// Copyright 2014 Manu Martinez-Almeida. All rights reserved.
// Use of this source code is governed by a MIT style
// license that can be found in the LICENSE file.

package ginx

import (
	"crypto/subtle"
	"encoding/base64"
	"net/http"
	"strconv"

	"github.com/gin-gonic/gin"
)

// AuthUserKey is the cookie name for user credential in basic auth.
const AuthUserKey = "user"

// Accounts defines a key/value for user/pass list of authorized logins.
type Accounts []Account

type Account struct {
	User     string
	Password string
}

type authPair struct {
	value string
	user  string
}

type authPairs []authPair

func (a authPairs) searchCredential(authValue string) (string, bool) {
	if authValue == "" {
		return "", false
	}
	for _, pair := range a {
		if subtle.ConstantTimeCompare(StringToBytes(pair.value), StringToBytes(authValue)) == 1 {
			return pair.user, true
		}
	}
	return "", false
}

// BasicAuthForRealm returns a Basic HTTP Authorization middleware. It takes as arguments a map[string]string where
// the key is the user name and the value is the password, as well as the name of the Realm.
// If the realm is empty, "Authorization Required" will be used by default.
// (see http://tools.ietf.org/html/rfc2617#section-1.2)
func BasicAuthForRealm(accounts Accounts, realm string) gin.HandlerFunc {
	if realm == "" {
		realm = "Authorization Required"
	}
	realm = "Basic realm=" + strconv.Quote(realm)
	pairs := processAccounts(accounts)
	return func(c *gin.Context) {
		// Search user in the slice of allowed credentials
		user, found := pairs.searchCredential(c.Request.Header.Get("Authorization"))
		if !found {
			// Credentials doesn't match, we return 401 and abort handlers chain.
			c.Header("WWW-Authenticate", realm)
			c.AbortWithStatus(http.StatusUnauthorized)
			return
		}

		// The user credentials was found, set user's id to key AuthUserKey in this context, the user's id can be read later using
		// c.MustGet(gin.AuthUserKey).
		c.Set(AuthUserKey, user)
	}
}

// BasicAuth returns a Basic HTTP Authorization middleware. It takes as argument a map[string]string where
// the key is the user name and the value is the password.
func BasicAuth(accounts Accounts) gin.HandlerFunc {
	return BasicAuthForRealm(accounts, "")
}

func processAccounts(accounts Accounts) authPairs {
	length := len(accounts)
	assert1(length > 0, "Empty list of authorized credentials")
	pairs := make(authPairs, 0, length)
	for _, account := range accounts {
		assert1(account.User != "", "User can not be empty")
		value := authorizationHeader(account.User, account.Password)
		pairs = append(pairs, authPair{
			value: value,
			user:  account.User,
		})
	}
	return pairs
}

func authorizationHeader(user, password string) string {
	base := user + ":" + password
	return "Basic " + base64.StdEncoding.EncodeToString(StringToBytes(base))
}

func assert1(guard bool, text string) {
	if !guard {
		panic(text)
	}
}