var metric;
var VO2Max;

function initGlobals() {
  metric = false;
  VO2Max = -1;
}

function  runConversion() {
  var frm = document.forms.input1VO2max;
  // race time in min, length in m and speed in m/min.
  var time = document.forms.input1VO2max.hours.value * 60 + document.forms.input1VO2max.minutes.value * 1 + document.forms.input1VO2max.seconds.value / 60;
  var rlength = document.forms.input1VO2max.length.value;
  var speed;
  
  if(time <= 0 || isNaN(time)) {
    alert('Please input a valid time');
    return;
  }
  
  if(rlength <= 0 || isNaN(rlength)) {
    alert('Please input a valid race length.');
    return;
  }
  
  if(frm.units.options[0].selected){
    rlength *= 1000;
  }  else {
    rlength *= 1609;
  }
  
  speed = rlength / time;
  
  VO2Max = velToVO2(speed) / timeToPercentVO2Max(time) ;
  makeCalculations();
}


function makeCalculations () {
								// Toggle output type of paces.
								if(document.forms.input1VO2max.paceType.options[1].selected) {
									metric = false;
								} 
								else {
									metric = true;
								}
  if(VO2Max <= 0){
    return;
  }
    
  var velEasy     = VO2ToVel(VO2Max * .7);
  var velTempo   = VO2ToVel(VO2Max * .88);
  var velMaximum = VO2ToVel(VO2Max);
  var velSpeed   = VO2ToVel(VO2Max * 1.1);
  var velxlong     = VO2ToVel(VO2Max * .6);
  var velYasso = velMaximum * 1.95;  
  
  var toAppend;
  if (metric) {
    toAppend=' min/km';
  } else {
    toAppend=' min/mile';
  }

  var frm = document.forms.input1VO2max;

  frm.easy.value    = '' + timeConvert(velEasy)     + toAppend;
  frm.tempo.value    = '' + timeConvert(velTempo)   + toAppend;
  frm.maximum.value  = '' + timeConvert(velMaximum) + toAppend;
  frm.speed.value    = '' + timeConvert(velSpeed)   + toAppend;
  frm.xlong.value    = '' + timeConvert(velEasy)
           + ' - ' + timeConvert(velxlong)    + toAppend;
  var oldMetric = metric;
  metric = false;
  frm.yasso.value    = '' + timeConvert(velYasso)  + ' min/800';
  metric = oldMetric;
}

 // Toggle output type of paces.
function toggleMetric() {
  if(document.forms.input1VO2max.paceType.options[1].selected) {
    metric = false;
  } else {
    metric = true;
  }
  makeCalculations();
}
 
// Takes a velocity and converts it to a VO2 level.   
function velToVO2 (vel) {
  return (-4.60 + 0.182258 * vel + 0.000104 * vel * vel);
}
  
// Takes a VO2 measurement and converts it to a velocity.
function  VO2ToVel (VO2) {
  return (29.54 + 5.000663 * VO2 - 0.007546 * VO2 * VO2);
}

// Takes a time in minutes and uses EQ 2 to convert it to a percent of VO2 maximum.   
function timeToPercentVO2Max (minutes) {
  return (.8 + 0.1894393 * Math.exp(-.012778 * minutes) + 0.2989558 * Math.exp(-.1932695 * minutes));
}

// Takes a speed in metres / minute a converts it to a string representing a pace in
// minutes per mile or km.   
function timeConvert (speed) {
  var ans;
  if(!metric){
    ans = (1 / speed) * 1609;
  } else {
    ans = (1 / speed) * 1000;
  }
  minutes = Math.floor(ans);
  seconds = Math.floor((ans - minutes) * 60);
  if(seconds > 9){
    return '' + minutes + ':' + seconds;
  } else {
    return '' + minutes + ':0' + seconds;
  }
}

//przypisanie zdarzenia onchange="toggleMetric()" do <select name="paceType" >
function przypiszZdarzenie() { 
				var selektor = document.getElementById('paceType');
				selektor.onchange = function () { toggleMetric();};
}
window.onload = przypiszZdarzenie;