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Scroll.purs
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Scroll.purs
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module Halogen.Infinite.Scroll (class FeedOrder, feedOrder, class Feed, ScrollFeed(..), element, onElement, feedAbove, feedBelow, feedInsert, feedDelete, FeedParams,defaultFeedParams,component ) where
import Prelude hiding (top, bottom)
import CSS (height, marginRight, opacity, paddingRight, pct, position, relative, top, width, zIndex)
import CSS.Overflow (overflow, overflowY, scroll, hidden, overflowAuto)
import CSS.Size (px)
import Control.Monad.Free (Free, liftF, runFreeM)
import Control.Monad.Rec.Class (tailRecM, Step(..))
import Control.Monad.Resource (Resource, runResource)
import Control.Monad.State (State, execState, modify_)
import Data.Array (cons, fold, head, last, null)
import Data.Array as A
import Data.List as List
import Data.Map (Map)
import Data.Map as Map
import Data.Maybe (Maybe(..), isJust, maybe)
import Data.Options ((:=))
import Data.Ord (abs)
import Data.Traversable (sum, traverse, traverse_)
import Data.Tuple (Tuple(..))
import Data.Tuple.Nested ((/\))
import Effect (Effect)
import Effect.AVar (AVar)
import Effect.Aff (delay, Milliseconds(..))
import Effect.Aff.AVar (new, put, tryTake)
import Effect.Aff.Class (class MonadAff)
import Effect.Class (liftEffect)
import Halogen as H
import Halogen.HTML as HH
import Halogen.HTML.CSS (style)
import Halogen.HTML.Properties as HP
import Halogen.Subscription as HS
import Pipes ((>->))
import Pipes.Core (Producer)
import Pipes.Prelude as Pipes
import Prelude as Prelude
import Type.Proxy (Proxy(..))
import Web.DOM.Element (Element, scrollTop, setScrollTop)
import Web.Intersection.Observer (newIntersectionObserver)
import Web.Intersection.Observer as WIO
import Web.Intersection.Observer.Entry (IntersectionObserverEntry)
import Web.Intersection.Observer.Options (root)
import Web.Resize.Observer (newResizeObserver)
import Web.Resize.Observer as WRO
import Web.Resize.Observer.Entry (ResizeObserverEntry)
class (Ord e) <= FeedOrder e where
feedOrder :: e -> e -> Ordering
class (FeedOrder e, MonadAff m) <= Feed e m where
element :: forall q o . H.Component q e o m
onElement :: e -> m Unit
feedAbove :: e -> m (Producer e Resource Unit)
feedBelow :: e -> m (Producer e Resource Unit)
feedInsert :: m (Maybe (HS.Emitter e))
feedDelete :: m (Maybe (HS.Emitter e))
type FeedParams e =
{ initialElement :: e
, pageSize :: Int
, hiddenPages :: Int
, preloadedPages :: Int
, enableTop :: Boolean
, preloadMillis :: Number
}
defaultFeedParams :: forall e . e -> FeedParams e
defaultFeedParams e =
{ initialElement: e
, pageSize: 10
, hiddenPages: 3
, preloadedPages: 3
, enableTop: false
, preloadMillis: 333.3
}
data ScrollFeed = ScrollFeed (Number -> Effect Unit)
component :: forall e q m .
Ord e
=> Feed e m
=> H.Component q (FeedParams e) ScrollFeed m
component =
H.mkComponent
{ initialState: \feedParams ->
{ feedParams
, pages: Map.empty
, preloaded: Map.empty
, lock: Nothing
, update: { topLoad: Nothing, bottomLoad: Nothing, scroll: Nothing }
}
, render: renderFeed
, eval: H.mkEval $ H.defaultEval { handleAction = handleFeedAction
, initialize = Just InitializeFeed
}
}
data Pos = Below Int | Inside Int | Above Int
instance Monoid Pos where
mempty = Below Prelude.top
instance Semigroup Pos where
append (Inside a) _ = Inside a
append _ (Inside a) = Inside a
append (Below a) (Below b) = Below (min a b)
append (Above a) (Above b) = Above (max a b)
append (Below a) _ = Inside a
append (Above a) _ = Inside a
findBucket :: forall e . FeedOrder e => e -> Map Int (Page e) -> Int
findBucket e m =
case fold $ List.toUnfoldable $ Map.values (bounds <$> m) of
Below a -> a
Above a -> a
Inside a -> a
where
bounds { id, elements } =
case (head elements /\ last elements) of
(Just h /\ Just l)->
case (e `feedOrder` h /\ e `feedOrder` l) of
(LT /\ _) -> Below id
(_ /\ GT) -> Above id
_ -> Inside id
_ -> Above id
type FeedState e =
{ feedParams :: FeedParams e
, pages :: Map Int (Page e)
, preloaded :: Map Int (Page e)
, lock :: Maybe (AVar Unit)
, update :: {
topLoad :: Maybe { key :: Int, value :: Page e }
, bottomLoad :: Maybe { key :: Int, value :: Page e }
, scroll :: Maybe Number
}
}
data FeedAction e =
InitializeFeed
| PageOutput PageOutput
| FeedInsertElement e
type FeedSlots e = ( page :: H.Slot (PageInsert e) PageOutput Int )
_page = Proxy :: Proxy "page"
handleFeedAction :: forall e m .
Feed e m
=> FeedAction e -> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) ScrollFeed m Unit
handleFeedAction InitializeFeed = do
H.getRef (H.RefLabel "feed") >>= traverse_ initializeFeed
e <- H.lift feedInsert
traverse_ (\x -> void $ H.subscribe (FeedInsertElement <$> x)) e
where
initializeFeed feed = do
H.raise $ ScrollFeed $ \n -> do
t <- scrollTop feed
setScrollTop (t + n) feed
zerothPage <- loadInitialPage feed
H.modify_ (\st -> st {
pages = Map.singleton 0 zerothPage
}
)
params <- H.gets (\st -> st.feedParams)
void $ tailRecM (fillPreload params feed) 0
lock <- H.liftAff do
delay (Milliseconds params.preloadMillis)
new unit
H.modify_ (\st -> st { lock = Just lock })
fillPreload params feed i = do
if i >= params.preloadedPages
then pure (Done i)
else do
managePreload feed
pure (Loop (i+1))
handleFeedAction (FeedInsertElement e) = do
state <- H.get
H.lift $ onElement e
let b = findBucket e (Map.union state.preloaded state.pages)
H.modify_ (insertIntoPage b)
H.tell _page b (PageInsert e)
where
insertIntoPage p st = st { pages = Map.alter insertInto p st.pages
, preloaded = Map.alter insertInto p st.preloaded
}
insertInto Nothing = Nothing
insertInto (Just page) = Just (page { elements = A.nub $ A.insertBy feedOrder e page.elements })
handleFeedAction (PageOutput (PageHeight {id, height})) = do
H.modify_ setPageHeight
where
setPageHeight st = st { pages = Map.alter setHeight id st.pages
, preloaded = Map.alter setHeight id st.preloaded
}
setHeight Nothing = Nothing
setHeight (Just page) = Just (page { pageHeight = height })
handleFeedAction (PageOutput (PageIntersection page)) = mask do
feed' <- H.getRef (H.RefLabel "feed")
flip traverse_ feed' $ \feed -> do
st <- H.modify (\st -> execState (stateUpdate (computeUpdate st page)) st)
t <- H.liftEffect $ scrollTop feed
H.liftEffect $ traverse_ (\o -> setScrollTop (t + o) feed) st.update.scroll
H.modify_ (\s -> s { update = { topLoad: Nothing, bottomLoad: Nothing, scroll: Nothing } })
flip traverse_ st.update.topLoad $ \kv -> do
a <- loadPageAbove feed kv.value
traverse_ (\p -> H.modify_ (\s -> s { preloaded = Map.insert p.id p st.preloaded } )) a
flip traverse_ st.update.bottomLoad $ \kv -> do
a <- loadPageBelow feed kv.value
traverse_ (\p -> H.modify_ (\s -> s { pages = Map.insert p.id p s.pages } )) a
handleFeedAction (PageOutput (PageEmpty i)) = do
H.modify_ (\st -> st { pages = Map.delete i st.pages })
managePreload :: forall e o m .
Feed e m
=> Element -> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m Unit
managePreload feed = do
state <- H.get
let tooFew = Map.size state.preloaded < state.feedParams.preloadedPages
tooMany = Map.size state.preloaded > state.feedParams.preloadedPages
when tooFew do
let top = maybe (Map.findMin state.pages) Just (Map.findMin state.preloaded)
a <- join <$> traverse (\kv -> loadPageAbove feed kv.value) top
traverse_ (\p -> H.modify_ (\st -> st { preloaded = Map.insert p.id p st.preloaded } )) a
when tooMany do
H.modify_ (\st -> st { preloaded = maybe st.preloaded
(\kv -> Map.delete kv.key st.preloaded)
(Map.findMin st.preloaded)
})
data UpdateF e a =
TopShift { key :: Int, value :: Page e } a
| TopUnshift { key :: Int, value :: Page e } a
| TopLoad { key :: Int, value :: Page e } a
| TopDelete { key :: Int, value :: Page e } a
| BottomLoad { key :: Int, value :: Page e } a
| BottomDelete { key :: Int, value :: Page e } a
| UpdateIntersection PageIntersection a
instance Functor (UpdateF e) where
map f (TopShift page a) = TopShift page (f a)
map f (TopUnshift page a) = TopUnshift page (f a)
map f (TopLoad page a) = TopLoad page (f a)
map f (TopDelete page a) = TopDelete page (f a)
map f (BottomLoad page a) = BottomLoad page (f a)
map f (BottomDelete page a) = BottomDelete page (f a)
map f (UpdateIntersection page a) = UpdateIntersection page (f a)
type Update e = Free (UpdateF e)
topShift :: forall e. { key :: Int, value :: Page e } -> Update e Unit
topShift page = liftF $ TopShift page unit
topUnshift :: forall e. { key :: Int, value :: Page e } -> Update e Unit
topUnshift page = liftF $ TopUnshift page unit
topLoad :: forall e. { key :: Int, value :: Page e } -> Update e Unit
topLoad page = liftF $ TopLoad page unit
topDelete :: forall e. { key :: Int, value :: Page e } -> Update e Unit
topDelete page = liftF $ TopDelete page unit
bottomLoad :: forall e. { key :: Int, value :: Page e } -> Update e Unit
bottomLoad page = liftF $ BottomLoad page unit
bottomDelete :: forall e. { key :: Int, value :: Page e } -> Update e Unit
bottomDelete page = liftF $ BottomDelete page unit
updateIntersection :: forall e. PageIntersection -> Update e Unit
updateIntersection page = liftF $ UpdateIntersection page unit
stateUpdate :: forall e. Update e Unit -> State (FeedState e) Unit
stateUpdate f = do
modify_ (\st -> st { update = st.update { scroll = Nothing } })
runFreeM go f
where
go (TopShift page a) = do
modify_ (\st -> st {
pages = Map.insert page.key page.value st.pages
, preloaded = Map.delete page.key st.preloaded
, update = st.update { scroll = Just page.value.pageHeight }
} )
pure a
go (TopUnshift page a) = do
modify_ (\st -> st {
pages = Map.delete page.key st.pages
, preloaded = Map.insert page.key page.value st.preloaded
, update = st.update { scroll = Just (-page.value.pageHeight) }
})
pure a
go (TopLoad page a) = do
modify_ (\st -> st {
update = if ((\u -> u.key) <$> st.update.topLoad) == Just page.key
then st.update { topLoad = Nothing }
else st.update { topLoad = Just page }
})
pure a
go (TopDelete page a) = do
modify_ (\st -> st {
preloaded = Map.delete page.key st.preloaded
, update = st.update { topLoad = Nothing }
})
pure a
go (BottomLoad page a) = do
modify_ (\st -> st {
update = if ((\u -> u.key) <$> st.update.bottomLoad) == Just page.key
then st.update { bottomLoad = Nothing }
else st.update { bottomLoad = Just page }
})
pure a
go (BottomDelete page a) = do
modify_ (\st -> st {
pages = Map.delete page.key st.pages
, update = st.update { bottomLoad = Nothing }
})
pure a
go (UpdateIntersection { id, height } a) = do
let setIntersection Nothing = Nothing
setIntersection (Just page) = Just (page { visibleHeight = height })
modify_ (\st -> st {
pages = Map.alter setIntersection id st.pages
})
pure a
computeUpdate :: forall e. FeedState e -> PageIntersection -> Update e Unit
computeUpdate { feedParams, pages, preloaded } page =
let notVisible (Tuple _ p) = p.visibleHeight == 0.0
extraAbove = A.length $ A.takeWhile notVisible $ Map.toUnfoldable pages
tooFewAbove = extraAbove < feedParams.hiddenPages
tooManyAbove = extraAbove > feedParams.hiddenPages
tooFewPreload = Map.size preloaded < feedParams.preloadedPages
tooManyPreload = Map.size preloaded > feedParams.preloadedPages
extraBelow = A.length $ A.takeWhile notVisible $ A.reverse $ Map.toUnfoldable pages
tooFewBelow = extraBelow < feedParams.hiddenPages
tooManyBelow = extraBelow > feedParams.hiddenPages
in do
updateIntersection page
when (feedParams.enableTop && tooFewAbove) $ traverse_ topShift (Map.findMax preloaded)
when (feedParams.enableTop && tooManyAbove) $ traverse_ topUnshift (Map.findMin pages)
when (feedParams.enableTop && tooFewPreload) $ traverse_ topLoad (Map.findMin preloaded)
when (feedParams.enableTop && tooManyPreload) $ traverse_ topDelete (Map.findMin preloaded)
when tooFewBelow $ traverse_ bottomLoad (Map.findMax pages)
when tooManyBelow $ traverse_ bottomDelete (Map.findMax pages)
mask :: forall e o m .
Feed e m
=> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m Unit
-> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m Unit
mask f = do
lock <- H.gets (\st -> st.lock)
traverse_ go lock
where
go lock = do
free <- H.liftAff $ tryTake lock
when (isJust free) (f *> (H.liftAff $ put unit lock))
loadInitialPage :: forall e o m .
Feed e m
=> Element -> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m (Page e)
loadInitialPage feed = do
elements <- loadInitialPageElements
H.lift $ traverse_ onElement elements
pure { id: 0
, elements
, parent: feed
, pageHeight: 0.0
, visibleHeight: 0.0
}
where
loadInitialPageElements = do
init <- H.gets (\st -> st.feedParams.initialElement)
params <- H.gets (\st -> st.feedParams)
below <- H.lift $ feedBelow init
let source = A.fromFoldable <$> Pipes.toListM (below >-> Pipes.take (params.pageSize - 1))
cons init <$> (H.liftAff $ runResource source)
loadPageAbove :: forall e o m .
Feed e m
=> Element
-> Page e
-> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m (Maybe (Page e))
loadPageAbove feed page = join <$> traverse loadNextPageUp (head page.elements)
where
loadNextPageUp :: e -> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m (Maybe (Page e))
loadNextPageUp element = do
params <- H.gets (\st -> st.feedParams)
above <- H.lift $ feedAbove element
let source = A.fromFoldable <$> Pipes.toListM (above >-> Pipes.take params.pageSize)
elements <- A.reverse <$> (H.liftAff $ runResource source)
H.lift $ traverse_ onElement elements
if null elements
then pure Nothing
else pure $ Just { id: page.id - 1
, elements
, parent: feed
, pageHeight: 0.0
, visibleHeight: 0.0
}
loadPageBelow :: forall e o m .
Feed e m
=> Element
-> Page e
-> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m (Maybe (Page e))
loadPageBelow feed page = join <$> traverse loadNextPageUp (last page.elements)
where
loadNextPageUp :: e -> H.HalogenM (FeedState e) (FeedAction e) (FeedSlots e) o m (Maybe (Page e))
loadNextPageUp element = do
params <- H.gets (\st -> st.feedParams)
below <- H.lift $ feedBelow element
let source = A.fromFoldable <$> Pipes.toListM (below >-> Pipes.take params.pageSize)
elements <- H.liftAff $ runResource source
H.lift $ traverse_ onElement elements
if null elements
then pure Nothing
else pure $ Just { id: page.id + 1
, elements
, parent: feed
, pageHeight: 0.0
, visibleHeight: 0.0
}
renderFeed :: forall e m .
Feed e m
=> FeedState e -> H.ComponentHTML (FeedAction e) (FeedSlots e) m
renderFeed feedState = do
HH.div
[ style do
width (pct 100.0)
height (pct 100.0)
overflow hidden
]
[ renderLoaded
, renderBarrier
, renderPreloaded
]
where
renderPageSlot (Tuple i page) = HH.slot _page i pageComponent page PageOutput
renderLoaded =
HH.div [ HP.ref (H.RefLabel "feed")
, style do
marginRight (px (-50.0))
paddingRight (px 50.0)
height (pct 100.0)
overflowY scroll
]
(renderPageSlot <$> Map.toUnfoldable feedState.pages)
renderBarrier =
HH.div [ style do
marginRight (px (-50.0))
paddingRight (px 50.0)
height (pct 100.0)
zIndex (-1)
position relative
top (pct (-100.0))
]
[
]
renderPreloaded =
HH.div [ style do
zIndex (-2)
position relative
]
(preload <$> Map.toUnfoldable feedState.preloaded)
preload page@(Tuple i _) =
HH.div [ style do
zIndex ((-2) - (abs i))
opacity 0.0
position relative
]
[ renderPageSlot page
]
type Page e =
{ id :: Int
, elements :: Array e
, parent :: Element
, pageHeight :: Number
, visibleHeight :: Number
}
data PageInsert e a =
PageInsert e a
data PageAction e =
InitializePage
| PageResize (Array ResizeObserverEntry)
| PageIntersect (Array IntersectionObserverEntry)
| PageDeleteElement e
type PageIntersection = {
id :: Int
, height :: Number
}
data PageOutput =
PageHeight {
id :: Int
, height :: Number
}
| PageIntersection PageIntersection
| PageEmpty Int
type PageSlots e = ( pageElement :: forall q o . H.Slot q o e )
_pageElement = Proxy :: Proxy "pageElement"
pageComponent :: forall e m .
Feed e m
=> H.Component (PageInsert e) (Page e) PageOutput m
pageComponent =
H.mkComponent
{ initialState: identity
, render: renderPage
, eval: H.mkEval $ H.defaultEval { handleAction = pageAction
, handleQuery = pageInsert
, initialize = Just InitializePage
}
}
where
renderPage page =
HH.div
[ HP.ref (H.RefLabel "page")
, style do
overflow overflowAuto
]
((\e -> HH.slot_ _pageElement e element e) <$> page.elements)
pageInsert :: forall a . PageInsert e a -> H.HalogenM (Page e) (PageAction e) (PageSlots e) PageOutput m (Maybe a)
pageInsert (PageInsert e a) = do
H.modify_ (\st -> st { elements = A.nub $ A.insertBy feedOrder e st.elements })
pure $ Just a
pageAction :: PageAction e -> H.HalogenM (Page e) (PageAction e) (PageSlots e) PageOutput m Unit
pageAction InitializePage = do
H.getRef (H.RefLabel "page") >>= traverse_ observe
e <- H.lift feedDelete
traverse_ (\x -> void $ H.subscribe (PageDeleteElement <$> x)) e
where
observe page = observeHeight page *> observeIntersection page
observeIntersection page = do
parent <- H.gets (\p -> p.parent)
{ emitter, listener } <- H.liftEffect HS.create
void $ H.subscribe emitter
io <- H.liftEffect $ newIntersectionObserver
(\a _ -> HS.notify listener (PageIntersect a))
(root := parent)
liftEffect $ WIO.observe io page
observeHeight page = do
{ emitter, listener } <- H.liftEffect HS.create
void $ H.subscribe emitter
ro <- H.liftEffect $ newResizeObserver (\a _ -> HS.notify listener (PageResize a))
liftEffect $ WRO.observe ro page
pageAction (PageResize o) = do
pageId <- H.gets (\page -> page.id)
let h = sum ((\e -> e.contentRect.height) <$> o)
H.raise (PageHeight { id: pageId, height: h })
pageAction (PageIntersect o) = do
let h = sum ((\e -> e.intersectionRect.height) <$> o)
pageId <- H.gets (\page -> page.id)
H.modify_ (\st -> st { visibleHeight = h})
H.raise (PageIntersection { id: pageId, height: h })
pageAction (PageDeleteElement e) = do
state <- H.modify (\st -> st { elements = A.delete e st.elements })
when (null state.elements) $ H.raise (PageEmpty state.id)