function isValidDate(dateStr) {

    var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/; // requires 4 digit year
    var matchArray = dateStr.match(datePat); // is the format ok?

    if (matchArray == null) {
        alert("El formato de la fecha no es válido. Debés ingresarla en la forma DD/MM/AAAA.")
        return false;
    }

    month = matchArray[3]; // parse date into variables
    day = matchArray[1];
    year = matchArray[4];

    if (month < 1 || month > 12) { // check month range
        alert("El mes debe estar entre 1 y 12.");
        return false;
    }

    if (day < 1 || day > 31) {
        alert("El día debe estar entre 1 y 31.");
        return false;
    }

    if ((month == 4 || month == 6 || month == 9 || month == 11) && day == 31) {
        alert("Este mes no tiene 31 días.");
        return false;
    }

    if (month == 2) { // check for february 29th
        var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));

        if (day > 29 || (day == 29 && !isleap)) {
            alert("Febrero de " + year + " no tiene " + day + " días.");
            return false;
        }
    }
    dateStr = month + "/" + day + "/" + year;
    
    return true;
}

function formatInput(dateStr) {

    var datePat = /^(\d{1,2})(\/|-)(\d{1,2})\2(\d{4})$/;
    var matchArray = dateStr.match(datePat);

    month = matchArray[3];
    day = matchArray[1];
    year = matchArray[4];

    return (month + "/" + day + "/" + year);
}


var processOk = false;


function dispDate(dateObj) {
    month = dateObj.getMonth() + 1;
    month = (month < 10) ? "0" + month : month;

    day = dateObj.getDate();
    day = (day < 10) ? "0" + day : day;
    
    year = dateObj.getYear();

    if (year < 2000) year += 1900;
    
    return (day + "/" + month + "/" + year);
}



function pregnancyCalc(pregform) {

    menstrual = new Date(); // creates new date objects
    ovulation = new Date();
    duedate = new Date();
    today = new Date();
    
    cycle = 0, luteal = 0; // sets variables to invalid state ==> 0

    if (isValidDate(pregform.menstrual.value)) { // Validates menstual date 
        menstrualinput = new Date(formatInput(pregform.menstrual.value));
        menstrual.setTime(menstrualinput.getTime())
    } else {
        return false; // otherwise exits
    }

    cycle = (pregform.cycle.value == "" ? 28 : pregform.cycle.value); // defaults to 28
    // validates cycle range, from 22 to 45
    if (pregform.cycle.value != "" && (pregform.cycle.value < 22 || pregform.cycle.value > 45)) 
    {
        alert(  "Tu ciclo es demasiado corto o demasiado largo \n"
                + "para que el calculo sea preciso! Igualmente intentaremos \n"
                + "completar el calculo con los valores ingresados. ");
    }

    luteal = (pregform.luteal.value == "" ? 14 : pregform.luteal.value); // defaults to 14

    // validates luteal range, from 9 to 16

    if (pregform.luteal.value != "" && (pregform.luteal.value < 9 || pregform.luteal.value > 16)) 
    {

        alert(  "Tu fase lutea es demasiada corta o demasiada larga \n"
                + "para que el calculo sea preciso! Igualmente intentaremos \n"
                + "completar el calculo con los valores ingresados. ");

    }

    // sets ovulation date to menstrual date + cycle days - luteal days
    // the '*86400000' is necessary because date objects track time
    // in milliseconds;  86400000 milliseconds equals one day

    ovulation.setTime(menstrual.getTime() + (cycle * 86400000) - (luteal * 86400000));
    $('#fechaEmbarazo').html(dispDate(ovulation));

    // sets due date to ovulation date plus 269 days
    duedate.setTime(ovulation.getTime() + 266 * 86400000);
     $('#dueDate').html(dispDate(duedate));
    processOk = true;

    // sets fetal age to 14 + 266 (pregnancy time) - time left
    var fetalage = 14 + 266 - ((duedate - today) / 86400000);
    weeks = parseInt(fetalage / 7); // sets weeks to whole number of weeks
    days = Math.floor(fetalage % 7); // sets days to the whole number remainder

    // fetal age message, automatically includes 's' on week and day if necessary
    fetalage = weeks + " semana" + (weeks > 1 ? "s" : "") + ", " + days + " dÈas";
    document.getElementById('fetalage').value = fetalage;

    return false; // form should never submit, returns false
}