/*
 * Name: Mike Cifelli
 * Course: CIS 443 - Programming Languages
 * Assignment: Lisp Interpreter 1
 */

package main;

import parser.*;
import eval.*;
import error.ErrorManager;
import java.io.*;
import java.text.MessageFormat;

/**
 * <code>LispInterpreter</code> is an interpreter for the Lisp programming
 * language. It takes the name of a file as a command-line argument, evaluates
 * the S-expressions found in the file and then prints the results to the
 * console. If no file name is provided at the command-line, this program will
 * read from standard input.
 */
public class LispInterpreter {

    private static final String GREETING = "SUNY Potsdam Lisp Interpreter - Version 1.0.1";
    private static final String PROMPT = "~ ";

    public static final String ANSI_RESET = "\u001B[0m";
    public static final String ANSI_GREEN = "\u001B[32m";

    /**
     * Evaluate the S-expressions found in the file given as a command-line
     * argument and print the results to the console. If no file name was
     * given, retrieve the S-expressions from standard input.
     *
     * @param args
     *  the command-line arguments:
     *  <ul>
     *      <li><code>args[0]</code> - file name (optional)</li>
     *  </ul>
     */
    public static void main(String[] args) {
        LispParser parser = null;
        boolean interactive = false;

        if (args.length > 0) {
            // a file name was given at the command-line, attempt to create a
            // 'LispParser' on it
            try {
                parser = new LispParser(new FileInputStream(args[0]), args[0]);
            } catch (FileNotFoundException e) {
                ErrorManager.generateError(e.getMessage(), ErrorManager.CRITICAL_LEVEL);
            }
        } else {
            // no file name was given, create a 'LispParser' on standard input
            parser = new LispParser(System.in, "System.in");
            interactive = true;

            System.out.println(GREETING);
            System.out.println();
            System.out.print(PROMPT);
        }

        while (! parser.eof()) {
            try {
                SExpression sexpr = parser.getSExpr();
                String result = MessageFormat.format("{0}{1}{2}", ANSI_GREEN, EVAL.eval(sexpr), ANSI_RESET);

                LispInterpreter.erasePrompt(interactive);
                System.out.println(result);
            } catch (RuntimeException e) {
                LispInterpreter.erasePrompt(interactive);
                ErrorManager.generateError(e.getMessage(), 2);
            } catch (IOException e) {
                ErrorManager.generateError(e.getMessage(), ErrorManager.CRITICAL_LEVEL);
            }

            if (interactive) {
                System.out.print(PROMPT);
            }
        }
    }

    private static void erasePrompt(boolean interactive) {
        if (interactive) {
            for (int i = 0; i < PROMPT.length(); i++) {
                System.out.print("\b");
            }
        }
    }

}