/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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.
   */
  /*
   * Written by Robert Harder and released to the public domain, as explained at
   * https://creativecommons.org/licenses/publicdomain
   */
  package io.netty.handler.codec.base64;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufAllocator;
  import io.netty.buffer.Unpooled;
  import io.netty.util.ByteProcessor;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.PlatformDependent;
  
  import java.nio.ByteOrder;
  
  /**
   * Utility class for {@link ByteBuf} that encodes and decodes to and from
   * <a href="https://en.wikipedia.org/wiki/Base64">Base64</a> notation.
   * <p>
   * The encoding and decoding algorithm in this class has been derived from
   * <a href="http://iharder.sourceforge.net/current/java/base64/">Robert Harder's Public Domain
   * Base64 Encoder/Decoder</a>.
   */
  public final class Base64 {
  
      /** Maximum line length (76) of Base64 output. */
      private static final int MAX_LINE_LENGTH = 76;
  
      /** The equals sign (=) as a byte. */
      private static final byte EQUALS_SIGN = (byte) '=';
  
      /** The new line character (\n) as a byte. */
      private static final byte NEW_LINE = (byte) '\n';
  
      private static final byte WHITE_SPACE_ENC = -5; // Indicates white space in encoding
  
      private static final byte EQUALS_SIGN_ENC = -1; // Indicates equals sign in encoding
  
      private static byte[] alphabet(Base64Dialect dialect) {
          return ObjectUtil.checkNotNull(dialect, "dialect").alphabet;
      }
  
      private static byte[] decodabet(Base64Dialect dialect) {
          return ObjectUtil.checkNotNull(dialect, "dialect").decodabet;
      }
  
      private static boolean breakLines(Base64Dialect dialect) {
          return ObjectUtil.checkNotNull(dialect, "dialect").breakLinesByDefault;
      }
  
      public static ByteBuf encode(ByteBuf src) {
          return encode(src, Base64Dialect.STANDARD);
      }
  
      public static ByteBuf encode(ByteBuf src, Base64Dialect dialect) {
          return encode(src, breakLines(dialect), dialect);
      }
  
      public static ByteBuf encode(ByteBuf src, boolean breakLines) {
          return encode(src, breakLines, Base64Dialect.STANDARD);
      }
  
      public static ByteBuf encode(ByteBuf src, boolean breakLines, Base64Dialect dialect) {
          ObjectUtil.checkNotNull(src, "src");
  
          ByteBuf dest = encode(src, src.readerIndex(), src.readableBytes(), breakLines, dialect);
          src.readerIndex(src.writerIndex());
          return dest;
      }
  
      public static ByteBuf encode(ByteBuf src, int off, int len) {
          return encode(src, off, len, Base64Dialect.STANDARD);
      }
  
      public static ByteBuf encode(ByteBuf src, int off, int len, Base64Dialect dialect) {
          return encode(src, off, len, breakLines(dialect), dialect);
      }
  
      public static ByteBuf encode(
              ByteBuf src, int off, int len, boolean breakLines) {
          return encode(src, off, len, breakLines, Base64Dialect.STANDARD);
      }
  
      public static ByteBuf encode(
             ByteBuf src, int off, int len, boolean breakLines, Base64Dialect dialect) {
         return encode(src, off, len, breakLines, dialect, src.alloc());
     }
 
     public static ByteBuf encode(
             ByteBuf src, int off, int len, boolean breakLines, Base64Dialect dialect, ByteBufAllocator allocator) {
         ObjectUtil.checkNotNull(src, "src");
         ObjectUtil.checkNotNull(dialect, "dialect");
 
         int capacity = encodedBufferSize(len, breakLines);
         ByteBuf destBuf = allocator.buffer(capacity).order(src.order());
         // Ensure the destination buffer is flat, if possible, and avoid leak detection checks on every write:
         ByteBuf dest = destBuf.unwrap() == null || !destBuf.isContiguous() ? destBuf :
                 destBuf.hasArray() ?
                         Unpooled.wrappedBuffer(destBuf.array(), destBuf.arrayOffset(), capacity).order(src.order()) :
                         Unpooled.wrappedBuffer(destBuf.internalNioBuffer(0, capacity)).order(src.order());
 
         byte[] alphabet = alphabet(dialect);
         int d = 0;
         int e = 0;
         int len2 = len - 2;
         int lineLength = 0;
         for (; d < len2; d += 3, e += 4) {
             encode3to4(src, d + off, 3, dest, e, alphabet);
 
             lineLength += 4;
 
             if (breakLines && lineLength == MAX_LINE_LENGTH) {
                 dest.setByte(e + 4, NEW_LINE);
                 e ++;
                 lineLength = 0;
             } // end if: end of line
         } // end for: each piece of array
 
         if (d < len) {
             encode3to4(src, d + off, len - d, dest, e, alphabet);
             e += 4;
         } // end if: some padding needed
 
         // Remove last byte if it's a newline
         if (e > 1 && dest.getByte(e - 1) == NEW_LINE) {
             e--;
         }
         if (dest != destBuf) {
             dest.release();
         }
         return destBuf.setIndex(0, e);
     }
 
     private static void encode3to4(
             ByteBuf src, int srcOffset, int numSigBytes, ByteBuf dest, int destOffset, byte[] alphabet) {
         //           1         2         3
         // 01234567890123456789012345678901 Bit position
         // --------000000001111111122222222 Array position from threeBytes
         // --------|    ||    ||    ||    | Six bit groups to index ALPHABET
         //          >>18  >>12  >> 6  >> 0  Right shift necessary
         //                0x3f  0x3f  0x3f  Additional AND
 
         // Create buffer with zero-padding if there are only one or two
         // significant bytes passed in the array.
         // We have to shift left 24 in order to flush out the 1's that appear
         // when Java treats a value as negative that is cast from a byte to an int.
         if (src.order() == ByteOrder.BIG_ENDIAN) {
             final int inBuff;
             switch (numSigBytes) {
                 case 1:
                     inBuff = toInt(src.getByte(srcOffset));
                     break;
                 case 2:
                     inBuff = toIntBE(src.getShort(srcOffset));
                     break;
                 default:
                     inBuff = numSigBytes <= 0 ? 0 : toIntBE(src.getMedium(srcOffset));
                     break;
             }
             encode3to4BigEndian(inBuff, numSigBytes, dest, destOffset, alphabet);
         } else {
             final int inBuff;
             switch (numSigBytes) {
                 case 1:
                     inBuff = toInt(src.getByte(srcOffset));
                     break;
                 case 2:
                     inBuff = toIntLE(src.getShort(srcOffset));
                     break;
                 default:
                     inBuff = numSigBytes <= 0 ? 0 : toIntLE(src.getMedium(srcOffset));
                     break;
             }
             encode3to4LittleEndian(inBuff, numSigBytes, dest, destOffset, alphabet);
         }
     }
 
     // package-private for testing
     static int encodedBufferSize(int len, boolean breakLines) {
         // Cast len to long to prevent overflow
         long len43 = ((long) len << 2) / 3;
 
         // Account for padding
         long ret = (len43 + 3) & ~3;
 
         if (breakLines) {
             ret += len43 / MAX_LINE_LENGTH;
         }
 
         return ret < Integer.MAX_VALUE ? (int) ret : Integer.MAX_VALUE;
     }
 
     private static int toInt(byte value) {
         return (value & 0xff) << 16;
     }
 
     private static int toIntBE(short value) {
         return (value & 0xff00) << 8 | (value & 0xff) << 8;
     }
 
     private static int toIntLE(short value) {
         return (value & 0xff) << 16 | (value & 0xff00);
     }
 
     private static int toIntBE(int mediumValue) {
         return (mediumValue & 0xff0000) | (mediumValue & 0xff00) | (mediumValue & 0xff);
     }
 
     private static int toIntLE(int mediumValue) {
         return (mediumValue & 0xff) << 16 | (mediumValue & 0xff00) | (mediumValue & 0xff0000) >>> 16;
     }
 
     private static void encode3to4BigEndian(
             int inBuff, int numSigBytes, ByteBuf dest, int destOffset, byte[] alphabet) {
         // Packing bytes into an int to reduce bound and reference count checking.
         switch (numSigBytes) {
             case 3:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ] << 24 |
                                         alphabet[inBuff >>> 12 & 0x3f] << 16 |
                                         alphabet[inBuff >>>  6 & 0x3f] << 8  |
                                         alphabet[inBuff        & 0x3f]);
                 break;
             case 2:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ] << 24 |
                                         alphabet[inBuff >>> 12 & 0x3f] << 16 |
                                         alphabet[inBuff >>> 6  & 0x3f] << 8  |
                                         EQUALS_SIGN);
                 break;
             case 1:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ] << 24 |
                                         alphabet[inBuff >>> 12 & 0x3f] << 16 |
                                         EQUALS_SIGN << 8                     |
                                         EQUALS_SIGN);
                 break;
             default:
                 // NOOP
                 break;
         }
     }
 
     private static void encode3to4LittleEndian(
             int inBuff, int numSigBytes, ByteBuf dest, int destOffset, byte[] alphabet) {
         // Packing bytes into an int to reduce bound and reference count checking.
         switch (numSigBytes) {
             case 3:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ]       |
                                         alphabet[inBuff >>> 12 & 0x3f] << 8  |
                                         alphabet[inBuff >>>  6 & 0x3f] << 16 |
                                         alphabet[inBuff        & 0x3f] << 24);
                 break;
             case 2:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ]       |
                                         alphabet[inBuff >>> 12 & 0x3f] << 8  |
                                         alphabet[inBuff >>> 6  & 0x3f] << 16 |
                                         EQUALS_SIGN << 24);
                 break;
             case 1:
                 dest.setInt(destOffset, alphabet[inBuff >>> 18       ]      |
                                         alphabet[inBuff >>> 12 & 0x3f] << 8 |
                                         EQUALS_SIGN << 16                   |
                                         EQUALS_SIGN << 24);
                 break;
             default:
                 // NOOP
                 break;
         }
     }
 
     public static ByteBuf decode(ByteBuf src) {
         return decode(src, Base64Dialect.STANDARD);
     }
 
     public static ByteBuf decode(ByteBuf src, Base64Dialect dialect) {
         ObjectUtil.checkNotNull(src, "src");
 
         ByteBuf dest = decode(src, src.readerIndex(), src.readableBytes(), dialect);
         src.readerIndex(src.writerIndex());
         return dest;
     }
 
     public static ByteBuf decode(
             ByteBuf src, int off, int len) {
         return decode(src, off, len, Base64Dialect.STANDARD);
     }
 
     public static ByteBuf decode(
             ByteBuf src, int off, int len, Base64Dialect dialect) {
         return decode(src, off, len, dialect, src.alloc());
     }
 
     public static ByteBuf decode(
             ByteBuf src, int off, int len, Base64Dialect dialect, ByteBufAllocator allocator) {
         ObjectUtil.checkNotNull(src, "src");
         ObjectUtil.checkNotNull(dialect, "dialect");
 
         // Using a ByteProcessor to reduce bound and reference count checking.
         return new Decoder().decode(src, off, len, allocator, dialect);
     }
 
     // package-private for testing
     static int decodedBufferSize(int len) {
         return len - (len >>> 2);
     }
 
     private static final class Decoder implements ByteProcessor {
         private final byte[] b4 = new byte[4];
         private int b4Posn;
         private byte[] decodabet;
         private int outBuffPosn;
         private ByteBuf dest;
 
         ByteBuf decode(ByteBuf src, int off, int len, ByteBufAllocator allocator, Base64Dialect dialect) {
             dest = allocator.buffer(decodedBufferSize(len)).order(src.order()); // Upper limit on size of output
 
             decodabet = decodabet(dialect);
             try {
                 src.forEachByte(off, len, this);
                 return dest.slice(0, outBuffPosn);
             } catch (Throwable cause) {
                 dest.release();
                 PlatformDependent.throwException(cause);
                 return null;
             }
         }
 
         @Override
         public boolean process(byte value) throws Exception {
             if (value > 0) {
                 byte sbiDecode = decodabet[value];
                 if (sbiDecode >= WHITE_SPACE_ENC) { // White space, Equals sign or better
                     if (sbiDecode >= EQUALS_SIGN_ENC) { // Equals sign or better
                         b4[b4Posn ++] = value;
                         if (b4Posn > 3) { // Quartet built
                             outBuffPosn += decode4to3(b4, dest, outBuffPosn, decodabet);
                             b4Posn = 0;
 
                             // If that was the equals sign, break out of 'for' loop
                             return value != EQUALS_SIGN;
                         }
                     }
                     return true;
                 }
             }
             throw new IllegalArgumentException(
                     "invalid Base64 input character: " + (short) (value & 0xFF) + " (decimal)");
         }
 
         private static int decode4to3(byte[] src, ByteBuf dest, int destOffset, byte[] decodabet) {
             final byte src0 = src[0];
             final byte src1 = src[1];
             final byte src2 = src[2];
             final int decodedValue;
             if (src2 == EQUALS_SIGN) {
                 // Example: Dk==
                 try {
                     decodedValue = (decodabet[src0] & 0xff) << 2 | (decodabet[src1] & 0xff) >>> 4;
                 } catch (IndexOutOfBoundsException ignored) {
                     throw new IllegalArgumentException("not encoded in Base64");
                 }
                 dest.setByte(destOffset, decodedValue);
                 return 1;
             }
 
             final byte src3 = src[3];
             if (src3 == EQUALS_SIGN) {
                 // Example: DkL=
                 final byte b1 = decodabet[src1];
                 // Packing bytes into a short to reduce bound and reference count checking.
                 try {
                     if (dest.order() == ByteOrder.BIG_ENDIAN) {
                         // The decodabet bytes are meant to straddle byte boundaries and so we must carefully mask out
                         // the bits we care about.
                         decodedValue = ((decodabet[src0] & 0x3f) << 2 | (b1 & 0xf0) >> 4) << 8 |
                                         (b1 & 0xf) << 4 | (decodabet[src2] & 0xfc) >>> 2;
                     } else {
                         // This is just a simple byte swap of the operation above.
                         decodedValue = (decodabet[src0] & 0x3f) << 2 | (b1 & 0xf0) >> 4 |
                                       ((b1 & 0xf) << 4 | (decodabet[src2] & 0xfc) >>> 2) << 8;
                     }
                 } catch (IndexOutOfBoundsException ignored) {
                     throw new IllegalArgumentException("not encoded in Base64");
                 }
                 dest.setShort(destOffset, decodedValue);
                 return 2;
             }
 
             // Example: DkLE
             try {
                 if (dest.order() == ByteOrder.BIG_ENDIAN) {
                     decodedValue = (decodabet[src0] & 0x3f) << 18 |
                                    (decodabet[src1] & 0xff) << 12 |
                                    (decodabet[src2] & 0xff) << 6 |
                                     decodabet[src3] & 0xff;
                 } else {
                     final byte b1 = decodabet[src1];
                     final byte b2 = decodabet[src2];
                     // The goal is to byte swap the BIG_ENDIAN case above. There are 2 interesting things to consider:
                     // 1. We are byte swapping a 3 byte data type. The left and the right byte switch, but the middle
                     //    remains the same.
                     // 2. The contents straddles byte boundaries. This means bytes will be pulled apart during the byte
                     //    swapping process.
                     decodedValue = (decodabet[src0] & 0x3f) << 2 |
                                    // The bottom half of b1 remains in the middle.
                                    (b1 & 0xf) << 12 |
                                    // The top half of b1 are the least significant bits after the swap.
                                    (b1 & 0xf0) >>> 4 |
                                    // The bottom 2 bits of b2 will be the most significant bits after the swap.
                                    (b2 & 0x3) << 22 |
                                    // The remaining 6 bits of b2 remain in the middle.
                                    (b2 & 0xfc) << 6 |
                                    (decodabet[src3] & 0xff) << 16;
                 }
             } catch (IndexOutOfBoundsException ignored) {
                 throw new IllegalArgumentException("not encoded in Base64");
             }
             dest.setMedium(destOffset, decodedValue);
             return 3;
         }
     }
 
     private Base64() {
         // Unused
     }
 }