function add(a, b) {
    return a + b;
}

function substract(a, b) {
    return a - b;
}

function multiply(a, b) {
    return a * b;
}

function divide(a, b) {
    return a / b;
}

function operate(equals) {
    switch(equals.operator) {
        case "+":
            return add(+equals.a, +equals.b);
        case "-":
            return substract(+equals.a, +equals.b);
        case "*":
            return multiply(+equals.a, +equals.b);
        case "/":
            return divide(+equals.a, +equals.b);
    }
}

function execute(operation) {
    if (operation.equal) {
        const result = operate(operation);
        operation.a_b = !operation.a_b;
        operation.equal = false;
        operation.operator = "";
        if (operation.a_b) {
            operation.a = `${result}`;
            operation.b = "";
        }
        console.table(operation);
        console.log(`Result: ${result}`);
    }
}

let operation = {
    a: "",
    operator: "",
    b: "",
    a_b: true,
    equal: false,
}

let equal = "";

function click(value) {
    if (!isNaN(+value)) {
        if (operation.a_b) {
            operation.a += value;
        } else {
            operation.b += value;
            operation.equal = true;
        }
    } else if (value == "=") {
        execute(operation);
    } else {
        if (operation.operator == "") {
            operation.a_b = !operation.a_b;
            operation.operator = value;
        }
        if (operation.a_b) {
            operation.operator = value;
        }
    }
    console.table(operation);
}

function generateGui() {

    const buttonsValues = [
        [7,8,9,"+"],
        [4,5,6,"-"],
        [1,2,3,"*"],
        [0,".","=","/"],
    ];

    const buttonsDiv = document.querySelector("#buttons");

    for (let i = 0; i < 4; i++) {
        let button_row = document.createElement("div");
        button_row.classList.add("buttons-flex");
        for (let j = 0; j < 4; j++) {
            let button = document.createElement("div");
            button.classList.add("button");
            button.setAttribute("value", buttonsValues[i][j]);
            button.textContent = `${buttonsValues[i][j]}`;
            button.addEventListener("click", (event) => {
                click(event.target.getAttribute("value"));
            });
            button_row.append(button);
        }
        buttonsDiv.append(button_row);
    }
}

generateGui();