import java.io.IOException;
import java.io.PrintWriter;


public class Hotplate {

	/**This program calculates the heat distribution on a hotplate with boundary conditions given.
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException
	{
		// TODO Auto-generated method stub
		//initilize numbers of rows and columns
		final int rows = 20;
		final int columns = 20;
		//set initial conditions
		final double topTemperature = 100;
		final double bottomTemperature = 100;
		final double leftTemperature = 0;
		final double rightTemperature = 0;
		//create hotplate matrix
		double[][] hotplate = new double[rows][columns];
		//iterate through top and bottom rows and make equal to top and bottom initial conditions
		for(int i=1; i<rows-1; i++)
		{
			hotplate[i][0] = topTemperature;
			hotplate[i][rows-1] = bottomTemperature;
		}
		//iterate through left and right columns and make equal to left and right inital conditions
		for(int j=0; j<columns; j++)
		{
			hotplate[0][j] = leftTemperature;
			hotplate[columns-1][j] = rightTemperature;
		}
		//calculate the temperature distribution and then print the matrix the the screen
		//then print the matrix to a CSV file
		calculateTemperatureDistribution(rows,columns,hotplate);
		printToScreen(rows,columns,hotplate);
		printToFile(rows,columns,hotplate);
	}
	/**this method calculates the internal temperature distribution
	 * @param int rows, int columns, double[][] hotplate
	 * @return double[][]
	 */
	public static double[][] calculateTemperatureDistribution (int rows, int columns, double[][] hotplate)
	{
		//initialize tolerance value
		final double tolerance = .1;
		//give largestDifference any value greater than tolerance to start the while loop at least once
		double largestDifference = 100;
		//while loop will update calculations for the whole matrix once, find the greatest difference,
		//then if the greatest difference of the whole matrix update was less than .1 then terminate loop
		while(largestDifference > tolerance)
		{
			//after while loop starts make reset largest difference to 0
			largestDifference = 0;
			//iterate through rows excluding the first and last
			for (int i=1; i<rows-1; i++)
			{
				//iterate through columns excluding the first and last
				for(int j=1; j<columns-1; j++)
				{
					//save the old temperature value and calculate the new temperature value so that they may be compared
					double oldTemperatureValue = hotplate[i][j];
					//new temperature equals the average of the temperatures arround it
					double newTemperatureValue = (hotplate[i-1][j] + hotplate[i+1][j] + hotplate[i][j-1] + hotplate[i][j+1])/4;
					//update the hotplate matrix with the new value
					hotplate[i][j] = newTemperatureValue;
					//find the maximum absolute differences of the new temperature - the old temperature
					//store this maximum as largestDifference for while loop to compare to tolerance
					if(Math.abs(newTemperatureValue - oldTemperatureValue) > largestDifference)
					{
						largestDifference = Math.abs(newTemperatureValue - oldTemperatureValue);
					}
				}
			}
			//print out largest difference for user to see
			System.out.println(largestDifference);
		}
		//return the new hotplate data
		return hotplate;
	}
	/**this method prints the hotplate matrix for the user
	 * @param int rows, int columns, double[][] hotplate
	 */
	public static void printToScreen(int rows, int columns, double[][] hotplate)
	{
		//iterate through every row and column and print out each value
		for(int i=0; i<rows; i++)
      	{
			//start each row with [ to make look nice
			System.out.print("[");
      		for(int j=0; j<columns; j++)
      		{
      			//format each value so that they will line up
      			System.out.printf("%6.1f", hotplate[i][j]);
      		}
      		//end each row with ] to make look nice
      		System.out.println("]");
      	}
	}
	/**this method prints the hotplate matrix to a CSV file named output
	 * @param int rows, int columns, double[][] hotplate
	 * @throws IOException 
	 */
	public static void printToFile (int rows, int columns, double[][] hotplate) throws IOException
	{
		//make a new printWriter to write to output.csv
		PrintWriter out = new PrintWriter("output.csv");
		//iterate through every row and column to print each value to file
      	for(int i=0; i<rows; i++)
      	{
      		for(int j=0; j<columns; j++)
      		{
      			//print each value and add a , to the end of each for excel to read
      			out.print(hotplate[i][j]+",");
      		}
      		//make each row on a new line
      		out.println();
      	}
      	//close file once finished
      	out.close();
	}
}