var display = $("#ans");
var nSym = [];
var stimes = 0;
const sysm = ['+', "-", "*", "/", "=", "Enter"];
const nums = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.'];
var backSpaced = false;
$(".butn").on("click", function() {
    var curChar = this.textContent;
    var need = display.text();
    if (curChar == '.' && display.text().slice(display.text().length - 1) == '.') {
        display.text(need)
    } else {
        display.text(need + curChar);
    }
})

$(".sbutn").on("click", function() {
    stimes++;
    var cs = this.textContent;
    if (backSpaced) {
        display.text(display.text() + cs);
    }
    if (sysm.includes(display.text().slice(display.text().length - 1))) {
        stimes--;
        nSym.pop();
        nSym.push(cs);
        display.text(display.text().slice(0, display.text().length - 1) + cs);
        backSpaced = false;
    } else {
        backSpaced = false;
        nSym.push(cs);
        check();
        if (cs == "=") {
            display.text(display.text())
        } else {
            display.text(display.text() + cs);
        }
    }
})

function check() {

    if (stimes != 0 && stimes != 1) {
        if (nSym[stimes - 2] == '+') {
            var alist = display.text().split("+");
            var ans = parseFloat(alist[0]) + parseFloat(alist[1]);
        } else if (nSym[stimes - 2] == '-') {
            var alist = display.text().split("-");
            var ans = parseFloat(alist[0]) - parseFloat(alist[1]);
        } else if (nSym[stimes - 2] == '*') {
            var alist = display.text().split("*");
            var ans = parseFloat(alist[0]) * parseFloat(alist[1]);
        } else if (nSym[stimes - 2] == '/') {
            var alist = display.text().split("/");
            var ans = parseFloat(alist[0]) / parseFloat(alist[1]);
        }
        display.text(ans);
    }

}
$(".del").on("click", function() {
    display.text(" ");
    nSym = [];
    stimes = 0;
})
$(".back").on("click", function() {
    var removed = display.text().slice(-1);
    if (sysm.includes(removed)) {
        stimes--;
        nSym.pop();
        backSpaced = true;
        display.text(display.text().slice(0, -1));
    } else {
        display.text(display.text().slice(0, -1));
    }
})

// code to operate keyboard keys
$(document).on("keypress", function() {
    var curChar = event.key;
    var cs = curChar;
    if (cs == ".") {
        mkAnimation("dot");
        var need = display.text();
        if (curChar == '.' && display.text().slice(display.text().length - 1) == '.') {
            display.text(need)
        } else {
            display.text(need + curChar);
        }
    } else if (nums.includes(curChar)) {
        mkAnimation(curChar);
        var need = display.text();
        display.text(need + curChar);
    } else if (sysm.includes(curChar)) {
        stimes++;

        if (backSpaced) {
            display.text(display.text() + cs);
        }

        if (sysm.includes(display.text().slice(display.text().length - 1))) {
            stimes--;
            nSym.pop();
            nSym.push(curChar);
            display.text(display.text().slice(0, display.text().length - 1) + cs);
            backSpaced = false;
            if (curChar == "+") {
                mkAnimation("plus");
            } else if (curChar == "-") {
                mkAnimation("minus");
            } else if (curChar == "*") {
                mkAnimation("into");
            } else if (curChar == "/") {
                mkAnimation("by");
            }
        } else {
            backSpaced = false;
            if (cs == "Enter") {
                cs = "=";
            }
            nSym.push(cs);
            check();
            if (cs == "=") {
                display.text(display.text());
            } else {
                display.text(display.text() + cs);
            }
        }
    }
})

$(document).on("keydown", function() {
    var bigKey = event.key;
    mkAnimation(bigKey);
    if (bigKey == "Backspace") {
        var removed = display.text().slice(-1);
        if (sysm.includes(removed)) {
            stimes--;
            nSym.pop();
            backSpaced = true;
            display.text(display.text().slice(0, -1));
        } else {
            display.text(display.text().slice(0, -1));
        }
    }
    if (bigKey == "Delete") {
        display.text(" ");
        nSym = [];
        stimes = 0;
    }
})

function mkAnimation(e) {
    $("." + e).addClass("pressed");
    setTimeout(function() {
        $("." + e).removeClass("pressed");
    }, 100)
}