// CSE 143, Winter 2009, Marty Stepp
// Homework 5 (Grammar Solver)
//
// Instructor-provided testing program.
// Original version by Stuart Reges; modified by Marty Stepp

import java.io.*;     // for File, FileNotFoundException
import java.util.*;   // for Scanner, List, Set, Collections

/**
 * GrammarMain contains a client program that prompts a user for the name of a
 * grammar file and then gives the user the opportunity to generate random
 * versions of various elements of the grammar.
 */
public class GrammarMain {
    public static void main(String[] args) throws FileNotFoundException {
        System.out.println("Welcome to the CSE 143 random sentence generator!");
        System.out.println();

        // open grammar file
        System.out.print("What is the name of the grammar file? ");
        Scanner console = new Scanner(System.in);
        String fileName = console.nextLine();
        List<String> lines = readLines(fileName);

        // construct grammar solver and begin user input loop
        GrammarSolver solver = new GrammarSolver(Collections.unmodifiableList(lines));
        
        // repeatedly prompt for symbols to generate, and generate them
        String symbol = getSymbol(console, solver);
        while (symbol.length() > 0) {
            if (solver.contains(symbol)) {
                doGenerate(console, solver, symbol);
            } else {
                System.out.println("Illegal symbol.");
            }
            
            symbol = getSymbol(console, solver);
        }
    }
    
    /**
     * Displays all non-terminal symbols, prompts for a symbol to generate,
     * and returns the symbol as a string.
     */
    public static String getSymbol(Scanner console, GrammarSolver solver) {
        System.out.println();
        System.out.println("Available symbols to generate are:");
        Set<String> symbols = solver.getSymbols();
        System.out.println(symbols);

        System.out.print("What do you want to generate (Enter to quit)? ");
        String target = console.nextLine().trim();
        return target;
    }
    
    /**
     * Generates some number of instances of the given symbol.
     */
    public static void doGenerate(Scanner console, GrammarSolver solver, String symbol) {
        System.out.print("How many do you want me to generate? ");
        if (console.hasNextInt()) {
            int number = console.nextInt();
            if (number < 0) {
                System.out.println("No negatives allowed.");
            } else {
                System.out.println();
                for (int i = 0; i < number; i++) {
                    String result = solver.generate(symbol);
                    System.out.println(result);
                }
            }
        } else {
            System.out.println("That is not a valid integer.");
        }
        console.nextLine();   // to position to next line
    }

    /**
     * Reads the text from the file with the given name and returns it all
     * as one big string.  Strips empty lines and trims leading/trailing 
     * whitespace from each line.  Throws a FileNotFoundException if the
     * file with the given name is not found.
     */
    public static List<String> readLines(String fileName) throws FileNotFoundException {
        List<String> lines = new ArrayList<String>();
        Scanner input = new Scanner(new File(fileName));
        while (input.hasNextLine()) {
            String line = input.nextLine().trim();
            if (line.length() > 0) {
                lines.add(line);
            }
        }
        return lines;
    }
}