Allow to select multiple items for deletion and edit

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

@@ -0,0 +1,32 @@
+module Data.ItemSelection exposing
+    ( ItemSelection(..)
+    , isActive
+    , isSelected
+    )
+
+import Set exposing (Set)
+
+
+type ItemSelection
+    = Inactive
+    | Active (Set String)
+
+
+isSelected : String -> ItemSelection -> Bool
+isSelected id set =
+    case set of
+        Inactive ->
+            False
+
+        Active ids ->
+            Set.member id ids
+
+
+isActive : ItemSelection -> Bool
+isActive sel =
+    case sel of
+        Active _ ->
+            True
+
+        Inactive ->
+            False

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

@@ -1,12 +1,14 @@
 module Data.Items exposing
     ( concat
     , first
+    , idSet
     , length
     )
 
 import Api.Model.ItemLight exposing (ItemLight)
 import Api.Model.ItemLightGroup exposing (ItemLightGroup)
 import Api.Model.ItemLightList exposing (ItemLightList)
+import Set exposing (Set)
 import Util.List
 
 
@@ -65,3 +67,15 @@ lastGroup : ItemLightList -> Maybe ItemLightGroup
 lastGroup list =
     List.reverse list.groups
         |> List.head
+
+
+idSet : ItemLightList -> Set String
+idSet items =
+    List.map idSetGroup items.groups
+        |> List.foldl Set.union Set.empty
+
+
+idSetGroup : ItemLightGroup -> Set String
+idSetGroup group =
+    List.map .id group.items
+        |> Set.fromList