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

static char logic_log[4096];

typedef struct {
    const char *buffer;
    int pos;
} Parser;

static double parse_expression(Parser *p);

static void skip_ws(Parser *p) {
    while (p->buffer[p->pos] == ' ') p->pos++;
}

static double parse_factor(Parser *p) {
    skip_ws(p);
    if (p->buffer[p->pos] == '-') {
        p->pos++;
        return -parse_factor(p);
    }
    if (p->buffer[p->pos] == '(') {
        p->pos++;
        double res = parse_expression(p);
        if (p->buffer[p->pos] == ')') p->pos++;
        return res;
    }
    char *endptr;
    double val = strtod(&p->buffer[p->pos], &endptr);
    p->pos = (int)(endptr - p->buffer);
    return val;
}

static double parse_term(Parser *p) {
    double left = parse_factor(p);
    while (1) {
        skip_ws(p);
        char op = p->buffer[p->pos];
        if (op == '*' || op == '/') {
            p->pos++;
            double right = parse_factor(p);
            double old = left;
            left = (op == '*') ? left * right : left / right;

            char step[256];

            snprintf(step, sizeof(step), "<div>%g %c %g = <b>%g</b></div>", old, op,
                     right, left);
            strncat(logic_log, step, sizeof(logic_log) - strlen(logic_log) - 1);
        } else
            break;
    }
    return left;
}

static double parse_expression(Parser *p) {
    double left = parse_term(p);
    while (1) {
        skip_ws(p);
        char op = p->buffer[p->pos];
        if (op == '+' || op == '-') {
            p->pos++;
            double right = parse_term(p);
            double old = left;
            left = (op == '+') ? left + right : left - right;

            char step[256];

            snprintf(step, sizeof(step), "<div>%g %c %g = <b>%g</b></div>", old, op,
                     right, left);
            strncat(logic_log, step, sizeof(logic_log) - strlen(logic_log) - 1);
        } else
            break;
    }
    return left;
}

double evaluate(const char *expr) {
    logic_log[0] = '\0';
    if (!expr || strlen(expr) == 0) return 0.0;
    Parser p = {expr, 0};
    return parse_expression(&p);
}

InfoBox fetch_calc_data(char *math_input) {
    InfoBox info = {NULL, NULL, NULL, NULL};
    if (!math_input) return info;

    double result = evaluate(math_input);

    char html_output[5120];
    snprintf(html_output, sizeof(html_output),
             "<div class='calc-container' style='line-height: 1.6;'>"
             "%s"
             "<div style='margin-top: 8px; border-top: 1px solid #eee; "
             "padding-top: 8px; font-size: 1.2em;'>"
             "<b>%g</b>"
             "</div>"
             "</div>",
             strlen(logic_log) > 0 ? logic_log : "<div>Constant value</div>",
             result);

    info.title = strdup("Calculation");
    info.extract = strdup(html_output);
    info.thumbnail_url =
    strdup("/static/calculation.svg");
    info.url = strdup("#");

    return info;
}