package main

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base32"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"math/rand"
	"net/http"
	"os"
	"strings"
)

var apiSecret string

type addyForm struct {
	Alias       string `json:"alias"`
	Description string `json:"description"`
	Domain      string `json:"domain"`
}

type addyResponse struct {
	Data addyResponseData `json:"data"`
}
type addyResponseData struct {
	Email string `json:"email"`
}

func init() {
	if val, ok := os.LookupEnv("ADDY_API_SECRET"); ok {
		apiSecret = val
	}

	flag.StringVar(&apiSecret, "addy-api-secret", apiSecret, "Secret used for the HMAC protecting addy.io-like API")
}

func AddyAPISignature(username string) []byte {
	mac := hmac.New(sha256.New224, []byte(apiSecret))
	mac.Write([]byte(username))
	return mac.Sum(nil)
}

func AddyAPIToken(username string) string {
	chain := []byte(username + ":")
	chain = append(chain, AddyAPISignature(username)...)
	return base32.StdEncoding.EncodeToString(chain)
}

func checkAddyApiAuthorization(authorization []byte) *string {
	fields := bytes.SplitN(authorization, []byte(":"), 2)
	if len(fields) != 2 {
		return nil
	}

	username := string(fields[0])

	expectedSign := AddyAPISignature(username)
	if !hmac.Equal(expectedSign, fields[1]) {
		return nil
	}

	return &username
}

func addyAliasAPIAuth(r *http.Request) (*string, error) {
	// Check authorization header
	fields := strings.Fields(r.Header.Get("Authorization"))
	if len(fields) != 2 || fields[0] != "Bearer" {
		return nil, fmt.Errorf("Authorization header should be a valid Bearer token")
	}

	// Decode header
	authorization, err := base32.StdEncoding.DecodeString(fields[1])
	if err != nil {
		log.Println("Invalid Authorization header: %s", err.Error())
		return nil, err
	}

	user := checkAddyApiAuthorization(authorization)
	if user == nil {
		return nil, fmt.Errorf("Not authorized")
	}

	return user, nil
}

func addyAliasAPI(w http.ResponseWriter, r *http.Request) {
	user, err := addyAliasAPIAuth(r)
	if err != nil {
		http.Error(w, err.Error(), http.StatusUnauthorized)
		return
	}

	// Decode body
	var body addyForm
	err = json.NewDecoder(r.Body).Decode(&body)
	if err != nil {
		http.Error(w, "Invalid body", http.StatusBadRequest)
		return
	}

	conn, err := myLDAP.Connect()
	if err != nil || conn == nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	err = conn.ServiceBind()
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	dn, err := conn.SearchDN(*user, true)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	if len(body.Alias) == 0 {
		body.Alias = generateRandomString(10)
	}

	email := body.Alias + "@" + body.Domain
	nb, err := conn.SearchMailAlias(email)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	if nb != 0 {
		http.Error(w, fmt.Sprintf("The alias %q is already used.", email), http.StatusBadRequest)
		return
	}

	err = conn.AddMailAlias(dn, email)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	log.Printf("New alias created for %s: %s", dn, email)

	res := addyResponse{
		Data: addyResponseData{
			Email: email,
		},
	}
	err = json.NewEncoder(w).Encode(res)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func addyAliasAPIDelete(w http.ResponseWriter, r *http.Request) {
	user, err := addyAliasAPIAuth(r)
	if err != nil {
		http.Error(w, err.Error(), http.StatusUnauthorized)
		return
	}

	email := r.PathValue("alias")

	conn, err := myLDAP.Connect()
	if err != nil || conn == nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	err = conn.ServiceBind()
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	dn, err := conn.SearchDN(*user, true)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	err = conn.DelMailAlias(dn, email)
	if err != nil {
		log.Println(err)
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	log.Printf("Alias deleted for %s: %s", dn, email)
	http.Error(w, "", http.StatusOK)
}

func generateRandomString(length int) string {
	charset := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	result := make([]byte, length)
	for i := range result {
		result[i] = charset[rand.Intn(len(charset))]
	}
	return string(result)
}