// Package basic provides a simple authentication scheme that checks for the
// user credential hash in an htpasswd formatted file in a configuration-determined
// location.
//
// The use of SHA hashes (htpasswd -s) is enforced since MD5 is insecure and simple
// system crypt() may be as well.
//
// This authentication method MUST be used under TLS, as simple token-replay attack is possible.

package basic

import (
	"encoding/base64"
	"errors"
	"fmt"
	"net/http"
	"strings"

	ctxu "github.com/docker/distribution/context"
	"github.com/docker/distribution/registry/auth"
	"golang.org/x/net/context"
)

type accessController struct {
	realm    string
	htpasswd *HTPasswd
}

type challenge struct {
	realm string
	err   error
}

var _ auth.AccessController = &accessController{}
var (
	ErrPasswordRequired  = errors.New("authorization credential required")
	ErrInvalidCredential = errors.New("invalid authorization credential")
)

func newAccessController(options map[string]interface{}) (auth.AccessController, error) {
	realm, present := options["realm"]
	if _, ok := realm.(string); !present || !ok {
		return nil, fmt.Errorf(`"realm" must be set for basic access controller`)
	}

	path, present := options["path"]
	if _, ok := path.(string); !present || !ok {
		return nil, fmt.Errorf(`"path" must be set for basic access controller`)
	}

	return &accessController{realm: realm.(string), htpasswd: NewHTPasswd(path.(string))}, nil
}

func (ac *accessController) Authorized(ctx context.Context, accessRecords ...auth.Access) (context.Context, error) {
	req, err := ctxu.GetRequest(ctx)
	if err != nil {
		return nil, err
	}

	authHeader := req.Header.Get("Authorization")

	if authHeader == "" {
		challenge := challenge{
			realm: ac.realm,
		}
		return nil, &challenge
	}

	parts := strings.Split(req.Header.Get("Authorization"), " ")

	challenge := challenge{
		realm: ac.realm,
	}

	if len(parts) != 2 || strings.ToLower(parts[0]) != "basic" {
		challenge.err = ErrPasswordRequired
		return nil, &challenge
	}

	text, err := base64.StdEncoding.DecodeString(parts[1])
	if err != nil {
		challenge.err = ErrInvalidCredential
		return nil, &challenge
	}

	credential := strings.Split(string(text), ":")
	if len(credential) != 2 {
		challenge.err = ErrInvalidCredential
		return nil, &challenge
	}

	if res, _ := ac.htpasswd.AuthenticateUser(credential[0], credential[1]); !res {
		challenge.err = ErrInvalidCredential
		return nil, &challenge
	}

	return auth.WithUser(ctx, auth.UserInfo{Name: credential[0]}), nil
}

func (ch *challenge) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	header := fmt.Sprintf("Realm realm=%q", ch.realm)
	w.Header().Set("WWW-Authenticate", header)
	w.WriteHeader(http.StatusUnauthorized)
}

func (ch *challenge) Error() string {
	return fmt.Sprintf("basic authentication challenge: %#v", ch)
}

func init() {
	auth.Register("basic", auth.InitFunc(newAccessController))
}