/*

 * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.javac.parser;

import java.nio.CharBuffer;

import java.util.Arrays;

import com.sun.tools.javac.file.JavacFileManager;

import com.sun.tools.javac.util.ArrayUtils;

import com.sun.tools.javac.util.Log;

import com.sun.tools.javac.util.Name;

import com.sun.tools.javac.util.Names;

import static com.sun.tools.javac.util.LayoutCharacters.*;

/** The char reader used by the javac lexer/tokenizer. Returns the sequence of

 * characters contained in the input stream, handling unicode escape accordingly.

 * Additionally, it provides features for saving chars into a buffer and to retrieve

 * them at a later stage.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class UnicodeReader {

    /** The input buffer, index of next character to be read,

     *  index of one past last character in buffer.

     */

    protected char[] buf;

    protected int bp;

    protected final int buflen;

    /** The current character.

     */

    protected char ch;

    /** The buffer index of the last converted unicode character

     */

    protected int unicodeConversionBp = -1;

    protected Log log;

    protected Names names;

    /** A character buffer for saved chars.

     */

    protected char[] sbuf = new char[128];

    protected int sp;

    /**

     * Create a scanner from the input array.  This method might

     * modify the array.  To avoid copying the input array, ensure

     * that {@code inputLength < input.length} or

     * {@code input[input.length -1]} is a white space character.

     *

     * @param sf the factory which created this Scanner

     * @param buffer the input, might be modified

     * Must be positive and less than or equal to input.length.

     */

    protected UnicodeReader(ScannerFactory sf, CharBuffer buffer) {

        this(sf, JavacFileManager.toArray(buffer), buffer.limit());

    }

    protected UnicodeReader(ScannerFactory sf, char[] input, int inputLength) {

        log = sf.log;

        names = sf.names;

        if (inputLength == input.length) {

            if (input.length > 0 && Character.isWhitespace(input[input.length - 1])) {

                inputLength--;

            } else {

                input = Arrays.copyOf(input, inputLength + 1);

            }

        }

        buf = input;

        buflen = inputLength;

        buf[buflen] = EOI;

        bp = -1;

        scanChar();

    }

    /** Read next character.

     */

    protected void scanChar() {

        if (bp < buflen) {

            ch = buf[++bp];

            if (ch == '\\') {

                convertUnicode();

            }

        }

    }

    /** Read next character in comment, skipping over double '\' characters.

     */

    protected void scanCommentChar() {

        scanChar();

        if (ch == '\\') {

            if (peekChar() == '\\' && !isUnicode()) {

                skipChar();

            } else {

                convertUnicode();

            }

        }

    }

    /** Append a character to sbuf.

     */

    protected void putChar(char ch, boolean scan) {

        sbuf = ArrayUtils.ensureCapacity(sbuf, sp);

        sbuf[sp++] = ch;

        if (scan)

            scanChar();

    }

    protected void putChar(char ch) {

        putChar(ch, false);

    }

    protected void putChar(boolean scan) {

        putChar(ch, scan);

    }

    Name name() {

        return names.fromChars(sbuf, 0, sp);

    }

    String chars() {

        return new String(sbuf, 0, sp);

    }

    /** Convert unicode escape; bp points to initial '\' character

     *  (Spec 3.3).

     */

    protected void convertUnicode() {

        if (ch == '\\' && unicodeConversionBp != bp) {

            bp++; ch = buf[bp];

            if (ch == 'u') {

                do {

                    bp++; ch = buf[bp];

                } while (ch == 'u');

                int limit = bp + 3;

                if (limit < buflen) {

                    int d = digit(bp, 16);

                    int code = d;

                    while (bp < limit && d >= 0) {

                        bp++; ch = buf[bp];

                        d = digit(bp, 16);

                        code = (code << 4) + d;

                    }

                    if (d >= 0) {

                        ch = (char)code;

                        unicodeConversionBp = bp;

                        return;

                    }

                }

            } else {

                bp--;

                ch = '\\';

            }

        }

    }

    /** Are surrogates supported?

     */

    final static boolean surrogatesSupported = surrogatesSupported();

    private static boolean surrogatesSupported() {

        try {

            Character.isHighSurrogate('a');

            return true;

        } catch (NoSuchMethodError ex) {

            return false;

        }

    }

    /** Scan surrogate pairs.  If 'ch' is a high surrogate and

     *  the next character is a low surrogate, returns the code point

     *  constructed from these surrogates. Otherwise, returns -1.

     *  This method will not consume any of the characters.

     */

    protected int peekSurrogates() {

        if (surrogatesSupported && Character.isHighSurrogate(ch)) {

            char high = ch;

            int prevBP = bp;

            scanChar();

            char low = ch;

            ch = high;

            bp = prevBP;

            if (Character.isLowSurrogate(low)) {

                return Character.toCodePoint(high, low);

            }

        }

        return -1;

    }

    /** Convert an ASCII digit from its base (8, 10, or 16)

     *  to its value.

     */

    protected int digit(int pos, int base) {

        char c = ch;

        if ('0' <= c && c <= '9')

            return Character.digit(c, base); //a fast common case

        int codePoint = peekSurrogates();

        int result = codePoint >= 0 ? Character.digit(codePoint, base) : Character.digit(c, base);

        if (result >= 0 && c > 0x7f) {

            if (codePoint >= 0)

                scanChar();

            ch = "0123456789abcdef".charAt(result);

        }

        return result;

    }

    protected boolean isUnicode() {

        return unicodeConversionBp == bp;

    }

    protected void skipChar() {

        bp++;

    }

    protected char peekChar() {

        return buf[bp + 1];

    }

    /**

     * Returns a copy of the input buffer, up to its inputLength.

     * Unicode escape sequences are not translated.

     */

    public char[] getRawCharacters() {

        char[] chars = new char[buflen];

        System.arraycopy(buf, 0, chars, 0, buflen);

        return chars;

    }

    /**

     * Returns a copy of a character array subset of the input buffer.

     * The returned array begins at the {@code beginIndex} and

     * extends to the character at index {@code endIndex - 1}.

     * Thus the length of the substring is {@code endIndex-beginIndex}.

     * This behavior is like

     * {@code String.substring(beginIndex, endIndex)}.

     * Unicode escape sequences are not translated.

     *

     * @param beginIndex the beginning index, inclusive.

     * @param endIndex the ending index, exclusive.

     * @throws ArrayIndexOutOfBoundsException if either offset is outside of the

     *         array bounds

     */

    public char[] getRawCharacters(int beginIndex, int endIndex) {

        int length = endIndex - beginIndex;

        char[] chars = new char[length];

        System.arraycopy(buf, beginIndex, chars, 0, length);

        return chars;

    }

}