/**
 * File: FFTSpectrum.java
 * Author: Brian Borowski
 * Date created: October 2000
 * Date last modified: July 1, 2011
 */
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.Rectangle2D;

import javax.swing.JPanel;

public class FFTSpectrum extends JPanel {
    public static final int MAX_HARMONICS = 64;

    private static final long serialVersionUID = 1L;
    private double[] data = null;
    private double min, max;
    private String errStr = null;
    private final Color maroon = new Color(113, 0, 17);
    private final Font font = new Font("Monospaced", Font.PLAIN, 16);

    public FFTSpectrum() {
        setBackground(Color.black);
    }

    public Dimension getPreferredSize() {
        return new Dimension(250, 100);
    }

    public void plot(final double[] ar, final double[] ai, final int numOfPoints) {
        errStr = null;
        if (numOfPoints > MAX_HARMONICS) {
            errStr = "Too many harmonics to display.";
        } else if (numOfPoints == 0) {
            errStr = "All harmonics are filtered out.";
        } else {
            data = new double[numOfPoints];
            double realVal = ar[1],
                   imagVal = ai[1];
            max = min = data[0] = Math.sqrt(realVal * realVal +
                                            imagVal * imagVal);
            for (int i = 1; i < numOfPoints; ++i) {
                realVal = ar[i + 1];
                imagVal = ai[i + 1];
                data[i] = Math.sqrt(realVal * realVal + imagVal * imagVal);
                if (data[i] > max) {
                    max = data[i];
                }
                if (data[i] < min) {
                    min = data[i];
                }
            }
        }
        repaint();
    }

    private int scalePoint(final double point) {
        final int heightOfMax = (int)(0.99 * this.getSize().height);
        return (int)(point / max * heightOfMax);
    }

    protected void paintComponent(final Graphics g) {
        final Graphics2D g2d = (Graphics2D)g;

        g2d.setColor(Color.black);
        final int width =  this.getSize().width,
                  height = this.getSize().height;
        g2d.fillRect(0, 0, width, height);

        if (errStr != null) {
            final int length = getFontMetrics(font).stringWidth(errStr);
            g2d.setColor(Color.white);
            g2d.setFont(font);
            g2d.drawString(errStr, (width - length) / 2, height / 2);
        } else if (data != null) {
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                                 RenderingHints.VALUE_ANTIALIAS_ON);

            final int barWidth = width / data.length;
            final int offset = (width - barWidth * data.length) / 2;

            for (int i = 0; i < data.length; ++i) {
                final int barHeight = scalePoint(data[i]),
                                  x = i * barWidth + 1 + offset,
                                  y = height - barHeight;
                final GradientPaint redToMaroon =
                    new GradientPaint(x, y, Color.red, x, height, maroon);
                g2d.setPaint(redToMaroon);
                g2d.fill(new Rectangle2D.Double(x, y, barWidth - 1, height));
            }
        }
    }
}