/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * 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 com.android.ike.ikev2.message;

import android.annotation.IntDef;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.nio.ByteBuffer;

/**
 * IkePayload is an abstract class that represents the common information for all IKE payload types.
 *
 * <p>Each types of IKE payload should implement its own subclass with its own decoding and encoding
 * logic.
 *
 * @see <a href="https://tools.ietf.org/html/rfc7296#section-3.2">RFC 7296, Internet Key Exchange
 *     Protocol Version 2 (IKEv2)</a>
 */
public abstract class IkePayload {
    // Critical bit and following reserved 7 bits in payload generic header must all be zero
    private static final byte PAYLOAD_HEADER_CRITICAL_BIT_UNSET = 0;
    /** Length of a generic IKE payload header */
    public static final int GENERIC_HEADER_LENGTH = 4;

    /**
     * Payload types as defined by IANA:
     *
     * @see <a href="https://www.iana.org/assignments/ikev2-parameters/ikev2-parameters.xhtml">
     */
    @Retention(RetentionPolicy.SOURCE)
    @IntDef({
        PAYLOAD_TYPE_NO_NEXT,
        PAYLOAD_TYPE_SA,
        PAYLOAD_TYPE_KE,
        PAYLOAD_TYPE_CERT,
        PAYLOAD_TYPE_AUTH,
        PAYLOAD_TYPE_ID_INITIATOR,
        PAYLOAD_TYPE_ID_RESPONDER,
        PAYLOAD_TYPE_NONCE,
        PAYLOAD_TYPE_NOTIFY,
        PAYLOAD_TYPE_DELETE,
        PAYLOAD_TYPE_VENDOR,
        PAYLOAD_TYPE_TS_INITIATOR,
        PAYLOAD_TYPE_TS_RESPONDER,
        PAYLOAD_TYPE_SK
    })
    public @interface PayloadType {}

    /** No Next Payload */
    public static final int PAYLOAD_TYPE_NO_NEXT = 0;
    /** Security Association Payload */
    public static final int PAYLOAD_TYPE_SA = 33;
    /** Key Exchange Payload */
    public static final int PAYLOAD_TYPE_KE = 34;
    /** Identification Payload for IKE SA Initiator */
    public static final int PAYLOAD_TYPE_ID_INITIATOR = 35;
    /** Identification Payload for IKE SA Responder */
    public static final int PAYLOAD_TYPE_ID_RESPONDER = 36;
    /** Certification Payload */
    public static final int PAYLOAD_TYPE_CERT = 37;
    /** Authentication Payload */
    public static final int PAYLOAD_TYPE_AUTH = 39;
    /** Nonce Payload */
    public static final int PAYLOAD_TYPE_NONCE = 40;
    /** Notify Payload */
    public static final int PAYLOAD_TYPE_NOTIFY = 41;
    /** Delete Payload */
    public static final int PAYLOAD_TYPE_DELETE = 42;
    /** Vendor Payload */
    public static final int PAYLOAD_TYPE_VENDOR = 43;
    /** Traffic Selector Payload of Child SA Initiator */
    public static final int PAYLOAD_TYPE_TS_INITIATOR = 44;
    /** Traffic Selector Payload of Child SA Responder */
    public static final int PAYLOAD_TYPE_TS_RESPONDER = 45;
    /** Encrypted and Authenticated Payload */
    public static final int PAYLOAD_TYPE_SK = 46;

    // TODO: List all payload types.

    @Retention(RetentionPolicy.SOURCE)
    @IntDef({
        PROTOCOL_ID_UNSET,
        PROTOCOL_ID_IKE,
        PROTOCOL_ID_AH,
        PROTOCOL_ID_ESP,
    })
    public @interface ProtocolId {}

    public static final int PROTOCOL_ID_UNSET = 0;
    public static final int PROTOCOL_ID_IKE = 1;
    public static final int PROTOCOL_ID_AH = 2;
    public static final int PROTOCOL_ID_ESP = 3;

    public static final byte SPI_LEN_NOT_INCLUDED = 0;
    public static final byte SPI_LEN_IPSEC = 4;
    public static final byte SPI_LEN_IKE = 8;

    public static final int SPI_NOT_INCLUDED = 0;

    /** Length of port number in bytes */
    public static final int IP_PORT_LEN = 2;

    public final int payloadType;
    public final boolean isCritical;

    /**
     * Construct a instance of IkePayload in the context of a IkePayloadFactory.
     *
     * <p>It should be overrided by subclass of IkePayload
     *
     * @param payload the payload type. All supported types will fall in {@link
     *     IkePayload.PayloadType}
     * @param critical indicates if this payload is critical. Ignore it when payload type is
     *     supported.
     */
    IkePayload(int payload, boolean critical) {
        payloadType = payload;
        isCritical = critical;
    }

    /**
     * Encode generic payload header to ByteBuffer.
     *
     * @param nextPayload type of payload that follows this payload.
     * @param payloadLength length of the entire payload
     * @param byteBuffer destination ByteBuffer that stores encoded payload header
     */
    protected static void encodePayloadHeaderToByteBuffer(
            @PayloadType int nextPayload, int payloadLength, ByteBuffer byteBuffer) {
        byteBuffer
                .put((byte) nextPayload)
                .put(PAYLOAD_HEADER_CRITICAL_BIT_UNSET)
                .putShort((short) payloadLength);
    }

    /**
     * Encode payload to ByteBuffer.
     *
     * @param nextPayload type of payload that follows this payload.
     * @param byteBuffer destination ByteBuffer that stores encoded payload.
     */
    protected abstract void encodeToByteBuffer(@PayloadType int nextPayload, ByteBuffer byteBuffer);

    /**
     * Get entire payload length.
     *
     * @return entire payload length.
     */
    protected abstract int getPayloadLength();

    /**
     * Return the payload type as a String.
     *
     * @return the payload type as a String.
     */
    public abstract String getTypeString();
}