/*
 * The contents of this file are subject to the terms of the Common Development and
 * Distribution License (the License). You may not use this file except in compliance with the
 * License.
 *
 * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
 * specific language governing permission and limitations under the License.
 *
 * When distributing Covered Software, include this CDDL Header Notice in each file and include
 * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
 * Header, with the fields enclosed by brackets [] replaced by your own identifying
 * information: "Portions copyright [year] [name of copyright owner]".
 *
 * Copyright 2015-2016 ForgeRock AS.
 */


package org.forgerock.util.encode;

import java.util.Arrays;

/**
 * A very fast and memory efficient class to encode and decode to and from
 * BASE64 in full accordance with RFC 2045.<br>
 * <br>
 * On Windows XP sp1 with 1.4.2_04 and later ;), this encoder and decoder is
 * about 10 times faster on small arrays (10 - 1000 bytes) and 2-3 times as fast
 * on larger arrays (10000 - 1000000 bytes) compared to
 * <code>sun.misc.Encoder()/Decoder()</code>.<br>
 * <br>
 * On byte arrays the encoder is about 20% faster than Jakarta Commons Base64
 * Codec for encode and about 50% faster for decoding large arrays. This
 * implementation is about twice as fast on very small arrays (&lt; 30 bytes).
 * If source/destination is a <code>String</code> this version is about three
 * times as fast due to the fact that the Commons Codec result has to be recoded
 * to a <code>String</code> from <code>byte[]</code>, which is very expensive.<br>
 * <br>
 * This encode/decode algorithm doesn't create any temporary arrays as many
 * other codecs do, it only allocates the resulting array. This produces less
 * garbage and it is possible to handle arrays twice as large as algorithms that
 * create a temporary array. (E.g. Jakarta Commons Codec). It is unknown whether
 * Sun's <code>sun.misc.Encoder()/Decoder()</code> produce temporary arrays but
 * since performance is quite low it probably does.<br>
 * <br>
 * The encoder produces the same output as the Sun one except that the Sun's
 * encoder appends a trailing line separator if the last character isn't a pad.
 * Unclear why but it only adds to the length and is probably a side effect.
 * Both are in conformance with RFC 2045 though.<br>
 * Commons codec seem to always att a trailing line separator.<br>
 * <br>
 * <b>Note!</b> The encode/decode method pairs (types) come in three versions
 * with the <b>exact</b> same algorithm and thus a lot of code redundancy. This
 * is to not create any temporary arrays for transcoding to/from different
 * format types. The methods not used can simply be commented out.<br>
 * <br>
 * There is also a "fast" version of all decode methods that works the same way
 * as the normal ones, but har a few demands on the decoded input. Normally
 * though, these fast verions should be used if the source if the input is known
 * and it hasn't bee tampered with.<br>
 * <br>
 * If you find the code useful or you find a bug, please send me a note at
 * base64 @ miginfocom . com.
 *
 * @version 2.2
 */
public final class Base64 {

    private static final char[] CA =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
    private static final int[] IA = new int[256];

    static {
        Arrays.fill(IA, -1);
        for (int i = 0, iS = CA.length; i < iS; i++) {
            IA[CA[i]] = i;
        }
        IA['='] = 0;
    }

    /**
     * Decodes a BASE64 encoded byte array. All illegal characters will be
     * ignored and can handle both arrays with and without line separators.
     *
     * @param sArr
     *            The source array. Length 0 will return an empty array.
     *            <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0. Will be
     *         <code>null</code> if the legal characters (including '=') isn't
     *         divideable by 4. (I.e. definitely corrupted).
     */
    public static byte[] decode(final byte[] sArr) {
        // Check special case
        final int sLen = sArr.length;

        /*
         * Count illegal characters (including '\r', '\n') to know what size the
         * returned array will be, so we don't have to reallocate & copy it
         * later.
         */
        int sepCnt = 0; // Number of separator characters. (Actually illegal characters, but that's a bonus...)
        // If input is "pure" (I.e. no line separators or illegal chars) base64 this loop can be removed.
        for (byte aSArr : sArr) {
            if (IA[aSArr & 0xff] < 0) {
                sepCnt++;
            }
        }

        /*
         * Check so that legal chars (including '=') are evenly divideable by 4
         * as specified in RFC 2045.
         */
        if ((sLen - sepCnt) % 4 != 0) {
            return null;
        }

        int pad = 0;
        for (int i = sLen; i > 1 && IA[sArr[--i] & 0xff] <= 0;) {
            if (sArr[i] == '=') {
                pad++;
            }
        }

        final int len = ((sLen - sepCnt) * 6 >> 3) - pad;

        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        for (int s = 0, d = 0; d < len;) {
            // Assemble three bytes into an int from four "valid" characters.
            int i = 0;
            for (int j = 0; j < 4; j++) { // j only increased if a valid char was found.
                final int c = IA[sArr[s++] & 0xff];
                if (c >= 0) {
                    i |= c << 18 - j * 6;
                } else {
                    j--;
                }
            }

            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            if (d < len) {
                dArr[d++] = (byte) (i >> 8);
                if (d < len) {
                    dArr[d++] = (byte) i;
                }
            }
        }

        return dArr;
    }

    /**
     * Decodes a BASE64 encoded char array. All illegal characters will be
     * ignored and can handle both arrays with and without line separators.
     *
     * @param sArr
     *            The source array. <code>null</code> or length 0 will return an
     *            empty array.
     * @return The decoded array of bytes. May be of length 0. Will be
     *         <code>null</code> if the legal characters (including '=') isn't
     *         divideable by 4. (I.e. definitely corrupted).
     */
    public static byte[] decode(final char[] sArr) {
        // Check special case
        final int sLen = sArr != null ? sArr.length : 0;
        if (sLen == 0) {
            return new byte[0];
        }

        /*
         * Count illegal characters (including '\r', '\n') to know what size the
         * returned array will be, so we don't have to reallocate & copy it
         * later.
         */
        // Number of separator characters. (Actually illegal characters, but that's a bonus...)
        int sepCnt = 0;
        // If input is "pure" (I.e. no line separators or illegal chars) base64 this loop can be commented out.
        for (int i = 0; i < sLen; i++) {
            if (IA[sArr[i]] < 0) {
                sepCnt++;
            }
        }

        /*
         * Check so that legal chars (including '=') are evenly divideable by 4
         * as specified in RFC 2045.
         */
        if ((sLen - sepCnt) % 4 != 0) {
            return null;
        }

        int pad = 0;
        for (int i = sLen; i > 1 && IA[sArr[--i]] <= 0;) {
            if (sArr[i] == '=') {
                pad++;
            }
        }

        final int len = ((sLen - sepCnt) * 6 >> 3) - pad;

        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        for (int s = 0, d = 0; d < len;) {
            // Assemble three bytes into an int from four "valid" characters.
            int i = 0;
            for (int j = 0; j < 4; j++) { // j only increased if a valid char was found.
                final int c = IA[sArr[s++]];
                if (c >= 0) {
                    i |= c << 18 - j * 6;
                } else {
                    j--;
                }
            }
            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            if (d < len) {
                dArr[d++] = (byte) (i >> 8);
                if (d < len) {
                    dArr[d++] = (byte) i;
                }
            }
        }
        return dArr;
    }

    /**
     * Decodes a BASE64 encoded <code>String</code>. All illegal characters will
     * be ignored and can handle both strings with and without line separators.<br>
     * <b>Note!</b> It can be up to about 2x the speed to call
     * <code>decode(str.toCharArray())</code> instead. That will create a
     * temporary array though. This version will use <code>str.charAt(i)</code>
     * to iterate the string.
     *
     * @param str
     *            The source string. <code>null</code> or length 0 will return
     *            an empty array.
     * @return The decoded array of bytes. May be of length 0. Will be
     *         <code>null</code> if the legal characters (including '=') isn't
     *         divideable by 4. (I.e. definitely corrupted).
     */
    public static byte[] decode(final String str) {
        // Check special case
        final int sLen = str != null ? str.length() : 0;
        if (sLen == 0) {
            return new byte[0];
        }

        /*
         * Count illegal characters (including '\r', '\n') to know what size the
         * returned array will be, so we don't have to reallocate & copy it
         * later.
         */
        // Number of separator characters. (Actually illegal characters, but that's a bonus...)
        int sepCnt = 0;
        // If input is "pure" (I.e. no line separators or illegal chars) base64 this loop can be commented out.
        for (int i = 0; i < sLen; i++) {
            if (IA[str.charAt(i)] < 0) {
                sepCnt++;
            }
        }

        /*
         * Check so that legal chars (including '=') are evenly divideable by 4
         * as specified in RFC 2045.
         */
        if ((sLen - sepCnt) % 4 != 0) {
            return null;
        }

        // Count '=' at end
        int pad = 0;
        for (int i = sLen; i > 1 && IA[str.charAt(--i)] <= 0;) {
            if (str.charAt(i) == '=') {
                pad++;
            }
        }

        final int len = ((sLen - sepCnt) * 6 >> 3) - pad;

        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        for (int s = 0, d = 0; d < len;) {
            // Assemble three bytes into an int from four "valid" characters.
            int i = 0;
            for (int j = 0; j < 4; j++) { // j only increased if a valid char was found.
                final int c = IA[str.charAt(s++)];
                if (c >= 0) {
                    i |= c << 18 - j * 6;
                } else {
                    j--;
                }
            }
            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            if (d < len) {
                dArr[d++] = (byte) (i >> 8);
                if (d < len) {
                    dArr[d++] = (byte) i;
                }
            }
        }
        return dArr;
    }

    /**
     * Decodes a BASE64 encoded byte array that is known to be resonably well
     * formatted. The method is about twice as fast as {@link #decode(byte[])}.
     * The preconditions are:<br>
     * + The array must have a line length of 76 chars OR no line separators at
     * all (one line).<br>
     * + Line separator must be "\r\n", as specified in RFC 2045 + The array
     * must not contain illegal characters within the encoded string<br>
     * + The array CAN have illegal characters at the beginning and end, those
     * will be dealt with appropriately.<br>
     *
     * @param sArr
     *            The source array. Length 0 will return an empty array.
     *            <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0.
     */
    public static byte[] decodeFast(final byte[] sArr) {
        // Check special case
        final int sLen = sArr.length;
        if (sLen == 0) {
            return new byte[0];
        }

        int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.

        // Trim illegal chars from start
        while (sIx < eIx && IA[sArr[sIx] & 0xff] < 0) {
            sIx++;
        }

        // Trim illegal chars from end
        while (eIx > 0 && IA[sArr[eIx] & 0xff] < 0) {
            eIx--;
        }

        // get the padding count (=) (0, 1 or 2)
        final int pad = sArr[eIx] == '=' ? sArr[eIx - 1] == '=' ? 2 : 1 : 0; // Count '=' at end.
        final int cCnt = eIx - sIx + 1; // Content count including possible separators
        final int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;

        final int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        // Decode all but the last 0 - 2 bytes.
        int d = 0;
        for (int cc = 0, eLen = len / 3 * 3; d < eLen;) {
            // Assemble three bytes into an int from four "valid" characters.
            final int i =
                    IA[sArr[sIx++]] << 18 | IA[sArr[sIx++]] << 12 | IA[sArr[sIx++]] << 6
                            | IA[sArr[sIx++]];

            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            dArr[d++] = (byte) (i >> 8);
            dArr[d++] = (byte) i;

            // If line separator, jump over it.
            if (sepCnt > 0 && ++cc == 19) {
                sIx += 2;
                cc = 0;
            }
        }

        if (d < len) {
            // Decode last 1-3 bytes (incl '=') into 1-3 bytes
            int i = 0;
            for (int j = 0; sIx <= eIx - pad; j++) {
                i |= IA[sArr[sIx++]] << 18 - j * 6;
            }

            for (int r = 16; d < len; r -= 8) {
                dArr[d++] = (byte) (i >> r);
            }
        }

        return dArr;
    }

    /**
     * Decodes a BASE64 encoded char array that is known to be resonably well
     * formatted. The method is about twice as fast as {@link #decode(char[])}.
     * The preconditions are:<br>
     * + The array must have a line length of 76 chars OR no line separators at
     * all (one line).<br>
     * + Line separator must be "\r\n", as specified in RFC 2045 + The array
     * must not contain illegal characters within the encoded string<br>
     * + The array CAN have illegal characters at the beginning and end, those
     * will be dealt with appropriately.<br>
     *
     * @param sArr
     *            The source array. Length 0 will return an empty array.
     *            <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0.
     */
    public static byte[] decodeFast(final char[] sArr) {
        // Check special case
        final int sLen = sArr.length;
        if (sLen == 0) {
            return new byte[0];
        }

        int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.

        // Trim illegal chars from start
        while (sIx < eIx && IA[sArr[sIx]] < 0) {
            sIx++;
        }

        // Trim illegal chars from end
        while (eIx > 0 && IA[sArr[eIx]] < 0) {
            eIx--;
        }

        // get the padding count (=) (0, 1 or 2)
        final int pad = sArr[eIx] == '=' ? sArr[eIx - 1] == '=' ? 2 : 1 : 0; // Count '=' at end.
        final int cCnt = eIx - sIx + 1; // Content count including possible separators
        final int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;

        final int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        // Decode all but the last 0 - 2 bytes.
        int d = 0;
        for (int cc = 0, eLen = len / 3 * 3; d < eLen;) {
            // Assemble three bytes into an int from four "valid" characters.
            final int i =
                    IA[sArr[sIx++]] << 18 | IA[sArr[sIx++]] << 12 | IA[sArr[sIx++]] << 6
                            | IA[sArr[sIx++]];

            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            dArr[d++] = (byte) (i >> 8);
            dArr[d++] = (byte) i;

            // If line separator, jump over it.
            if (sepCnt > 0 && ++cc == 19) {
                sIx += 2;
                cc = 0;
            }
        }

        if (d < len) {
            // Decode last 1-3 bytes (incl '=') into 1-3 bytes
            int i = 0;
            for (int j = 0; sIx <= eIx - pad; j++) {
                i |= IA[sArr[sIx++]] << 18 - j * 6;
            }

            for (int r = 16; d < len; r -= 8) {
                dArr[d++] = (byte) (i >> r);
            }
        }

        return dArr;
    }

    /**
     * Decodes a BASE64 encoded string that is known to be resonably well
     * formatted. The method is about twice as fast as {@link #decode(String)}.
     * The preconditions are:<br>
     * + The array must have a line length of 76 chars OR no line separators at
     * all (one line).<br>
     * + Line separator must be "\r\n", as specified in RFC 2045 + The array
     * must not contain illegal characters within the encoded string<br>
     * + The array CAN have illegal characters at the beginning and end, those
     * will be dealt with appropriately.<br>
     *
     * @param s
     *            The source string. Length 0 will return an empty array.
     *            <code>null</code> will throw an exception.
     * @return The decoded array of bytes. May be of length 0.
     */
    public static byte[] decodeFast(final String s) {
        // Check special case
        final int sLen = s.length();
        if (sLen == 0) {
            return new byte[0];
        }

        int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.

        // Trim illegal chars from start
        while (sIx < eIx && IA[s.charAt(sIx) & 0xff] < 0) {
            sIx++;
        }

        // Trim illegal chars from end
        while (eIx > 0 && IA[s.charAt(eIx) & 0xff] < 0) {
            eIx--;
        }

        // get the padding count (=) (0, 1 or 2)
        final int pad = s.charAt(eIx) == '=' ? s.charAt(eIx - 1) == '=' ? 2 : 1 : 0; // Count '=' at end.
        final int cCnt = eIx - sIx + 1; // Content count including possible separators
        final int sepCnt = sLen > 76 ? (s.charAt(76) == '\r' ? cCnt / 78 : 0) << 1 : 0;

        final int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
        final byte[] dArr = new byte[len]; // Preallocate byte[] of exact length

        // Decode all but the last 0 - 2 bytes.
        int d = 0;
        for (int cc = 0, eLen = len / 3 * 3; d < eLen;) {
            // Assemble three bytes into an int from four "valid" characters.
            final int i =
                    IA[s.charAt(sIx++)] << 18 | IA[s.charAt(sIx++)] << 12
                            | IA[s.charAt(sIx++)] << 6 | IA[s.charAt(sIx++)];

            // Add the bytes
            dArr[d++] = (byte) (i >> 16);
            dArr[d++] = (byte) (i >> 8);
            dArr[d++] = (byte) i;

            // If line separator, jump over it.
            if (sepCnt > 0 && ++cc == 19) {
                sIx += 2;
                cc = 0;
            }
        }

        if (d < len) {
            // Decode last 1-3 bytes (incl '=') into 1-3 bytes
            int i = 0;
            for (int j = 0; sIx <= eIx - pad; j++) {
                i |= IA[s.charAt(sIx++)] << 18 - j * 6;
            }

            for (int r = 16; d < len; r -= 8) {
                dArr[d++] = (byte) (i >> r);
            }
        }

        return dArr;
    }

    /**
     * This method is using {@link #encode(byte[], boolean)}, and it only exists
     * so we don't break the API.
     *
     * @param content
     *            The bytearray that needs to be Base64 encoded
     * @return the Base64 encoded
     */
    public static String encode(final byte[] content) {
        return encode(content, false);
    }

    /**
     * Encodes a raw byte array into a BASE64 <code>String</code> representation
     * i accordance with RFC 2045.
     *
     * @param sArr
     *            The bytes to convert. If <code>null</code> or length 0 an
     *            empty array will be returned.
     * @param lineSep
     *            Optional "\r\n" after 76 characters, unless end of file.<br>
     *            No line separator will be in breach of RFC 2045 which
     *            specifies max 76 per line but will be a little faster.
     * @return A BASE64 encoded array. Never <code>null</code>.
     */
    public static String encode(final byte[] sArr, final boolean lineSep) {
        /*
         * Reuse char[] since we can't create a String incrementally anyway and
         * StringBuffer/Builder would be slower.
         */
        return new String(encodeToChar(sArr, lineSep));
    }

    /**
     * Encodes a raw byte array into a BASE64 <code>byte[]</code> representation
     * i accordance with RFC 2045.
     *
     * @param sArr
     *            The bytes to convert. If <code>null</code> or length 0 an
     *            empty array will be returned.
     * @param lineSep
     *            Optional "\r\n" after 76 characters, unless end of file.<br>
     *            No line separator will be in breach of RFC 2045 which
     *            specifies max 76 per line but will be a little faster.
     * @return A BASE64 encoded array. Never <code>null</code>.
     */
    public static byte[] encodeToByte(final byte[] sArr, final boolean lineSep) {
        // Check special case
        final int sLen = sArr != null ? sArr.length : 0;
        if (sLen == 0) {
            return new byte[0];
        }

        final int eLen = sLen / 3 * 3; // Length of even 24-bits.
        final int cCnt = (sLen - 1) / 3 + 1 << 2; // Returned character count
        final int dLen = cCnt + (lineSep ? (cCnt - 1) / 76 << 1 : 0); // Length of returned array
        final byte[] dArr = new byte[dLen];

        // Encode even 24-bits
        for (int s = 0, d = 0, cc = 0; s < eLen;) {
            // Copy next three bytes into lower 24 bits of int, paying attension to sign.
            final int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8 | sArr[s++] & 0xff;

            // Encode the int into four chars
            dArr[d++] = (byte) CA[i >>> 18 & 0x3f];
            dArr[d++] = (byte) CA[i >>> 12 & 0x3f];
            dArr[d++] = (byte) CA[i >>> 6 & 0x3f];
            dArr[d++] = (byte) CA[i & 0x3f];

            // Add optional line separator
            if (lineSep && ++cc == 19 && d < dLen - 2) {
                dArr[d++] = '\r';
                dArr[d++] = '\n';
                cc = 0;
            }
        }

        // Pad and encode last bits if source isn't an even 24 bits.
        final int left = sLen - eLen; // 0 - 2.
        if (left > 0) {
            // Prepare the int
            final int i =
                    (sArr[eLen] & 0xff) << 10 | (left == 2 ? (sArr[sLen - 1] & 0xff) << 2 : 0);

            // Set last four chars
            dArr[dLen - 4] = (byte) CA[i >> 12];
            dArr[dLen - 3] = (byte) CA[i >>> 6 & 0x3f];
            dArr[dLen - 2] = left == 2 ? (byte) CA[i & 0x3f] : (byte) '=';
            dArr[dLen - 1] = '=';
        }
        return dArr;
    }

    /**
     * Encodes a raw byte array into a BASE64 <code>char[]</code> representation
     * i accordance with RFC 2045.
     *
     * @param sArr
     *            The bytes to convert. If <code>null</code> or length 0 an
     *            empty array will be returned.
     * @param lineSep
     *            Optional "\r\n" after 76 characters, unless end of file.<br>
     *            No line separator will be in breach of RFC 2045 which
     *            specifies max 76 per line but will be a little faster.
     * @return A BASE64 encoded array. Never <code>null</code>.
     */
    public static char[] encodeToChar(final byte[] sArr, final boolean lineSep) {
        // Check special case
        final int sLen = sArr != null ? sArr.length : 0;
        if (sLen == 0) {
            return new char[0];
        }

        final int eLen = sLen / 3 * 3; // Length of even 24-bits.
        final int cCnt = (sLen - 1) / 3 + 1 << 2; // Returned character count
        final int dLen = cCnt + (lineSep ? (cCnt - 1) / 76 << 1 : 0); // Length of returned array
        final char[] dArr = new char[dLen];

        // Encode even 24-bits
        for (int s = 0, d = 0, cc = 0; s < eLen;) {
            // Copy next three bytes into lower 24 bits of int, paying attension to sign.
            final int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8 | sArr[s++] & 0xff;

            // Encode the int into four chars
            dArr[d++] = CA[i >>> 18 & 0x3f];
            dArr[d++] = CA[i >>> 12 & 0x3f];
            dArr[d++] = CA[i >>> 6 & 0x3f];
            dArr[d++] = CA[i & 0x3f];

            // Add optional line separator
            if (lineSep && ++cc == 19 && d < dLen - 2) {
                dArr[d++] = '\r';
                dArr[d++] = '\n';
                cc = 0;
            }
        }

        // Pad and encode last bits if source isn't even 24 bits.
        final int left = sLen - eLen; // 0 - 2.
        if (left > 0) {
            // Prepare the int
            final int i =
                    (sArr[eLen] & 0xff) << 10 | (left == 2 ? (sArr[sLen - 1] & 0xff) << 2 : 0);

            // Set last four chars
            dArr[dLen - 4] = CA[i >> 12];
            dArr[dLen - 3] = CA[i >>> 6 & 0x3f];
            dArr[dLen - 2] = left == 2 ? CA[i & 0x3f] : '=';
            dArr[dLen - 1] = '=';
        }
        return dArr;
    }

    private Base64() {
        // No impl.
    }
}
