    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.text.translate;
    018
    019import java.io.IOException;
    020import java.io.StringWriter;
    021import java.io.UncheckedIOException;
    022import java.io.Writer;
    023import java.util.Locale;
    024
    025import org.apache.commons.lang3.Validate;
    026
    027/**
    028 * An API for translating text.
    029 * Its core use is to escape and unescape text. Because escaping and unescaping
    030 * is completely contextual, the API does not present two separate signatures.
    031 *
    032 * @since 1.0
    033 */
    034public abstract class CharSequenceTranslator {
    035
    036    /**
    037     * Array containing the hexadecimal alphabet.
    038     */
    039    static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
    040
    041    /**
    042     * Returns an upper case hexadecimal {@code String} for the given
    043     * character.
    044     *
    045     * @param codePoint The code point to convert.
    046     * @return An upper case hexadecimal {@code String}
    047     */
    048    public static String hex(final int codePoint) {
    049        return Integer.toHexString(codePoint).toUpperCase(Locale.ENGLISH);
    050    }
    051
    052    /**
    053     * Construct a new instance.
    054     */
    055    public CharSequenceTranslator() {
    056        // empty
    057    }
    058
    059    /**
    060     * Helper for non-Writer usage.
    061     * @param input CharSequence to be translated
    062     * @return String output of translation
    063     */
    064    public final String translate(final CharSequence input) {
    065        if (input == null) {
    066            return null;
    067        }
    068        try {
    069            final StringWriter writer = new StringWriter(input.length() * 2);
    070            translate(input, writer);
    071            return writer.toString();
    072        } catch (final IOException ioe) {
    073            // this should never ever happen while writing to a StringWriter
    074            throw new UncheckedIOException(ioe);
    075        }
    076    }
    077
    078    /**
    079     * Translate a set of code points, represented by an int index into a CharSequence,
    080     * into another set of code points. The number of code points consumed must be returned,
    081     * and the only IOExceptions thrown must be from interacting with the Writer so that
    082     * the top level API may reliably ignore StringWriter IOExceptions.
    083     *
    084     * @param input CharSequence that is being translated
    085     * @param index int representing the current point of translation
    086     * @param writer Writer to translate the text to
    087     * @return int count of code points consumed
    088     * @throws IOException if and only if the Writer produces an IOException
    089     */
    090    public abstract int translate(CharSequence input, int index, Writer writer) throws IOException;
    091
    092    /**
    093     * Translate an input onto a Writer. This is intentionally final as its algorithm is
    094     * tightly coupled with the abstract method of this class.
    095     *
    096     * @param input CharSequence that is being translated
    097     * @param writer Writer to translate the text to
    098     * @throws IOException if and only if the Writer produces an IOException
    099     */
    100    public final void translate(final CharSequence input, final Writer writer) throws IOException {
    101        Validate.isTrue(writer != null, "The Writer must not be null");
    102        if (input == null) {
    103            return;
    104        }
    105        int pos = 0;
    106        final int len = input.length();
    107        while (pos < len) {
    108            final int consumed = translate(input, pos, writer);
    109            if (consumed == 0) {
    110                // inlined implementation of Character.toChars(Character.codePointAt(input, pos))
    111                // avoids allocating temp char arrays and duplicate checks
    112                final char c1 = input.charAt(pos);
    113                writer.write(c1);
    114                pos++;
    115                if (Character.isHighSurrogate(c1) && pos < len) {
    116                    final char c2 = input.charAt(pos);
    117                    if (Character.isLowSurrogate(c2)) {
    118                      writer.write(c2);
    119                      pos++;
    120                    }
    121                }
    122                continue;
    123            }
    124            // contract with translators is that they have to understand code points
    125            // and they just took care of a surrogate pair
    126            for (int pt = 0; pt < consumed; pt++) {
    127                pos += Character.charCount(Character.codePointAt(input, pos));
    128            }
    129        }
    130    }
    131
    132    /**
    133     * Helper method to create a merger of this translator with another set of
    134     * translators. Useful in customizing the standard functionality.
    135     *
    136     * @param translators CharSequenceTranslator array of translators to merge with this one
    137     * @return CharSequenceTranslator merging this translator with the others
    138     */
    139    public final CharSequenceTranslator with(final CharSequenceTranslator... translators) {
    140        final CharSequenceTranslator[] newArray = new CharSequenceTranslator[translators.length + 1];
    141        newArray[0] = this;
    142        System.arraycopy(translators, 0, newArray, 1, translators.length);
    143        return new AggregateTranslator(newArray);
    144    }
    145
    146}