Add a load-more button to item list

modules/webapp/src/main/elm/Data/Items.elm

@@ -0,0 +1,67 @@
+module Data.Items exposing
+    ( concat
+    , first
+    , length
+    )
+
+import Api.Model.ItemLight exposing (ItemLight)
+import Api.Model.ItemLightGroup exposing (ItemLightGroup)
+import Api.Model.ItemLightList exposing (ItemLightList)
+import Util.List
+
+
+concat : ItemLightList -> ItemLightList -> ItemLightList
+concat l0 l1 =
+    let
+        lastOld =
+            lastGroup l0
+
+        firstNew =
+            List.head l1.groups
+    in
+    case ( lastOld, firstNew ) of
+        ( Nothing, Nothing ) ->
+            l0
+
+        ( Just _, Nothing ) ->
+            l0
+
+        ( Nothing, Just _ ) ->
+            l1
+
+        ( Just o, Just n ) ->
+            if o.name == n.name then
+                let
+                    ng =
+                        ItemLightGroup o.name (o.items ++ n.items)
+
+                    prev =
+                        Util.List.dropRight 1 l0.groups
+
+                    suff =
+                        List.drop 1 l1.groups
+                in
+                ItemLightList (prev ++ [ ng ] ++ suff)
+
+            else
+                ItemLightList (l0.groups ++ l1.groups)
+
+
+first : ItemLightList -> Maybe ItemLight
+first list =
+    List.head list.groups
+        |> Maybe.map .items
+        |> Maybe.withDefault []
+        |> List.head
+
+
+length : ItemLightList -> Int
+length list =
+    List.map (\g -> List.length g.items) list.groups
+        |> List.sum
+
+
+lastGroup : ItemLightList -> Maybe ItemLightGroup
+lastGroup list =
+    List.reverse list.groups
+        |> List.head