-- | Running and disturbance.
module Game.LambdaHack.Running
  ( run, continueRun
  ) where

import Control.Monad.State hiding (State, state)
import qualified Data.List as L
import qualified Data.IntMap as IM
import qualified Data.IntSet as IS

import Game.LambdaHack.Utils.Assert
import Game.LambdaHack.Action
import Game.LambdaHack.Actions
import Game.LambdaHack.Point
import Game.LambdaHack.Vector
import Game.LambdaHack.PointXY
import Game.LambdaHack.Level
import Game.LambdaHack.Msg
import Game.LambdaHack.Actor
import Game.LambdaHack.ActorState
import Game.LambdaHack.Perception
import Game.LambdaHack.State
import qualified Game.LambdaHack.Tile as Tile
import qualified Game.LambdaHack.Kind as Kind
import qualified Game.LambdaHack.Feature as F

-- | Start running in the given direction and with the given number
-- of tiles already traversed (usually 0). The first step of running
-- succeeds much more often than subsequent steps, because most
-- of the disturbances are ignored, since the player is aware of them
-- and still explicitly requests a run.
run :: (Vector, Int) -> Action ()
run (dir, dist) = do
  cops <- contentOps
  pl <- gets splayer
  locHere <- gets (bloc . getPlayerBody)
  lvl <- gets slevel
  targeting <- gets (ctargeting . scursor)
  if targeting /= TgtOff
    then moveCursor dir 10
    else do
      let accessibleDir loc d = accessible cops lvl loc (loc `shift` d)
          -- Do not count distance if we just open a door.
          distNew = if accessibleDir locHere dir then dist + 1 else dist
      updatePlayerBody (\ p -> p { bdir = Just (dir, distNew) })
      -- attacks and opening doors disallowed while running
      moveOrAttack False pl dir

-- | Player running mode, determined from the nearby cave layout.
data RunMode =
    RunOpen                     -- ^ open space, in particular the T crossing
  | RunHub                      -- ^ a hub of separate corridors
  | RunCorridor (Vector, Bool)  -- ^ a single corridor, turning here or not
  | RunDeadEnd                  -- ^ dead end

-- | Determine the running mode. For corridors, pick the running direction
-- trying to explore all corners, by prefering cardinal to diagonal moves.
runMode :: Point -> Vector -> (Point -> Vector -> Bool) -> X -> RunMode
runMode loc dir dirEnterable lxsize =
  let dirNearby dir1 dir2 = euclidDistSq lxsize dir1 dir2 == 1
      dirBackward d = euclidDistSq lxsize (neg dir) d <= 1
      dirAhead d = euclidDistSq lxsize dir d <= 2
      findOpen =
        let f dirC open = open ++
              case L.filter (dirNearby dirC) dirsEnterable of
                l | dirBackward dirC -> dirC : l  -- points backwards
                []  -> []  -- a narrow corridor, just one tile wide
                [_] -> []  -- a turning corridor, two tiles wide
                l   -> dirC : l  -- too wide
        in L.foldr f []
      dirsEnterable = L.filter (dirEnterable loc) (moves lxsize)
  in case dirsEnterable of
    [] -> assert `failure` (loc, dir)
    [negdir] -> assert (negdir == neg dir) $ RunDeadEnd
    _ ->
      let dirsOpen = findOpen dirsEnterable
          dirsCorridor = dirsEnterable L.\\ dirsOpen
      in case dirsCorridor of
        [] -> RunOpen  -- no corridors
        _ | L.any dirAhead dirsOpen -> RunOpen  -- open space ahead
        [d] -> RunCorridor (d, False)  -- corridor with no turn
        [d1, d2] | dirNearby d1 d2 ->  -- corridor with a turn
          -- Prefer cardinal to diagonal dirs, for hero safety,
          -- even if that means changing direction.
          RunCorridor (if diagonal lxsize d1 then d2 else d1, True)
        _ -> RunHub  -- a hub of many separate corridors

-- | Check for disturbances to running such newly visible items, monsters, etc.
runDisturbance :: Point -> Int -> Msg -> Party -> Party -> Perception -> Point
               -> (F.Feature -> Point -> Bool) -> (Point -> Bool) -> X -> Y
               -> (Vector, Int) -> Maybe (Vector, Int)
runDisturbance locLast distLast msg hs ms per locHere
               locHasFeature locHasItems lxsize lysize (dirNew, distNew) =
  let msgShown  = not (L.null msg)
      mslocs    = IS.delete locHere $ IS.fromList (L.map bloc (IM.elems ms))
      enemySeen = not (IS.null (mslocs `IS.intersection` totalVisible per))
      surrLast  = locLast : vicinity lxsize lysize locLast
      surrHere  = locHere : vicinity lxsize lysize locHere
      locThere  = locHere `shift` dirNew
      heroThere = locThere `elem` L.map bloc (IM.elems hs)
      -- Stop if you touch any individual tile with these propereties
      -- first time, unless you enter it next move, in which case stop then.
      touchList = [ locHasFeature F.Exit
                  , locHasItems
                  ]
      -- Here additionally ignore a tile property if you stand on such tile.
      standList = [ locHasFeature F.Path
                  , not . locHasFeature F.Lit
                  ]
      -- Here stop only if you touch any such tile for the first time.
      -- TODO: stop when running along a path and it ends (or turns).
      -- TODO: perhaps in open areas change direction to follow lit and paths.
      firstList = [ locHasFeature F.Lit
                  , not . locHasFeature F.Path
                  ]
      -- TODO: stop when walls vanish from cardinal directions or when any
      -- walls re-appear again. Actually stop one tile before that happens.
      -- Then remove some other, subsumed conditions.
      -- This will help with corridors starting in dark rooms.
      touchNew fun =
        let touchLast = L.filter fun surrLast
            touchHere = L.filter fun surrHere
        in touchHere L.\\ touchLast
      touchExplore fun = touchNew fun == [locThere]
      touchStop fun = touchNew fun /= []
      standNew fun = L.filter (\ loc -> locHasFeature F.Walkable loc ||
                                        locHasFeature F.Openable loc)
                       (touchNew fun)
      standExplore fun = not (fun locHere) && standNew fun == [locThere]
      standStop fun = not (fun locHere) && standNew fun /= []
      firstNew fun = L.all (not . fun) surrLast &&
                     L.any fun surrHere
      firstExplore fun = firstNew fun && fun locThere
      firstStop = firstNew
      tryRunMaybe
        | msgShown || enemySeen
          || heroThere || distLast >= 40  = Nothing
        | L.any touchExplore touchList    = Just (dirNew, 1000)
        | L.any standExplore standList    = Just (dirNew, 1000)
        | L.any firstExplore firstList    = Just (dirNew, 1000)
        | L.any touchStop touchList       = Nothing
        | L.any standStop standList       = Nothing
        | L.any firstStop firstList       = Nothing
        | otherwise                       = Just (dirNew, distNew)
  in tryRunMaybe

-- | This function implements the actual logic of running. It checks if we
-- have to stop running because something interesting cropped up,
-- it ajusts the direction given by the vector if we reached
-- a corridor's corner (we never change direction except in corridors)
-- and it increments the counter of traversed tiles.
continueRun :: (Vector, Int) -> Action ()
continueRun (dirLast, distLast) = do
  cops@Kind.COps{cotile} <- contentOps
  locHere <- gets (bloc . getPlayerBody)
  per <- currentPerception
  msg <- currentMsg
  ms  <- gets (lmonsters . slevel)
  hs  <- gets (lheroes . slevel)
  lvl@Level{lxsize, lysize} <- gets slevel
  let locHasFeature f loc = Tile.hasFeature cotile f (lvl `at` loc)
      locHasItems loc = not $ L.null $ lvl `atI` loc
      locLast = if distLast == 0 then locHere else locHere `shift` neg dirLast
      tryRunDist (dir, distNew)
        | accessibleDir locHere dir =
          maybe abort run $
            runDisturbance locLast distLast msg hs ms per locHere
              locHasFeature locHasItems lxsize lysize (dir, distNew)
        | otherwise = abort  -- do not open doors in the middle of a run
      tryRun dir = tryRunDist (dir, distLast)
      tryRunAndStop dir = tryRunDist (dir, 1000)
      accessibleDir loc dir = accessible cops lvl loc (loc `shift` dir)
      openableDir loc dir   = Tile.hasFeature cotile F.Openable
                                (lvl `at` (loc `shift` dir))
      dirEnterable loc d = accessibleDir loc d || openableDir loc d
  case runMode locHere dirLast dirEnterable lxsize of
    RunDeadEnd -> abort                   -- we don't run backwards
    RunOpen    -> tryRun dirLast          -- run forward into the open space
    RunHub     -> abort                   -- stop and decide where to go
    RunCorridor (dirNext, turn) ->        -- look ahead
      case runMode (locHere `shift` dirNext) dirNext dirEnterable lxsize of
        RunDeadEnd     -> tryRun dirNext  -- explore the dead end
        RunCorridor _  -> tryRun dirNext  -- follow the corridor
        RunOpen | turn -> abort           -- stop and decide when to turn
        RunHub  | turn -> abort           -- stop and decide when to turn
        RunOpen -> tryRunAndStop dirNext  -- no turn, get closer and stop
        RunHub  -> tryRunAndStop dirNext  -- no turn, get closer and stop