package main

import (
	"encoding/json"
	"fmt"
	"log"
	"math/rand/v2"
	"net/http"
	"unicode/utf8"
)

const charSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
const version = "0.0.1"

var Table map[string]string = make(map[string]string)

type Request struct {
	URL string
}

type Response struct {
	Version  string
	Status   string
	Original string
	New      string
}

func NewRequest(r *http.Request) (Request, error) {
	var request Request

	err := json.NewDecoder(r.Body).Decode(&request)

	return request, err
}

func log_header(r *http.Request) {
	log.Println("Header {")
	for k, v := range r.Header {
		log.Printf("\t\"%s\": \"%s\"\n", k, v)
	}
	log.Println("}")
}

func redirect(w http.ResponseWriter, r *http.Request) {
	log.Println("Request for:", r.URL.String())
	log_header(r)

	_, i := utf8.DecodeRuneInString(r.URL.String())
	url := r.URL.String()[i:]

	original, ok := Table[url]

	if ok {
		log.Println("Found:", original)

		w.Header().Set("location", original)
		http.Error(w, http.StatusText(301), 301)
	} else {
		log.Println("Unable to find website for", url)
		http.Error(w, http.StatusText(404), 404)
	}
}

func FindOrGenerate(url string) string {
	for key, value := range Table {
		if value == url {
			return key
		}
	}

	short := GenerateString(4)
	_, ok := Table[short]

	for ok {
		short = GenerateString(4)
		_, ok = Table[short]
	}

	Table[short] = url

	return short
}

func shorten(w http.ResponseWriter, r *http.Request) {
	log.Println("Request to Shorten")
	log_header(r)

	request, err := NewRequest(r)
	if err != nil {
		http.Error(w, http.StatusText(500), 500)
	}

	url := FindOrGenerate(request.URL)

	response := Response{version, "ok", request.URL, url}

	data, err := json.Marshal(response)
	if err != nil {
		http.Error(w, http.StatusText(500), 500)
	}

	fmt.Fprintf(w, "%s", string(data))
}

func GenerateString(size uint) string {
	buffer := make([]rune, size)

	for i := uint(0); i < size; i++ {
		index := rand.Uint() % uint(len(charSet))
		buffer[i] = []rune(charSet)[index]
	}

	return string(buffer)
}

func main() {
	http.HandleFunc("/shorten", shorten)
	http.HandleFunc("/", redirect)
	log.Fatal(http.ListenAndServe(":8000", nil))
}