "HEAD", "POST", "PUT", "DELETE"}
	w.Header().Set("Access-Control-Allow-Methods", strings.Join(methods, ","))
	log.Printf("preflight request for %s", r.URL.Path)
}