// JScript File
/*
Copyright (C) 2007 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

onTimer();

// Called when the timer goes off
function onTimer() {
  // Compute the moon phase each time timer is called
  var cal = new Date();
  // Base the computation off of UTC time, to the nearest hour
  var phase = computeMoonPhase(cal.getUTCFullYear(), 
                               cal.getUTCMonth() + 1,
                               cal.getUTCDate(),
                               cal.getUTCHours());
  var truncPhase = Math.floor(phase) % 30;

  // Find the text description of the current phase
  var desc;
  if (truncPhase === 0) {
    desc = "Luna nuova";
  } else if (truncPhase == 7) {
    desc = "Primo quarto";
  } else if (truncPhase == 15) {
    desc = "Luna piena";
  } else if (truncPhase == 23) {
    desc = "Terzo quarto";
  } else if (truncPhase > 0 && phase < 7) {
    desc = "Luna crescente";
  } else if (truncPhase > 7 && phase < 15) {
    desc = "Gibbosa crescente";
  } else if (truncPhase > 15 && phase < 23) {
    desc = "Gibbosa calante";
  } else {
    desc = "Luna calante";
  }

  var moonImage = document.getElementById("moonImage");
  // Set the image and text component appropriately
  moonImage.src = "img/moon/moon" + truncPhase + ".gif";
  document.getElementById("phaseAge").innerHTML = "La luna e' di " + (Math.floor(phase * 100) / 100) + " giorni.<br/>" + desc;
}


// Compute the moon phase.
// Code is based upon Bradley E. Schaefer''s well-known moon phase algorithm.
function computeMoonPhase(year, month, day, hours) {
  var MOON_PHASE_LENGTH = 29.530588853;

  // Convert the year into the format expected by the algorithm
  var transformedYear = year - Math.floor((12 - month) / 10);

  // Convert the month into the format expected by the algorithm
  var transformedMonth = month + 9;
  if (transformedMonth >= 12) {
    transformedMonth = transformedMonth - 12;
  }

  // Logic to compute moon phase as a fraction between 0 and 1
  var term1 = Math.floor(365.25 * (transformedYear + 4712));
  var term2 = Math.floor(30.6 * transformedMonth + 0.5);
  var term3 = Math.floor(Math.floor((transformedYear / 100) + 49) * 0.75) - 38;
  var intermediate = term1 + term2 + (day + (hours - 1) / 24) + 59;
  if (intermediate > 2299160) {
    intermediate = intermediate - term3;
  }
  var normalizedPhase = (intermediate - 2451550.1) / MOON_PHASE_LENGTH;
  normalizedPhase = normalizedPhase - Math.floor(normalizedPhase);
  if (normalizedPhase < 0) {
    normalizedPhase = normalizedPhase + 1;
  }

  // Return the result as a value between 0 and MOON_PHASE_LENGTH
  return normalizedPhase * MOON_PHASE_LENGTH;
}