run "library/lib_math".

declare function WaitForEngineStart{
	wait until AnyEngineActive().
}

declare function GetDrag{
	parameter localGravity.
	return ship:sensors:acc:mag + localGravity.
}

declare function GetDragDir{
	parameter localGravity.
	parameter dir.
	return vDot(ship:sensors:acc, dir) + localGravity.
}

declare function AnyEngineActive{
	list engines in allEngines.
	for eng in allEngines{
		if eng:ignition {
			return true.
		}
	}
	return false.
}

declare function GetIsp{
	LIST ENGINES IN allEngines.
	declare local totalThrust is ship:maxThrust.
	local sum is 0.
	local weights is 0.
	for eng in allEngines{
		if eng:IGNITION and not eng:flameout{
			local w is  eng:AVAILABLETHRUST / totalThrust.
			local ispW is eng:isp * w.
			set sum to sum + ispW.
			set weights to weights + w.
		}
	}
	return sum / weights.
}

declare function GetMaxMassFlow{
	LIST ENGINES IN allEngines.
	local sum is 0.
	for eng in allEngines{
		if eng:IGNITION and not eng:flameout{
			set sum to sum + eng:maxmassflow.
		}
	}
	return sum.
}




declare function CalculateSuicideBurnDuration
{
	parameter isp.
	return CalculateBurnDuration(verticalSpeed, isp, ship:mass, GetMaxMassFlow() * 1000).
}

declare function CalculateBurnDuration
{
	parameter dv.
	parameter burnIsp.
	parameter initialMass.
	parameter massFlow.

	set dv to abs(dv).
	local exp is -dv / (burnIsp * constant:g0).
	local massRatio is ApproximateExp(-exp).
	local finalMass is initialMass / massRatio.
	local fuelUsed is initialMass - finalMass.

	if massFlow <= 0{
		return 0.
	}

	return fuelUsed / massFlow.
}


declare function CalculateSuicideBurnAltitude
{
	parameter vertSpeed.
	parameter localGravity.
	parameter tgtAltitude is 0.0.
	parameter drag is 0.0.

	local vertAcc is CalculateAverageDecceleration(localGravity).
	local burnAltitude is ((vertSpeed^2) / (2 * (vertAcc))).
	return burnAltitude + tgtAltitude.
}

declare function CalculateSuicideBurnAltitudeV2
{
	
	parameter vertSpeed.
	parameter localGravity.
	parameter tgtAltitude is 0.0.


	local vs is vertSpeed * -1.
	local a is CalculateAverageDecceleration(localGravity).
	local dt is 0.05.
	local result is 0.0.
	local h is alt:radar.

	until vs <= 0 {
        set vs to vs + a * dt.
        set result to result + vs * dt.

        if result > h { return result. } 
    }

    return result.
}


declare function CalculateAverageDecceleration{
	parameter localGravity.
	local maxVertAcc is (ship:availablethrust / ship:mass) - localGravity.

	return maxVertAcc + localGravity.
}

declare function GetLocalGravity{
	parameter curAltitude is -1.
	
	if curAltitude = -1 {
		set curAltitude to altitude.
	}
	return body:mu / (curAltitude + body:radius)^2.
}

declare function CalculateTimeToImpact{
	parameter vertSpeed.
	parameter curAltitude.
	parameter gravity.
	parameter tgtAltitude is 0.0.

	if gravity <= 0 or curAltitude <= 0{
		print "[warn]: invalid altitude or gravity.".
		return 0.0.
	}

	local vs is abs(vertSpeed).
	local g is gravity.
	local hRel is curAltitude - tgtAltitude.
	local disc is ((vs^2) + (2 * g * hRel)).
	return (vs + sqrt(disc)) / g.
}