/*
 * #%L
 * Alfresco Repository
 * %%
 * Copyright (C) 2005 - 2016 Alfresco Software Limited
 * %%
 * This file is part of the Alfresco software. 
 * If the software was purchased under a paid Alfresco license, the terms of 
 * the paid license agreement will prevail.  Otherwise, the software is 
 * provided under the following open source license terms:
 * 
 * Alfresco is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * Alfresco is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with Alfresco. If not, see <http://www.gnu.org/licenses/>.
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 */
package org.alfresco.encryption;

import java.io.Serializable;
import java.security.InvalidKeyException;
import java.security.Key;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;

import org.alfresco.repo.transaction.RetryingTransactionHelper;
import org.alfresco.repo.transaction.RetryingTransactionHelper.RetryingTransactionCallback;
import org.alfresco.service.cmr.attributes.AttributeService;
import org.alfresco.service.cmr.attributes.AttributeService.AttributeQueryCallback;
import org.alfresco.service.transaction.TransactionService;
import org.alfresco.util.EqualsHelper;
import org.alfresco.util.GUID;
import org.alfresco.util.Pair;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Registered Encryption Keys are stored in the AttributeService directly under a top level key defined by
 * TOP_LEVEL_KEY (which means that all key aliases must be unique across however many keystores are being used).
 * 
 * @since 4.0
 *
 */
// TODO caching? This will probably not be used extensively.
// TODO instead of persisting the Pair when registering a key, create two attributes per key (one for the
// guid and one for the encrypted value of the guid). This means a custom class does not need to be bound to
// the attribute service.
public class EncryptionKeysRegistryImpl implements EncryptionKeysRegistry
{
    public static String TOP_LEVEL_KEY = "keyCheck";
    private static final Log logger = LogFactory.getLog(EncryptionKeysRegistryImpl.class);

    private TransactionService transactionService;
    private AttributeService attributeService;
    private String cipherAlgorithm;
    private String cipherProvider;

    public void setAttributeService(AttributeService attributeService)
    {
        this.attributeService = attributeService;
    }

    public void setCipherAlgorithm(String cipherAlgorithm)
    {
        this.cipherAlgorithm = cipherAlgorithm;
    }

    public void setCipherProvider(String cipherProvider)
    {
        this.cipherProvider = cipherProvider;
    }

    public void setTransactionService(TransactionService transactionService)
    {
        this.transactionService = transactionService;
    }

    protected Encryptor getEncryptor(final KeyMap keys)
    {
        DefaultEncryptor encryptor = new DefaultEncryptor();
        encryptor.setCipherAlgorithm(cipherAlgorithm);
        encryptor.setCipherProvider(cipherProvider);
        encryptor.setKeyProvider(new KeyProvider()
        {
            @Override
            public Key getKey(String keyAlias)
            {
                return keys.getCachedKey(keyAlias).getKey();
            }
        });
        return encryptor;
    }

    public void init()
    {
    }

    public void registerKey(String keyAlias, Key key)
    {
        if(isKeyRegistered(keyAlias))
        {
            throw new IllegalArgumentException("Key " + keyAlias + " is already registered");
        }

        // register the key by creating an attribute that stores a guid and its encrypted value
        String guid = GUID.generate();

        KeyMap keys = new KeyMap();
        keys.setKey(keyAlias, key);
        Encryptor encryptor = getEncryptor(keys);
        Serializable encrypted = encryptor.sealObject(keyAlias, null, guid);
        Pair<String, Serializable> keyCheck = new Pair<String, Serializable>(guid, encrypted);
        attributeService.createAttribute(keyCheck, TOP_LEVEL_KEY, keyAlias);
        logger.info("Registered key " + keyAlias);
    }
    
    public void unregisterKey(String keyAlias)
    {
        attributeService.removeAttribute(TOP_LEVEL_KEY, keyAlias);
    }
    
    public boolean isKeyRegistered(String keyAlias)
    {
        try
        {
            return (attributeService.getAttribute(TOP_LEVEL_KEY, keyAlias) != null);
        }
        catch(Throwable e)
        {
            // there is an issue getting the attribute. Remove it.
            attributeService.removeAttribute(TOP_LEVEL_KEY, keyAlias);
            return (attributeService.getAttribute(TOP_LEVEL_KEY, keyAlias) != null);
        }
    }
    
    public List<String> getRegisteredKeys(final Set<String> keyStoreKeys)
    {
        final List<String> registeredKeys = new ArrayList<String>();

        attributeService.getAttributes(new AttributeQueryCallback()
        {
            public boolean handleAttribute(Long id, Serializable value,
                    Serializable[] keys)
            {
                // Add as a registered key if the keystore contains the key
                String keyAlias = (String)keys[1];
                if(keyStoreKeys.contains(keyAlias))
                {
                    registeredKeys.add(keyAlias);
                }
                return true;
            }

        },
        TOP_LEVEL_KEY);

        return registeredKeys;
    }

    @SuppressWarnings("unchecked")
    public KEY_STATUS checkKey(String keyAlias, Key key)
    {
        Pair<String, Serializable> keyCheck = null;

        if(attributeService.exists(TOP_LEVEL_KEY, keyAlias))
        {
            try
            {
                // check that the key has not changed by decrypting the encrypted guid attribute
                // comparing against the guid
                try
                {
                    keyCheck = (Pair<String, Serializable>)attributeService.getAttribute(TOP_LEVEL_KEY, keyAlias);
                }
                catch(Throwable e)
                {
                    // there is an issue getting the attribute. Remove it.
                    attributeService.removeAttribute(TOP_LEVEL_KEY, keyAlias);
                    return KEY_STATUS.MISSING;
                }
                
                if(keyCheck == null)
                {
                    return KEY_STATUS.MISSING;
                }

                KeyMap keys = new KeyMap();
                keys.setKey(keyAlias, key);
                Encryptor encryptor = getEncryptor(keys);
                Serializable storedGUID = encryptor.unsealObject(keyAlias, keyCheck.getSecond());
                return EqualsHelper.nullSafeEquals(storedGUID, keyCheck.getFirst()) ? KEY_STATUS.OK : KEY_STATUS.CHANGED;
            }
            catch(InvalidKeyException e)
            {
                // key exception indicates that the key has changed - it can't decrypt the
                // previously-encrypted data
                return KEY_STATUS.CHANGED;
            }
        }
        else
        {
            return KEY_STATUS.MISSING;
        }        
    }
    
    // note that this removes _all_ keys in the keystore. Use with care.
    public void removeRegisteredKeys(final Set<String> keys)
    {
        RetryingTransactionHelper retryingTransactionHelper = transactionService.getRetryingTransactionHelper();
        final RetryingTransactionCallback<Void> removeKeysCallback = new RetryingTransactionCallback<Void>()
        {
            public Void execute() throws Throwable
            {
                for(String keyAlias : keys)
                {
                    attributeService.removeAttribute(TOP_LEVEL_KEY, keyAlias);
                }

                return null;
            }
        };
        retryingTransactionHelper.doInTransaction(removeKeysCallback, false);
    }
}