{-# LANGUAGE BangPatterns #-}

module Common.World
	( World(..)
	, advanceWorld)
where
import Common.Body
import qualified Data.Vector.Unboxed		as V

data World 
	= World
	{ -- | Bodies in the simulation.
	  worldBodies	:: !(V.Vector Body)

	  -- | Number of steps taken in the simulation so far.
	, worldSteps	:: !Int }


-- | Advance the world forward in time.
advanceWorld 
	:: (V.Vector MassPoint	-> V.Vector Accel)
				-- ^ Fn to compute accelerations of each point.
	-> Double		-- ^ Time step.
	-> World
	-> World

advanceWorld calcAccels timeStep world
 = let	
	-- Calculate the accelerations on each body.
	accels	= calcAccels 
		$ V.map massPointOfBody 
		$ worldBodies world

	-- Apply the accelerations to the bodies and advance them.
	bodies'	= V.zipWith 
		(\body (ax, ay) 
			-> advanceBody timeStep
				(setAccelOfBody (-ax, -ay) body))
		(worldBodies world)
		accels

	-- Update the world.
	steps'	= worldSteps world + 1

   in	world	{ worldBodies	= bodies'
		, worldSteps	= steps' }