package main

import (
	"encoding/json"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"regexp"
	"os"
	"slices"
)

type Config struct {
	Port          string
	Allowed       []string
	HomeHtml      string
	MainTemplate  string
	ErrorTemplate string
}

var config Config

func GetFiles(w http.ResponseWriter, r *http.Request) {
	log.Println("Request for:", r.URL.String())
	url := fmt.Sprintf("static%s", r.URL.String())
	htmlRegex, err := regexp.Compile("^static/.*\\.html$")
	if err != nil {
		ErrorPage(w, "Internal Server Error", 500)
		return
	}

	if url == "static/" {
		url = config.HomeHtml
	}

	if slices.Contains(config.Allowed, url) {
		if htmlRegex.MatchString(url) {
			t := template.Must(template.ParseFiles(config.MainTemplate))

			html, err := os.ReadFile(url)
			if err != nil {
				ErrorPage(w, "Internal Server Error", 500)
				return
			}

			t.Execute(w, template.HTML(html))
		} else {
			http.ServeFile(w, r, url)
		}
	} else {
		ErrorPage(w, "Page Not Found.", 404)
	}
}

func ErrorPage(w http.ResponseWriter, message string, code int) {
	log.Println(code, message)
	t := template.Must(template.ParseFiles(config.ErrorTemplate))
	t.Execute(w, struct {
		Code    int
		Message string
	}{
		Code:    code,
		Message: message,
	})
}

func Usage() {
	fmt.Fprintf(os.Stderr, "%s [--port port]\n", os.Args[0])
}

func ParseConfigFile(path string) error {
	configJson, err := os.ReadFile("config.json")
	if err != nil {
		return err
	}

	err = json.Unmarshal(configJson, &config)
	return err
}

func LogConfiguration() {
	log.Println("Port:", config.Port)
	log.Println("Allowed:")
	for i, a := range config.Allowed {
		log.Printf("%d: %s\n", i, a)
	}
	log.Println("HomeHtml:", config.HomeHtml)
	log.Println("MainTemplate:", config.MainTemplate)
	log.Println("ErrorTemplate:", config.ErrorTemplate)
}

func main() {
	portFlagSet := false
	port := ":8000"

	for i := 1; i < len(os.Args); i++ {
		switch os.Args[i] {
		case "--port":
			if i+1 >= len(os.Args) {
				Usage()
			} else {
				portFlagSet = true
				port = ":" + os.Args[i+1]
				i++
			}
		default:
			log.Println("Unknown option: ", os.Args[i])
			Usage()
		}
	}

	err := ParseConfigFile("config.json")
	if err != nil {
		panic(err)
	}

	if !portFlagSet {
		port = ":" + config.Port
	} else {
		config.Port = port
	}

	LogConfiguration()

	http.HandleFunc("/", GetFiles)
	log.Fatal(http.ListenAndServe(port, nil))
}