#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>
#include "calc.h"

void usage (char * p)
{
	fprintf (stderr, "usage: %s 'expression'\n", p);
	fprintf (stderr, "Note: Don't forget the sinlge quotes ('(3+4)')\n");
	exit (1);
}

#define STACKLEN 100000

char opstack[STACKLEN];
int opos = 0; 
int  valstack[STACKLEN];
int vpos = 0;

#define ANY 1
#define NUMBER 2
#define OP 3
#define PARENOPEN 4
#define PARENCLOSE 5

int state = ANY;
int depth = 0;

void pop ()
{
	assert (opos > 0);
	opos--;
	assert (vpos >= 2);
	vpos--;
	switch  (opstack[opos]) {
	case '*':
		valstack[vpos-1] = domul (valstack[vpos-1], valstack[vpos]);
		break;
	case '/':
		valstack[vpos-1] = dodiv (valstack[vpos-1], valstack[vpos]);
		break;
	case '+':
		valstack[vpos-1] = doadd (valstack[vpos-1], valstack[vpos]);
		break;
	case '-':
		valstack[vpos-1] = dosub (valstack[vpos-1], valstack[vpos]);
		break;
	default:
		assert (0);
	}
}

int main (int argc, char ** argv)
{
	int val, count;
	char * p = argv[1];
	char ch, ch2;
	if (argc != 2)
		usage (argv[0]);
	 
	while (*p) {
		if (isspace ((int)(*p))) {
			p++;
			continue;
		}
		if ((state != NUMBER) && (state != PARENCLOSE)
		    && (sscanf (p, "%d%n", &val, &count) >= 1)) {
			assert (vpos < STACKLEN);
			state = NUMBER;
			valstack[vpos] = val;
			vpos++;
			p += count;
			continue;
		}
		if (sscanf (p, "%c", &ch) == 1) {
			p++;
			switch (ch) {
			case '*':
			case '+':
			case '/':
			case '-':
				assert ((state == NUMBER) || (state == ANY) || (state == PARENCLOSE));
				state = OP;
				break;
			case '(':
				assert ((state == ANY) || (state == OP) || (state == PARENOPEN));
				state = PARENOPEN;
				depth++;
				break;
			case ')':
				assert (depth);
				depth--;
				assert ((state == NUMBER) || (state == PARENCLOSE));
				state = PARENCLOSE;
				break;
			}
			if ((ch == '+') || (ch == '-')) {
				while (opos > 0) {
					ch2 = opstack[opos-1];
					if (ch2 == '(')
						break;
					pop ();
				}
				assert (opos < STACKLEN);
				opstack[opos] = ch;
				opos++;
			} else if ((ch == '/') || (ch == '*')) {
				while (opos > 0) {
					ch2 = opstack[opos-1];
					if (ch2 == '(')
						break;
					if ((ch2 == '+') || (ch2 == '-'))
						break;
					pop ();
				}
				assert (opos < STACKLEN);
				opstack[opos] = ch;
				opos++;
			} else if (ch == ')') {
				assert (opos > 0);
				while (opstack[opos-1] != '(') {
					pop ();
					assert (opos > 0);
				}
				opos--;
			} else if (ch == '(') {
				assert (opos < STACKLEN);
				opstack[opos] = ch;
				opos++;
			}
			continue;
		}
		assert (0);
	}
	while (opos)
		pop ();
	assert (vpos == 1);
	printf ("%s=%d\n", argv[1], valstack[0]);
	return 0;
}