/*

 * Copyright (c) 2015, 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.

 *

 * 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.

 */

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.FilterReader;

import java.io.FilterWriter;

import java.io.IOException;

import java.io.Reader;

import java.io.Writer;

import java.nio.charset.Charset;

import java.nio.charset.CharsetEncoder;

import java.nio.file.Files;

import java.nio.file.Path;

import static java.nio.charset.StandardCharsets.*;

/**

 * Simple utility to convert from native encoding file to ascii or reverse

 * including \udddd Unicode notation.

 */

public class Native2Ascii {

    final Charset cs;

    final CharsetEncoder encoder;

    public Native2Ascii(Charset cs) {

        this.cs = cs;

        this.encoder = cs.newEncoder();

    }

    /**

     * ASCII to Native conversion

     */

    public void asciiToNative(Path infile, Path outfile) throws IOException {

        try (BufferedReader in = Files.newBufferedReader(infile, US_ASCII);

             BufferedReader reader = new BufferedReader(new A2NFilter(in));

             BufferedWriter writer = Files.newBufferedWriter(outfile, cs)) {

            String line;

            while ((line = reader.readLine()) != null) {

                writer.write(line.toCharArray());

                writer.newLine();

            }

        }

    }

    /**

     * Native to ASCII conversion

     */

    public void nativeToAscii(Path infile, Path outfile) throws IOException {

        try (BufferedReader reader = Files.newBufferedReader(infile, cs);

             BufferedWriter out = Files.newBufferedWriter(outfile, US_ASCII);

             BufferedWriter writer = new BufferedWriter(new N2AFilter(out))) {

            String line;

            while ((line = reader.readLine()) != null) {

                writer.write(line.toCharArray());

                writer.newLine();

            }

        }

    }

    // A copy of native2ascii N2AFilter

    class N2AFilter extends FilterWriter {

        public N2AFilter(Writer out) { super(out); }

        public void write(char b) throws IOException {

            char[] buf = new char[1];

            buf[0] = b;

            write(buf, 0, 1);

        }

        public void write(char[] buf, int off, int len) throws IOException {

            for (int i = 0; i < len; i++) {

                if ((buf[i] > '\u007f')) {

                    // write \udddd

                    out.write('\\');

                    out.write('u');

                    String hex = Integer.toHexString(buf[i]);

                    StringBuilder hex4 = new StringBuilder(hex);

                    hex4.reverse();

                    int length = 4 - hex4.length();

                    for (int j = 0; j < length; j++) {

                        hex4.append('0');

                    }

                    for (int j = 0; j < 4; j++) {

                        out.write(hex4.charAt(3 - j));

                    }

                } else

                    out.write(buf[i]);

            }

        }

    }

    // A copy of native2ascii A2NFilter

    class A2NFilter extends FilterReader {

        // maintain a trailing buffer to hold any incompleted

        // unicode escaped sequences

        private char[] trailChars = null;

        public A2NFilter(Reader in) {

            super(in);

        }

        public int read(char[] buf, int off, int len) throws IOException {

            int numChars = 0;        // how many characters have been read

            int retChars = 0;        // how many characters we'll return

            char[] cBuf = new char[len];

            int cOffset = 0;         // offset at which we'll start reading

            boolean eof = false;

            // copy trailing chars from previous invocation to input buffer

            if (trailChars != null) {

                for (int i = 0; i < trailChars.length; i++)

                    cBuf[i] = trailChars[i];

                numChars = trailChars.length;

                trailChars = null;

            }

            int n = in.read(cBuf, numChars, len - numChars);

            if (n < 0) {

                eof = true;

                if (numChars == 0)

                    return -1;              // EOF;

            } else {

                numChars += n;

            }

            for (int i = 0; i < numChars; ) {

                char c = cBuf[i++];

                if (c != '\\' || (eof && numChars <= 5)) {

                    // Not a backslash, so copy and continue

                    // Always pass non backslash chars straight thru

                    // for regular encoding. If backslash occurs in

                    // input stream at the final 5 chars then don't

                    // attempt to read-ahead and de-escape since these

                    // are literal occurrences of U+005C which need to

                    // be encoded verbatim in the target encoding.

                    buf[retChars++] = c;

                    continue;

                }

                int remaining = numChars - i;

                if (remaining < 5) {

                    // Might be the first character of a unicode escape, but we

                    // don't have enough characters to tell, so save it and finish

                    trailChars = new char[1 + remaining];

                    trailChars[0] = c;

                    for (int j = 0; j < remaining; j++)

                        trailChars[1 + j] = cBuf[i + j];

                    break;

                }

                // At this point we have at least five characters remaining

                c = cBuf[i++];

                if (c != 'u') {

                    // Not a unicode escape, so copy and continue

                    buf[retChars++] = '\\';

                    buf[retChars++] = c;

                    continue;

                }

                // The next four characters are the hex part of a unicode escape

                char rc = 0;

                boolean isUE = true;

                try {

                    rc = (char) Integer.parseInt(new String(cBuf, i, 4), 16);

                } catch (NumberFormatException x) {

                    isUE = false;

                }

                if (isUE && encoder.canEncode(rc)) {

                    // We'll be able to convert this

                    buf[retChars++] = rc;

                    i += 4; // Align beyond the current uXXXX sequence

                } else {

                    // We won't, so just retain the original sequence

                    buf[retChars++] = '\\';

                    buf[retChars++] = 'u';

                    continue;

                }

            }

            return retChars;

        }

        public int read() throws IOException {

            char[] buf = new char[1];

            if (read(buf, 0, 1) == -1)

                return -1;

            else

                return (int) buf[0];

        }

    }

}