// Command gunk-example-server-gw is a grpc-gateway example implementation for
// the gunk-example-server.
package main

import (
	"context"
	"flag"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"

	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
	codequestpb "github.com/hhhapz/codequest/api/v1"
	"github.com/peterbourgon/ff/v3"
	"google.golang.org/grpc"
	"google.golang.org/grpc/grpclog"
	"google.golang.org/protobuf/encoding/protojson"
)

func main() {
	fs := flag.NewFlagSet("codequest", flag.ExitOnError)

	addr := fs.String("l", "0.0.0.0:8080", "listen address")
	endpoint := fs.String("endpoint", "localhost:10000", "grpc endpoint")

	if err := ff.Parse(fs, os.Args[1:], ff.WithEnvVarPrefix("CQ")); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	if err := run(context.Background(), *addr, *endpoint); err != nil {
		fmt.Fprintf(os.Stderr, "error: %v\n", err)
		os.Exit(1)
	}
}

// run creates and runs the gateway instance.
func run(ctx context.Context, addr, endpoint string) error {
	// build gateway mux
	gw, opts := runtime.NewServeMux(
		runtime.WithMarshalerOption(runtime.MIMEWildcard, &runtime.JSONPb{
			MarshalOptions: protojson.MarshalOptions{
				EmitUnpopulated: true,
			},
		}),
	), []grpc.DialOption{grpc.WithInsecure()}
	for _, f := range []func(context.Context, *runtime.ServeMux, string, []grpc.DialOption) error{
		codequestpb.RegisterAuthServiceHandlerFromEndpoint,
		codequestpb.RegisterUserServiceHandlerFromEndpoint,
		codequestpb.RegisterQuestServiceHandlerFromEndpoint,
	} {
		if err := f(ctx, gw, endpoint, opts); err != nil {
			return err
		}
	}
	log := grpclog.NewLoggerV2(io.Discard, os.Stderr, os.Stderr)
	grpclog.SetLoggerV2(log)
	log.Info("Serving gateway on http://", addr)

	server := &http.Server{
		Addr:    addr,
		Handler: allowCORS(gw),
	}
	return server.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)
	})
}

// preflightHandler adds the necessary headers in order to serve
// CORS from any origin using the methods "GET", "HEAD", "POST", "PUT", "DELETE"
// We insist, don't do this without consideration in production systems.
func preflightHandler(w http.ResponseWriter, r *http.Request) {
	headers := []string{"Content-Type", "Accept", "Authorization"}
	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, ","))
}