    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     * Helper for non-Writer usage.
    054     * @param input CharSequence to be translated
    055     * @return String output of translation
    056     */
    057    public final String translate(final CharSequence input) {
    058        if (input == null) {
    059            return null;
    060        }
    061        try {
    062            final StringWriter writer = new StringWriter(input.length() * 2);
    063            translate(input, writer);
    064            return writer.toString();
    065        } catch (final IOException ioe) {
    066            // this should never ever happen while writing to a StringWriter
    067            throw new UncheckedIOException(ioe);
    068        }
    069    }
    070
    071    /**
    072     * Translate a set of code points, represented by an int index into a CharSequence,
    073     * into another set of code points. The number of code points consumed must be returned,
    074     * and the only IOExceptions thrown must be from interacting with the Writer so that
    075     * the top level API may reliably ignore StringWriter IOExceptions.
    076     *
    077     * @param input CharSequence that is being translated
    078     * @param index int representing the current point of translation
    079     * @param writer Writer to translate the text to
    080     * @return int count of code points consumed
    081     * @throws IOException if and only if the Writer produces an IOException
    082     */
    083    public abstract int translate(CharSequence input, int index, Writer writer) throws IOException;
    084
    085    /**
    086     * Translate an input onto a Writer. This is intentionally final as its algorithm is
    087     * tightly coupled with the abstract method of this class.
    088     *
    089     * @param input CharSequence that is being translated
    090     * @param writer Writer to translate the text to
    091     * @throws IOException if and only if the Writer produces an IOException
    092     */
    093    public final void translate(final CharSequence input, final Writer writer) throws IOException {
    094        Validate.isTrue(writer != null, "The Writer must not be null");
    095        if (input == null) {
    096            return;
    097        }
    098        int pos = 0;
    099        final int len = input.length();
    100        while (pos < len) {
    101            final int consumed = translate(input, pos, writer);
    102            if (consumed == 0) {
    103                // inlined implementation of Character.toChars(Character.codePointAt(input, pos))
    104                // avoids allocating temp char arrays and duplicate checks
    105                final char c1 = input.charAt(pos);
    106                writer.write(c1);
    107                pos++;
    108                if (Character.isHighSurrogate(c1) && pos < len) {
    109                    final char c2 = input.charAt(pos);
    110                    if (Character.isLowSurrogate(c2)) {
    111                      writer.write(c2);
    112                      pos++;
    113                    }
    114                }
    115                continue;
    116            }
    117            // contract with translators is that they have to understand code points
    118            // and they just took care of a surrogate pair
    119            for (int pt = 0; pt < consumed; pt++) {
    120                pos += Character.charCount(Character.codePointAt(input, pos));
    121            }
    122        }
    123    }
    124
    125    /**
    126     * Helper method to create a merger of this translator with another set of
    127     * translators. Useful in customizing the standard functionality.
    128     *
    129     * @param translators CharSequenceTranslator array of translators to merge with this one
    130     * @return CharSequenceTranslator merging this translator with the others
    131     */
    132    public final CharSequenceTranslator with(final CharSequenceTranslator... translators) {
    133        final CharSequenceTranslator[] newArray = new CharSequenceTranslator[translators.length + 1];
    134        newArray[0] = this;
    135        System.arraycopy(translators, 0, newArray, 1, translators.length);
    136        return new AggregateTranslator(newArray);
    137    }
    138
    139}