/*
 * Copyright 2016 OpenMarket Ltd
 * Copyright 2016 Vector Creations Ltd
 *
 * 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 org.matrix.olm;

import android.text.TextUtils;
import android.util.Log;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

import java.util.Arrays;

/**
 * Session class used to create Olm sessions in conjunction with {@link OlmAccount} class.<br>
 * Olm session is used to encrypt data between devices, especially to create Olm group sessions (see {@link OlmOutboundGroupSession} and {@link OlmInboundGroupSession}).<br>
 * To establish an Olm session with Bob, Alice calls {@link #initOutboundSession(OlmAccount, String, String)} with Bob's identity and onetime keys. Then Alice generates an encrypted PRE_KEY message ({@link #encryptMessage(String)})
 * used by Bob to open the Olm session in his side with {@link #initOutboundSession(OlmAccount, String, String)}.
 * From this step on, messages can be exchanged by using {@link #encryptMessage(String)} and {@link #decryptMessage(OlmMessage)}.
 * <br><br>Detailed implementation guide is available at <a href="http://matrix.org/docs/guides/e2e_implementation.html">Implementing End-to-End Encryption in Matrix clients</a>.
 */
public class OlmSession extends CommonSerializeUtils implements Serializable {
    private static final long serialVersionUID = -8975488639186976419L;
    private static final String LOG_TAG = "OlmSession";

    /** Session Id returned by JNI.
     * This value uniquely identifies the native session instance.
     **/
    private transient long mNativeId;

    public OlmSession() throws OlmException {
        try {
            mNativeId = createNewSessionJni();
        } catch (Exception e) {
            throw new OlmException(OlmException.EXCEPTION_CODE_INIT_SESSION_CREATION, e.getMessage());
        }
    }

    /**
     * Create an OLM session in native side.<br>
     * Do not forget to call {@link #releaseSession()} when JAVA side is done.
     * @return native account instance identifier or throw an exception.
     */
    private native long createNewSessionJni();

    /**
     * Getter on the session ID.
     * @return native session ID
     */
    long getOlmSessionId(){
        return mNativeId;
    }

    /**
     * Destroy the corresponding OLM session native object.<br>
     * This method must ALWAYS be called when this JAVA instance
     * is destroyed (ie. garbage collected) to prevent memory leak in native side.
     * See {@link #createNewSessionJni()}.
     */
    private native void releaseSessionJni();

    /**
     * Release native session and invalid its JAVA reference counter part.<br>
     * Public API for {@link #releaseSessionJni()}.
     */
    public void releaseSession() {
        if (0 != mNativeId) {
            releaseSessionJni();
        }
        mNativeId = 0;
    }

    /**
     * Return true the object resources have been released.<br>
     * @return true the object resources have been released
     */
    public boolean isReleased() {
        return (0 == mNativeId);
    }

    /**
     * Creates a new out-bound session for sending messages to a recipient
     * identified by an identity key and a one time key.<br>
     * @param aAccount the account to associate with this session
     * @param aTheirIdentityKey the identity key of the recipient
     * @param aTheirOneTimeKey the one time key of the recipient
     * @exception OlmException the failure reason
     */
    public void initOutboundSession(OlmAccount aAccount, String aTheirIdentityKey, String aTheirOneTimeKey) throws OlmException {
        if ((null == aAccount) || TextUtils.isEmpty(aTheirIdentityKey) || TextUtils.isEmpty(aTheirOneTimeKey)) {
            Log.e(LOG_TAG, "## initOutboundSession(): invalid input parameters");
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_OUTBOUND_SESSION, "invalid input parameters");
        } else {
            try {
                initOutboundSessionJni(aAccount.getOlmAccountId(), aTheirIdentityKey.getBytes("UTF-8"), aTheirOneTimeKey.getBytes("UTF-8"));
            } catch (Exception e) {
                Log.e(LOG_TAG, "## initOutboundSession(): " + e.getMessage());
                throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_OUTBOUND_SESSION, e.getMessage());
            }
        }
    }

    /**
     * Create a new in-bound session for sending/receiving messages from an
     * incoming PRE_KEY message.<br> The recipient is defined as the entity
     * with whom the session is established.
     * An exception is thrown if the operation fails.
     * @param aOlmAccountId account instance
     * @param aTheirIdentityKey the identity key of the recipient
     * @param aTheirOneTimeKey the one time key of the recipient
     **/
    private native void initOutboundSessionJni(long aOlmAccountId, byte[] aTheirIdentityKey, byte[] aTheirOneTimeKey);

    /**
     * Create a new in-bound session for sending/receiving messages from an
     * incoming PRE_KEY message ({@link OlmMessage#MESSAGE_TYPE_PRE_KEY}).<br>
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * @param aAccount the account to associate with this session
     * @param aPreKeyMsg PRE KEY message
     * @exception OlmException the failure reason
     */
    public void initInboundSession(OlmAccount aAccount, String aPreKeyMsg) throws OlmException {
        if ((null == aAccount) || TextUtils.isEmpty(aPreKeyMsg)){
            Log.e(LOG_TAG, "## initInboundSession(): invalid input parameters");
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_INBOUND_SESSION, "invalid input parameters");
        } else {
            try {
                initInboundSessionJni(aAccount.getOlmAccountId(), aPreKeyMsg.getBytes("UTF-8"));
            } catch (Exception e) {
                Log.e(LOG_TAG, "## initInboundSession(): " + e.getMessage());
                throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_INBOUND_SESSION, e.getMessage());
            }
        }
    }

    /**
     * Create a new in-bound session for sending/receiving messages from an
     * incoming PRE_KEY message.<br>
     * An exception is thrown if the operation fails.
     * @param aOlmAccountId account instance
     * @param aOneTimeKeyMsg PRE_KEY message
     */
    private native void initInboundSessionJni(long aOlmAccountId, byte[] aOneTimeKeyMsg);

    /**
     * Create a new in-bound session for sending/receiving messages from an
     * incoming PRE_KEY({@link OlmMessage#MESSAGE_TYPE_PRE_KEY}) message based on the sender identity key.<br>
     * Public API for {@link #initInboundSessionFromIdKeyJni(long, byte[], byte[])}.
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * This method must only be called the first time a pre-key message is received from an inbound session.
     * @param aAccount the account to associate with this session
     * @param aTheirIdentityKey the sender identity key
     * @param aPreKeyMsg PRE KEY message
     * @exception OlmException the failure reason
     */
    public void initInboundSessionFrom(OlmAccount aAccount, String aTheirIdentityKey, String aPreKeyMsg) throws OlmException {
        if ( (null==aAccount) || TextUtils.isEmpty(aPreKeyMsg)){
            Log.e(LOG_TAG, "## initInboundSessionFrom(): invalid input parameters");
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_INBOUND_SESSION_FROM, "invalid input parameters");
        } else {
            try {
                initInboundSessionFromIdKeyJni(aAccount.getOlmAccountId(), aTheirIdentityKey.getBytes("UTF-8"), aPreKeyMsg.getBytes("UTF-8"));
            } catch (Exception e) {
                Log.e(LOG_TAG, "## initInboundSessionFrom(): " + e.getMessage());
                throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_INIT_INBOUND_SESSION_FROM, e.getMessage());
            }
        }
    }

    /**
     * Create a new in-bound session for sending/receiving messages from an
     * incoming PRE_KEY message based on the recipient identity key.<br>
     * An exception is thrown if the operation fails.
     * @param aOlmAccountId account instance
     * @param aTheirIdentityKey the identity key of the recipient
     * @param aOneTimeKeyMsg encrypted message
     */
    private native void initInboundSessionFromIdKeyJni(long aOlmAccountId, byte[] aTheirIdentityKey, byte[] aOneTimeKeyMsg);

    /**
     * Get the session identifier.<br> Will be the same for both ends of the
     * conversation. The session identifier is returned as a String object.
     * Session Id sample: "session_id":"M4fOVwD6AABrkTKl"
     * Public API for {@link #getSessionIdentifierJni()}.
     * @return the session ID
     * @exception OlmException the failure reason
     */
    public String sessionIdentifier() throws OlmException {
        try {
            byte[] buffer = getSessionIdentifierJni();

            if (null != buffer) {
                return new String(buffer, "UTF-8");
            }
        } catch (Exception e) {
            Log.e(LOG_TAG, "## sessionIdentifier(): " + e.getMessage());
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_SESSION_IDENTIFIER, e.getMessage());
        }

        return null;
    }

    /**
     * Get the session identifier for this session.
     * An exception is thrown if the operation fails.
     * @return the session identifier
     */
    private native byte[] getSessionIdentifierJni();

    /**
     * Checks if the PRE_KEY({@link OlmMessage#MESSAGE_TYPE_PRE_KEY}) message is for this in-bound session.<br>
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * Public API for {@link #matchesInboundSessionJni(byte[])}.
     * @param aOneTimeKeyMsg PRE KEY message
     * @return true if the one time key matches.
     */
    public boolean matchesInboundSession(String aOneTimeKeyMsg) {
        boolean retCode = false;

        try {
            retCode = matchesInboundSessionJni(aOneTimeKeyMsg.getBytes("UTF-8"));
        } catch (Exception e) {
            Log.e(LOG_TAG, "## matchesInboundSession(): failed " + e.getMessage());
        }

        return retCode;
    }

    /**
     * Checks if the PRE_KEY message is for this in-bound session.<br>
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * An exception is thrown if the operation fails.
     * @param aOneTimeKeyMsg PRE KEY message
     * @return true if the PRE_KEY message matches
     */
    private native boolean matchesInboundSessionJni(byte[] aOneTimeKeyMsg);

    /**
     * Checks if the PRE_KEY({@link OlmMessage#MESSAGE_TYPE_PRE_KEY}) message is for this in-bound session based on the sender identity key.<br>
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * Public API for {@link #matchesInboundSessionJni(byte[])}.
     * @param aTheirIdentityKey the sender identity key
     * @param aOneTimeKeyMsg PRE KEY message
     * @return this if operation succeed, null otherwise
     */
    public boolean matchesInboundSessionFrom(String aTheirIdentityKey, String aOneTimeKeyMsg) {
        boolean retCode = false;

        try {
            retCode = matchesInboundSessionFromIdKeyJni(aTheirIdentityKey.getBytes("UTF-8"), aOneTimeKeyMsg.getBytes("UTF-8"));
        } catch (Exception e) {
            Log.e(LOG_TAG, "## matchesInboundSessionFrom(): failed " + e.getMessage());
        }

        return retCode;
    }

    /**
     * Checks if the PRE_KEY message is for this in-bound session based on the sender identity key.<br>
     * This API may be used to process a "m.room.encrypted" event when type = 1 (PRE_KEY).
     * An exception is thrown if the operation fails.
     * @param aTheirIdentityKey the identity key of the sender
     * @param aOneTimeKeyMsg PRE KEY message
     * @return true if the PRE_KEY message matches.
     */
    private native boolean matchesInboundSessionFromIdKeyJni(byte[] aTheirIdentityKey, byte[] aOneTimeKeyMsg);

    /**
     * Encrypt a message using the session.<br>
     * The encrypted message is returned in a OlmMessage object.
     * Public API for {@link #encryptMessageJni(byte[], OlmMessage)}.
     * @param aClearMsg message to encrypted
     * @return the encrypted message
     * @exception OlmException the failure reason
     */
    public OlmMessage encryptMessage(String aClearMsg) throws OlmException {
        if (null == aClearMsg) {
            return null;
        }

        OlmMessage encryptedMsgRetValue = new OlmMessage();

        try {
            byte[] clearMsgBuffer = aClearMsg.getBytes("UTF-8");
            byte[] encryptedMessageBuffer = encryptMessageJni(clearMsgBuffer, encryptedMsgRetValue);
            Arrays.fill(clearMsgBuffer, (byte) 0);

            if (null != encryptedMessageBuffer) {
                encryptedMsgRetValue.mCipherText = new String(encryptedMessageBuffer, "UTF-8");
            }
        } catch (Exception e) {
            Log.e(LOG_TAG, "## encryptMessage(): failed " + e.getMessage());
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_ENCRYPT_MESSAGE, e.getMessage());
        }

        return encryptedMsgRetValue;
    }

    /**
     * Encrypt a message using the session.<br>
     * An exception is thrown if the operation fails.
     * @param aClearMsg clear text message
     * @param aEncryptedMsg ciphered message
     * @return the encrypted message
     */
    private native byte[] encryptMessageJni(byte[] aClearMsg, OlmMessage aEncryptedMsg);

    /**
     * Decrypt a message using the session.<br>
     * The encrypted message is given as a OlmMessage object.
     * @param aEncryptedMsg message to decrypt
     * @return the decrypted message
     * @exception OlmException the failure reason
     */
    public String decryptMessage(OlmMessage aEncryptedMsg) throws OlmException {
        if (null == aEncryptedMsg) {
            return null;
        }

        try {
            byte[] plaintextBuffer = decryptMessageJni(aEncryptedMsg);
            String plaintext = new String(plaintextBuffer, "UTF-8");
            Arrays.fill(plaintextBuffer, (byte) 0);
            return plaintext;
        } catch (Exception e) {
            Log.e(LOG_TAG, "## decryptMessage(): failed " + e.getMessage());
            throw new OlmException(OlmException.EXCEPTION_CODE_SESSION_DECRYPT_MESSAGE, e.getMessage());
        }
    }
    /**
     * Decrypt a message using the session.<br>
     * An exception is thrown if the operation fails.
     * @param aEncryptedMsg message to decrypt
     * @return the decrypted message
     */
    private native byte[] decryptMessageJni(OlmMessage aEncryptedMsg);

    //==============================================================================================================
    // Serialization management
    //==============================================================================================================

    /**
     * Kick off the serialization mechanism.
     * @param aOutStream output stream for serializing
     * @throws IOException exception
     */
    private void writeObject(ObjectOutputStream aOutStream) throws IOException {
        serialize(aOutStream);
    }

    /**
     * Kick off the deserialization mechanism.
     * @param aInStream input stream
     * @throws IOException exception
     * @throws ClassNotFoundException exception
     */
    private void readObject(ObjectInputStream aInStream) throws Exception {
        deserialize(aInStream);
    }

    /**
     * Return a session as a bytes buffer.<br>
     * The account is serialized and encrypted with aKey.
     * In case of failure, an error human readable
     * description is provide in aErrorMsg.
     * @param aKey encryption key
     * @param aErrorMsg error message description
     * @return session as a bytes buffer
     */
    @Override
    protected byte[] serialize(byte[] aKey, StringBuffer aErrorMsg) {
        byte[] pickleRetValue = null;

        // sanity check
        if(null == aErrorMsg) {
            Log.e(LOG_TAG,"## serializeDataWithKey(): invalid parameter - aErrorMsg=null");
        } else if (null == aKey) {
            aErrorMsg.append("Invalid input parameters in serializeDataWithKey()");
        } else {
            aErrorMsg.setLength(0);
            try {
                pickleRetValue = serializeJni(aKey);
            } catch (Exception e) {
                Log.e(LOG_TAG,"## serializeDataWithKey(): failed " + e.getMessage());
                aErrorMsg.append(e.getMessage());
            }
        }

        return pickleRetValue;
    }

    /**
     * Serialize and encrypt session instance.<br>
     * An exception is thrown if the operation fails.
     * @param aKeyBuffer key used to encrypt the serialized account data
     * @return the serialised account as bytes buffer.
     **/
    private native byte[] serializeJni(byte[] aKeyBuffer);

    /**
     * Loads an account from a pickled base64 string.<br>
     * See {@link #serialize(byte[], StringBuffer)}
     * @param aSerializedData pickled account in a base64 string format
     * @param aKey key used to encrypted
     */
    @Override
    protected void deserialize(byte[] aSerializedData, byte[] aKey) throws Exception {
        String errorMsg = null;

        try {
            if ((null == aSerializedData) || (null == aKey)) {
                Log.e(LOG_TAG, "## deserialize(): invalid input parameters");
                errorMsg = "invalid input parameters";
            } else {
                mNativeId = deserializeJni(aSerializedData, aKey);
            }
        } catch (Exception e) {
            Log.e(LOG_TAG, "## deserialize() failed " + e.getMessage());
            errorMsg = e.getMessage();
        }

        if (!TextUtils.isEmpty(errorMsg)) {
            releaseSession();
            throw new OlmException(OlmException.EXCEPTION_CODE_ACCOUNT_DESERIALIZATION, errorMsg);
        }
    }
    /**
     * Allocate a new session and initialize it with the serialisation data.<br>
     * An exception is thrown if the operation fails.
     * @param aSerializedData the session serialisation buffer
     * @param aKey the key used to encrypt the serialized account data
     * @return the deserialized session
     **/
    private native long deserializeJni(byte[] aSerializedData, byte[] aKey);
}