/*
 * Copyright (C) 2010 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.google.android.marvin.talkback.formatter;

import com.google.android.marvin.talkback.Formatter;
import com.google.android.marvin.talkback.R;
import com.google.android.marvin.talkback.Utils;
import com.google.android.marvin.talkback.Utterance;

import org.xml.sax.SAXException;

import android.content.Context;
import android.text.TextUtils;
import android.util.Xml;
import android.view.accessibility.AccessibilityEvent;

import java.util.regex.Pattern;

/**
 * Formatter for web content.
 *
 * @author svetoslavganov@google.com (Svetoslav Ganov)
 * @author credo@google.com (Tim Credo)
 */
@SuppressWarnings("unused")
public final class WebContentFormatter implements Formatter {
    
    private static final int ACTION_SET_CURRENT_AXIS = 0;
    private static final int ACTION_TRAVERSE_CURRENT_AXIS = 1;
    private static final int ACTION_TRAVERSE_GIVEN_AXIS = 2;
    private static final int ACTION_PERFORM_AXIS_TRANSITION = 3;
    private static final int ACTION_TRAVERSE_DEFAULT_WEB_VIEW_BEHAVIOR_AXIS = 4;

    private static String[] sAxisNames;

    /**
     * A template to apply to markup before sending it to an XML parser.
     */
    private static final String XML_TEMPLATE =
            "<?xml version=\"1.0\" encoding=\"UTF-8\" ?><div>%s</div>";

    /**
     * Regular expression that matches all HTML tags.
     */
    private final Pattern mStripMarkupPattern = Pattern.compile("<(.)+?>");
    
    /**
     * Regular expression that matches all entity codes.
     */
    private final Pattern mStripEntitiesPattern = Pattern.compile("&(.)+?;");
    
    /**
     * Regular expression that matches all div or span tags.
     */
    private final Pattern mStripDivSpanPattern = Pattern.compile(
            "</?(div|span).*?>", Pattern.CASE_INSENSITIVE);

    /**
     * Regular expression that matches some common singleton tags.
     */
    private final Pattern mCloseTagPattern = Pattern.compile(
            "(<(img|input|br).+?)>", Pattern.CASE_INSENSITIVE);

    /**
     * A handler for processing HTML and generating output for speaking.
     */
    private WebContentHandler mHtmlHandler = null;
    
    
    private final Action mTempAction = new Action();

    @Override
    public void format(AccessibilityEvent event, Context context, Utterance utterance,
            Object args) {
        // for now ... lookup and announce axis transitions
        CharSequence contentDescription = event.getContentDescription();
        if (TextUtils.isEmpty(contentDescription)) {
            return;
        }
        Action action = mTempAction;
        action.init(contentDescription.toString());
        int actionCode = mTempAction.mActionCode;
        if (actionCode == ACTION_PERFORM_AXIS_TRANSITION) {
            String axisAnnouncement = getAxisAnnouncement(context, action.mSecondArgument);
            utterance.getText().append(axisAnnouncement);
            return;
        }
        // for now ... disregard content description
        String markup = Utils.getEventText(context, event).toString();
        String noTags = mStripMarkupPattern.matcher(markup).replaceAll("");
        String cleaned = cleanMarkup(markup);
        if (mHtmlHandler == null) {
            mHtmlHandler = new TalkBackWebContentHandler(context.getResources()); 
        }
        try {
            Xml.parse(cleaned, mHtmlHandler);
            String speech = mHtmlHandler.getOutput();
            utterance.getText().append(speech);
        } catch (SAXException e) {
            e.printStackTrace();
            utterance.getText().append(noTags);
        }
    }
    
    /**
     * Process HTML to remove markup that can't be handled by the SAX parser.
     * 
     * @param markup Input HTML generated by system.
     * @return A string of cleaned HTML.
     */
    public String cleanMarkup(String markup) {
        String noDivOrSpan = mStripDivSpanPattern.matcher(markup).replaceAll("");
        String noEntities = mStripEntitiesPattern.matcher(noDivOrSpan).replaceAll(" ");
        String tagsClosed = mCloseTagPattern.matcher(noEntities).replaceAll("$1/>");
        return String.format(XML_TEMPLATE, tagsClosed);
    }

    /**
     * Gets an announcement for a navigation axis given its code.
     *
     * @param context Context for loading resources.
     * @param axisCode The code the the axis.
     * @return The axis announcement.
     */
    private String getAxisAnnouncement(Context context, int axisCode) {
        if (sAxisNames == null) {
            sAxisNames = new String[] {
                    context.getString(R.string.axis_character),
                    context.getString(R.string.axis_word),
                    context.getString(R.string.axis_sentence),
                    context.getString(R.string.axis_heading),
                    context.getString(R.string.axis_sibling),
                    context.getString(R.string.axis_parent_first_child),
                    context.getString(R.string.axis_document),
                    context.getString(R.string.axis_default_web_view_behavior)
            };
        }
        return sAxisNames[axisCode];
    }

    /**
     * Represents an action.
     */
    private class Action {
        private static final int ACTION_OFFSET = 24;
        private static final int ACTION_MASK = 0xFF000000;

        private static final int FIRST_ARGUMENT_OFFSET = 16;
        private static final int FIRST_ARGUMENT_MASK = 0x00FF0000;

        private static final int SECOND_ARGUMENT_OFFSET = 8;
        private static final int SECOND_ARGUMENT_MASK = 0x0000FF00;

        private static final int THIRD_ARGUMENT_OFFSET = 0;
        private static final int THIRD_ARGUMENT_MASK = 0x000000FF;

        private int mActionCode;
        private int mFirstArgument;
        private int mSecondArgument;
        private int mThirdArgument;

        public void init(String encodedActionString) {
            int encodedAction = 0;
            try {
                // hack
                encodedAction = Integer.decode("0x" + encodedActionString);
            } catch (NumberFormatException nfe) {
                return;
            }
            mActionCode = (encodedAction & ACTION_MASK) >> ACTION_OFFSET;
            mFirstArgument = (encodedAction & FIRST_ARGUMENT_MASK) >> FIRST_ARGUMENT_OFFSET;
            mSecondArgument = (encodedAction & SECOND_ARGUMENT_MASK) >> SECOND_ARGUMENT_OFFSET;
            mThirdArgument = (encodedAction & THIRD_ARGUMENT_OFFSET) >> THIRD_ARGUMENT_MASK;
        }
    }
}