/*

 * Copyright (c) 2001, 2005, 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

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 */

/**

 * This FilterReader class processes a sequence of characters from

 * a source stream containing a mixture of 7-bit ASCII data and

 * 'back-tick U' escaped sequences representing characters which have

 * the possibility of being encoded in a user specified encoding

 * The filter relies on knowing the target encoding and makes a

 * determination as to whether a given supplied character in its

 * source character stream is encodeable in the target encoding.

 * If not, it is remains in its back-tick U escaped form.

 */

package sun.tools.native2ascii;

import java.io.*;

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 && Main.canConvert(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];

    }

}