#include "calculator.h"
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <math.h>

static const char *cur;



static void skip_ws(void) {
    while (*cur && isspace(*cur)) {
        cur++;
    }
}

static int starts_with(const char *name) {
    int len = strlen(name);
    if (strncmp(cur, name, len) == 0) {
        cur += len;
        return 1;
    }
    return 0;
}



static double read_expr(void);

static double read_number(void) {
    skip_ws();
    char *end;
    double res = strtod(cur, &end);
    cur = end;
    return res;
}

static double read_factor(void) {
    skip_ws();

    if (*cur == '(') {
        cur++;
        double res = read_expr();
        skip_ws();
        if (*cur == ')') {
            cur++;
        }
        return res;
    }

    if (starts_with("sin")) {
        skip_ws();
        return sin(read_factor());
    }
    if (starts_with("cos")) {
        skip_ws();
        return cos(read_factor());
    }
    if (starts_with("sqrt")) {
        skip_ws();
        return sqrt(read_factor());
    }
    if (starts_with("log")) {
        skip_ws();
        return log(read_factor());
    }
    if (starts_with("pow")) {
        skip_ws();
        if (*cur == '(') cur++;
        double left = read_expr();
        skip_ws();
        if (*cur == ',') cur++;
        double right = read_expr();
        skip_ws();
        if (*cur == ')') cur++;
        return pow(left, right);
    }

    return read_number();
}

static double read_term(void) {
    double res = read_factor();

    while (1) {
        skip_ws();
        if (*cur == '*') {
            cur++;
            res *= read_factor();
        } else if (*cur == '/') {
            cur++;
            res /= read_factor();
        } else {
            break;
        }
    }

    return res;
}

static double read_expr(void) {
    double res = read_term();

    while (1) {
        skip_ws();
        if (*cur == '+') {
            cur++;
            res += read_term();
        } else if (*cur == '-') {
            cur++;
            res -= read_term();
        } else {
            break;
        }
    }

    return res;
}



double evaluate_expression(const char *expr) {
    cur = expr;
    return read_expr();
}