//CS1501 Fall 2006 Assignment 1: Anagrams

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

public class MakeString
{
	private final String FILENAME = "letters";
	private final int NUMLETTERS = 26;
	//percentage of occurrences of each letter
	private final double E = .1174;
	private final double I = .0865;
	private final double S = .0815;
	private final double A = .0797;
	private final double R = .0744;
	private final double N = .0742;
	private final double T = .0676;
	private final double O = .0594;
	private final double L = .0535;
	private final double C = .0413;
	private final double D = .0381;
	private final double U = .0322;
	private final double G = .0284;
	private final double P = .0277;
	private final double M = .0270;
	private final double H = .0215;
	private final double B = .0203;
	private final double Y = .0165;
	private final double F = .0135;
	private final double V = .0109;
	private final double K = .0088;
	private final double W = .0085;
	private final double Z = .0045;
	private final double X = .0029;
	private final double J = .0020;
	private final double Q = .0019;
	//put the percentages into an array
	private final double freq[] = {E,I,S,A,R,N,T,O,L,C,D,U,G,P,M,H,B,Y,F,V,K,W,Z,X,J,Q};
	//a parallel array that holds the letters themselves
	private final String letters[] = {"e","i","s","a","r","n","t","o","l","c",
			"d","u","g","p","m","h","b","y","f","v","k","w","z","x","j","q"};	
	//yet another parallel array that will hold the sums of the probabilities, i.e., 
	//the Upper Bound of the random number that corresponds to a particular letter,
	//e.g., UB[1] = E+I, freq[1] = I, and letter[1] = "i"
	private double UB[];
	
	//set up the upper bound array for the randomLetter function
	public MakeString(){ 
		UB = new double[NUMLETTERS]; //initialize array
		UB[0] = E;
		for (int index = 1; index < NUMLETTERS; index++){
			UB[index] = UB[index - 1] + freq[index];
		}
	}//end constructor

	//returns a random letter according to the probabilities provided in assignment sheet
	public String randomLetter(){
		Random generator = new Random();
		double rnum = generator.nextDouble(); //a random value in the interval [0,1)
		if (rnum < UB[0]) //if rnum is less than E = .1174
			return letters[0]; //return the letter "e"
		for (int index = 0; index < NUMLETTERS; index++){ //for the rest of the letters
			//check that rnum is within the appropriate bounds
			if (rnum >= UB[index] && rnum < UB[index+1]) 
				return letters[index+1];
		}
		return "?"; //if a random letter was not returned (should never happen)
	}//end randomLetter

	//creates a random string of length k
	public void generate(int k)
	{
		try {
        	BufferedWriter out = new BufferedWriter(new FileWriter(FILENAME));
			//out.write(k + "\n");
			//for each slot in the board, generate a random letter and print it out
			for (int i = 1; i <= k; i++){
				String rletter = randomLetter();
	    	    out.write(rletter);
	        }
	        out.close();
    	} catch (IOException e) {
    		System.out.println(e);
    	}
	}//end generate
	

	public static void main (String [] args)
	{
		MakeString ms = new MakeString();
		System.out.println("Please enter the length of the string you would like to generate.");
		System.out.print(">> ");
		BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
		try
		{
			String strSize = keyboard.readLine();
			int size = Integer.parseInt(strSize); //convert user input to an integer
			ms.generate(size); //use input to generate string of that length
			System.out.println("Your string has been written in the file \"" + ms.FILENAME + "\"");
		}
		catch (Exception e)
		{
			System.out.println(e);
		}
	}
}