/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.facebook.thrift.protocol;

/**
 * Class for encoding and decoding Base64 data.
 *
 * <p>This class is kept at package level because the interface does no input validation and is
 * therefore too low-level for generalized reuse.
 *
 * <p>Note also that the encoding does not pad with equal signs , as discussed in section 2.2 of the
 * RFC (http://www.faqs.org/rfcs/rfc3548.html). Furthermore, bad data encountered when decoding is
 * neither rejected or ignored but simply results in bad decoded data -- this is not in compliance
 * with the RFC but is done in the interest of performance.
 */
class TBase64Utils {
  private static final String ENCODE_TABLE =
      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  /**
   * Encode len bytes of data in src at offset srcOff, storing the result into dst at offset dstOff.
   * len must be 1, 2, or 3. dst must have at least len+1 bytes of space at dstOff. src and dst
   * should not be the same object. This method does no validation of the input values in the
   * interest of performance.
   *
   * @param src the source of bytes to encode
   * @param srcOff the offset into the source to read the unencoded bytes
   * @param len the number of bytes to encode (must be 1, 2, or 3).
   * @param dst the destination for the encoding
   * @param dstOff the offset into the destination to place the encoded bytes
   */
  static final void encode(byte[] src, int srcOff, int len, byte[] dst, int dstOff) {
    dst[dstOff] = (byte) ENCODE_TABLE.charAt((src[srcOff] >>> 2) & 0x3F);
    if (len == 3) {
      dst[dstOff + 1] =
          (byte)
              ENCODE_TABLE.charAt(((src[srcOff] << 4) & 0x30) | ((src[srcOff + 1] >>> 4) & 0x0F));
      dst[dstOff + 2] =
          (byte)
              ENCODE_TABLE.charAt(
                  ((src[srcOff + 1] << 2) & 0x3C) | ((src[srcOff + 2] >>> 6) & 0x03));
      dst[dstOff + 3] = (byte) ENCODE_TABLE.charAt(src[srcOff + 2] & 0x3F);
    } else if (len == 2) {
      dst[dstOff + 1] =
          (byte)
              ENCODE_TABLE.charAt(((src[srcOff] << 4) & 0x30) | ((src[srcOff + 1] >>> 4) & 0x0F));
      dst[dstOff + 2] = (byte) ENCODE_TABLE.charAt((src[srcOff + 1] << 2) & 0x3F);

    } else { // len == 1) {
      dst[dstOff + 1] = (byte) ENCODE_TABLE.charAt((src[srcOff] << 4) & 0x3F);
    }
  }

  private static final byte[] DECODE_TABLE = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
    -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
    -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
  };

  /**
   * Decode len bytes of data in src at offset srcOff, storing the result into dst at offset dstOff.
   * len must be 2, 3, or 4. dst must have at least len-1 bytes of space at dstOff. src and dst may
   * be the same object as long as dstoff <= srcOff. This method does no validation of the input
   * values in the interest of performance.
   *
   * @param src the source of bytes to decode
   * @param srcOff the offset into the source to read the encoded bytes
   * @param len the number of bytes to decode (must be 2, 3, or 4)
   * @param dst the destination for the decoding
   * @param dstOff the offset into the destination to place the decoded bytes
   */
  static final void decode(byte[] src, int srcOff, int len, byte[] dst, int dstOff) {
    dst[dstOff] =
        (byte)
            ((DECODE_TABLE[src[srcOff] & 0x0FF] << 2)
                | (DECODE_TABLE[src[srcOff + 1] & 0x0FF] >> 4));
    if (len > 2) {
      dst[dstOff + 1] =
          (byte)
              (((DECODE_TABLE[src[srcOff + 1] & 0x0FF] << 4) & 0xF0)
                  | (DECODE_TABLE[src[srcOff + 2] & 0x0FF] >> 2));
      if (len > 3) {
        dst[dstOff + 2] =
            (byte)
                (((DECODE_TABLE[src[srcOff + 2] & 0x0FF] << 6) & 0xC0)
                    | DECODE_TABLE[src[srcOff + 3] & 0x0FF]);
      }
    }
  }
}
