// A helper function to compute the calories per hour for
// an activity at a certain intensity
function caloriesPerHour(activity,intensity) {
  var result = 0;

  if(activity=='walking' && intensity=='low')
    result = 176;
  else if(activity=='walking' && intensity=='medium')
    result = 232;
  else if(activity=='walking' && intensity=='high')
    result = 352;
  else if(activity=='cycling' && intensity=='low')
    result = 422;
  else if(activity=='cycling' && intensity=='medium')
    result = 563;
  else if(activity=='cycling' && intensity=='high')
    result = 704;
  else if(activity=='running' && intensity=='low')
    result = 704;
  else if(activity=='running' && intensity=='medium')
    result = 880;
  else if(activity=='running' && intensity=='high')
    result = 1126;
  else if(activity=='swimming' && intensity=='low')
    result = 422;
  else if(activity=='swimming' && intensity=='medium')
    result = 563;
  else if(activity=='swimming' && intensity=='high')
    result = 704;

  return result;
}

function computeHandler() {
  var activitySelector,intensitySelector,durationText,resultPar;
  var activity,intensity,duration,calories;

  // Gather the page elements we need to interact with
  activitySelector = document.getElementById('activity');
  intensitySelector = document.getElementById('intensity');
  durationText = document.getElementById('duration');
  resultPar = document.getElementById('result');

  // Gather inputs
  activity = activitySelector.value;
  intensity = intensitySelector.value;
  duration = durationText.value;

  // Do the computation
  calories = caloriesPerHour(activity,intensity)*duration/60;
  // Round result to the nearest calorie
  calories = Math.round(calories);

  // Present the result
  resultPar.textContent = 'This activity will burn a total of ' + calories + ' calories.';
}

function setup() {
    var computeButton;

    computeButton = document.getElementById('compute');
    computeButton.addEventListener('click',computeHandler,false);
}

window.addEventListener('load',setup,false);