source: branches/0.17.x/abcl/src/org/armedbear/lisp/java/DialogPromptStream.java

package org.armedbear.lisp.java;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
import java.io.StringWriter;

import org.armedbear.lisp.Stream;

/**
 * A bidirectional stream that captures input from a modal dialog. The dialog reports a label (prompt line)
 * which shows to the user everything that has been printed to the stream up to the moment when the dialog
 * became visible. It is usable as a drop-in replacement for e.g. *debug-io*.<br />
 * This is an abstract class that does not depend on any GUI library. Subclasses are expected to provide
 * the actual code to show the dialog and read input from the user.
 * @author Alessio Stalla
 *
 */
public abstract class DialogPromptStream extends Stream {

  private StringWriter writtenSoFar = new StringWriter();
  private Reader reader = new Reader() {

    private StringReader stringReader = null;
    private int inputSize = 0;
    
    public void close() throws IOException {
      closeDialog();
    }

    public int read(char[] cbuf, int off, int len) throws IOException {
      if(stringReader == null) {
        writtenSoFar.flush();
        String promptText = writtenSoFar.toString();
        writtenSoFar.getBuffer().delete(0, Integer.MAX_VALUE);
        String inputStr = readInputFromModalDialog(promptText) + System.getProperty("line.separator", "\n");
        stringReader = new StringReader(inputStr);
        inputSize = inputStr.length();
      }
      int read = stringReader.read(cbuf, off, len);
      if(read != -1) {
        inputSize -= read;
      }
      if(read == -1 || inputSize == 0) {
        inputSize = 0;
        stringReader = null;
      }
      return read;
    }
    
  };

  /**
   * Inits this stream. Should be called by subclasses' constructors.
   */
  protected DialogPromptStream() {
    initAsCharacterOutputStream(writtenSoFar);
    initAsCharacterInputStream(reader);
  }
  
  /**
   * Closes the dialog when this stream is closed, aborting the read operation.
   */
  protected abstract void closeDialog();
  
  /**
   * Shows the dialog and blocks the calling thread until the user has closed the dialog.
   * @param promptText the text to be shown to the user (the prompt).
   * @return a string holding input from the user.
   */
  protected abstract String readInputFromModalDialog(String promptText); 
  
}