Add first design of timeline

The current unfinished design is a first implementation of how the timeline could be built properly. It yet needs a simple way of adding data types, however, which should be a bit more universal.

src/Internal/Values/Timeline.elm

@@ -6,367 +6,484 @@ a simple way to view events.
 -}
 
 import FastDict as Dict exposing (Dict)
-import Internal.Config.Leaking as Leaking
-import Internal.Tools.Fold as Fold
-import Internal.Values.Event as Event exposing (IEvent)
-import Internal.Values.StateManager as StateManager exposing (StateManager)
-import Internal.Tools.DefaultDict as DefaultDict exposing (DefaultDict)
-import Internal.Tools.Hashdict as Hashdict exposing (Hashdict)
 import Internal.Tools.Iddict as Iddict exposing (Iddict)
 import Internal.Tools.Filters.Main as Filter exposing (Filter)
-import Internal.Config.Leaking exposing (nextBatch)
+import Internal.Tools.Iddict as Iddict
 
-{-| The Timeline is a comprehensive object describing a timeline in a room.
+type alias Timeline =
-
+    { mostRecentToken : TokenId
-Any Timeline type contains the following pieces of information:
+    , slices : Iddict Slice
-
+    , tokenToId : Dict String TokenId
-- `events` Comprehensive dictionary containing all locally stored timeline events
+    , tokens : Iddict Token
-- `batches` Comprehensive dictionary containing all batches. Batches are pieces 
-    of the timeline that have been sent by the homeserver.
-- `token` Dictionary that maps for each batch token which batches it borders
-- `mostRecentSync` Id of the most "recent" batch in the timeline
--}
-type Timeline
-    = Timeline
-        { events : Hashdict IEvent
-        , batches : Iddict TimelineBatch
-        , token : DefaultDict String (List Int)
-        , mostRecentSync : Maybe Int
-        }
-
-{-| A BatchToken is a token that has been handed out by the server to mark the end of a  -}
-type alias BatchToken = String
-
-type alias TimelineBatch =
-    { prevBatch : List Batch
-    , nextBatch : List Batch
-    , filter : Filter
-    , events : List String
-    , stateDelta : StateManager
     }
 
-type Batch
+type TokenId = TokenId Int
-    = Token BatchToken
-    | Batch Int
 
-addNewSync :
+type SliceId = SliceId Int
-    { events : List IEvent
-    , filter : Filter
-    , limited : Bool
-    , nextBatch : String
-    , prevBatch : String
-    , stateDelta : Maybe StateManager
-    } -> Timeline -> Timeline
-addNewSync data (Timeline timeline) =
-    let
-        batchToInsert : TimelineBatch
-        batchToInsert =
-            { prevBatch = 
-                [ Just <| Token data.prevBatch
-                , Maybe.map Batch timeline.mostRecentSync
-                ]
-                    |> List.filterMap identity
-            , nextBatch =
-                [ Token data.nextBatch ]
-            , filter = data.filter
-            , events = List.map Event.eventId data.events
-            , stateDelta = Maybe.withDefault StateManager.empty data.stateDelta
-            }
-    in
-        case Iddict.insert batchToInsert timeline.batches of
-            ( batchId, batches ) ->
-                Timeline
-                    { events = List.foldl Hashdict.insert timeline.events data.events
-                    , batches = batches
-                    , mostRecentSync = Just batchId
-                    , token =
-                        timeline.token
-                            |> DefaultDict.update data.prevBatch
-                                (\value ->
-                                    case value of
-                                        Just v ->
-                                            Just (batchId :: v)
-                                        Nothing ->
-                                            Just [ batchId ]
-                                )
-                            |> DefaultDict.update data.nextBatch
-                                (\value ->
-                                    case value of
-                                        Just v ->
-                                            Just (batchId :: v)
-                                        Nothing ->
-                                            Just [ batchId ]
-                                )
-                    }
 
+type Slice
+    = Slice
+        { events : List EventId
+        , filter : Filter
+        , next : List TokenId
+        , previous : List TokenId
+        }
+
+type Token
+    = Token
+        { next : List SliceId
+        , previous : List SliceId
+        , head : String
+        , tail : List String
+        }
+
+type alias EventId = String
+
+{-| Add a new token to the timeline. If it already exists, this function does
+nothing and instead returns the existing token id.
+-}
+addToken : Token -> Timeline -> ( TokenId, Timeline )
+addToken ((Token { head }) as token) timeline =
+    case Dict.get head timeline.tokenToId of
+        Just tokenId ->
+            ( tokenId, timeline )
+        
+        Nothing ->
+            insertToken token timeline
+
+{-| Sometimes two separate tokens point to the same location in the timeline.
+You can add a new token value as an alias to the timeline using this function.
+ -}
+addTokenAlias : String -> String -> Timeline -> Timeline
+addTokenAlias old new timeline =
+    case Dict.get old timeline.tokenToId of
+        Just tokenId ->
+            timeline
+                -- Update the token
+                |> mapToken 
+                    tokenId 
+                    (\(Token t) ->
+                        Token { t | head = new, tail = t.head :: t.tail }
+                    )
+                -- Add a token pointer for the new value
+                |> (\tl -> { tl | tokenToId = Dict.insert new tokenId tl.tokenToId })
+        
+        Nothing ->
+            timeline
+
+{-| Get an empty timeline.
+-}
+empty : Timeline
+empty =
+    { mostRecentToken = TokenId 0
+    , slices = Iddict.empty
+    , tokenToId = Dict.empty
+    , tokens = Iddict.empty
+    }
+
+{-| Get a slice of events from the timeline.
+-}
+getSlice : SliceId -> Timeline -> Maybe Slice
+getSlice (SliceId key) { slices } =
+    Iddict.get key slices
+
+{-| Get a token value from the timeline.
+-}
+getToken : TokenId -> Timeline -> Maybe Token
+getToken (TokenId key) { tokens } =
+    Iddict.get key tokens
+
+{-| Get the token id of an existing token value.
+-}
+getTokenId : String -> Timeline -> Maybe TokenId
+getToken v timeline =
+    Dict.get v timeline.tokenToId
+
+{-| Insert a new slice into the timeline.
+-}
+insertSlice : Slice -> Timeline -> ( SliceId, Timeline )
+insertSlice slice timeline =
+    timeline.slices
+        |> Iddict.insert slice
+        |> Tuple.mapBoth SliceId (\x -> { timeline | slices = x })
+
+{-| Insert a new token into the timeline.
+-}
+insertToken : Token -> Timeline -> ( TokenId, Timeline )
+insertToken ((Token { head }) as token) timeline =
+    case Iddict.insert token timeline.tokens of
+        ( tokenId, tokens ) ->
+            ( TokenId tokenId
+            , { timeline
+              | tokenToId = Dict.insert head (TokenId tokenId) timeline.tokenToId
+              , tokens = tokens
+              }
+            )
+
+{-| Update an existing slice based on its id.
+-}
+mapSlice : SliceId -> (Slice -> Slice) -> Timeline -> Timeline
+mapSlice (SliceId sliceId) f timeline =
+    { timeline | slices = Iddict.map sliceId f timeline.slices }
+
+{-| Update an existing token based on its id.
+-}
+mapToken : TokenId -> (Token -> Token) -> Timeline -> Timeline
+mapToken (TokenId tokenId) f timeline =
+    { timeline | tokens = Iddict.map tokenId f timeline.tokens }
+
+
+-- {-| The Timeline is a comprehensive object describing a timeline in a room.
+
+-- Any Timeline type contains the following pieces of information:
+
+-- - `events` Comprehensive dictionary containing all locally stored timeline events
+-- - `batches` Comprehensive dictionary containing all batches. Batches are pieces 
+--     of the timeline that have been sent by the homeserver.
+-- - `token` Dictionary that maps for each batch token which batches it borders
+-- - `mostRecentSync` Id of the most "recent" batch in the timeline
+-- -}
 -- type Timeline
 --     = Timeline
---         { prevBatch : String
+--         { events : Hashdict IEvent
---         , nextBatch : String
+--         , batches : Iddict TimelineBatch
---         , events : List IEvent
+--         , token : DefaultDict String (List Int)
---         , stateAtStart : StateManager
+--         , mostRecentSync : Maybe Int
---         , previous : BeforeTimeline
+--         }
+
+-- {-| A BatchToken is a token that has been handed out by the server to mark the end of a  -}
+-- type alias BatchToken = String
+
+-- type alias TimelineBatch =
+--     { prevBatch : List Batch
+--     , nextBatch : List Batch
+--     , filter : Filter
+--     , events : List String
+--     , stateDelta : StateManager
+--     }
+
+-- type Batch
+--     = Token BatchToken
+--     | Batch Int
+
+-- addNewSync :
+--     { events : List IEvent
+--     , filter : Filter
+--     , limited : Bool
+--     , nextBatch : String
+--     , prevBatch : String
+--     , stateDelta : Maybe StateManager
+--     } -> Timeline -> Timeline
+-- addNewSync data (Timeline timeline) =
+--     let
+--         batchToInsert : TimelineBatch
+--         batchToInsert =
+--             { prevBatch = 
+--                 [ Just <| Token data.prevBatch
+--                 , Maybe.map Batch timeline.mostRecentSync
+--                 ]
+--                     |> List.filterMap identity
+--             , nextBatch =
+--                 [ Token data.nextBatch ]
+--             , filter = data.filter
+--             , events = List.map Event.eventId data.events
+--             , stateDelta = Maybe.withDefault StateManager.empty data.stateDelta
+--             }
+--     in
+--         case Iddict.insert batchToInsert timeline.batches of
+--             ( batchId, batches ) ->
+--                 Timeline
+--                     { events = List.foldl Hashdict.insert timeline.events data.events
+--                     , batches = batches
+--                     , mostRecentSync = Just batchId
+--                     , token =
+--                         timeline.token
+--                             |> DefaultDict.update data.prevBatch
+--                                 (\value ->
+--                                     case value of
+--                                         Just v ->
+--                                             Just (batchId :: v)
+--                                         Nothing ->
+--                                             Just [ batchId ]
+--                                 )
+--                             |> DefaultDict.update data.nextBatch
+--                                 (\value ->
+--                                     case value of
+--                                         Just v ->
+--                                             Just (batchId :: v)
+--                                         Nothing ->
+--                                             Just [ batchId ]
+--                                 )
+--                     }
+
+-- -- type Timeline
+-- --     = Timeline
+-- --         { prevBatch : String
+-- --         , nextBatch : String
+-- --         , events : List IEvent
+-- --         , stateAtStart : StateManager
+-- --         , previous : BeforeTimeline
+-- --         }
+
+
+-- type BeforeTimeline
+--     = Endless String
+--     | Gap Timeline
+--     | StartOfTimeline
+
+
+-- {-| Add a new batch of events to the front of the timeline.
+-- -}
+-- addNewEvents :
+--     { events : List IEvent
+--     , limited : Bool
+--     , nextBatch : String
+--     , prevBatch : String
+--     , stateDelta : Maybe StateManager
+--     }
+--     -> Timeline
+--     -> Timeline
+-- addNewEvents { events, limited, nextBatch, prevBatch, stateDelta } (Timeline t) =
+--     Timeline
+--         (if prevBatch == t.nextBatch || not limited then
+--             { t
+--                 | events = t.events ++ events
+--                 , nextBatch = nextBatch
+--             }
+
+--          else
+--             { prevBatch = prevBatch
+--             , nextBatch = nextBatch
+--             , events = events
+--             , stateAtStart =
+--                 t
+--                     |> Timeline
+--                     |> mostRecentState
+--                     |> StateManager.updateRoomStateWith
+--                         (stateDelta
+--                             |> Maybe.withDefault StateManager.empty
+--                         )
+--             , previous = Gap (Timeline t)
+--             }
+--         )
+
+
+-- {-| Create a new timeline.
+-- -}
+-- newFromEvents :
+--     { events : List IEvent
+--     , nextBatch : String
+--     , prevBatch : Maybe String
+--     , stateDelta : Maybe StateManager
+--     }
+--     -> Timeline
+-- newFromEvents { events, nextBatch, prevBatch, stateDelta } =
+--     Timeline
+--         { events = events
+--         , nextBatch = nextBatch
+--         , prevBatch =
+--             prevBatch
+--                 |> Maybe.withDefault Leaking.prevBatch
+--         , previous =
+--             prevBatch
+--                 |> Maybe.map Endless
+--                 |> Maybe.withDefault StartOfTimeline
+--         , stateAtStart =
+--             stateDelta
+--                 |> Maybe.withDefault StateManager.empty
 --         }
 
 
-type BeforeTimeline
+-- {-| Insert events starting from a known batch token.
-    = Endless String
+-- -}
-    | Gap Timeline
+-- insertEvents :
-    | StartOfTimeline
+--     { events : List IEvent
+--     , nextBatch : String
+--     , prevBatch : Maybe String
+--     , stateDelta : Maybe StateManager
+--     }
+--     -> Timeline
+--     -> Timeline
+-- insertEvents ({ events, nextBatch, prevBatch, stateDelta } as data) (Timeline t) =
+--     Timeline
+--         (case prevBatch of
+--             -- No prevbatch suggests the start of the timeline.
+--             -- This means that we must recurse until we've hit the bottom,
+--             -- and then mark the bottom of the timeline.
+--             Nothing ->
+--                 case t.previous of
+--                     Gap prevT ->
+--                         { t
+--                             | previous =
+--                                 prevT
+--                                     |> insertEvents data
+--                                     |> Gap
+--                         }
+
+--                     _ ->
+--                         if nextBatch == t.prevBatch then
+--                             { t | previous = StartOfTimeline, events = events ++ t.events, stateAtStart = StateManager.empty }
+
+--                         else
+--                             { t | previous = Gap <| newFromEvents data }
+
+--             -- If there is a prevbatch, it is not the start of the timeline
+--             -- and could be located anywhere.
+--             -- Starting at the front, look for a way to match it with the existing timeline.
+--             Just p ->
+--                 -- Piece connects to the front of the timeline.
+--                 if t.nextBatch == p then
+--                     { t
+--                         | events = t.events ++ events
+--                         , nextBatch = nextBatch
+--                     }
+--                     -- Piece connects to the back of the timeline.
+
+--                 else if nextBatch == t.prevBatch then
+--                     case t.previous of
+--                         Gap (Timeline prevT) ->
+--                             -- Piece also connects to the timeline in the back,
+--                             -- allowing the two timelines to merge.
+--                             if prevT.nextBatch == p then
+--                                 { events = prevT.events ++ events ++ t.events
+--                                 , nextBatch = t.nextBatch
+--                                 , prevBatch = prevT.prevBatch
+--                                 , stateAtStart = prevT.stateAtStart
+--                                 , previous = prevT.previous
+--                                 }
+
+--                             else
+--                                 { t
+--                                     | events = events ++ t.events
+--                                     , prevBatch = p
+--                                     , stateAtStart =
+--                                         stateDelta
+--                                             |> Maybe.withDefault StateManager.empty
+--                                 }
+
+--                         Endless _ ->
+--                             { t
+--                                 | events = events ++ t.events
+--                                 , prevBatch = p
+--                                 , stateAtStart =
+--                                     stateDelta
+--                                         |> Maybe.withDefault StateManager.empty
+--                                 , previous = Endless p
+--                             }
+
+--                         _ ->
+--                             { t
+--                                 | events = events ++ t.events
+--                                 , prevBatch = p
+--                                 , stateAtStart =
+--                                     stateDelta
+--                                         |> Maybe.withDefault StateManager.empty
+--                             }
+--                     -- Piece doesn't connect to this piece of the timeline.
+--                     -- Consequently, look for previous parts of the timeline to see if it connects.
+
+--                 else
+--                     case t.previous of
+--                         Gap prevT ->
+--                             { t
+--                                 | previous =
+--                                     prevT
+--                                         |> insertEvents data
+--                                         |> Gap
+--                             }
+
+--                         _ ->
+--                             t
+--         )
 
 
-{-| Add a new batch of events to the front of the timeline.
+-- {-| Get the width of the latest gap. This data is usually accessed when trying to get more messages.
--}
+-- -}
-addNewEvents :
+-- latestGap : Timeline -> Maybe { from : Maybe String, to : String }
-    { events : List IEvent
+-- latestGap (Timeline t) =
-    , limited : Bool
+--     case t.previous of
-    , nextBatch : String
+--         StartOfTimeline ->
-    , prevBatch : String
+--             Nothing
-    , stateDelta : Maybe StateManager
-    }
-    -> Timeline
-    -> Timeline
-addNewEvents { events, limited, nextBatch, prevBatch, stateDelta } (Timeline t) =
-    Timeline
-        (if prevBatch == t.nextBatch || not limited then
-            { t
-                | events = t.events ++ events
-                , nextBatch = nextBatch
-            }
 
-         else
+--         Endless prevBatch ->
-            { prevBatch = prevBatch
+--             Just { from = Nothing, to = prevBatch }
-            , nextBatch = nextBatch
+
-            , events = events
+--         Gap (Timeline pt) ->
-            , stateAtStart =
+--             Just { from = Just pt.nextBatch, to = t.prevBatch }
-                t
-                    |> Timeline
-                    |> mostRecentState
-                    |> StateManager.updateRoomStateWith
-                        (stateDelta
-                            |> Maybe.withDefault StateManager.empty
-                        )
-            , previous = Gap (Timeline t)
-            }
-        )
 
 
-{-| Create a new timeline.
+-- {-| Get the longest uninterrupted length of most recent events.
--}
+-- -}
-newFromEvents :
+-- localSize : Timeline -> Int
-    { events : List IEvent
+-- localSize =
-    , nextBatch : String
+--     mostRecentEvents >> List.length
-    , prevBatch : Maybe String
-    , stateDelta : Maybe StateManager
-    }
-    -> Timeline
-newFromEvents { events, nextBatch, prevBatch, stateDelta } =
-    Timeline
-        { events = events
-        , nextBatch = nextBatch
-        , prevBatch =
-            prevBatch
-                |> Maybe.withDefault Leaking.prevBatch
-        , previous =
-            prevBatch
-                |> Maybe.map Endless
-                |> Maybe.withDefault StartOfTimeline
-        , stateAtStart =
-            stateDelta
-                |> Maybe.withDefault StateManager.empty
-        }
 
 
-{-| Insert events starting from a known batch token.
+-- {-| Get a list of the most recent events recorded.
--}
+-- -}
-insertEvents :
+-- mostRecentEvents : Timeline -> List IEvent
-    { events : List IEvent
+-- mostRecentEvents (Timeline t) =
-    , nextBatch : String
+--     t.events
-    , prevBatch : Maybe String
-    , stateDelta : Maybe StateManager
-    }
-    -> Timeline
-    -> Timeline
-insertEvents ({ events, nextBatch, prevBatch, stateDelta } as data) (Timeline t) =
-    Timeline
-        (case prevBatch of
-            -- No prevbatch suggests the start of the timeline.
-            -- This means that we must recurse until we've hit the bottom,
-            -- and then mark the bottom of the timeline.
-            Nothing ->
-                case t.previous of
-                    Gap prevT ->
-                        { t
-                            | previous =
-                                prevT
-                                    |> insertEvents data
-                                    |> Gap
-                        }
-
-                    _ ->
-                        if nextBatch == t.prevBatch then
-                            { t | previous = StartOfTimeline, events = events ++ t.events, stateAtStart = StateManager.empty }
-
-                        else
-                            { t | previous = Gap <| newFromEvents data }
-
-            -- If there is a prevbatch, it is not the start of the timeline
-            -- and could be located anywhere.
-            -- Starting at the front, look for a way to match it with the existing timeline.
-            Just p ->
-                -- Piece connects to the front of the timeline.
-                if t.nextBatch == p then
-                    { t
-                        | events = t.events ++ events
-                        , nextBatch = nextBatch
-                    }
-                    -- Piece connects to the back of the timeline.
-
-                else if nextBatch == t.prevBatch then
-                    case t.previous of
-                        Gap (Timeline prevT) ->
-                            -- Piece also connects to the timeline in the back,
-                            -- allowing the two timelines to merge.
-                            if prevT.nextBatch == p then
-                                { events = prevT.events ++ events ++ t.events
-                                , nextBatch = t.nextBatch
-                                , prevBatch = prevT.prevBatch
-                                , stateAtStart = prevT.stateAtStart
-                                , previous = prevT.previous
-                                }
-
-                            else
-                                { t
-                                    | events = events ++ t.events
-                                    , prevBatch = p
-                                    , stateAtStart =
-                                        stateDelta
-                                            |> Maybe.withDefault StateManager.empty
-                                }
-
-                        Endless _ ->
-                            { t
-                                | events = events ++ t.events
-                                , prevBatch = p
-                                , stateAtStart =
-                                    stateDelta
-                                        |> Maybe.withDefault StateManager.empty
-                                , previous = Endless p
-                            }
-
-                        _ ->
-                            { t
-                                | events = events ++ t.events
-                                , prevBatch = p
-                                , stateAtStart =
-                                    stateDelta
-                                        |> Maybe.withDefault StateManager.empty
-                            }
-                    -- Piece doesn't connect to this piece of the timeline.
-                    -- Consequently, look for previous parts of the timeline to see if it connects.
-
-                else
-                    case t.previous of
-                        Gap prevT ->
-                            { t
-                                | previous =
-                                    prevT
-                                        |> insertEvents data
-                                        |> Gap
-                            }
-
-                        _ ->
-                            t
-        )
 
 
-{-| Get the width of the latest gap. This data is usually accessed when trying to get more messages.
+-- {-| Get the needed `since` parameter to get the latest events.
--}
+-- -}
-latestGap : Timeline -> Maybe { from : Maybe String, to : String }
+-- nextSyncToken : Timeline -> String
-latestGap (Timeline t) =
+-- nextSyncToken (Timeline t) =
-    case t.previous of
+--     t.nextBatch
-        StartOfTimeline ->
-            Nothing
-
-        Endless prevBatch ->
-            Just { from = Nothing, to = prevBatch }
-
-        Gap (Timeline pt) ->
-            Just { from = Just pt.nextBatch, to = t.prevBatch }
 
 
-{-| Get the longest uninterrupted length of most recent events.
+-- {-| Get the state of the room after the most recent event.
--}
+-- -}
-localSize : Timeline -> Int
+-- mostRecentState : Timeline -> StateManager
-localSize =
+-- mostRecentState (Timeline t) =
-    mostRecentEvents >> List.length
+--     t.stateAtStart
+--         |> StateManager.updateRoomStateWith
+--             (StateManager.fromEventList t.events)
 
 
-{-| Get a list of the most recent events recorded.
+-- {-| Get the timeline's room state at any given event. The function returns `Nothing` if the event is not found in the timeline.
--}
+-- -}
-mostRecentEvents : Timeline -> List IEvent
+-- stateAtEvent : IEvent -> Timeline -> Maybe StateManager
-mostRecentEvents (Timeline t) =
+-- stateAtEvent event (Timeline t) =
-    t.events
+--     if
+--         t.events
+--             |> List.map Event.eventId
+--             |> List.member (Event.eventId event)
+--     then
+--         Fold.untilCompleted
+--             List.foldl
+--             (\e ->
+--                 StateManager.addEvent e
+--                     >> (if Event.eventId e == Event.eventId event then
+--                             Fold.AnswerWith
+
+--                         else
+--                             Fold.ContinueWith
+--                        )
+--             )
+--             t.stateAtStart
+--             t.events
+--             |> Just
+
+--     else
+--         case t.previous of
+--             Gap prevT ->
+--                 stateAtEvent event prevT
+
+--             _ ->
+--                 Nothing
 
 
-{-| Get the needed `since` parameter to get the latest events.
+-- {-| Count how many events the current timeline is storing.
--}
+-- -}
-nextSyncToken : Timeline -> String
+-- size : Timeline -> Int
-nextSyncToken (Timeline t) =
+-- size (Timeline t) =
-    t.nextBatch
+--     (case t.previous of
+--         Gap prev ->
+--             size prev
 
-
+--         _ ->
-{-| Get the state of the room after the most recent event.
+--             0
--}
+--     )
-mostRecentState : Timeline -> StateManager
+--         + List.length t.events
-mostRecentState (Timeline t) =
-    t.stateAtStart
-        |> StateManager.updateRoomStateWith
-            (StateManager.fromEventList t.events)
-
-
-{-| Get the timeline's room state at any given event. The function returns `Nothing` if the event is not found in the timeline.
--}
-stateAtEvent : IEvent -> Timeline -> Maybe StateManager
-stateAtEvent event (Timeline t) =
-    if
-        t.events
-            |> List.map Event.eventId
-            |> List.member (Event.eventId event)
-    then
-        Fold.untilCompleted
-            List.foldl
-            (\e ->
-                StateManager.addEvent e
-                    >> (if Event.eventId e == Event.eventId event then
-                            Fold.AnswerWith
-
-                        else
-                            Fold.ContinueWith
-                       )
-            )
-            t.stateAtStart
-            t.events
-            |> Just
-
-    else
-        case t.previous of
-            Gap prevT ->
-                stateAtEvent event prevT
-
-            _ ->
-                Nothing
-
-
-{-| Count how many events the current timeline is storing.
--}
-size : Timeline -> Int
-size (Timeline t) =
-    (case t.previous of
-        Gap prev ->
-            size prev
-
-        _ ->
-            0
-    )
-        + List.length t.events