import java.awt.*;
import java.applet.*;

public class AliasingDemo extends Applet implements Runnable {

  Thread runner;
  boolean isStandalone = false;
  BorderLayout borderLayout1 = new BorderLayout();
  Panel pnlDisplay = new Panel();
  Panel pnlControls = new Panel();
  BorderLayout borderLayout2 = new BorderLayout();
  FlowLayout flowLayout1 = new FlowLayout();
  Label lblFrequency = new Label();
  TextField tfFrequency = new TextField("7000", 5);
  Label lblFreqUnit = new Label();
  Button btnPlot = new Button();
  AliasPlot ap = new AliasPlot();
  float rate = 8000.0f;
  int plotPts = 500;
  float sampleLength = 0.004f; // 4 ms sample length
  float dt = sampleLength / plotPts;
  float pi = (float)Math.PI;
  float f;
  Checkbox chbSignal = new Checkbox();
  Checkbox chbSamples = new Checkbox();
  Checkbox chbAlias = new Checkbox();
  Checkbox chbGrid = new Checkbox();

  //Get a parameter value
  public String getParameter(String key, String def) {
    return isStandalone ? System.getProperty(key, def) :
      (getParameter(key) != null ? getParameter(key) : def);
  }

  //Construct the applet
  public AliasingDemo() {
  }

  public void start() {
    if (runner == null) {
      runner = new Thread(this);
      runner.start();
    }
  }

  public void stop() {
    if (runner != null) {
      runner.stop();
      runner = null;
    }
  }

  public void run() {
  }

  //Initialize the applet
  public void init() {
    try { jbInit(); } catch (Exception e) { e.printStackTrace(); }
  }

  //Component initialization
  public void jbInit() throws Exception{
    Font font = new Font("Dialog", 0, 11);
    lblFrequency.setFont(font);
    lblFrequency.setAlignment(2);
    lblFrequency.setText("Input frequency:");
    tfFrequency.setFont(font);
    lblFreqUnit.setFont(font);
    lblFreqUnit.setText("Hz");
    btnPlot.setFont(font);
    btnPlot.setLabel("Plot");
    chbSamples.setFont(font);
    chbSamples.setLabel("Sample points");
    chbSignal.setState(true);
    chbAlias.setFont(font);
    chbAlias.setLabel("Alias frequency");
    chbGrid.setFont(font);
    chbGrid.setLabel("Grid");
    chbSignal.setFont(font);
    chbSignal.setLabel("Input signal");
    pnlControls.setLayout(flowLayout1);
    pnlDisplay.setLayout(borderLayout2);
    this.setLayout(borderLayout1);
    this.add("Center", pnlDisplay);
    pnlDisplay.add("Center", ap);
    this.add("South", pnlControls);
    pnlControls.add(lblFrequency);
    pnlControls.add(tfFrequency);
    pnlControls.add(lblFreqUnit);
    pnlControls.add(btnPlot);
    pnlControls.add(chbSignal);
    pnlControls.add(chbGrid);
    pnlControls.add(chbSamples);
    pnlControls.add(chbAlias);
  }

  //Get Applet information
  public String getAppletInfo() {
    return "Applet Information";
  }

  //Get parameter info
  public String[][] getParameterInfo() {
    return null;
  }

  public boolean action(Event evt, Object arg) {

    if (evt.target == btnPlot) {
      float[] signal = new float[plotPts];
      float theta, phi;
      f = Float.valueOf(tfFrequency.getText()).floatValue();
      theta = 2.0f*pi*f*dt;
      for (int p = 0; p < plotPts; p++)
        signal[p] = (float)Math.sin(p*theta);
      ap.setYmax(1.2f);
      ap.setSignalData(signal);
      int nSamples = Math.round(rate*sampleLength);
      float[] samples = new float[nSamples];
      phi = 2.0f*pi*f/rate;
      for (int i = 0; i < nSamples; i++)
        samples[i] = (float)Math.sin(i*phi);
      ap.setSamples(samples);
      float fa;
      boolean aliased = f > rate/2;
      chbAlias.hide();
      if (aliased) {
        chbAlias.show();
        while (f > rate) f -= rate;  // shift frequency down to sampling rate band
        int sign = 1;
        fa = f;
        if (f > rate/2) {
          fa = rate - f;  // alias frequency
          sign = -1;
        }
        theta = 2.0f*pi*fa*dt;
        float[] alias = new float[plotPts];
        for (int p = 0; p < plotPts; p++)
          alias[p] = sign * (float)Math.sin(p*theta);
        ap.setAliasData(alias);
      }
      ap.setSignalVisibility(chbSignal.getState());
      ap.setAliasVisibility(aliased && chbAlias.getState());
      ap.setSamplesVisibility(chbSamples.getState());
      ap.repaint();
      return true;
    }

    if (evt.target == chbSignal) {
      ap.setSignalVisibility(chbSignal.getState());
      ap.repaint();
      return true;
    }

    if (evt.target == chbSamples) {
      ap.setSamplesVisibility(chbSamples.getState());
      ap.repaint();
      return true;
    }

    if (evt.target == chbAlias) {
      ap.setAliasVisibility(chbAlias.getState());
      ap.repaint();
      return true;
    }

    if (evt.target == chbGrid) {
      ap.setGridVisibility(chbGrid.getState());
      ap.repaint();
      return true;
    }
    // otherwise ...
    return false;
  }

}