module Travel
    (stepCreature,
     turnCreature,
     TeleportJumpOutcome,
     resolveTeleportJump,
     executeTeleportJump)
    where

import Control.Monad.Maybe
import Facing
import DB
import Plane
import Data.Maybe
import Control.Monad
import Control.Monad.Trans
import Data.Ord
import Position
import TerrainData
import Data.List (minimumBy)
import Creature
import CreatureData

walkCreature :: (DBReadable db) => Facing -> (Integer,Integer) -> 
                                     Location m CreatureRef () -> db (Location m CreatureRef ())
walkCreature face (x',y') l = liftM (fromMaybe l) $ runMaybeT $
    do (plane_ref,Position (x,y)) <- MaybeT $ return $ extractLocation l
       let standing = Standing { standing_plane = plane_ref,
                                 standing_position = Position (x+x',y+y'),
                                 standing_facing = face } 
       flip unless (fail "") =<< (lift $ isTerrainPassable plane_ref (entity l) $ standing_position standing)
       return $ generalizeLocation $ toStanding standing l

stepCreature :: (DBReadable db) => Facing -> Location m CreatureRef () -> db (Location m CreatureRef ())
stepCreature face = walkCreature face (facingToRelative face)

turnCreature :: (DBReadable db) => Facing -> Location m CreatureRef () -> db (Location m CreatureRef ())
turnCreature face = walkCreature face (0,0)

-------------------------------------------------------------------------------------------------------------
--	Teleportation/Jumping
-------------------------------------------------------------------------------------------------------------

-- |
-- Try to teleport the creature to the specified Position.  The teleport attempt can be automatically retried a number of times, and the most accurate attempt will be used.
-- If the retries are negative, the teleport will be made artificially innacurate.
--
randomTeleportLanding :: (DBReadable db) => Integer -> PlaneRef -> Position -> Position -> db Position
randomTeleportLanding retries plane_ref source_destination goal_destination =
    do landings <- replicateM (fromInteger $ max 1 retries) $ (pickRandomClearSite 3) 0 0 goal_destination (not . (`elem` impassable_terrains)) plane_ref
       return $ minimumBy (comparing $ \p -> distanceBetweenSquared goal_destination p ^ 2 * distanceBetweenSquared source_destination p) landings

data TeleportJumpOutcome =
    TeleportJumpGood CreatureRef Standing
  | TeleportJumpFailed

-- |
-- Teleport jump a creature about 7 units in the specified direction.
--
resolveTeleportJump :: (DBReadable db) => CreatureRef -> Facing -> db TeleportJumpOutcome
resolveTeleportJump creature_ref face = liftM (fromMaybe TeleportJumpFailed) $ runMaybeT $
    do start_location <- lift $ dbWhere creature_ref
       jump_roll <- liftM roll_log $ lift $ rollCreatureAbilityScore JumpSkill 0 (entity start_location)
       standing_location <- MaybeT $ return $ extractLocation start_location
       landing_position <- lift $ randomTeleportLanding jump_roll (standing_plane standing_location) (standing_position standing_location) $
           offsetPosition (facingToRelative7 face) $ standing_position standing_location
       case () of
           () | jump_roll <= 0 -> return TeleportJumpFailed
           () | otherwise -> return $ TeleportJumpGood (entity start_location) $ standing_location { standing_position = landing_position, standing_facing = face }

-- | Execute a resolved teleport jump.
executeTeleportJump :: TeleportJumpOutcome -> DB ()
executeTeleportJump TeleportJumpFailed = return ()
executeTeleportJump (TeleportJumpGood creature_ref standing_location) = 
    do _ <- dbMove (return . toStanding standing_location) creature_ref
       dbPushSnapshot $ TeleportEvent creature_ref
       return ()