import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

/**
 * Reads a data set from a file. The file must have the format numberOfValues
 * value1 value2 . . .
 * 
 * Copyright: Horstmann, Big Java 3e, Chapter 11
 */
public class DataSetReader {
	
	/**
	 * Reads a data set.
	 * 
	 * @param filename
	 *            the name of the file holding the data
	 * @return the data in the file
	 */
	public double[] readFile(String filename) throws IOException,
			BadDataException {
		FileReader reader = new FileReader(filename);
		try {
			Scanner in = new Scanner(reader);
			readData(in);
		} finally {
			reader.close();
		}
		return data;
	}

	/**
	 * Reads all data.
	 * 
	 * @param in
	 *            the scanner that scans the data
	 */
	private void readData(Scanner in) throws BadDataException {
		if (!in.hasNextInt()) {
			throw new BadDataException("Length expected");
		}
		int numberOfValues = in.nextInt();
		data = new double[numberOfValues];

		for (int i = 0; i < numberOfValues; i++) {
			readValue(in, i);
		}

		if (in.hasNext()) {
			throw new BadDataException("End of file expected");
		}
	}

	/**
	 * Reads one data value.
	 * 
	 * @param in
	 *            the scanner that scans the data
	 * @param i
	 *            the position of the value to read
	 */
	private void readValue(Scanner in, int i) throws BadDataException {
		if (!in.hasNextDouble()) {
			throw new BadDataException("Data value expected");
		}
		data[i] = in.nextDouble();
	}

	private double[] data;
}