/*
 *
 * Copyright 2021 gRPC authors.
 *
 * 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 google

import (
	"context"
	"net"
	"strings"

	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/internal"
)

const cfeClusterNamePrefix = "google_cfe_"

// clusterTransportCreds is a combo of TLS + ALTS.
//
// On the client, ClientHandshake picks TLS or ALTS based on address attributes.
// - if attributes has cluster name
//   - if cluster name has prefix "google_cfe_", use TLS
//   - otherwise, use ALTS
// - else, do TLS
//
// On the server, ServerHandshake always does TLS.
type clusterTransportCreds struct {
	tls  credentials.TransportCredentials
	alts credentials.TransportCredentials
}

func newClusterTransportCreds(tls, alts credentials.TransportCredentials) *clusterTransportCreds {
	return &clusterTransportCreds{
		tls:  tls,
		alts: alts,
	}
}

func (c *clusterTransportCreds) ClientHandshake(ctx context.Context, authority string, rawConn net.Conn) (net.Conn, credentials.AuthInfo, error) {
	chi := credentials.ClientHandshakeInfoFromContext(ctx)
	if chi.Attributes == nil {
		return c.tls.ClientHandshake(ctx, authority, rawConn)
	}
	cn, ok := internal.GetXDSHandshakeClusterName(chi.Attributes)
	if !ok || strings.HasPrefix(cn, cfeClusterNamePrefix) {
		return c.tls.ClientHandshake(ctx, authority, rawConn)
	}
	// If attributes have cluster name, and cluster name is not cfe, it's a
	// backend address, use ALTS.
	return c.alts.ClientHandshake(ctx, authority, rawConn)
}

func (c *clusterTransportCreds) ServerHandshake(conn net.Conn) (net.Conn, credentials.AuthInfo, error) {
	return c.tls.ServerHandshake(conn)
}

func (c *clusterTransportCreds) Info() credentials.ProtocolInfo {
	// TODO: this always returns tls.Info now, because we don't have a cluster
	// name to check when this method is called. This method doesn't affect
	// anything important now. We may want to revisit this if it becomes more
	// important later.
	return c.tls.Info()
}

func (c *clusterTransportCreds) Clone() credentials.TransportCredentials {
	return &clusterTransportCreds{
		tls:  c.tls.Clone(),
		alts: c.alts.Clone(),
	}
}

func (c *clusterTransportCreds) OverrideServerName(s string) error {
	if err := c.tls.OverrideServerName(s); err != nil {
		return err
	}
	return c.alts.OverrideServerName(s)
}
