Add predicates, properties, exports

Author: MonoidMusician

src/DOM/Util/TextCursor.purs

@@ -1,12 +1,16 @@
 module DOM.Util.TextCursor
     ( TextCursor(..)
+    , content, length, null, empty, single
     , _before, _selected, _after
+    , atStart, atEnd, allSelected
+    , isCursor, cursorAtStart, cursorAtEnd
+    , isSelection, selectionAtStart, selectionAtEnd
     , selectAll, moveCursorToStart, moveCursorToEnd
-    , content, empty, single
     , insert, mapAll
     ) where
 
 import Prelude
+import Data.String (length, null) as S
 import Data.Symbol (SProxy(..))
 import Data.Newtype (class Newtype)
 import Data.Lens (Lens', (.~))
@@ -25,15 +29,56 @@ newtype TextCursor = TextCursor
 
 derive instance textCursorNewtype :: Newtype TextCursor _
 
+data ContentTest = Null | Any | Full
+type ContentPredicate =
+    { before :: ContentTest
+    , selected :: ContentTest
+    , after :: ContentTest
+    }
+testContent :: ContentPredicate -> TextCursor -> Boolean
+testContent
+    { before, selected, after }
+    (TextCursor { before: b, selected: s, after: a }) =
+        test before b && test selected s && test after a
+    where
+        test Any _ = true
+        test Null t = S.null t
+        test Full t = not (S.null t)
+
 -- | Get the current text in the field. (Everything before, inside, and after
 -- | the selection.)
 content :: TextCursor -> String
 content (TextCursor { before, selected, after }) = before <> selected <> after
 
+-- | Get the length of the content of a `TextCursor`.
+-- check: length textcursor == length (content textcursor)
+length :: TextCursor -> Int
+length (TextCursor { before, selected, after }) =
+    S.length before + S.length selected + S.length after
+
 -- | An empty input field. No selection.
 empty :: TextCursor
 empty = TextCursor { before: "", selected: "", after: "" }
 
+-- | Test whether the content of a `TextCursor` is empty.
+-- check: null textcursor == null (content textcursor)
+null :: TextCursor -> Boolean
+null = testContent { before: Null, selected: Null, after: Null }
+
+-- | Test whether the selection is collapsed, i.e. acts like a cursor.
+isCursor :: TextCursor -> Boolean
+isCursor = testContent { before: Any, selected: Null, after: Any }
+
+-- | Test whether some text is selected.
+isSelection :: TextCursor -> Boolean
+isSelection = testContent { before: Any, selected: Full, after: Any }
+
+-- | Apply a `Lens` setting a value to an empty `TextCursor`. When used with
+-- | `_before`, `_selected`, or `_after` this will provide a `TextCursor` with
+-- | only one non-empty field.
+single :: Lens' TextCursor String -> String -> TextCursor
+single l v = l .~ v $ empty
+
 -- | Lens for the text before the selection. Empty if the cursor is at the
 -- | beginning or the selection starts from the beginning.
 _before :: Lens' TextCursor String
@@ -48,12 +93,6 @@ _selected = _Newtype <<< prop (SProxy :: SProxy "selected")
 _after :: Lens' TextCursor String
 _after = _Newtype <<< prop (SProxy :: SProxy "after")
 
--- | Apply a `Lens` setting a value to an empty `TextCursor`. When used with
--- | `beforeL`, `selectedL`, or `afterL` this will provide a `TextCursor` with
--- | only one non-empty field.
-single :: Lens' TextCursor String -> String -> TextCursor
-single l v = l .~ v $ empty
-
 -- | Map all three fields of the `TextCursor` with an endomorphism, performing
 -- | a replacement or other transformation such as normalization.
 mapAll :: (String -> String) -> TextCursor -> TextCursor
@@ -65,6 +104,7 @@ mapAll f (TextCursor { before, selected, after }) = TextCursor
 
 -- | Move the cursor to the start of a field, preserving the overall text
 -- | content.
+-- Content-preserving idempotent endomorphism
 moveCursorToStart :: TextCursor -> TextCursor
 moveCursorToStart tc = TextCursor
     { before: ""
@@ -75,6 +115,7 @@ moveCursorToStart tc = TextCursor
 -- | Select all of the text in a field.
 -- |
 -- | Note: selection direction is not specified.
+-- Content-preserving idempotent endomorphism
 selectAll :: TextCursor -> TextCursor
 selectAll tc = TextCursor
     { before: ""
@@ -83,15 +124,47 @@ selectAll tc = TextCursor
     }
 
 -- | Move the cursor to the end of a field, preserving the overall text content.
+-- Content-preserving idempotent endomorphism
 moveCursorToEnd :: TextCursor -> TextCursor
 moveCursorToEnd tc = TextCursor
     { before: content tc
     , selected: ""
     , after: ""
     }
 
+-- | Test whether there is a selection that ranges to the start.
+selectionAtStart :: TextCursor -> Boolean
+selectionAtStart = isSelection && atStart
+
+-- | Test whether the cursor is at the start with no selection.
+cursorAtStart :: TextCursor -> Boolean
+cursorAtStart = isCursor && atStart
+
+-- | Test whether the cursor or selection touches the start.
+atStart :: TextCursor -> Boolean
+atStart = testContent { before: Null, selected: Null, after: Any }
+
+-- | Test whether the cursor has selected the whole field.
+allSelected :: TextCursor -> Boolean
+allSelected = testContent { before: Null, selected: Any, after: Null }
+
+-- | Test whether the cursor or selection reaches the end.
+atEnd :: TextCursor -> Boolean
+atEnd = testContent { before: Any, selected: Any, after: Null }
+
+-- | Test whether the cursor is at the end with no selection.
+cursorAtEnd :: TextCursor -> Boolean
+cursorAtEnd = isCursor && atEnd
+
+-- | Test whether there is a selection that reaches the end.
+selectionAtEnd :: TextCursor -> Boolean
+selectionAtEnd = isSelection && atEnd
+
 -- | Insert a string at the cursor position. If text is selected, the insertion
 -- | will be part of the selection. Otherwise it is inserted before the cursor.
+-- check:
+--     length (insert insertion textcursor)
+--  == length insertion + length textcursor
 insert :: String -> TextCursor -> TextCursor
 insert insertion = case _ of
     TextCursor { before, selected: "", after } -> TextCursor