/*
 * Minio Cloud Storage, (C) 2016, 2017, 2018 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 cmd

import (
	"strconv"
	"time"

	"github.com/minio/dsync"
)

// Allow any RPC call request time should be no more/less than 15 minutes.
// 15 minute is chosen to be best for majority use cases.
const rpcSkewTimeAllowed = 15 * time.Minute

// RPC V1 - Initial version
// RPC V2 - format.json XL version changed to 2
// RPC V3 - format.json XL version changed to 3
// Current RPC version
var globalRPCAPIVersion = semVersion{3, 0, 0}

func isRequestTimeAllowed(requestTime time.Time) bool {
	// Check whether request time is within acceptable skew time.
	utcNow := UTCNow()
	return !(requestTime.Sub(utcNow) > rpcSkewTimeAllowed ||
		utcNow.Sub(requestTime) > rpcSkewTimeAllowed)
}

// semVersion - RPC semantic versioning.
type semVersion struct {
	Major uint64
	Minor uint64
	Patch uint64
}

// semver comparator implementation based on the semver 2.0.0 https://semver.org/.
func (v semVersion) Compare(o semVersion) int {
	if v.Major != o.Major {
		if v.Major > o.Major {
			return 1
		}
		return -1
	}
	if v.Minor != o.Minor {
		if v.Minor > o.Minor {
			return 1
		}
		return -1
	}
	if v.Patch != o.Patch {
		if v.Patch > o.Patch {
			return 1
		}
		return -1
	}
	return 0
}

func (v semVersion) String() string {
	b := make([]byte, 0, 5)
	b = strconv.AppendUint(b, v.Major, 10)
	b = append(b, '.')
	b = strconv.AppendUint(b, v.Minor, 10)
	b = append(b, '.')
	b = strconv.AppendUint(b, v.Patch, 10)
	return string(b)
}

// AuthRPCArgs represents minimum required arguments to make any authenticated RPC call.
type AuthRPCArgs struct {
	// Authentication token to be verified by the server for every RPC call.
	AuthToken string
	Version   semVersion
}

// SetAuthToken - sets the token to the supplied value.
func (args *AuthRPCArgs) SetAuthToken(authToken string) {
	args.AuthToken = authToken
}

// SetRPCAPIVersion - sets the rpc version to the supplied value.
func (args *AuthRPCArgs) SetRPCAPIVersion(version semVersion) {
	args.Version = version
}

// IsAuthenticated - validated whether this auth RPC args are already authenticated or not.
func (args AuthRPCArgs) IsAuthenticated() error {
	// checks if rpc Version is not equal to current server rpc version.
	// this is fine for now, but in future when we add backward compatible
	// APIs we need to make sure to allow lesser versioned clients to
	// talk over RPC, until then we are fine with this check.
	if args.Version.Compare(globalRPCAPIVersion) != 0 {
		return errRPCAPIVersionUnsupported
	}

	// Check whether the token is valid
	if !isAuthTokenValid(args.AuthToken) {
		return errInvalidToken
	}

	// Good to go.
	return nil
}

// AuthRPCReply represents minimum required reply for any authenticated RPC call.
type AuthRPCReply struct{}

// LoginRPCArgs - login username and password for RPC.
type LoginRPCArgs struct {
	AuthToken   string
	Version     semVersion
	RequestTime time.Time
}

// IsValid - validates whether this LoginRPCArgs are valid for authentication.
func (args LoginRPCArgs) IsValid() error {
	// checks if rpc Version is not equal to current server rpc version.
	// this is fine for now, but in future when we add backward compatible
	// APIs we need to make sure to allow lesser versioned clients to
	// talk over RPC, until then we are fine with this check.
	if args.Version.Compare(globalRPCAPIVersion) != 0 {
		return errRPCAPIVersionUnsupported
	}

	if !isRequestTimeAllowed(args.RequestTime) {
		return errServerTimeMismatch
	}

	return nil
}

// LoginRPCReply - login reply is a dummy struct perhaps for future use.
type LoginRPCReply struct{}

// LockArgs represents arguments for any authenticated lock RPC call.
type LockArgs struct {
	AuthRPCArgs
	LockArgs dsync.LockArgs
}

func newLockArgs(args dsync.LockArgs) LockArgs {
	return LockArgs{LockArgs: args}
}