/*
  Functions:

    event-driven functions:
      - onLoadBody ()                       when html-body is loaded
      - onChangeTabCalculation ()           when activating the calculation bar
      - onChangeCalculationItem ()          when changing the item to be calculated in sink-rate-dialog
      - onChangeItem ()                     when changing editable items in sink-rate-dialog
      - onChangeUnits ()                    when changing editable units in ?-dialog
      - onChangeProperties ()               when changing properties in ?-dialog
      - onChangeShowAircraftInfos ()        when selecting an other aircraft to show its infos

    internal functions:
      - setObjectVariables ()               set the calculation input-object-variables
      - setCalculationDefault ()            determine option-group-field that should be calculated
      - setConnotationHeadline ()           display connotation h2 as sub navigation
      - setConnotationHeadlineLinks ()      set connotation headline links (only called, when they have been conversted into html links)
      - setFocusToCalculationElement ()     set focus to most edited field
      - clearCssClassOfInputFields ()       removes css-class from all input fields except the one to be calculated
      - clearCssClassOfInputField ()        removes css-class from the given input field
      - calculateDefaultItem ()             calculate default item
      - calculateItem ()                    calculate given item
      - convertTimeToHMM ()                 converts numeric value to time in h:mm-format

    calculation functions:
      - calculateDistance ()                calculate distance in nm
      - calculateHeight ()                  calculate height in hundreds of feet
      - calculateSpeed ()                   calculate speed in kts
      - calculateRate ()                    calculate rate in ft / min
      - calculateDegrees ()                 calculate slope in degrees
      - calculateTime ()                    calculate time in h:mm
*/

// CONSTANTS

const NUMBER_OF_MINUTES_IN_HOUR        = 60;
const NAUTIC_MILE_IN_FEET              = 6076.12;
const METER_IN_FEET                    = 3.28;
const METER_PER_SECOND_IN_KNOTS        = 1.94;
const KILOMETER_IN_KNOTS               = 0.54;
const KILOMETER_IN_MILES_PER_HOUR      = 0.62;
const MILES_PER_HOUR_IN_KNOTS          = 0.87;

// VARIABLES

// html-input-field-objects
var objHorizontalDistanceInNauticMiles;
var objVerticalDistanceInFeet;
var objGroundSpeedInKts;
var objRateInFtPerMinute;
var objRateInDegrees;
var objAmountOfTime;


// EVENT-DRIVEN FUNCTIONS


function onLoadBody ()
{
  setCalculationDefault ();
  setObjectVariables ();
  setConnotationHeadline ();
}


function onChangeTabCalculation ()
{
  setFocusToCalculationElement ();
  calculateDefaultItem ();
}


function onChangeCalculationItem (item)
{
  var currentCalculationItem = item.value;

  clearCssClassOfInputFields (currentCalculationItem);

  document.getElementById(currentCalculationItem).className = "disabled";
  document.getElementById(currentCalculationItem).disabled = true;
}


function onChangeItem (item)
{
  calculateItem (document.calculation_form.calculation_group.value);
}


function onChangeUnits (item)
{
  var val = 0;
  var objUnits = document.getElementById("units");
  var objInputLeft = document.getElementById("input_left");
  var objInputRight = document.getElementById("input_right");
  var objLabelLeft = document.getElementById("label_input_left");
  var objLabelRight = document.getElementById("label_input_right");

  switch (objUnits.value)
  {
    case 'm_ft':
      if (item.id == "input_left")
      {
        val = item.value * METER_IN_FEET;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / METER_IN_FEET;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "m";
        objInputLeft.value = 0;
        objInputLeft.step = 100;
        objLabelRight.innerHTML = "ft";
        objInputRight.value = 0;
        objInputRight.step = 500;
      }
      break;
    case 'm/s_kts':
      if (item.id == "input_left")
      {
        val = item.value * METER_PER_SECOND_IN_KNOTS;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / METER_PER_SECOND_IN_KNOTS;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "m/s";
        objInputLeft.value = 0;
        objInputLeft.step = 1;
        objLabelRight.innerHTML = "kts";
        objInputRight.value = 0;
        objInputRight.step = 1;
      }
      break;
    case 'kmh_kts':
      if (item.id == "input_left")
      {
        val = item.value * KILOMETER_IN_KNOTS;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / KILOMETER_IN_KNOTS;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "km/h";
        objInputLeft.value = 0;
        objInputLeft.step = 10;
        objLabelRight.innerHTML = "kts";
        objInputRight.value = 0;
        objInputRight.step = 10;
      }
      break;
    case 'kmh_mph':
      if (item.id == "input_left")
      {
        val = item.value * KILOMETER_IN_MILES_PER_HOUR;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / KILOMETER_IN_MILES_PER_HOUR;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "km/h";
        objInputLeft.value = 0;
        objInputLeft.step = 10;
        objLabelRight.innerHTML = "mph";
        objInputRight.value = 0;
        objInputRight.step = 10;
      }
      break;
    case 'mph_kts':
      if (item.id == "input_left")
      {
        val = item.value * MILES_PER_HOUR_IN_KNOTS;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / MILES_PER_HOUR_IN_KNOTS;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "mph";
        objInputLeft.value = 0;
        objInputLeft.step = 10;
        objLabelRight.innerHTML = "kts";
        objInputRight.value = 0;
        objInputRight.step = 10;
      }
      break;
    case 'km_nm':
      if (item.id == "input_left")
      {
        val = item.value * KILOMETER_IN_KNOTS;
        objInputRight.value = val.toFixed(0);
      }
      else if (item.id == "input_right")
      {
        val = item.value / KILOMETER_IN_KNOTS;
        objInputLeft.value = val.toFixed(0);
      }
      else if (item.id == "units")
      {
        objLabelLeft.innerHTML = "km";
        objInputLeft.value = 0;
        objInputLeft.step = 10;
        objLabelRight.innerHTML = "nm";
        objInputRight.value = 0;
        objInputRight.step = 10;
      }
      break;
  }
}


function onChangeProperties (item)
{
  var objTableDiv = document.getElementById("property_table");

  switch (item.value)
  {
    case 'default':
      objTableDiv.innerHTML = "";
      break;
    case 'rw_departure':
      objTableDiv.innerHTML = "<table class='r3'><tr><td>Volocopter Volocity</td><td>no data</td><td>ft</td></tr><tr><td>Wright Flyer</td><td>no data</td><td>ft<br />ft</td></tr><tr><td>Zlin Savage Carbon</td><td>200<br />100</td><td>ft<br />ft</td></tr><tr><td>Zlin Savage Shock Ultra</td><td>200<br />100</td><td>ft<br />ft</td></tr><tr><td>Zlin Savage Cub</td><td>400<br />250</td><td>ft<br />ft</td></tr><tr><td>Pitts Special</td><td>500</td><td>ft</td></tr><tr><td>DHC-2 Beaver</td><td>560</td><td>ft</td></tr><tr><td>Icon A5</td><td>590<br />450</td><td>ft<br />ft</td></tr><tr><td>Cub Crafters XCub</td><td>600<br />280</td><td>ft<br />ft</td></tr><tr><td>Cub Crafters NXCub</td><td>600<br />150</td><td>ft<br />ft</td></tr><tr><td>JMB VL-3 915</td><td>600<br />420</td><td>ft<br />ft</td></tr><tr><td>Extra 330 LT</td><td>1000<br />700</td><td>ft<br />ft</td></tr><tr><td>Whittaker MW6</td><td>1000<br />700</td><td>ft<br />ft</td></tr><tr><td>Pipistrel Virus SW 121</td><td>1050<br />525</td><td>ft<br />ft</td></tr><tr><td>Diamond Aircraft DV20</td><td>1100</td><td>ft</td></tr><tr><td>Diamond Aircraft DA40 TDI</td><td>1200<br />950</td><td>ft<br />ft</td></tr><tr><td>Diamond Aircraft DA40 NG</td><td>1300<br />990</td><td>ft<br />ft</td></tr><tr><td>Cessna 152</td><td>1385<br />750</td><td>ft<br />ft</td></tr><tr><td>Ryan Spirit Of St. Louis NYP</td><td>1500</td><td>ft</td></tr><tr><td>Curtiss JN-4D</td><td>1500</td><td>ft</td></tr><tr><td>Cessna 172 Skyhawk</td><td>1525<br />865</td><td>ft<br />ft</td></tr><tr><td>Cirrus SR22</td><td>1593<br />1082</td><td>ft<br />ft</td></tr><tr><td>Douglas DC-3 S</td><td>1600<br />900</td><td>ft<br />ft</td></tr><tr><td>Robin Regent DR400-180</td><td>2000<br />1034</td><td>ft<br />ft</td></tr><tr><td>Cessna 208B Grand Caravan EX</td><td>2160<br />1400</td><td>ft<br />ft</td></tr><tr><td>Beechcraft Bonanza G36</td><td>2180<br />1300</td><td>ft<br />ft</td></tr><tr><td>Beechcraft Baron G58</td><td>2345<br />1373</td><td>ft<br />ft</td></tr><tr><td>Daher TBM 930</td><td>2380<br />1800</td><td>ft<br />ft</td></tr><tr><td>Diamond Aircraft DA62</td><td>2897<br />1574</td><td>ft<br />ft</td></tr><tr><td>Rutan Boomerang</td><td>3000</td><td>ft</td></tr><tr><td>Beechcraft King Air 350i</td><td>3300</td><td>ft</td></tr><tr><td>Cessna CJ4 Citation</td><td>4000<br />5000</td><td>ft<br />ft</td></tr><tr><td>Cessna Citation Longitude</td><td>4810</td><td>ft</td></tr></table>";
      break;
    case 'rw_approach':
      objTableDiv.innerHTML = "<table class='r3'><tr><td>Volocopter Volocity</td><td>no data</td><td>ft</td></tr><tr><td>Wright Flyer</td><td>no data</td><td>ft<br />ft</td></tr><tr><td>Zlin Savage Carbon</td><td>200<br />15<br />15</td><td>ft<br />ft<br />kts</td></tr><tr><td>Zlin Savage Shock Ultra</td><td>200<br />58<br />16</td><td>ft<br />ft<br />kts</td></tr><tr><td>Zlin Savage Cub</td><td>400<br />200<br />15</td><td>ft<br />ft<br />kts</td></tr><tr><td>DHC-2 Beaver</td><td>500<br />10</td><td>ft<br />kts</td></tr><tr><td>Cub Crafters XCub</td><td>500<br />170<br />11</td><td>ft<br />ft<br />kts</td></tr><tr><td>Cub Crafters NXCub</td><td>500<br />150<br />11</td><td>ft<br />ft<br />kts</td></tr><tr><td>Icon A5</td><td>530<br />450<br />12</td><td>ft<br />ft<br />kts</td></tr><tr><td>JMB VL-3 915</td><td>600<br />420<br />10</td><td>ft<br />ft<br />kts</td></tr><tr><td>Diamond Aircraft DV20</td><td>750<br />15</td><td>ft<br />kts</td></tr><tr><td>Whittaker MW6</td><td>800<br />300</td><td>ft<br />ft</td></tr><tr><td>Diamond Aircraft DA40 TDI</td><td>942<br />850<br />20</td><td>ft<br />ft<br />kts</td></tr><tr><td>Extra 330 LT</td><td>1000<br />500<br />15</td><td>ft<br />ft<br />kts</td></tr><tr><td>Diamond Aircraft DA40 NG</td><td>1040<br />890<br />20</td><td>ft<br />ft<br />kts</td></tr><tr><td>Pipistrel Virus SW 121</td><td>1050<br />525<br />18</td><td>ft<br />ft<br />kts</td></tr><tr><td>Cessna 152</td><td>1075<br />500<br />15</td><td>ft<br />ft<br />kts</td></tr><tr><td>Cessna 172 Skyhawk</td><td>1250<br />520<br />17</td><td>ft<br />ft<br />kts</td></tr><tr><td>Pitts Special</td><td>1500<br />17</td><td>ft<br />kts</td></tr><tr><td>Curtiss JN-4D</td><td>1500<br />10</td><td>ft<br />kts</td></tr><tr><td>Douglas DC-3 S</td><td>1600<br />15</td><td>ft<br />kts</td></tr><tr><td>Beechcraft Bonanza G36</td><td>1700<br />920<br />17</td><td>ft<br />ft<br />kts</td></tr><tr><td>Robin Regent DR400-180</td><td>1740<br />820<br />22</td><td>ft<br />ft<br />kts</td></tr><tr><td>Cessna 208B Grand Caravan EX</td><td>1850<br />1000<br />20</td><td>ft<br />ft<br />kts</td></tr><tr><td>Ryan Spirit Of St. Louis NYP</td><td>2000</td><td>ft</td></tr><tr><td>Cirrus SR22</td><td>2343<br />1178<br />21</td><td>ft<br />ft<br />kts</td></tr><tr><td>Daher TBM 930</td><td>2430<br />1300<br />20</td><td>ft<br />ft<br />kts</td></tr><tr><td>Beechcraft Baron G58</td><td>2490<br />1440<br />22</td><td>ft<br />ft<br />kts</td></tr><tr><td>Diamond Aircraft DA62</td><td>2556<br />1447<br />25</td><td>ft<br />ft<br />kts</td></tr><tr><td>Beechcraft King Air 350i</td><td>2700<br />20</td><td>ft<br />kts</td></tr><tr><td>Cessna CJ4 Citation</td><td>3000<br />19</td><td>ft<br />kts</td></tr><tr><td>Cessna Citation Longitude</td><td>3170<br />25</td><td>ft<br />kts</td></tr><tr><td>Rutan Boomerang</td><td>3200<br />1500<br />25</td><td>ft<br />ft<br />kts</td></tr></table>";
      break;
    case 'cruise_speed':
      objTableDiv.innerHTML = "<table class='r3'><tr><td>Cessna CJ4 Citation</td><td>no data</td><td>KIAS</td></tr><tr><td>Beechcraft King Air 350i</td><td>no data</td><td>KIAS</td></tr><tr><td>Cessna Citation Longitude</td><td>no data</td><td>KIAS</td></tr><tr><td>Wright Flyer</td><td>22</td><td>mph</td></tr><tr><td>Curtiss JN-4D</td><td>52</td><td>kts</td></tr><tr><td>Volocopter Volocity</td><td>54</td><td>kts</td></tr><tr><td>Whittaker MW6</td><td>55</td><td>mph</td></tr><tr><td>Icon A5</td><td>84</td><td>KTAS</td></tr><tr><td>Ryan Spirit Of St. Louis NYP</td><td>100</td><td>mph</td></tr><tr><td>Cessna 152</td><td>107</td><td>KIAS</td></tr><tr><td>Zlin Savage Carbon</td><td>110</td><td>kts</td></tr><tr><td>Diamond Aircraft DV20</td><td>117</td><td>KIAS</td></tr><tr><td>Pipistrel Virus SW 121</td><td>120</td><td>KIAS</td></tr><tr><td>Cessna 172 Skyhawk</td><td>122</td><td>KIAS</td></tr><tr><td>Diamond Aircraft DA40 NG</td><td>125</td><td>KIAS</td></tr><tr><td>Cub Crafters NXCub</td><td>126</td><td>KIAS</td></tr><tr><td>Cub Crafters XCub</td><td>126</td><td>KIAS</td></tr><tr><td>Diamond Aircraft DA40 TDI</td><td>129</td><td>KIAS</td></tr><tr><td>Pitts Special</td><td>137</td><td>mph</td></tr><tr><td>Zlin Savage Shock Ultra</td><td>140</td><td>IAS</td></tr><tr><td>JMB VL-3 915</td><td>153</td><td>KIAS</td></tr><tr><td>DHC-2 Beaver</td><td>156</td><td>mph</td></tr><tr><td>Beechcraft Baron G58</td><td>163</td><td>KIAS</td></tr><tr><td>Cessna 208B Grand Caravan EX</td><td>164</td><td>KIAS</td></tr><tr><td>Zlin Savage Cub</td><td>165</td><td>IAS</td></tr><tr><td>Cirrus SR22</td><td>170</td><td>KIAS</td></tr><tr><td>Diamond Aircraft DA62</td><td>171</td><td>KIAS</td></tr><tr><td>Extra 330 LT</td><td>173</td><td>KIAS</td></tr><tr><td>Beechcraft Bonanza G36</td><td>174</td><td>KIAS</td></tr><tr><td>Douglas DC-3 S</td><td>204</td><td>mph</td></tr><tr><td>Rutan Boomerang</td><td>220</td><td>KIAS</td></tr><tr><td>Daher TBM 930</td><td>252</td><td>KIAS</td></tr><tr><td>Robin Regent DR400-180</td><td>254</td><td>km/h</td></tr></table>";
      break;
    case 'service_ceiling':
      objTableDiv.innerHTML = "<table class='r3'><tr><td>Whittaker MW6</td><td>no data</td><td>ft</td></tr><tr><td>Wright Flyer</td><td>30</td><td>ft</td></tr><tr><td>Volocopter Volocity</td><td>6500</td><td>ft</td></tr><tr><td>Curtiss JN-4D</td><td>6500</td><td>ft</td></tr><tr><td>Diamond Aircraft DV20</td><td>13120</td><td>ft</td></tr><tr><td>Cessna 172 Skyhawk</td><td>13500</td><td>ft</td></tr><tr><td>Cub Crafters XCub</td><td>14000</td><td>ft</td></tr><tr><td>Cub Crafters NXCub</td><td>14000</td><td>ft</td></tr><tr><td>Zlin Savage Cub</td><td>14400</td><td>ft</td></tr><tr><td>Cessna 152</td><td>14700</td><td>ft</td></tr><tr><td>Icon A5</td><td>15000</td><td>ft</td></tr><tr><td>Robin Regent DR400-180</td><td>15500</td><td>ft</td></tr><tr><td>Zlin Savage Shock Ultra</td><td>15750</td><td>ft</td></tr><tr><td>Extra 330 LT</td><td>16000</td><td>ft</td></tr><tr><td>Ryan Spirit Of St. Louis NYP</td><td>16400</td><td>ft</td></tr><tr><td>Diamond Aircraft DA40 NG</td><td>16400</td><td>ft</td></tr><tr><td>Diamond Aircraft DA40 TDI</td><td>16400</td><td>ft</td></tr><tr><td>Cirrus SR22</td><td>17500</td><td>ft</td></tr><tr><td>Pipistrel Virus SW 121</td><td>18000</td><td>ft</td></tr><tr><td>Zlin Savage Carbon</td><td>18000</td><td>ft</td></tr><tr><td>DHC-2 Beaver</td><td>18000</td><td>ft</td></tr><tr><td>Beechcraft Bonanza G36</td><td>18500</td><td>ft</td></tr><tr><td>JMB VL-3 915</td><td>20000</td><td>ft</td></tr><tr><td>Diamond Aircraft DA62</td><td>20000</td><td>ft</td></tr><tr><td>Pitts Special</td><td>20000</td><td>ft</td></tr><tr><td>Beechcraft Baron G58</td><td>20000</td><td>ft</td></tr><tr><td>Cessna 208B Grand Caravan EX</td><td>20000</td><td>ft</td></tr><tr><td>Douglas DC-3 S</td><td>20800</td><td>ft</td></tr><tr><td>Rutan Boomerang</td><td>22000</td><td>ft</td></tr><tr><td>Daher TBM 930</td><td>31000</td><td>ft</td></tr><tr><td>Beechcraft King Air 350i</td><td>35000</td><td>ft</td></tr><tr><td>Cessna Citation Longitude</td><td>45000</td><td>ft</td></tr><tr><td>Cessna CJ4 Citation</td><td>45000<br />28000</td><td>ft<br />ft</td></tr></table>";
      break;
    case 'range':
      objTableDiv.innerHTML = "<table class='r3'><tr><td>Wright Flyer</td><td>no data</td><td>nm</td></tr><tr><td>Whittaker MW6</td><td>no data</td><td>nm</td></tr><tr><td>Volocopter Volocity</td><td>20</td><td>nm</td></tr><tr><td>Curtiss JN-4D</td><td>135</td><td>nm</td></tr><tr><td>Pitts Special</td><td>277</td><td>nm</td></tr><tr><td>Extra 330 LT</td><td>350</td><td>nm</td></tr><tr><td>DHC-2 Beaver</td><td>395</td><td>nm</td></tr><tr><td>Zlin Savage Carbon</td><td>400</td><td>nm</td></tr><tr><td>Cessna 152</td><td>415</td><td>nm</td></tr><tr><td>Icon A5</td><td>427</td><td>nm</td></tr><tr><td>Zlin Savage Shock Ultra</td><td>598</td><td>km</td></tr><tr><td>Diamond Aircraft DV20</td><td>629</td><td>nm</td></tr><tr><td>Pipistrel Virus SW 121</td><td>642</td><td>nm</td></tr><tr><td>Cirrus SR22</td><td>659</td><td>nm</td></tr><tr><td>Diamond Aircraft DA40 NG</td><td>675</td><td>nm</td></tr><tr><td>Cessna 172 Skyhawk</td><td>696</td><td>nm</td></tr><tr><td>Cub Crafters NXCub</td><td>700</td><td>nm</td></tr><tr><td>Zlin Savage Cub</td><td>700</td><td>km</td></tr><tr><td>Cub Crafters XCub</td><td>700</td><td>nm</td></tr><tr><td>Diamond Aircraft DA40 TDI</td><td>741</td><td>nm</td></tr><tr><td>Robin Regent DR400-180</td><td>790</td><td>nm</td></tr><tr><td>JMB VL-3 915</td><td>800</td><td>nm</td></tr><tr><td>Beechcraft Bonanza G36</td><td>820</td><td>nm</td></tr><tr><td>Beechcraft Baron G58</td><td>942</td><td>nm</td></tr><tr><td>Cessna 208B Grand Caravan EX</td><td>1052</td><td>nm</td></tr><tr><td>Diamond Aircraft DA62</td><td>1290</td><td>nm</td></tr><tr><td>Daher TBM 930</td><td>1440<br />1730</td><td>nm<br />nm</td></tr><tr><td>Beechcraft King Air 350i</td><td>1500<br />1800</td><td>nm<br />nm</td></tr><tr><td>Rutan Boomerang</td><td>2053</td><td>nm</td></tr><tr><td>Cessna CJ4 Citation</td><td>2140</td><td>nm</td></tr><tr><td>Douglas DC-3 S</td><td>2500<br />3000</td><td>nm<br />nm</td></tr><tr><td>Cessna Citation Longitude</td><td>3500</td><td>nm</td></tr><tr><td>Ryan Spirit Of St. Louis NYP</td><td>3600</td><td>nm</td></tr></table>";
      break;
    default:
      objTableDiv.innerHTML = "<p>unknown value '" + item.value + "'.</p>";
      break;
  }
}


function onChangeShowAircraftInfos (item)
{
  window.location.href = "?aircraft=" + item.value;
}


// INTERNAL FUNCTIONS


function setObjectVariables ()
{
  objHorizontalDistanceInNauticMiles   = document.getElementById('distance-in-nm');
  objVerticalDistanceInFeet            = document.getElementById('height-difference-in-ft');
  objGroundSpeedInKts                  = document.getElementById('speed-in-kts');
  objRateInFtPerMinute                 = document.getElementById('rate-in-ft-per-min');
  objRateInDegrees                     = document.getElementById('rate-in-degrees');
  objAmountOfTime                      = document.getElementById('time-in-hmm');
}


function setCalculationDefault ()
{
  calculationDefaultItem = 'distance-in-nm';

  // option-group-value of the element that should be calculated by default
  document.calculation_form.calculation_group.value = calculationDefaultItem;

  // set input-field properties via css-class: border and background-color
  document.getElementById(calculationDefaultItem).className = "disabled";
  document.getElementById(calculationDefaultItem).disabled = true;
}


function setConnotationHeadline ()
{
  var s = '';
  var sHeadline = document.getElementById('connotations').innerHTML;
  var objCommonSpecialsPreparings = document.getElementById('common-specials-preparings');
  var objCommonSpecialsBeforeTakeOff = document.getElementById('common-specials-before-take-off');
  var objCommonSpecialsAfterTakeOff = document.getElementById('common-specials-after-take-off');
  var objCommonSpecialsAutopilot = document.getElementById('common-specials-autopilot');
  var objCommonSpecialsCutOff = document.getElementById('common-specials-cut-off');

  // check additional common-specials for transforming the connotation-headline into a html-link
  if (objCommonSpecialsPreparings || objCommonSpecialsBeforeTakeOff || objCommonSpecialsAfterTakeOff || objCommonSpecialsAutopilot || objCommonSpecialsCutOff)
    sHeadline = '<a href="" name="common-specials" onClick="setConnotationHeadlineLinks (this); return false;" style="color:black;">' + sHeadline + '</a>';

  // check additional common-specials for extending the connotations-headline

  if (objCommonSpecialsPreparings)
    s = s + ' / <a href="" name="common-specials-preparings" onClick="setConnotationHeadlineLinks (this); return false;" style="color:grey;">preparings</a>';

  if (objCommonSpecialsBeforeTakeOff)
    s = s + ' / <a href="" name="common-specials-before-take-off" onClick="setConnotationHeadlineLinks (this); return false;" style="color:grey;">&lt; take-off</a>';

  if (objCommonSpecialsAfterTakeOff)
    s = s + ' / <a href="" name="common-specials-after-take-off" onClick="setConnotationHeadlineLinks (this); return false;" style="color:grey;">&gt; take-off</a>';

  if (objCommonSpecialsAutopilot)
    s = s + ' / <a href="" name="common-specials-autopilot" onClick="setConnotationHeadlineLinks (this); return false;" style="color:grey;">autopilot</a>';

  if (objCommonSpecialsCutOff)
    s = s + ' / <a href="" name="common-specials-cut-off" onClick="setConnotationHeadlineLinks (this); return false;" style="color:grey;">cut-off</a>';

  // returning connotations-headline with html links
  if (s)
    document.getElementById('connotations').innerHTML = sHeadline + s;
}


function setConnotationHeadlineLinks (obj)
{
  var clickedLinkText = obj.innerHTML;
  var connotations = document.getElementById('connotations');

  for (var link=connotations.firstChild; link; link=link.nextSibling)
  {
    // loop through the html links inside the extended connotation headline, setting headline links and hiding/displaying according content
    if (link.tagName == 'A')
    {
      if (clickedLinkText == link.innerHTML)
      {
        link.style.color = 'black';
        document.getElementById(link.name).style.display = 'block';
      }
      else
      {
        link.style.color = 'grey';
        document.getElementById(link.name).style.display = 'none';
      }
    }
  }
}


function setFocusToCalculationElement ()
{
  // set focus to the calculation element as given in the ini-file
  document.getElementById('height-difference-in-ft').focus();
}

function clearCssClassOfInputFields (currentCalculationItem)
{
  clearCssClassOfInputField (currentCalculationItem, 'distance-in-nm');
  clearCssClassOfInputField (currentCalculationItem, 'height-difference-in-ft');
  clearCssClassOfInputField (currentCalculationItem, 'speed-in-kts');
  clearCssClassOfInputField (currentCalculationItem, 'rate-in-ft-per-min');
}


function clearCssClassOfInputField (currentCalculationItem, item)
{
  if (currentCalculationItem != item)
  {
    document.getElementById (item).className = '';
    document.getElementById (item).disabled = false;
  }
}


function calculateDefaultItem ()
{
  calculateItem ('distance-in-nm');
}


function calculateItem (itemHtmlId)
{
  switch (itemHtmlId)
  {
    case 'distance-in-nm':
      calculateDistance ();
      break;
    case 'height-difference-in-ft':
      calculateHeight ();
      break;
    case 'speed-in-kts':
      calculateSpeed ();
      break;
    case 'rate-in-ft-per-min':
      calculateRate ();
      break;
    default:
      calculateItem ('distance-in-nm');
  }

  calculateDegrees ();
  calculateTime ();
}


function convertTimeToHMM (num)
{
  num = parseInt (num);

  var hours = Math.floor (num / NUMBER_OF_MINUTES_IN_HOUR);
  var minutes = num % NUMBER_OF_MINUTES_IN_HOUR;

  minutes = minutes.toString ();

  return hours + ":" + minutes.padStart (2, '0');
}


// CALCULATION FUNCTIONS


function calculateDistance ()
{
  var distance = parseInt (objGroundSpeedInKts.value) * parseInt (objVerticalDistanceInFeet.value)  / parseInt (objRateInFtPerMinute.value) / NUMBER_OF_MINUTES_IN_HOUR;

  if (Number.isInteger(distance))
    objHorizontalDistanceInNauticMiles.value = distance;
  else
  {
    distance = distance.toFixed(1);
    objHorizontalDistanceInNauticMiles.value = distance;
  }
}


function calculateHeight ()
{
  var height = parseFloat (objHorizontalDistanceInNauticMiles.value) / parseInt (objGroundSpeedInKts.value) * parseInt (objRateInFtPerMinute.value) * NUMBER_OF_MINUTES_IN_HOUR;
  var heightInHundreds = height / 100;

  heightInHundreds = heightInHundreds.toFixed(0);
  height = heightInHundreds * 100;

  objVerticalDistanceInFeet.value = height;
}


function calculateSpeed ()
{
  var speed = parseFloat (objHorizontalDistanceInNauticMiles.value) / parseInt (objVerticalDistanceInFeet.value) * parseInt (objRateInFtPerMinute.value) * NUMBER_OF_MINUTES_IN_HOUR;

  objGroundSpeedInKts.value = speed.toFixed(0);
}


function calculateRate ()
{
  var rate = parseInt (objGroundSpeedInKts.value) / NUMBER_OF_MINUTES_IN_HOUR / parseFloat (objHorizontalDistanceInNauticMiles.value) * parseInt (objVerticalDistanceInFeet.value);

  objRateInFtPerMinute.value = rate.toFixed(0);
}


function calculateDegrees ()
{
  var horizontalDistance = parseFloat (objHorizontalDistanceInNauticMiles.value) * NAUTIC_MILE_IN_FEET;
  var verticalDistance = parseInt (objVerticalDistanceInFeet.value);

  var gradientInPercent = verticalDistance / horizontalDistance;
  var gradientInDegree  = Math.atan (gradientInPercent) * 180 / Math.PI;

  objRateInDegrees.value = gradientInDegree.toFixed(1);
}


function calculateTime ()
{
  var horizontalDistance = parseFloat (objHorizontalDistanceInNauticMiles.value);
  var groundSpeed = parseInt (objGroundSpeedInKts.value);

  objAmountOfTime.value = convertTimeToHMM (horizontalDistance / groundSpeed * NUMBER_OF_MINUTES_IN_HOUR);
}