package org.herac.tuxguitar.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;

import org.apache.log4j.Logger;

public class Base64Decoder {

  private static final int BUFFER_SIZE = 1024;

  private static int check(int ch) {
    if ((ch >= 'A') && (ch <= 'Z')) {
      return ch - 'A';
    } else if ((ch >= 'a') && (ch <= 'z')) {
      return ch - 'a' + 26;
    } else if ((ch >= '0') && (ch <= '9')) {
      return ch - '0' + 52;
    } else {
      switch (ch) {
      case '=':
        return 65;
      case '+':
        return 62;
      case '/':
        return 63;
      default:
        return -1;
      }
    }
  }

  public static byte[] decode(byte[] bytes) {
    try {
      ByteArrayInputStream in = new ByteArrayInputStream(bytes);
      ByteArrayOutputStream out = new ByteArrayOutputStream();

      byte buffer[] = new byte[BUFFER_SIZE];
      byte chunk[] = new byte[4];
      int got = -1;
      int ready = 0;

      fill: while ((got = in.read(buffer)) > 0) {
        int skiped = 0;

        while (skiped < got) {

          while (ready < 4) {
            if (skiped >= got) {
              continue fill;
            }
            int ch = check(buffer[skiped++]);
            if (ch >= 0) {
              chunk[ready++] = (byte) ch;
            }
          }

          if (chunk[2] == 65) {
            out.write(get1(chunk, 0));
            return out.toByteArray();
          } else if (chunk[3] == 65) {
            out.write(get1(chunk, 0));
            out.write(get2(chunk, 0));
            return out.toByteArray();
          } else {
            out.write(get1(chunk, 0));
            out.write(get2(chunk, 0));
            out.write(get3(chunk, 0));
          }
          ready = 0;
        }
      }
      if (ready == 0) {
        out.flush();
        return out.toByteArray();
      }

    } catch (Throwable throwable) {
      LOG.error(throwable);
    }

    return bytes;
  }

  /** The Logger for this class. */
  public static final transient Logger LOG = Logger
      .getLogger(Base64Decoder.class);

  private static int get1(byte buf[], int off) {
    return ((buf[off] & 0x3f) << 2) | ((buf[off + 1] & 0x30) >>> 4);
  }

  private static int get2(byte buf[], int off) {
    return ((buf[off + 1] & 0x0f) << 4) | ((buf[off + 2] & 0x3c) >>> 2);
  }

  private static int get3(byte buf[], int off) {
    return ((buf[off + 2] & 0x03) << 6) | (buf[off + 3] & 0x3f);
  }
}