// This program draws a scatter plot of exam midterm
// scores and exam score predictions.

import java.awt.*;
import java.util.*;
import java.io.*;

public class Scatterplot {
   public static final int WIDTH = 2100;
   public static final int HEIGHT = 1100;
   public static final int GUTTER = 200;
   
   public static final int Y_AXIS = HEIGHT + GUTTER;
   public static final int X_AXIS = GUTTER;
   
   public static final int TICK_SIZE = 10;
      
   public static final Font LABEL_FONT = new Font("monospace", Font.BOLD, 24);   
      
   public static void main(String[] args) throws FileNotFoundException {
      DrawingPanel panel = new DrawingPanel(WIDTH + 2 * GUTTER, HEIGHT + 2 * GUTTER);
      Graphics pen = panel.getGraphics();
      drawScatterPlot(pen);
   }
      
   // Draws a scatter plot of exam scores vs predicted scores
   public static void drawScatterPlot(Graphics pen) throws FileNotFoundException {
      drawAxes(pen);
      drawXTicks(pen, 10, 10);
      drawYTicks(pen, 20, 5);
      
      drawPoints(pen);
   }
   
   // Draw all the points that are in the data file on the graph
   public static void drawPoints(Graphics pen) throws FileNotFoundException {
      File file = new File("18wi-mid-scores.txt");
      Scanner input = new Scanner(file);
      
      // Scanner input = new Scanner(new File("18wi-mid-scores.txt"));
      while (input.hasNextLine()) {
         String line = input.nextLine();
         Scanner lineScan = new Scanner(line);
         
         // if lineScan.hasNextInt() wouldn't be a bad check.
         // but we know that every line in the input file has
         // at least an actual score
         int actual = lineScan.nextInt();
         
         if (lineScan.hasNextDouble()) {
            double prediction = lineScan.nextDouble();
            drawMark(pen, actual, prediction);
         } else {
            System.out.println("Error, no prediction on line: " + line);
         }
      }
   }
   

   // Uses the given Graphics to draw a point at the given actual/predicted
   // location. Assumes max score of 100 for graphing
   public static void drawMark(Graphics pen, int actual, double predicted) {
      int max = 100;
      int size = 8;
      int centering = size / 2;
      
      pen.setColor(Color.RED);
      int xOffset = (int) Math.round( (1.0 * actual / max) * WIDTH - centering );
      int yHeight = (int) Math.round( (predicted / max) * HEIGHT + centering );
      pen.fillOval(X_AXIS + xOffset, Y_AXIS - yHeight, size, size);
   }
      
   // Use the given Graphics to draw (marks + 1) tick marks, each mark representing
   // a jump of stepSize units on the x axis.
   public static void drawXTicks(Graphics pen, int marks, int stepSize) {
      int textSetback = 70;
      int textHeight = 18; // somehow related to Font size :(
      
      pen.setFont(LABEL_FONT);
      for (int i = 0; i <= marks; i++) {
         String label = "" + i * stepSize;
         int yHeight = i * (HEIGHT / marks);
         int y = Y_AXIS - yHeight;
         pen.drawString(label, X_AXIS - textSetback, y + textHeight / 2);
         pen.drawLine(X_AXIS, y, X_AXIS - TICK_SIZE, y);
      }
   }

   // Use the given Graphics to draw (marks + 1) tick marks, each mark representing
   // a jump of stepSize units on the y axis.
   public static void drawYTicks(Graphics pen, int marks, int stepSize) {
      int textSetback = 50;
      int textCharWidth = 12; // somehow related to Font size :(
      
      pen.setFont(LABEL_FONT);
      for (int i = 0; i <= marks; i++) {
         String label = "" + i * stepSize;
         int xOffset = i * (WIDTH / marks);
         int x = X_AXIS + xOffset;
         int labelX = x - label.length() * textCharWidth / 2;
         pen.drawString(label, labelX, Y_AXIS + textSetback);
         pen.drawLine(x, Y_AXIS, x, Y_AXIS + TICK_SIZE);
      }
   }

   // Use the given Graphics to draw the axes on the graph
   public static void drawAxes(Graphics pen) {
      pen.setColor(Color.BLACK);
      pen.drawLine(X_AXIS, Y_AXIS, X_AXIS, GUTTER);
      pen.drawLine(X_AXIS, Y_AXIS, WIDTH + GUTTER, Y_AXIS);
   }
}