common/mail/PackedString.java

/*
 * Copyright (C) 2015 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.phone.common.mail;

import java.util.HashMap;
import java.util.Map;

/**
 * A utility class for creating and modifying Strings that are tagged and packed together.
 *
 * Uses non-printable (control chars) for internal delimiters;  Intended for regular displayable
 * strings only, so please use base64 or other encoding if you need to hide any binary data here.
 *
 * Binary compatible with Address.pack() format, which should migrate to use this code.
 */
public class PackedString {

    /**
     * Packing format is:
     *   element : [ value ] or [ value TAG-DELIMITER tag ]
     *   packed-string : [ element ] [ ELEMENT-DELIMITER [ element ] ]*
     */
    private static final char DELIMITER_ELEMENT = '\1';
    private static final char DELIMITER_TAG = '\2';

    private String mString;
    private HashMap<String, String> mExploded;
    private static final HashMap<String, String> EMPTY_MAP = new HashMap<String, String>();

    /**
     * Create a packed string using an already-packed string (e.g. from database)
     * @param string packed string
     */
    public PackedString(String string) {
        mString = string;
        mExploded = null;
    }

    /**
     * Get the value referred to by a given tag.  If the tag does not exist, return null.
     * @param tag identifier of string of interest
     * @return returns value, or null if no string is found
     */
    public String get(String tag) {
        if (mExploded == null) {
            mExploded = explode(mString);
        }
        return mExploded.get(tag);
    }

    /**
     * Return a map of all of the values referred to by a given tag.  This is a shallow
     * copy, don't edit the values.
     * @return a map of the values in the packed string
     */
    public Map<String, String> unpack() {
        if (mExploded == null) {
            mExploded = explode(mString);
        }
        return new HashMap<String,String>(mExploded);
    }

    /**
     * Read out all values into a map.
     */
    private static HashMap<String, String> explode(String packed) {
        if (packed == null || packed.length() == 0) {
            return EMPTY_MAP;
        }
        HashMap<String, String> map = new HashMap<String, String>();

        int length = packed.length();
        int elementStartIndex = 0;
        int elementEndIndex = 0;
        int tagEndIndex = packed.indexOf(DELIMITER_TAG);

        while (elementStartIndex < length) {
            elementEndIndex = packed.indexOf(DELIMITER_ELEMENT, elementStartIndex);
            if (elementEndIndex == -1) {
                elementEndIndex = length;
            }
            String tag;
            String value;
            if (tagEndIndex == -1 || elementEndIndex <= tagEndIndex) {
                // in this case the DELIMITER_PERSONAL is in a future pair (or not found)
                // so synthesize a positional tag for the value, and don't update tagEndIndex
                value = packed.substring(elementStartIndex, elementEndIndex);
                tag = Integer.toString(map.size());
            } else {
                value = packed.substring(elementStartIndex, tagEndIndex);
                tag = packed.substring(tagEndIndex + 1, elementEndIndex);
                // scan forward for next tag, if any
                tagEndIndex = packed.indexOf(DELIMITER_TAG, elementEndIndex + 1);
            }
            map.put(tag, value);
            elementStartIndex = elementEndIndex + 1;
        }

        return map;
    }

    /**
     * Builder class for creating PackedString values.  Can also be used for editing existing
     * PackedString representations.
     */
    static public class Builder {
        HashMap<String, String> mMap;

        /**
         * Create a builder that's empty (for filling)
         */
        public Builder() {
            mMap = new HashMap<String, String>();
        }

        /**
         * Create a builder using the values of an existing PackedString (for editing).
         */
        public Builder(String packed) {
            mMap = explode(packed);
        }

        /**
         * Add a tagged value
         * @param tag identifier of string of interest
         * @param value the value to record in this position.  null to delete entry.
         */
        public void put(String tag, String value) {
            if (value == null) {
                mMap.remove(tag);
            } else {
                mMap.put(tag, value);
            }
        }

        /**
         * Get the value referred to by a given tag.  If the tag does not exist, return null.
         * @param tag identifier of string of interest
         * @return returns value, or null if no string is found
         */
        public String get(String tag) {
            return mMap.get(tag);
        }

        /**
         * Pack the values and return a single, encoded string
         */
        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();
            for (Map.Entry<String,String> entry : mMap.entrySet()) {
                if (sb.length() > 0) {
                    sb.append(DELIMITER_ELEMENT);
                }
                sb.append(entry.getValue());
                sb.append(DELIMITER_TAG);
                sb.append(entry.getKey());
            }
            return sb.toString();
        }
    }
}