Lesson 7 - Calculator

var Calculator  = function(el){

    var input = el.getElementsByTagName('input')[0];
    var buts  = el.getElementsByTagName('button');
    var keybOperations = {43:'+', 47:'/', 42:'*', 45:'-', 99:'C', 61:'='};
    var prevOperation = null;
    var prevNumber = null;
    var operationClicked = false;
    input.value=0;

    for(var i = 0 ;  i < buts.length;i++){
        buts[i].onclick=  press
    }

    input.onblur = function() {
        input.focus();
    };

    input.onkeypress = function(but) {
        but.preventDefault();
        console.log(but.charCode);
        for(key in keybOperations) {
            if (key == but.charCode){
                operationHandler(keybOperations[key]);
            }
        }
        if( 47 < but.charCode && but.charCode < 58 || but.charCode == 46) {
            var butNum = String.fromCharCode(but.keyCode);
            numberHandler(butNum)
            }
    };

    function press(){
        var symbol  = this.innerText;
        if(!isNaN(parseInt(symbol)) || symbol=='.'){
            console.log('number');
            numberHandler(symbol)
        }else{
            console.log('operation');
            operationHandler(symbol)
        }
    }
    function numberHandler(n){
        if(operationClicked){
            input.value="";
            operationClicked = false;
        }
        if(n=='0'&&input.value=='0') return;
        if(n!='0'&&n!='.'&&input.value=='0'){
            input.value=""
        }

        input.value=input.value+n;
    }

    function operationHandler(o){
        if(o=='C'){
            input.value="0";
            prevOperation = null;
            prevNumber=null;
            return;
        }
        operationClicked = true;
        if(prevNumber)
            switch(prevOperation){
                case '+':
                    input.value=  prevNumber+ parseFloat(input.value);
                    break;
                case '/':
                    input.value=  prevNumber/ parseFloat(input.value);
                    break;
                case '*':
                    input.value=  prevNumber* parseFloat(input.value);
                    break;
                case '-':
                    input.value=  prevNumber- parseFloat(input.value);
                    break;
            }
        prevNumber =  parseFloat(input.value);
        prevOperation  = o;
    }
};
new Calculator(document.getElementById('container'));