// 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.apache.tapestry5.internal.services;

import org.apache.tapestry5.Link;
import org.apache.tapestry5.ioc.ScopeConstants;
import org.apache.tapestry5.ioc.annotations.Scope;
import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
import org.apache.tapestry5.ioc.internal.util.InternalUtils;
import org.apache.tapestry5.services.*;

import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collection;
import java.util.Collections;
import java.util.Map;

/**
 * Manages client-persistent values on behalf of a {@link ClientPersistentFieldStorageImpl}. Some effort is made to
 * ensure that we don't uncessarily convert between objects and Base64 (the encoding used to record the value on the
 * client).
 */
@Scope(ScopeConstants.PERTHREAD)
public class ClientPersistentFieldStorageImpl implements ClientPersistentFieldStorage
{
    static final String PARAMETER_NAME = "t:state:client";

    private static class Key implements Serializable
    {
        private static final long serialVersionUID = -2741540370081645945L;

        private final String pageName;

        private final String componentId;

        private final String fieldName;

        Key(String pageName, String componentId, String fieldName)
        {
            this.pageName = pageName;
            this.componentId = componentId;
            this.fieldName = fieldName;
        }

        public boolean matches(String pageName)
        {
            return this.pageName.equals(pageName);
        }

        public PersistentFieldChange toChange(Object value)
        {
            return new PersistentFieldChangeImpl(componentId == null ? "" : componentId,
                    fieldName, value);
        }

        @Override
        public int hashCode()
        {
            final int PRIME = 31;

            int result = 1;

            result = PRIME * result + ((componentId == null) ? 0 : componentId.hashCode());

            // fieldName and pageName are never null

            result = PRIME * result + fieldName.hashCode();
            result = PRIME * result + pageName.hashCode();

            return result;
        }

        @Override
        public boolean equals(Object obj)
        {
            if (this == obj) return true;
            if (obj == null) return false;
            if (getClass() != obj.getClass()) return false;
            final Key other = (Key) obj;

            // fieldName and pageName are never null

            if (!fieldName.equals(other.fieldName)) return false;
            if (!pageName.equals(other.pageName)) return false;

            if (componentId == null)
            {
                if (other.componentId != null) return false;
            } else if (!componentId.equals(other.componentId)) return false;

            return true;
        }
    }

    private final ClientDataEncoder clientDataEncoder;

    private final SessionPersistedObjectAnalyzer analyzer;

    private final Map<Key, Object> persistedValues = CollectionFactory.newMap();

    private String clientData;

    private boolean mapUptoDate = false;

    public ClientPersistentFieldStorageImpl(Request request, ClientDataEncoder clientDataEncoder, SessionPersistedObjectAnalyzer analyzer)
    {
        this.clientDataEncoder = clientDataEncoder;
        this.analyzer = analyzer;

        // This, here, is the problem of TAPESTRY-2501; this call can predate
        // the check to set the character set based on meta data of the page.

        String value = request.getParameter(PARAMETER_NAME);

        // MIME can encode to a '+' character; the browser converts that to a space; we convert it
        // back.

        clientData = value == null ? null : value.replace(' ', '+');
    }

    public void updateLink(Link link)
    {
        refreshClientData();

        if (clientData != null) link.addParameter(PARAMETER_NAME, clientData);
    }

    public Collection<PersistentFieldChange> gatherFieldChanges(String pageName)
    {
        refreshMap();

        if (persistedValues.isEmpty()) return Collections.emptyList();

        Collection<PersistentFieldChange> result = CollectionFactory.newList();

        for (Map.Entry<Key, Object> e : persistedValues.entrySet())
        {
            Key key = e.getKey();

            if (key.matches(pageName)) result.add(key.toChange(e.getValue()));
        }

        return result;
    }

    public void discardChanges(String pageName)
    {
        refreshMap();

        Collection<Key> removedKeys = CollectionFactory.newList();

        for (Key key : persistedValues.keySet())
        {
            if (key.pageName.equals(pageName)) removedKeys.add(key);
        }

        for (Key key : removedKeys)
        {
            persistedValues.remove(key);
            clientData = null;
        }
    }

    public void postChange(String pageName, String componentId, String fieldName, Object newValue)
    {
        refreshMap();

        Key key = new Key(pageName, componentId, fieldName);

        if (newValue == null)
            persistedValues.remove(key);
        else
        {
            if (!Serializable.class.isInstance(newValue))
                throw new IllegalArgumentException(String.format("State persisted on the client must be serializable, but %s does not implement the Serializable interface.", newValue));

            persistedValues.put(key, newValue);
        }

        clientData = null;
    }

    /**
     * Refreshes the _persistedValues map if it is not up to date.
     */
    @SuppressWarnings("unchecked")
    private void refreshMap()
    {
        if (mapUptoDate) return;

        // Parse the client data to form the map.

        restoreMapFromClientData();

        mapUptoDate = true;
    }

    /**
     * Restores the _persistedValues map from the client data provided in the incoming Request.
     */
    private void restoreMapFromClientData()
    {
        persistedValues.clear();

        if (clientData == null) return;

        ObjectInputStream in = null;

        try
        {
            in = clientDataEncoder.decodeClientData(clientData);

            int count = in.readInt();

            for (int i = 0; i < count; i++)
            {
                Key key = (Key) in.readObject();
                Object value = in.readObject();

                persistedValues.put(key, value);
            }
        } catch (Exception ex)
        {
            throw new RuntimeException("Serialized client state was corrupted. This may indicate that too much state is being stored, which can cause the encoded string to be truncated by the client web browser.", ex);
        } finally
        {
            InternalUtils.close(in);
        }
    }

    private void refreshClientData()
    {
        // TAP5-2269: Even in the absense of a change to a persistent field, a mutable persistent object
        // may have changed.

        if (clientData != null)
        {
            for (Object value : persistedValues.values())
            {
                if (analyzer.checkAndResetDirtyState(value))
                {
                    clientData = null;
                    break;
                }
            }
        }

        // Client data will be null after a change to the map, or if there was no client data in the
        // request. In any other case where the client data is non-null, it is by definition
        // up-to date (since it is reset to null any time there's a change to the map).

        if (clientData != null) return;

        // Very typical: we're refreshing the client data but haven't created the map yet, and there
        // was no value in the request. Leave it as null.

        if (!mapUptoDate) return;

        // Null is also appropriate when the persisted values are empty.

        if (persistedValues.isEmpty()) return;

        // Otherwise, time to update clientData from persistedValues

        ClientDataSink sink = clientDataEncoder.createSink();

        ObjectOutputStream os = sink.getObjectOutputStream();

        try
        {
            os.writeInt(persistedValues.size());

            for (Map.Entry<Key, Object> e : persistedValues.entrySet())
            {
                os.writeObject(e.getKey());
                os.writeObject(e.getValue());
            }
        } catch (Exception ex)
        {
            throw new RuntimeException(ex.getMessage(), ex);
        } finally
        {
            InternalUtils.close(os);
        }

        clientData = sink.getClientData();
    }
}