/*
 * Copyright © 2002 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * California 95054, U.S.A. All rights reserved.  Sun Microsystems, Inc. has
 * intellectual property rights relating to technology embodied in the product
 * that is described in this document. In particular, and without limitation,
 * these intellectual property rights may include one or more of the U.S.
 * patents listed at http://www.sun.com/patents and one or more additional
 * patents or pending patent applications in the U.S. and in other countries.
 * U.S. Government Rights - Commercial software. Government users are subject
 * to the Sun Microsystems, Inc. standard license agreement and applicable
 * provisions of the FAR and its supplements.  Use is subject to license terms.
 * Sun,  Sun Microsystems,  the Sun logo and  Java are trademarks or registered
 * trademarks of Sun Microsystems, Inc. in the U.S. and other countries.  This
 * product is covered and controlled by U.S. Export Control laws and may be
 * subject to the export or import laws in other countries.  Nuclear, missile,
 * chemical biological weapons or nuclear maritime end uses or end users,
 * whether direct or indirect, are strictly prohibited.  Export or reexport
 * to countries subject to U.S. embargo or to entities identified on U.S.
 * export exclusion lists, including, but not limited to, the denied persons
 * and specially designated nationals lists is strictly prohibited.
 */

options {
  LOOKAHEAD = 2;
  CHOICE_AMBIGUITY_CHECK = 2;
  OTHER_AMBIGUITY_CHECK = 1;
  STATIC = false;
  DEBUG_PARSER = false;
  DEBUG_LOOKAHEAD = false;
  DEBUG_TOKEN_MANAGER = false;
  ERROR_REPORTING = true;
  JAVA_UNICODE_ESCAPE = false;
  UNICODE_INPUT = false;
  IGNORE_CASE = false;
  USER_TOKEN_MANAGER = false;
  USER_CHAR_STREAM = false;
  BUILD_PARSER = true;
  BUILD_TOKEN_MANAGER = true;
  SANITY_CHECK = true;
  FORCE_LA_CHECK = false;
}

PARSER_BEGIN(EXPR)

package org.turtleshell.cmd;

import java.io.Closeable;
import java.io.Reader;
import java.io.StringReader;
import org.turtleshell.TEnv;

/**
 * Performs mathematical operations
 **
 * This command performs basic mathematical operations within turtle shell.
 * This command prints the result of the formula to standard out, and also returns
 * the result of the formula as its execution status.
 *
 * COMMAND LINE ARGUMENTS
 * ----------------------
 * This command accepts an mathematical formula as its command line argument
 *
 * Currently expr supports the following numerical operators:
 *
 *  1. Multiplication (*)
 *  2. Division (*)
 *  3. Modululs (%)
 *  4. Addition (+)
 *  5. Subtraction (-)
 *
 * Currently expr ONLY SUPPORTS INTEGER MATH
 *
 * EXECUTION STATUS
 * ----------------
 * This command returns the numerical result of the mathematical formula as its
 * execution status.
 **
 * @author Graham Alvare
 * @author Brian Fristensky
 */
public class EXPR {
    /**
     * The main calling method for this command
     **
     * @param args see class description for a list of available command line arguments
     * @return the execution status of this command (see class description)
     */
    public static int main(String[] args) {
        return exec(null, args, System.out, null);
    }

    /**
     * The functional body of this command
     **
     * @param env the Turtle shell environment to read any necessary variable values from.
     * @param args see class description for a list of available command line arguments
     * @param output the standard output for this command
     * @param input the standard input for this command
     * @return the execution status of this command (see class description)
     */
    public static int exec (TEnv env, String[] args, Appendable output, Reader input) {
        int result = 0;
        StringBuilder builder = new StringBuilder();
        for (String arg : args) {
            builder.append(arg);
        }

        try {
            result = new EXPR(new StringReader(builder.toString())).eval();
            output.append(String.valueOf(result)).append("\n");
        } catch (Exception ex) {
            ex.printStackTrace(System.err);
        }

        return result;
    }
}

PARSER_END(EXPR)

/**
 * Performs a top level evaluation of a mathematical formula.
 * This formula branches based on level of scope.  Mult() is for multiplication,
 * division and modulus, Add() is for addition and subtraction, and Number() is
 * for numbers, and bracketed expressions.
 **
 * @return the result of the formula
 */
int eval () : {
    int result = 0;
}
{
    (
      result = Mult()
    | result = Add()
    | result = Number()
    )

    { return result; }
}

/**
 * Performs multiplication, division and modulus operations
 **
 * @return the result of the formula
 */
int Mult() : {
    int result;
}
{
      result = Number()
    (
      <MULT>  { result *= Number(); }
    | <DIV>   { result /= Number(); }
    | <MOD>   { result %= Number(); }
    )+

    { return result; }
}

/**
 * Performs addition and subtraction operations
 **
 * @return the result of the formula
 */
int Add() : {
    int result;
}
{
      result = Number()
    (
      <PLUS>  { result += Number(); }
    | <MINUS> { result -= Number(); }
    )+

    { return result; }
}

/**
 * Parses numbers and bracketed formulae.
 **
 * @return the parsed number
 */
int Number() : {
    Token t;
    int result = 0;
}
{
    (
      t=<NUMBER> {
        try {
            result = Integer.parseInt(t.image);
        } catch (Exception e) {
            e.printStackTrace();
        }
      }
    | <OPENP> result = eval() <CLOSEP>
    )
    { return result; }
}

<*> TOKEN: { < NUMBER: ( ["0"-"9"] )+ >
           | < PLUS:      "+"  >
           | < MINUS:     "-"  >
           | < MULT:      "*"  >
           | < DIV:       "/"  >
           | < MOD:       "%"  >
           | < LE:        "<=" >
           | < GE:        ">=" >
           | < LT:        "<"  >
           | < GT:        ">"  >
           | < EQ:        "="  >
           | < OR:        "|"  >
           | < AND:       "&"  >
           | < OPENP:     "("  >
           | < CLOSEP:    ")"  >
           | < OPENB:     "["  >
           | < CLOSEB:    "]"  >
           }
<*> SKIP: { < ~[] > }