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/*
 * Copyright (c) 1997, 2023 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.eclipse.angus.mail.imap.protocol;

import java.text.CharacterIterator;
import java.text.StringCharacterIterator;

/**
 * See the BASE64MailboxEncoder for a description of the RFC2060 and how
 * mailbox names should be encoded.  This class will do the correct decoding
 * for mailbox names.
 *
 * @author Christopher Cotton
 */

public class BASE64MailboxDecoder {

    /**
     * Creates a default {@code BASE64MailboxDecoder}.
     * This constructor should never be invoked.
     *
     * @deprecated This is static utility class.
     */
    @Deprecated
    public BASE64MailboxDecoder() {
        //TODO: Made private and hostile.
    }

    public static String decode(String original) {
        if (original == null || original.length() == 0)
            return original;

        boolean changedString = false;
        int copyTo = 0;
        // it will always be less than the original
        char[] chars = new char[original.length()];
        StringCharacterIterator iter = new StringCharacterIterator(original);

        for (char c = iter.first(); c != CharacterIterator.DONE;
             c = iter.next()) {

            if (c == '&') {
                changedString = true;
                copyTo = base64decode(chars, copyTo, iter);
            } else {
                chars[copyTo++] = c;
            }
        }

        // now create our string from the char array
        if (changedString) {
            return new String(chars, 0, copyTo);
        } else {
            return original;
        }
    }


    protected static int base64decode(char[] buffer, int offset,
                                      CharacterIterator iter) {
        boolean firsttime = true;
        int leftover = -1;

        while (true) {
            // get the first byte
            byte orig_0 = (byte) iter.next();
            if (orig_0 == -1) break; // no more chars
            if (orig_0 == '-') {
                if (firsttime) {
                    // means we got the string "&-" which is turned into a "&"
                    buffer[offset++] = '&';
                }
                // we are done now
                break;
            }
            firsttime = false;

            // next byte
            byte orig_1 = (byte) iter.next();
            if (orig_1 == -1 || orig_1 == '-')
                break; // no more chars, invalid base64

            byte a, b, current;
            a = pem_convert_array[orig_0 & 0xff];
            b = pem_convert_array[orig_1 & 0xff];
            // The first decoded byte
            current = (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3));

            // use the leftover to create a Unicode Character (2 bytes)
            if (leftover != -1) {
                buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
                leftover = -1;
            } else {
                leftover = current & 0xff;
            }

            byte orig_2 = (byte) iter.next();
            if (orig_2 == '=') { // End of this BASE64 encoding
                continue;
            } else if (orig_2 == -1 || orig_2 == '-') {
                break; // no more chars
            }

            // second decoded byte
            a = b;
            b = pem_convert_array[orig_2 & 0xff];
            current = (byte) (((a << 4) & 0xf0) | ((b >>> 2) & 0xf));

            // use the leftover to create a Unicode Character (2 bytes)
            if (leftover != -1) {
                buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
                leftover = -1;
            } else {
                leftover = current & 0xff;
            }

            byte orig_3 = (byte) iter.next();
            if (orig_3 == '=') { // End of this BASE64 encoding
                continue;
            } else if (orig_3 == -1 || orig_3 == '-') {
                break;  // no more chars
            }

            // The third decoded byte
            a = b;
            b = pem_convert_array[orig_3 & 0xff];
            current = (byte) (((a << 6) & 0xc0) | (b & 0x3f));

            // use the leftover to create a Unicode Character (2 bytes)
            if (leftover != -1) {
                buffer[offset++] = (char) (leftover << 8 | (current & 0xff));
                leftover = -1;
            } else {
                leftover = current & 0xff;
            }
        }

        return offset;
    }

    /**
     * This character array provides the character to value map
     * based on RFC1521, but with the modification from RFC2060
     * which changes the '/' to a ','.
     */

    // shared with BASE64MailboxEncoder
    static final char[] pem_array = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
            'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
            'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
            'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
            '4', '5', '6', '7', '8', '9', '+', ','  // 7
    };

    private static final byte[] pem_convert_array = new byte[256];

    static {
        for (int i = 0; i < 255; i++)
            pem_convert_array[i] = -1;
        for (int i = 0; i < pem_array.length; i++)
            pem_convert_array[pem_array[i]] = (byte) i;
    }
}