main.cpp

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <cmath>

#include "tokenizer.h"
#include "parser.h"
#include "evaluator.h"
#include "variables.h"
#include "history.h"

static std::string formatResult(double val) {
    if (val == std::floor(val) && std::abs(val) < 1e15)
        return std::to_string((long long)val);
    std::ostringstream oss;
    oss << std::setprecision(10) << std::noshowpoint << val;
    return oss.str();
}

// checks if input is "x = something"
static bool isAssignment(const std::string& input, std::string& varName, std::string& rhs) {
    auto eq = input.find('=');
    if (eq == std::string::npos) return false;

    std::string lhs = input.substr(0, eq);
    lhs.erase(0, lhs.find_first_not_of(" \t"));
    lhs.erase(lhs.find_last_not_of(" \t") + 1);

    if (lhs.empty()) return false;
    for (char c : lhs)
        if (!std::isalnum(c) && c != '_') return false;
    if (std::isdigit(lhs[0])) return false;
    if (lhs == "pi" || lhs == "e" || lhs == "ans") return false;

    varName = lhs;
    rhs = input.substr(eq + 1);
    return true;
}

int main() {
    std::cout << "Expression Evaluator — type 'help' for commands\n\n";

    Tokenizer tokenizer;
    Parser parser;
    VariableStore variables;
    History history;
    Evaluator evaluator(variables);

    std::string input;

    while (true) {
        std::cout << ">> ";
        if (!std::getline(std::cin, input)) break;

        input.erase(0, input.find_first_not_of(" \t"));
        input.erase(input.find_last_not_of(" \t") + 1);
        if (input.empty()) continue;

        if (input == "exit" || input == "quit") break;

        if (input == "help") {
            std::cout << "operators : + - * / ^ %\n";
            std::cout << "functions : sqrt sin cos tan log log2 ln abs floor ceil\n";
            std::cout << "constants : pi e\n";
            std::cout << "variables : x = 10, then use x in expressions\n";
            std::cout << "ans       : reuse last result\n";
            std::cout << "commands  : history, vars, clear, exit\n\n";
            continue;
        }

        if (input == "history") { history.print(); continue; }
        if (input == "vars")    { variables.list(); continue; }
        if (input == "clear")   { history.clear(); std::cout << "cleared\n"; continue; }

        // replace 'ans' with last result
        std::string expr = input;
        std::string lastAns = history.lastResult();
        size_t p = 0;
        while ((p = expr.find("ans", p)) != std::string::npos) {
            expr.replace(p, 3, "(" + lastAns + ")");
            p += lastAns.size() + 2;
        }

        try {
            std::string varName, rhs;
            if (isAssignment(expr, varName, rhs)) {
                auto tokens  = tokenizer.tokenize(rhs);
                auto postfix = parser.toPostfix(tokens);
                double val   = evaluator.evaluate(postfix);
                variables.set(varName, val);
                std::string result = formatResult(val);
                std::cout << varName << " = " << result << "\n";
                history.add(input, result);
                continue;
            }

            auto tokens  = tokenizer.tokenize(expr);
            auto postfix = parser.toPostfix(tokens);
            double val   = evaluator.evaluate(postfix);
            std::string result = formatResult(val);
            std::cout << "= " << result << "\n";
            history.add(input, result);

        } catch (const std::exception& ex) {
            std::cout << "error: " << ex.what() << "\n";
        }
    }

    return 0;
}