```{-# LANGUAGE DeriveGeneric #-}
-- | Basic operations on bounded 2D vectors, with an efficient, but not 1-1
-- and not monotonic @Enum@ instance.
module Game.LambdaHack.Common.Vector
( Vector(..), isUnit, isDiagonal, neg, chessDistVector, euclidDistSqVector
, moves, movesCardinal, movesDiagonal, compassText
, vicinity, vicinityUnsafe, vicinityCardinal, vicinityCardinalUnsafe
, squareUnsafeSet
, shift, shiftBounded, trajectoryToPath, trajectoryToPathBounded
, vectorToFrom, computeTrajectory
#ifdef EXPOSE_INTERNAL
-- * Internal operations
, maxVectorDim, _moveTexts, longMoveTexts, normalize, normalizeVector
, pathToTrajectory
#endif
) where

import Prelude ()

import Game.LambdaHack.Common.Prelude

import           Control.DeepSeq
import           Data.Binary
import qualified Data.EnumMap.Strict as EM
import qualified Data.EnumSet as ES
import           Data.Int (Int32)

import GHC.Generics (Generic)

import Game.LambdaHack.Common.Point
import Game.LambdaHack.Common.Time

-- | 2D vectors in cartesian representation. Coordinates grow to the right
-- and down, so that the (1, 1) vector points to the bottom-right corner
-- of the screen.
data Vector = Vector
{ vx :: X
, vy :: Y
}
deriving (Show, Read, Eq, Ord, Generic)

instance Binary Vector where
put = put . (fromIntegral :: Int -> Int32) . fromEnum
get = fmap (toEnum . (fromIntegral :: Int32 -> Int)) get

-- Note that the conversion is not monotonic wrt the natural @Ord@ instance,
-- to keep it in sync with Point.
instance Enum Vector where
fromEnum (Vector vx vy) = vx + vy * (2 ^ maxLevelDimExponent)
toEnum n =
let (y, x) = n `quotRem` (2 ^ maxLevelDimExponent)
(vx, vy) | x > maxVectorDim = (x - 2 ^ maxLevelDimExponent, y + 1)
| x < - maxVectorDim = (x + 2 ^ maxLevelDimExponent, y - 1)
| otherwise = (x, y)
in Vector{..}

instance NFData Vector

-- | Maximal supported vector X and Y coordinates.
maxVectorDim :: Int
{-# INLINE maxVectorDim #-}
maxVectorDim = 2 ^ (maxLevelDimExponent - 1) - 1

-- | Tells if a vector has length 1 in the chessboard metric.
isUnit :: Vector -> Bool
{-# INLINE isUnit #-}
isUnit v = chessDistVector v == 1

-- | Checks whether a unit vector is a diagonal direction,
-- as opposed to cardinal. If the vector is not unit,
-- it checks that the vector is not horizontal nor vertical.
isDiagonal :: Vector -> Bool
{-# INLINE isDiagonal #-}
isDiagonal (Vector x y) = x * y /= 0

-- | Reverse an arbirary vector.
neg :: Vector -> Vector
{-# INLINE neg #-}
neg (Vector vx vy) = Vector (-vx) (-vy)

-- | The lenght of a vector in the chessboard metric,
-- where diagonal moves cost 1.
chessDistVector :: Vector -> Int
{-# INLINE chessDistVector #-}
chessDistVector (Vector x y) = max (abs x) (abs y)

-- | Squared euclidean distance between two vectors.
euclidDistSqVector :: Vector -> Vector -> Int
euclidDistSqVector (Vector x0 y0) (Vector x1 y1) =
(x1 - x0) ^ (2 :: Int) + (y1 - y0) ^ (2 :: Int)

-- | Vectors of all unit moves in the chessboard metric,
-- clockwise, starting north-west.
moves :: [Vector]
moves =
map (uncurry Vector)
[(-1, -1), (0, -1), (1, -1), (1, 0), (1, 1), (0, 1), (-1, 1), (-1, 0)]

-- | Vectors of all cardinal direction unit moves, clockwise, starting north.
movesCardinal :: [Vector]
movesCardinal = map (uncurry Vector) [(0, -1), (1, 0), (0, 1), (-1, 0)]

-- | Vectors of all diagonal direction unit moves, clockwise, starting north.
movesDiagonal :: [Vector]
movesDiagonal = map (uncurry Vector) [(-1, -1), (1, -1), (1, 1), (-1, 1)]

-- | Currently unused.
_moveTexts :: [Text]
_moveTexts = ["NW", "N", "NE", "E", "SE", "S", "SW", "W"]

longMoveTexts :: [Text]
longMoveTexts = [ "northwest", "north", "northeast", "east"
, "southeast", "south", "southwest", "west" ]

compassText :: Vector -> Text
compassText v = let m = EM.fromList \$ zip moves longMoveTexts
assFail = error \$ "not a unit vector" `showFailure` v
in EM.findWithDefault assFail v m

-- | All (8 at most) closest neighbours of a point within an area.
vicinity :: X -> Y   -- ^ limit the search to this area
-> Point    -- ^ position to find neighbours of
-> [Point]
vicinity lxsize lysize p =
if inside p (1, 1, lxsize - 2, lysize - 2)
then vicinityUnsafe p
else [ res | dxy <- moves
, let res = shift p dxy
, inside res (0, 0, lxsize - 1, lysize - 1) ]

vicinityUnsafe :: Point -> [Point]
vicinityUnsafe p = [ shift p dxy | dxy <- moves ]

-- | All (4 at most) cardinal direction neighbours of a point within an area.
vicinityCardinal :: X -> Y   -- ^ limit the search to this area
-> Point    -- ^ position to find neighbours of
-> [Point]
vicinityCardinal lxsize lysize p =
[ res | dxy <- movesCardinal
, let res = shift p dxy
, inside res (0, 0, lxsize - 1, lysize - 1) ]

vicinityCardinalUnsafe :: Point -> [Point]
vicinityCardinalUnsafe p = [ shift p dxy | dxy <- movesCardinal ]

squareUnsafeSet :: Point -> ES.EnumSet Point
squareUnsafeSet (Point x y) =
ES.fromDistinctAscList \$ map (uncurry Point)
[ (x - 1, y - 1)
, (x,     y - 1)
, (x + 1, y - 1)
, (x - 1, y)
, (x,     y)  -- full square, including the origin
, (x + 1, y)
, (x - 1, y + 1)
, (x,     y + 1)
, (x + 1, y + 1) ]

-- | Translate a point by a vector.
shift :: Point -> Vector -> Point
{-# INLINE shift #-}
shift (Point x0 y0) (Vector x1 y1) = Point (x0 + x1) (y0 + y1)

-- | Translate a point by a vector, but only if the result fits in an area.
shiftBounded :: X -> Y -> Point -> Vector -> Point
shiftBounded lxsize lysize pos v@(Vector xv yv) =
if inside pos (-xv, -yv, lxsize - xv - 1, lysize - yv - 1)
then shift pos v
else pos

-- | A list of points that a list of vectors leads to.
trajectoryToPath :: Point -> [Vector] -> [Point]
trajectoryToPath _ [] = []
trajectoryToPath start (v : vs) = let next = shift start v
in next : trajectoryToPath next vs

-- | A list of points that a list of vectors leads to, bounded by level size.
trajectoryToPathBounded :: X -> Y -> Point -> [Vector] -> [Point]
trajectoryToPathBounded _ _ _ [] = []
trajectoryToPathBounded lxsize lysize start (v : vs) =
let next = shiftBounded lxsize lysize start v
in next : trajectoryToPathBounded lxsize lysize next vs

-- | The vector between the second point and the first. We have
--
-- > shift pos1 (pos2 `vectorToFrom` pos1) == pos2
--
-- The arguments are in the same order as in the underlying scalar subtraction.
vectorToFrom :: Point -> Point -> Vector
{-# INLINE vectorToFrom #-}
vectorToFrom (Point x0 y0) (Point x1 y1) = Vector (x0 - x1) (y0 - y1)

-- | A list of vectors between a list of points.
pathToTrajectory :: [Point] -> [Vector]
pathToTrajectory [] = []
pathToTrajectory lp1@(_ : lp2) = zipWith vectorToFrom lp2 lp1

computeTrajectory :: Int -> Int -> Int -> [Point] -> ([Vector], (Speed, Int))
computeTrajectory weight throwVelocity throwLinger path =
let speed = speedFromWeight weight throwVelocity
trange = rangeFromSpeedAndLinger speed throwLinger
btrajectory = pathToTrajectory \$ take (trange + 1) path
in (btrajectory, (speed, trange))

-- | Rotate a vector by the given angle (expressed in radians)
-- counterclockwise and return a unit vector approximately in the resulting
-- direction.
rotate :: RadianAngle -> Vector -> Vector
rotate angle (Vector x' y') =
let x = fromIntegral x'
y = fromIntegral y'
-- Minus before the angle comes from our coordinates being
-- mirrored along the X axis (Y coordinates grow going downwards).
dx = x * cos (-angle) - y * sin (-angle)
dy = x * sin (-angle) + y * cos (-angle)
in normalize dx dy

-- | Given a vector of arbitrary non-zero length, produce a unit vector
-- that points in the same direction (in the chessboard metric).
-- Of several equally good directions it picks one of those that visually
-- (in the euclidean metric) maximally align with the original vector.
normalize :: Double -> Double -> Vector
normalize dx dy =
assert (dx /= 0 || dy /= 0 `blame` "can't normalize zero" `swith` (dx, dy)) \$
let angle :: Double
angle = atan (dy / dx) / (pi / 2)
dxy | angle <= -0.75 && angle >= -1.25 = (0, -1)
| angle <= -0.25 = (1, -1)
| angle <= 0.25  = (1, 0)
| angle <= 0.75  = (1, 1)
| angle <= 1.25  = (0, 1)
| otherwise = error \$ "impossible angle" `showFailure` (dx, dy, angle)
in if dx >= 0
then uncurry Vector dxy
else neg \$ uncurry Vector dxy

normalizeVector :: Vector -> Vector
normalizeVector v@(Vector vx vy) =
let res = normalize (fromIntegral vx) (fromIntegral vy)
in assert (not (isUnit v) || v == res
`blame` "unit vector gets untrivially normalized"
`swith` (v, res))
res

-- | Given two distinct positions, determine the direction (a unit vector)
-- in which one should move from the first in order to get closer
-- to the second. Ignores obstacles. Of several equally good directions
-- (in the chessboard metric) it picks one of those that visually
-- (in the euclidean metric) maximally align with the vector between
-- the two points.
towards :: Point -> Point -> Vector
towards pos0 pos1 =
assert (pos0 /= pos1 `blame` "towards self" `swith` (pos0, pos1))
\$ normalizeVector \$ pos1 `vectorToFrom` pos0
```