// Template provided by Paul Amer for use in Project 3
// of CISC451/561: Data Compression for Multimedia
// This applet opens a text window and echos the contents
// of an ASCII file in that window.  Students must complete
// this template with their code for decoding amerRLE encoded
// files.

// Modified by Ezra Kissel and Dhaval Mehta
// Date: 4/20/03
// Project 3 - CISC451/651

// Included modified DecompressFile() method to display
// a decompressed file pointed to by FileToBeEchoed 
// in an applet window.

import java.net.*;
import java.io.*;
import java.applet.Applet;
import java.awt.*;  // Abstract Windowing Toolkit package is imported.

public class decode_applet extends Applet {

   // declare global applet variables
   private String filename;
   private TextArea outputArea;
   private DataInputStream inFile;

   // set length of the compressed file header
   static final int HEADER_LENGTH = 7;
   // make version equal to 1
   static final char VERSION = '1';
   // define alphabet size
   static final int ALPH_SIZE = 128;
   
   // define amerRLE header
   static final char[] amerRLE = {'a', 'm', 'e', 'r', 'R', 'L', 'E'};

   // init invoked automatically by browser.
   public void init () 
      {
      outputArea = new TextArea(15, 65);  // rows, columns
      outputArea.setEditable(false);      // make applet read-only
      outputArea.setFont(new Font("Courier", Font.PLAIN, 12)); // fixed-width font
      add(outputArea);          // show empty text area in applet 

      try {
          // file to be decoded should be a param in the html file 
          // if param doesn't exist the html file, give error message
          filename = getParameter("FileToBeEchoed");  
          if (filename == null)
              {
              outputArea.append("ERROR: parameter FileToBeEchoed missing in html file");
              return;
              }

          // create http connection to later get compressed file
          URL ourURLConnection = new URL(filename);
          // open the stream to be used for downloading the compressed file

          inFile = new DataInputStream(ourURLConnection.openStream()); 
	  DecompressFile();

          inFile.close();

          }
      catch (Exception e) { e.printStackTrace(); } 
      }

      // Method DecompressFile()
      // decompresses the file, outputs decompressed characters to output TextArea
      // return values : 1 if successful, 0 if an error was encountered
      // arguments     : none
      private int DecompressFile() {
        try {
            
	    // store a character of the input
            char charr;
	    // counters and temp holders
            int cur, prev = -1, count = 0, aLen = 0, replicator;
	    // store the header signature
            byte[] signature = new byte[HEADER_LENGTH];
	    // store the alphabet size
            byte[] alphaLen = new byte[3];
	    // store the alphabet
            byte[] alphabet = new byte[128];

	    // read in signature, validate
            inFile.read(signature);
            for(int i = 0; i < HEADER_LENGTH; ++i)
                if(signature[i] != amerRLE[i]) {
		    outputArea.append("\nERROR: Wrong signature.");
		    return 0;	
	    	}	

            // check for correct version   
            if(inFile.read() != VERSION)
		outputArea.append("\nERROR: Wrong version.");

            // find out the length of the alphabet
            inFile.read(alphaLen);
            aLen = Integer.parseInt(new String(alphaLen));
            
            // read the alphabet in a byte array
            for(int i = 0; i < aLen; ++i) {
                byte temp = (byte)inFile.read();
	                   alphabet[(int)temp] = temp;
            }

            // do the decompression
            while((replicator = inFile.read()) != -1) {
                // check if the replicator is in [1, 9]
                if((replicator-48) < 1 || (replicator-48) > 9) {
		    outputArea.append("\nERROR:Replicator not in 1-9.");
		    return 0;
		}
		
                // check if the character is in the alphabet
                charr = (char)inFile.read();
                if(charr != alphabet[(int)charr]) {
		    outputArea.append("\nERROR: '" + charr + "' not in the alphabet.");
		    return 0;
		}

                // if all is well, write to file  
                for(int i = 0; i < (replicator-48); ++i)
                    outputArea.append(String.valueOf(charr)); 
           }
        }
        catch (IOException e) {
            System.out.println("Exception raised: " + e);
            System.exit(-1);
        }
	return 1;
    }      
}