//set up global variables/objects
function Echo() 
{
    this.height = 0;
    this.weight = 0;
    this.bsa = 0;
    this.aao = 0;
    this.aov = 0;
}

var myAAO = new Echo(); 

function calculateAAO(form) 
{
    myAAO.height = parseFloat(form.height.value);
    myAAO.weight = parseFloat(form.weight.value);
    myAAO.bsa = calcAAOBSA();
    myAAO.aao = calcHMean();
    myAAO.aov = calcHAOV();
    form.bsa.value = myAAO.bsa.toFixed(2);
    form.HalifaxAOVMean.value = (Math.exp(myAAO.aov) / 10).toFixed(2);
    form.HalifaxMean.value = (Math.exp(myAAO.aao) / 10).toFixed(2);
    form.HalifaxRange.value = calcHRange();
    form.HalifaxRatio.value = (Math.exp(myAAO.aao) / Math.exp(myAAO.aov)).toFixed(2);
    form.DerivedAOV.value = (1.55 * Math.pow(myAAO.bsa, 0.5)).toFixed(2);
    form.DerivedMean.value = calcDerivedMean().toFixed(2);
    form.DerivedRange.value = calcDerivedRange();
    form.UCLAMean.value = calcUCLA().toFixed(2);

}// end main function

//calcBSA
function calcAAOBSA() 
{
    if (isNaN(myAAO.height) || myAAO.height === 0)
    {
        return 0.1 * Math.pow(myAAO.weight, (2 / 3));
    }
    else
    {    
        return 0.024265 * Math.pow(myAAO.height, 0.3964) * Math.pow(myAAO.weight, 0.5378);
    }
}

//calculate the Halifax mean, range
function calcHMean()
{
    var lnbsa = Math.log(myAAO.bsa);
    return lnbsa * 0.421 + 2.898;
}

function calcHRange()
{
    var lower = myAAO.aao - (1.96 * 0.09111);
    var upper = myAAO.aao + (1.96 * 0.09111);
    lower = Math.exp(lower);
    upper = Math.exp(upper);
    lower = lower / 10;
    upper = upper / 10;
    return lower.toFixed(2) + " - " + upper.toFixed(2);
}
//calculate the Boston AOV and the AAO diameter based on Boston AOV 

function calcDerivedMean()
{
    var avaMean = 1.55 * Math.pow(myAAO.bsa, 0.5);
    return 1.16 * avaMean;

}

function calcDerivedRange()
{
    var avaMean = 1.55 * Math.pow(myAAO.bsa, 0.5);
    var lower = 0.97 * avaMean;
    var upper = 1.35 * avaMean;
    return lower.toFixed(2) + " - " + upper.toFixed(2);
}

function calcHAOV()
{
    var lnbsa = Math.log(myAAO.bsa);
    return lnbsa * 0.426 + 2.732;

}

function calcUCLA()
{
    return (1.60 + 0.13 * myAAO.height) / 10;
}