Generalize the FocusTrap module

src/Nri/Ui/FocusTrap/V1.elm

@@ -7,8 +7,7 @@ module Nri.Ui.FocusTrap.V1 exposing (FocusTrap, toAttribute)
 -}
 
 import Accessibility.Styled as Html
-import Html.Styled.Events as Events
-import Json.Decode as Decode exposing (Decoder)
+import Nri.Ui.WhenFocusLeaves.V1 as WhenFocusLeaves
 
 
 {-| Defines how focus will wrap in reponse to tab keypresses in a part of the UI.
@@ -28,53 +27,13 @@ type alias FocusTrap msg =
 -}
 toAttribute : FocusTrap msg -> Html.Attribute msg
 toAttribute { firstId, lastId, focus } =
-    onTab <|
-        \elementId shiftKey ->
-            -- if the user tabs back while on the first id,
-            -- we want to wrap around to the last id.
-            if elementId == firstId && shiftKey then
-                Decode.succeed
-                    { message = focus lastId
-                    , preventDefault = True
-                    , stopPropagation = False
-                    }
-
-            else if elementId == lastId && not shiftKey then
-                -- if the user tabs forward while on the last id,
-                -- we want to wrap around to the first id.
-                Decode.succeed
-                    { message = focus firstId
-                    , preventDefault = True
-                    , stopPropagation = False
-                    }
-
-            else
-                Decode.fail "No need to intercept the key press"
-
-
-onTab :
-    (String
-     -> Bool
-     -> Decoder { message : msg, preventDefault : Bool, stopPropagation : Bool }
-    )
-    -> Html.Attribute msg
-onTab do =
-    Events.custom "keydown"
-        (Decode.andThen
-            (\( id, keyCode, shiftKey ) ->
-                if keyCode == 9 then
-                    do id shiftKey
-
-                else
-                    Decode.fail "No need to intercept the key press"
-            )
-            decodeKeydown
-        )
-
-
-decodeKeydown : Decoder ( String, Int, Bool )
-decodeKeydown =
-    Decode.map3 (\id keyCode shiftKey -> ( id, keyCode, shiftKey ))
-        (Decode.at [ "target", "id" ] Decode.string)
-        (Decode.field "keyCode" Decode.int)
-        (Decode.field "shiftKey" Decode.bool)
+    WhenFocusLeaves.toAttribute
+        { firstId = firstId
+        , lastId = lastId
+        , -- if the user tabs back while on the first id,
+          -- we want to wrap around to the last id.
+          tabBackAction = focus lastId
+        , -- if the user tabs forward while on the last id,
+          -- we want to wrap around to the first id.
+          tabForwardAction = focus firstId
+        }

src/Nri/Ui/WhenFocusLeaves/V1.elm

@@ -0,0 +1,78 @@
+module Nri.Ui.WhenFocusLeaves.V1 exposing (toAttribute)
+
+{-| Listen for when the focus leaves the area, and then do an action.
+
+@docs toAttribute
+
+-}
+
+import Accessibility.Styled as Html
+import Html.Styled.Events as Events
+import Json.Decode as Decode exposing (Decoder)
+
+
+{-| Attach this attribute to add a focus watcher to an HTML element and define
+what to do in reponse to tab keypresses in a part of the UI.
+
+The ids referenced here are expected to correspond to elements in the container
+we are adding the attribute to.
+
+-}
+toAttribute :
+    { firstId : String
+    , lastId : String
+    , tabBackAction : msg
+    , tabForwardAction : msg
+    }
+    -> Html.Attribute msg
+toAttribute { firstId, lastId, tabBackAction, tabForwardAction } =
+    onTab <|
+        \elementId shiftKey ->
+            -- if the user tabs back while on the first id,
+            -- we execute the action
+            if elementId == firstId && shiftKey then
+                Decode.succeed
+                    { message = tabBackAction
+                    , preventDefault = False
+                    , stopPropagation = False
+                    }
+
+            else if elementId == lastId && not shiftKey then
+                -- if the user tabs forward while on the last id,
+                -- we want to wrap around to the first id.
+                Decode.succeed
+                    { message = tabForwardAction
+                    , preventDefault = False
+                    , stopPropagation = False
+                    }
+
+            else
+                Decode.fail "No need to intercept the key press"
+
+
+onTab :
+    (String
+     -> Bool
+     -> Decoder { message : msg, preventDefault : Bool, stopPropagation : Bool }
+    )
+    -> Html.Attribute msg
+onTab do =
+    Events.custom "keydown"
+        (Decode.andThen
+            (\( id, keyCode, shiftKey ) ->
+                if keyCode == 9 then
+                    do id shiftKey
+
+                else
+                    Decode.fail "No need to intercept the key press"
+            )
+            decodeKeydown
+        )
+
+
+decodeKeydown : Decoder ( String, Int, Bool )
+decodeKeydown =
+    Decode.map3 (\id keyCode shiftKey -> ( id, keyCode, shiftKey ))
+        (Decode.at [ "target", "id" ] Decode.string)
+        (Decode.field "keyCode" Decode.int)
+        (Decode.field "shiftKey" Decode.bool)