module Geometry.LHS
    ( isLHS
    , isRHS
    ) where
import Geometry.Data
-- | Test whether a point is stricly on the LHS of a line.
-- Returns False if the line is of zero length.
isLHS 
    :: Point2  -- ^ First line point. 
    -> Point2  -- ^ Second line point.
    -> Point2  -- ^ Point not on line.
    -> Bool
{-# INLINE isLHS #-}
isLHS (V2 x y)      (V2 x' y')   (V2 x'' y'') 
    | (x,y) == (x',y')  = False
    | otherwise = a1 * b2 - a2 * b1 > 0
  where
    a1 = x' - x
    a2 = y' - y
    b1 = x'' - x
    b2 = y'' - y
-- | Test whether a point is on the RHS of a line.
-- Returns False if the line is of zero length.
isRHS 
    :: Point2 -- ^ First line point. 
    -> Point2 -- ^ Second line point.
    -> Point2 -- ^ Point not on line.
    -> Bool
{-# INLINE isRHS #-}
isRHS 
    (V2 x y)       
    (V2 x' y')    
    (V2 x'' y'')  
    | (x,y) == (x',y')  = False
    | otherwise = a1 * b2 - a2 * b1 < 0
  where 
    a1 = x' - x
    a2 = y' - y
    b1 = x'' - x
    b2 = y'' - y