@lazyglobal off.

// Returns the throttle value you should use to achieve the
// target TWR. If TWR can't be achieved, returns 1.0. (full throttle)
function ThrottleToTWR {
  parameter twr is 1.5.

  local m is SHIP:MASS.
  local g is 9.81.
  if HAS_GRAV_SENSOR = true {
    set g to SHIP:SENSORS:GRAV:MAG.
  }
  return min((twr*m*g)/SHIP:AVAILABLETHRUST, 1.0).
}

// Calculates the ship's current TWR.
function TWR {
  local m is ship:mass.
  local g is 9.81. // fallback to this approximation that doesn't deal with
                   // altitude change.
  if HAS_GRAV_SENSOR = true {
    set g to SHIP:SENSORS:GRAV:MAG.
  }
  local t is THROTTLE * SHIP:AVAILABLETHRUST.
  return t/(m*g).
}

// Check for various sensors and set appropriate global constants.
// Currently only checks for grav sensor, as that's the only one used by this library.
global HAS_GRAV_SENSOR is false.
function SensorCheck {
  local SensorList is 0.
  list SENSORS in SensorList.
  for s in SensorList {
    if s:type = "grav" {
      print "Gravometric sensor detected".
      set HAS_GRAV_SENSOR to true.
      return.
    }
  }
  set HAS_GRAV_SENSOR to false.
}

// adapted from https://github.com/sporadisk/KSP-KOS-scripts/blob/master/modules/GravityTurn.ks
// todo: I don't think I actually like this code...
function GravityTurn {
  parameter TargetDirection is 90.
  parameter TargetApoapsis is 80000.
  parameter Factor is 1.

  local remFactor is (2 / Factor).
  local remHeight is (SHIP:APOAPSIS/TargetApoapsis).
  local angle is (90 * (1 - (remHeight ^ remFactor))).
  return heading(TargetDirection, angle, 90).
}