/*
 * -----------------------------------------------------
 * CS2S03/SE2S03, October 2011
 * Assignment 3, Question 1
 * File: PE0408.cpp
 * -----------------------------------------------------
 * This program checks if the bracketing operators
 * (parantheses, brackets, and curly braces) in a string
 * are properly nested.
 * -----------------------------------------------------
 */
 
#include "genlib.h"
#include "simpio.h"
#include "stack.h"
#include <iostream>
 
/* Private function prototypes */

bool isOpenOp(char op);
bool isCloseOp(char op);
char CompanionOf(char op);
void CheckBracketing(string s);
 
/* Main program */
 
int main() {
    string s;

    cout << "Enter a line to check: ";
    s = GetLine();
    CheckBracketing(s);

    return 0;
}
 
/*
 * Function: isOpenOp
 * Usage: if (isOpenOp(op)) ...
 * -----------------------------------------------------
 * This function returns true if op is an open operator.
 */

bool isOpenOp(char op) {
    return (op == '(') || (op == '{') || (op == '[');
}

/*
 * Function: isCloseOp
 * Usage: if (isCloseOp(op)) ...
 * -----------------------------------------------------
 * This function returns true if op is a close operator.
 */

bool isCloseOp(char op) {
    return (op == ')') || (op == '}') || (op == ']');
}

/*
 * Function: CompanionOf
 * Usage: c = CompanionOf(op)
 * ---------------------------------------------------
 * This function returns the companion operator of op.
 */

char CompanionOf(char op) {
    switch(op) {
      case ')': return '(';
      case '}': return '{';
      case ']': return '[';
      case '(': return ')';
      case '{': return '}';
      case '[': return ']';
      default: return NULL;
    }
}

/*
 * Function: CheckBracketing
 * Usage: CheckBracketing(s)
 * ------------------------------------------------
 * This function checks if the bracketing operators
 * (parantheses, brackets, and curly braces) in s
 * are properly nested.
 */

void CheckBracketing(string s) {
    Stack<char> openOps;

    for (int i = 0; i < s.length(); i++) {
        if (isOpenOp(s[i])) {
            openOps.push(s[i]);
        } else if (isCloseOp(s[i])) {
            if (openOps.isEmpty()) {
                cout << "An close " << s[i] << " comes before an open ";
                cout << CompanionOf(s[i]) << endl;
                return;
            }
            if (CompanionOf(s[i]) != openOps.pop()) {
                cout << "The bracketing operators are improperly nested.";
                return;
            }
        }
    }
    // end of string is reached
    if (!openOps.isEmpty()) {
        cout << "The line is missing ";
        while (!openOps.isEmpty()) {
            cout << CompanionOf(openOps.pop()) << " ";
        }
        cout << endl;
    } else {
        cout << "Bracketing operators are properly nested.";
    }
    return;
}