/*
The distance between upper case characters and lower case characters in standard ASCII is 32.
A : 65    a : (65 + 32) = 97
B : 66    b : (66 + 32) = 98
C : 67    c : (67 + 32) = 99
...
*/


function convertToUpperCase(str) {
    var result = ''

    for (var i = 0; i < str.length; i++) {
        var code = str.charCodeAt(i)
        if (code > 97) {
            result += String.fromCharCode(code - 32)
        } else {
            result += str.charAt(i)
        }
    }
    return result
}

function convertToLowerCase(str) {
    var result = ''

    for (var i = 0; i < str.length; i++) {
        var code = str.charCodeAt(i)
        if (code > 64 && code < 91) {
            result += String.fromCharCode(code + 32)
        } else {
            result += str.charAt(i)
        }
    }
    return result
}

function converter(str, whichCase, invert) {
    if (whichCase === "low") {
        str = convertToLowerCase(str)
    } else {
        str = convertToUpperCase(str)
    }
    //String without first symbol
    var strNoFrst = str.substring(1, str.length - 1)
    if (invert === true) {
        code = str.charCodeAt(0)
        if (code > 64 && code < 91) {
            result = String.fromCharCode(code + 32)

        } else {
            result = String.fromCharCode(code - 32)
        }
        str = result + strNoFrst

    }
    return str
}


console.log (converter('ABdddDDsdfdfFDsdfDdC', 'up', false))
console.log (converter('ABdddDDsdfdfFDsdfDdC', 'low', false))
console.log (converter('ABdddDDsdfdfFDsdfDdC', 'up', true))
console.log (converter('ABdddDDsdfdfFDsdfDdC', 'low', true))