package at.gv.egiz.asic.impl;

import java.io.IOException;
import java.io.InputStream;

/**
 * Created by afitzek on 6/15/16.
 */
public class ZipCommentReaderStream extends InputStream {

  private final InputStream inputStream;

  private final int[] tempBuffer = new int[22];

  private int[] commentBuffer = null;

  private int commentBufferContentLen = 0;
  private int commentBufferContentOff = 0;

  private int tempBufferContentLen = 0;
  private int tempBufferContentOff = 0;

  private String fileComment = null;

  private static final byte[] directoryRecord = new byte[] { (byte) 0x50, (byte) 0x4b, 0x05, 0x06 };

  public ZipCommentReaderStream(InputStream inputStream) {
    this.inputStream = inputStream;
  }

  private int readIntIntoBuffer() throws IOException {
    final int tValue = this.inputStream.read();

    if (this.tempBuffer.length <= tempBufferContentOff) {
      throw new IOException("Temp Buffer is out of space! @ " + tempBufferContentOff);
    }

    this.tempBuffer[tempBufferContentOff] = tValue;
    tempBufferContentOff++;
    tempBufferContentLen++;

    return tValue;
  }

  private int readIntIntoCommentBuffer() throws IOException {
    final int tValue = this.inputStream.read();

    if (this.commentBuffer.length <= commentBufferContentOff) {
      throw new IOException("Comment Buffer is out of space! @ " + commentBufferContentOff);
    }

    this.commentBuffer[commentBufferContentOff] = tValue;
    commentBufferContentOff++;
    commentBufferContentLen++;

    return tValue;
  }

  private void checkMagicBytes() throws IOException {
    boolean foundMagic = true;
    tempBufferContentOff = 0;
    tempBufferContentLen = 0;
    for (int i = 1; i < directoryRecord.length; i++) {
      final int tValue = readIntIntoBuffer();
      if (tValue != directoryRecord[i]) {
        foundMagic = false;
        break;
      }
      if (tValue < 0) {
        // Found EOF
        return;
      }
    }

    if (foundMagic) {
      // read input stream until comment length
      for (int i = 0; i < 16; i++) {
        final int tValue = readIntIntoBuffer();

        if (tValue < 0) {
          // Found EOF
          return;
        }
      }

      final int commentlengthHigh = readIntIntoBuffer();

      if (commentlengthHigh < 0) {
        // Found EOF
        return;
      }

      final int commentlengthLow = readIntIntoBuffer();

      if (commentlengthLow < 0) {
        // Found EOF
        return;
      }

      final int commentLength = commentlengthLow * 255 + commentlengthHigh;

      if (commentLength == 0) {
        return;
      }

      this.commentBuffer = new int[commentLength];

      commentBufferContentOff = 0;
      commentBufferContentLen = 0;

      // read comment buffer string
      for (int i = 0; i < commentLength; i++) {
        final int tValue = readIntIntoCommentBuffer();

        if (tValue < 0) {
          // Found EOF
          return;
        }
      }

      final byte[] stringBuffer = new byte[this.commentBuffer.length];

      for (int i = 0; i < stringBuffer.length; i++) {
        stringBuffer[i] = (byte) this.commentBuffer[i];
      }

      this.fileComment = new String(stringBuffer);
    }
  }

  @Override
  public int read() throws IOException {
    int value = -1;
    if (tempBufferContentLen > 0) {
      value = this.tempBuffer[tempBufferContentOff];
      tempBufferContentOff++;

      // reset temp buffer
      if (tempBufferContentOff >= tempBufferContentLen) {
        tempBufferContentOff = 0;
        tempBufferContentLen = 0;
      }

      return value;
    }

    if (this.commentBuffer != null) {
      value = this.commentBuffer[commentBufferContentOff];

      commentBufferContentOff++;

      // reset comment buffer
      if (commentBufferContentOff >= commentBufferContentLen) {
        commentBufferContentOff = 0;
        commentBufferContentLen = 0;
        this.commentBuffer = null;
      }

      return value;
    }

    value = this.inputStream.read();

    if (value == directoryRecord[0] && this.fileComment == null) {
      // might have found start of magic bytes
      checkMagicBytes();
      // reset buffer offsets
      tempBufferContentOff = 0;
      commentBufferContentOff = 0;
    }

    return value;
  }

  public String getFileComment() {
    return this.fileComment;
  }
}