Missile Range Calculator

--[[
    From the Depths Missile Range Calculator

    Based on:
    Range Calculation by HerpeDerp      https://www.fromthedepthsgame.com/forum/showthread.php?tid=35722
    Missile module Data from Wiki       https://fromthedepths.gamepedia.com/Missile#Missile_modules
    A code example of how to traverse Lua Transceivers and Missiles from the Forum, I sadly can't find again.

    Requirements:
    Launchers need a Lua Transceiver (one per Launcher-Group should be enough, no need to recalculate for the same missiles).
    Missiles have to be launched and range is only calculated while flying. (Sounds stupid to calc instead of just waiting
    and watching the result, but it beats firing the missiles manually and following them with a stopwatch)

    Warning:
    This code has not been tested beyond the point of it printing data to the HUD, use at own risk!

    TODOs:
    Missiles are drawn in the wrong order. (pretty useless feature anyways ;-)
    Drag calculation might walk through missiles in the wrong order (more tests needed).
    Data (drag) in missile_module_table might be outdated.
    Keep showing calculated Data for some time after missiles are destroyed (already saved in missiles[]).
    Option to calculate drag based on current height instead of hardcoded value.
    Option to compare actual missile data to calculated values.
    Check for possibility to get number of ejectors from game instead of hardcoding.
--]]

-- BEGIN CONFIG AREA

-- height at which the missile will fly. The range will depend on this because the drag depends on the height.
local height = 10;

-- draw Missile in addition to writing data to hud
local draw_missile  = false;

-- Number of Ejectors attached to each Launchpad. Hardcoded since I have no idea how to find this in Lua.
-- Actually helpful in case of using 4 ejectors, when one has to be removed for the Lua Transceiver.
local numberOfEjectors = 2;

-- END CONFIG AREA


-- Globals
local API;
local missiles = {};

local missile_module_table = {};
missile_module_table["missile body"] =                        { name = "Body",                        drag = 0.01, icon = "[]", };
missile_module_table["missile fins"] =                        { name = "Fins",                        drag = 0.05, icon = ">>", };
missile_module_table["missile fuel tank"] =                   { name = "Fuel Tank",                     drag = 0.02, icon = "[O]", };
missile_module_table["missile short range thruster"] =        { name = "Short Range Thruster",        drag = 0.02, icon = "+>", };
missile_module_table["missile explosive warhead"] =           { name = "Explosive Warhead",             drag = 0.02, icon = "[X]", };
missile_module_table["missile predicted"] =                   { name = "Target Prediction Guidance",    drag = 0.02, icon = "[tp]", };
missile_module_table["missile APN"] =                         { name = "APN Guidance",                drag = 0.05, icon = "[ap]", };
missile_module_table["missile IR seeker"] =                   { name = "Infra-Red Seeker",            drag = 0.05, icon = "[ir]", };
missile_module_table["missile beam rider"] =                  { name = "Laser Beam Rider Receiver",     drag = 0.02, icon = "[br]", };
missile_module_table["missile laser designator receiver"] =   { name = "Laser Designator Receiver",     drag = 0.05, icon = "[ls]", };
missile_module_table["missile radar seeker"] =                { name = "Radar Seeker",                drag = 0.05, icon = "[rs]", };
missile_module_table["missile proximity fuse"] =              { name = "Proximity Fuse",                drag = 0.05, icon = "[|]", };
missile_module_table["missile fuse safety"] =                 { name = "Safety Fuse",                 drag = 0.02, icon = "[s]", };
missile_module_table["missile one turn"] =                    { name = "One Turn",                    drag = 0.02, icon = "[^]", };
missile_module_table["missile propeller"] =                   { name = "Torpedo Propeller",             drag = 0.02, icon = "[*]", };
missile_module_table["missile sonar"] =                       { name = "Torpedo Sonar",                 drag = 0.05, icon = "[@]", };
missile_module_table["missile magnet"] =                      { name = "Magnet",                        drag = 0.05, icon = "[U]", };
missile_module_table["missile ballast"] =                     { name = "Ballast Tanks",                 drag = 0.02, icon = "[~]", };
missile_module_table["missile regulator"] =                   { name = "Regulator",                     drag = 0.02, icon = "[+]", };
missile_module_table["missile frag warhead"] =                { name = "Fragmentation Warhead",         drag = 0.02, icon = "[F]", };
missile_module_table["missile camera"] =                      { name = "Camera",                        drag = 0.05, icon = "[o]", };
missile_module_table["missile cable drum"] =                  { name = "Cable Drum",                    drag = 0.05, icon = "[/]", };
missile_module_table["missile harpoon"] =                     { name = "Harpoon",                     drag = 0.02, icon = "[>>]", };
missile_module_table["missile sticky flare"] =                { name = "Sticky Flare",                drag = 0.05, icon = "[f]", };
missile_module_table["missile EMP warhead"] =                 { name = "EMP Warhead",                 drag = 0.02, icon = "[~]", };
missile_module_table["missile simple IR seeker"] =            { name = "Single-Pixel IR Seeker",        drag = 0.00, icon = "[.]", };
missile_module_table["missile interceptor"] =                 { name = "Missile Interceptor",         drag = 0.01, icon = "[i]", };
missile_module_table["missile variable speed thruster"] =     { name = "Variable Thruster",             drag = 0.02, icon = "~>", };
missile_module_table["missile thumper head"] =                { name = "Thumper Head",                drag = 0.00, icon = "}", };
missile_module_table["missile lua receiver"] =                { name = "LUA Receiver",                drag = 0.01, icon = "[#]", };
missile_module_table["missile radar buoy"] =                  { name = "radar buoy",                    drag = 0.02, icon = "(r)", };
missile_module_table["missile sonar buoy"] =                  { name = "sonar buoy",                    drag = 0.02, icon = "(s)", };


-- MAIN
function Update(I)
  API = I;
  API:ClearLogs();
  local message = "";
  for pad = 0, API:GetLuaTransceiverCount()-1 do
      for msl = 0, API:GetLuaControlledMissileCount(pad)-1 do
          local missile_structure = API:GetMissileInfo(pad, msl);
          local id = API:GetLuaControlledMissileInfo(pad, msl);
          local text = "";
          local missile = missiles[id];
          if missile == nil or missile["text"] == nil then
            text = GetMissileText(id, missile_structure);
          else
            text = missile["text"];
          end
          message = message .. text .. "\n";
      end
  end
  Print(message);
end


function GetMissileText(id, missile_structure)
  local Parts = missile_structure.Parts;
  local text = "";
  local Data = {
    length = 0,
    initialSpeed = numberOfEjectors * 70,
    displayedThrust = 0,
    thrust = 0,
    drag = 0.1,
    dragCoefficient = 0,
    fuelTime = 0,
    regulatorTime = 0,
    effectiveTime = 0,
    flightDistance = 0,
    mass = 0,
  };

  for _,Part in pairs(Parts) do
    local name = Part.Name;
    API:Log("Part: " .. name);
    Data.length = Data.length + 1;
    Data.mass = Data.mass + 0.1;
    local module_data = missile_module_table[name];
    Data.drag = Data.drag + module_data["drag"] / Data.length;

    if name == "missile thumper head" then
      Data.mass = Data.mass + 0.2;
    elseif name == "missile short range thruster" then
      Data.displayedThrust = Data.displayedThrust + 1000;
      Data.initialSpeed = Data.initialSpeed + 15;
    elseif name == "missile variable speed thruster" then
      Data.displayedThrust = Data.displayedThrust + Part.Registers[2];
      Data.initialSpeed = Data.initialSpeed + 15;
    elseif name == "missile torpedo propeller" then
      Data.displayedThrust = Data.displayedThrust + 500;
      Data.initialSpeed = Data.initialSpeed + 50;
    elseif name == "missile fuel tank" then
      Data.fuelTime = Data.fuelTime + 5000;
    elseif name == "missile regulator" then
      Data.regulatorTime  = Data.regulatorTime + 180;
    end

    if draw_missile then
      text = text .. DrawPart(Part);
    end
  end

  Data.dragCoefficient = Data.drag / 100
  Data.thrust = Data.displayedThrust / 40;
  Data.initialSpeed = Data.initialSpeed + 0.75 / Data.mass;
  Data.fuelTime = Data.fuelTime / Data.displayedThrust;
  Data.regulatorTime  = Data.regulatorTime + 60; -- was 30 for some reason
  Data.effectiveTime = math.min(Data.fuelTime, Data.regulatorTime);

  Data.flightDistance = getDistanceAfterTime(Data, Data.effectiveTime, height);

  if draw_missile then
    text = text .. "\n";
  end
  text = text .. "Range: " .. Data.flightDistance .. "m; TTL: " .. Data.effectiveTime .. "s.\n";

  for k,v in pairs(Data) do
    API:Log(k .. " " .. v);
  end

  local missile = {};
  missile["data"] = Data;
  missile["text"] = text;
  missiles[id] = missile;
  return text;
end


function DrawPart(Part)
    local name = Part.Name;
    local mod = missile_module_table[name];
    if mod ~= nil then
      return mod["icon"] .. " ";
    else
      return name .. ", ";
    end
end


function Print(message)
    API:LogToHud(message);
    API:LogToHud(" ");
    API:LogToHud("  ");
    API:LogToHud("   ");
    API:LogToHud("    ");
    API:LogToHud("     ");
end


function getDistanceAfterTime(m, totalFlightTime, height)
  local distanceTraveled = 0;
  local velocityMagnitude = 0;
  local timeStep = 0.025
  local time = 0
  while time < totalFlightTime do
    local accelerationMagnitude = getAcceleration(m, height, velocityMagnitude, timeStep)
    velocityMagnitude = velocityMagnitude + accelerationMagnitude * timeStep
    distanceTraveled = distanceTraveled + velocityMagnitude * timeStep
    time = time + timeStep
  end
  return distanceTraveled;
end


function getAcceleration(m, height, speed, timeStep)
  local newSpeed = speed + getThrustAccelerationMagnitude(m) * timeStep;
  return getThrustAccelerationMagnitude(m) - getDragAccelerationMagnitude(m, height, speed, newSpeed)
end


function getDragAccelerationMagnitude(m, height, speed, newSpeed)
  local airDensity = getAirDensityAtAltitude(height)
  local dragMagnitudePerVelocity = math.max(0.1, airDensity * speed * m.dragCoefficient)
  local dragMagnitude = dragMagnitudePerVelocity * newSpeed
  return dragMagnitude
end


function getThrustAccelerationMagnitude(m)
  return m.thrust / m.mass
end


function getAirDensityAtAltitude(altitude)
  if altitude < 0 then
    return 7
  elseif altitude < 275 then
    return 1 - altitude / 550
  else
    return 0.5 * math.pow(0.01, (altitude - 275) / (1200 - 275));
  end
end