/*
 * Minio Cloud Storage, (C) 2015 Minio, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package main

import (
	"bytes"
	"crypto/md5"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"io/ioutil"
	"net/http"
	"strings"
)

// Verify if request has JWT.
func isRequestJWT(r *http.Request) bool {
	if _, ok := r.Header["Authorization"]; ok {
		if strings.HasPrefix(r.Header.Get("Authorization"), jwtAlgorithm) {
			return true
		}
	}
	return false
}

// Verify if request has AWS Signature Version '4'.
func isRequestSignatureV4(r *http.Request) bool {
	if _, ok := r.Header["Authorization"]; ok {
		if strings.HasPrefix(r.Header.Get("Authorization"), signV4Algorithm) {
			return true
		}
	}
	return false
}

// Verify if request has AWS Presignature Version '4'.
func isRequestPresignedSignatureV4(r *http.Request) bool {
	if _, ok := r.URL.Query()["X-Amz-Credential"]; ok {
		return true
	}
	return false
}

// Verify if request has AWS Post policy Signature Version '4'.
func isRequestPostPolicySignatureV4(r *http.Request) bool {
	if _, ok := r.Header["Content-Type"]; ok {
		if strings.Contains(r.Header.Get("Content-Type"), "multipart/form-data") && r.Method == "POST" {
			return true
		}
	}
	return false
}

// Authorization type.
type authType int

// List of all supported auth types.
const (
	authTypeUnknown authType = iota
	authTypeAnonymous
	authTypePresigned
	authTypePostPolicy
	authTypeSigned
	authTypeJWT
)

// Get request authentication type.
func getRequestAuthType(r *http.Request) authType {
	if isRequestSignatureV4(r) {
		return authTypeSigned
	} else if isRequestPresignedSignatureV4(r) {
		return authTypePresigned
	} else if isRequestJWT(r) {
		return authTypeJWT
	} else if isRequestPostPolicySignatureV4(r) {
		return authTypePostPolicy
	} else if _, ok := r.Header["Authorization"]; !ok {
		return authTypeAnonymous
	}
	return authTypeUnknown
}

// sum256 calculate sha256 sum for an input byte array
func sum256(data []byte) []byte {
	hash := sha256.New()
	hash.Write(data)
	return hash.Sum(nil)
}

// sumMD5 calculate md5 sum for an input byte array
func sumMD5(data []byte) []byte {
	hash := md5.New()
	hash.Write(data)
	return hash.Sum(nil)
}

// Verify if request has valid AWS Signature Version '4'.
func isReqAuthenticated(r *http.Request) (s3Error APIErrorCode) {
	if r == nil {
		return ErrInternalError
	}
	payload, err := ioutil.ReadAll(r.Body)
	if err != nil {
		return ErrInternalError
	}
	// Verify Content-Md5, if payload is set.
	if r.Header.Get("Content-Md5") != "" {
		if r.Header.Get("Content-Md5") != base64.StdEncoding.EncodeToString(sumMD5(payload)) {
			return ErrBadDigest
		}
	}
	// Populate back the payload.
	r.Body = ioutil.NopCloser(bytes.NewReader(payload))
	validateRegion := true // Validate region.
	if isRequestSignatureV4(r) {
		return doesSignatureMatch(hex.EncodeToString(sum256(payload)), r, validateRegion)
	} else if isRequestPresignedSignatureV4(r) {
		return doesPresignedSignatureMatch(hex.EncodeToString(sum256(payload)), r, validateRegion)
	}
	return ErrAccessDenied
}

// authHandler - handles all the incoming authorization headers and
// validates them if possible.
type authHandler struct {
	handler http.Handler
}

// setAuthHandler to validate authorization header for the incoming request.
func setAuthHandler(h http.Handler) http.Handler {
	return authHandler{h}
}

// handler for validating incoming authorization headers.
func (a authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	switch getRequestAuthType(r) {
	case authTypeAnonymous, authTypePresigned, authTypeSigned, authTypePostPolicy:
		// Let top level caller validate for anonymous and known
		// signed requests.
		a.handler.ServeHTTP(w, r)
		return
	case authTypeJWT:
		// Validate Authorization header if its valid for JWT request.
		if !isJWTReqAuthenticated(r) {
			w.WriteHeader(http.StatusUnauthorized)
			return
		}
		a.handler.ServeHTTP(w, r)
	default:
		writeErrorResponse(w, r, ErrSignatureVersionNotSupported, r.URL.Path)
		return
	}
}