package main

import (
	"context"
	"errors"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/exec"
	"os/signal"
	"sync"
	"time"

	// we use pflag package because it understands double dashes
	flags "github.com/spf13/pflag"
)

var (
	servePort      string
	isHelp         bool
	cmd            string
	cmdArgs        []string
	commandExecDir string
)

// some args parsing
func init() {
	flags.StringVarP(&servePort, "port", "p", "8080", "Port to listen for incoming connections.")
	flags.BoolVarP(&isHelp, "help", "h", false, "Prints this help message and exits.")

	flags.StringVarP(&cmd, "cmd", "c", "", "REQUIRED: The command to execute.")
	flags.StringSliceVarP(&cmdArgs, "args", "a", []string{}, "Arguments for the command. Can be provided multiple times or as comma-separated string.")
	flags.StringVarP(&commandExecDir, "dir", "d", "", "The Directory to execute the command.\nDefaults to the directory the tool was called on.")
	flags.Parse()
}

// handles the webhook requests
func handler(w http.ResponseWriter, r *http.Request) {
	defer r.Body.Close() // so I don't forget to close it -> eventhough it's not read.

	cmd := exec.CommandContext(r.Context(), cmd, cmdArgs...)
	// set directory only if it's present.
	if commandExecDir != "" {
		cmd.Dir = commandExecDir
	}
	out, err := cmd.CombinedOutput()
	if err != nil {
		log.Println(err)
		fmt.Fprint(w, err.Error())
		w.WriteHeader(http.StatusBadGateway)
	}
	output := string(out)
	log.Println("Command output:\n" + output)
	fmt.Fprint(w, output)
	w.WriteHeader(http.StatusOK)
}

func main() {
	if isHelp {
		printHelp()
		// printing help is treated as a successful execution.
		os.Exit(0)
	}

	err := validateParams()
	if err != nil {
		log.Fatalln(err)
	}

	// use the default mux because it implements the Handler interface
	// which we need for the server struct.
	mux := http.NewServeMux()
	mux.HandleFunc("/", handler) // only add one handler on root path

	// custom server struct to set custom timeouts for better performance.
	server := &http.Server{
		Handler:      mux,
		Addr:         fmt.Sprintf(":%s", servePort),
		WriteTimeout: 15 * time.Second,
		ReadTimeout:  15 * time.Second,
		IdleTimeout:  120 * time.Second,
	}

	// server start and stop management
	var wg sync.WaitGroup
	wg.Add(2)
	go startHTTPServer(server, &wg)
	go listenToStopHTTPServer(server, &wg)
	wg.Wait()
}

func startHTTPServer(server *http.Server, wg *sync.WaitGroup) {
	defer wg.Done()
	log.Printf("The HTTP server is running: http://localhost:%s/\n", servePort)
	if err := server.ListenAndServe(); err != nil {
		if errors.Is(err, http.ErrServerClosed) {
			log.Println("Shutting down the server...")
			return
		}
		log.Fatalf("An unexpected error happened while running the HTTP server: %v\n", err)
	}
}

func listenToStopHTTPServer(server *http.Server, wg *sync.WaitGroup) {
	defer wg.Done()
	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt)
	<-stop // block til signal is captured.

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	if err := server.Shutdown(ctx); err != nil {
		log.Fatalf("An error happened on the shutdown of the server: %v", err)
	}
}

func printHelp() {
	fmt.Println(`A small server to listen for requests to execute some particular code.

USAGE:
  whook [FLAGS] --cmd [COMMAND [--args [ARGS]]
	
FLAGS:`)
	flags.PrintDefaults()
}

// validateParams if required params are present.
func validateParams() error {
	if cmd == "" {
		return errors.New("missing required 'cmd' parameter")
	}

	return nil
}