Update TextInput to handle text overflow.

README.md

@@ -58,7 +58,7 @@ python examples/simple_form.py
 ### TextInput 🔡
 
 - value - string
-- one line of text
+- one line of text with overflow support
 - placeholder and title support
 - password mode to hide input
 - syntax mode to highlight code

src/textual_inputs/text_input.py

@@ -37,8 +37,7 @@ def syntax_highlight_text(code: str, syntax: str) -> Text:
 
 
 class TextInput(Widget):
-    """
-    A simple text input widget.
+    """A simple text input widget.
 
     Args:
         name (Optional[str]): The unique name of the widget. If None, the
@@ -50,21 +49,21 @@ class TextInput(Widget):
             of the widget's border.
         password (bool, optional): Defaults to False. Hides the text
             input, replacing it with bullets.
-        syntax (Optional[str]): the name of the language for syntax highlighting.
+        syntax (Optional[str]): The name of the language for syntax highlighting.
 
     Attributes:
-        value (str): the value of the text field
+        value (str): The value of the text field
         placeholder (str): The placeholder message.
         title (str): The displayed title of the widget.
         has_password (bool): True if the text field masks the input.
         syntax (Optional[str]): the name of the language for syntax highlighting.
         has_focus (bool): True if the widget is focused.
         cursor (Tuple[str, Style]): The character used for the cursor
             and a rich Style object defining its appearance.
-        on_change_handler_name (str): name of handler function to be
+        on_change_handler_name (str): The name of handler function to be
             called when an on change event occurs. Defaults to
             handle_input_on_change.
-        on_focus_handler_name (name): name of handler function to be
+        on_focus_handler_name (name): The name of handler function to be
             called when an on focus event occurs. Defaults to
             handle_input_on_focus.
 
@@ -95,6 +94,7 @@ class TextInput(Widget):
             bold=True,
         ),
     )
+    """Character and style of the cursor."""
     _cursor_position: Reactive[int] = Reactive(0)
     _has_focus: Reactive[bool] = Reactive(False)
 
@@ -111,13 +111,22 @@ def __init__(
     ) -> None:
         super().__init__(name)
         self.value = value
+        """The value of the text field"""
         self.placeholder = placeholder
+        """
+        Text that appears in the widget when value is "" and the widget
+        is not focused.
+        """
         self.title = title
+        """The displayed title of the widget."""
         self.has_password = password
+        """True if the text field masks the input."""
         self.syntax = syntax
+        """The name of the language for syntax highlighting."""
         self._on_change_message_class = InputOnChange
         self._on_focus_message_class = InputOnFocus
         self._cursor_position = len(self.value)
+        self._text_offset = 0
 
     def __rich_repr__(self):
         yield "name", self.name
@@ -200,119 +209,170 @@ def render(self) -> RenderableType:
         )
 
     def _modify_text(self, segment: str) -> Union[str, Text]:
-        """
-        Produces the text with modifications, such as password concealing.
-        """
+        """Produces the text with modifications, such as password concealing."""
         if self.has_password:
             return conceal_text(segment)
         if self.syntax:
             return syntax_highlight_text(segment, self.syntax)
         return segment
 
-    def _render_text_with_cursor(self) -> List[Union[str, Text, Tuple[str, Style]]]:
+    @property
+    def _visible_width(self):
+        """Width in characters of the inside of the input"""
+        # remove 2, 1 for each of the border's edges
+        # remove 1 more for the cursor
+        # remove 2 for the padding either side of the input
+        width, _ = self.size
+        if self.border:
+            width -= 2
+        if self._has_focus:
+            width -= 1
+        width -= 2
+        return width
+
+    def _text_offset_window(self):
         """
-        Produces the renderable Text object combining value and cursor
+        Produce the start and end indices of the visible portions of the
+        text value.
         """
+        return self._text_offset, self._text_offset + self._visible_width
+
+    def _render_text_with_cursor(self) -> List[Union[str, Text, Tuple[str, Style]]]:
+        """Produces the renderable Text object combining value and cursor"""
         text = self._modify_text(self.value)
+
+        # trim the string to fit within the widgets dimensions
+        left, right = self._text_offset_window()
+        text = text[left:right]
+
+        # convert the cursor to be relative to this view
+        cursor_relative_position = self._cursor_position - self._text_offset
         return [
-            text[: self._cursor_position],
+            text[:cursor_relative_position],
             self.cursor,
-            text[self._cursor_position :],
+            text[cursor_relative_position:],
         ]
 
     async def on_focus(self, event: events.Focus) -> None:
+        """Handle Focus events
+
+        Args:
+            event (events.Focus): A Textual Focus event
+        """
         self._has_focus = True
         await self._emit_on_focus()
 
     async def on_blur(self, event: events.Blur) -> None:
+        """Handle Blur events
+
+        Args:
+            event (events.Blur): A Textual Blur event
+        """
         self._has_focus = False
 
+    def _update_offset_left(self):
+        """
+        Decrease the text offset if the cursor moves less than 3 characters
+        from the left edge. This will shift the text to the right and keep
+        the cursor 3 characters from the left edge. If the text offset is 0
+        then the cursor may continue to move until it reaches the left edge.
+        """
+        visibility_left = 3
+        if self._cursor_position < self._text_offset + visibility_left:
+            self._text_offset = max(0, self._cursor_position - visibility_left)
+
+    def _update_offset_right(self):
+        """
+        Increase the text offset if the cursor moves beyond the right
+        edge of the widget. This will shift the text left and make the
+        cursor visible at the right edge of the widget.
+        """
+        _, right = self._text_offset_window()
+        if self._cursor_position > right:
+            self._text_offset = self._cursor_position - self._visible_width
+
+    def _cursor_left(self):
+        """Handle key press Left"""
+        if self._cursor_position > 0:
+            self._cursor_position -= 1
+            self._update_offset_left()
+
+    def _cursor_right(self):
+        """Handle key press Right"""
+        if self._cursor_position < len(self.value):
+            self._cursor_position = self._cursor_position + 1
+            self._update_offset_right()
+
+    def _cursor_home(self):
+        """Handle key press Home"""
+        self._cursor_position = 0
+        self._update_offset_left()
+
+    def _cursor_end(self):
+        """Handle key press End"""
+        self._cursor_position = len(self.value)
+        self._update_offset_right()
+
+    def _key_backspace(self):
+        """Handle key press Backspace"""
+        if self._cursor_position > 0:
+            self.value = (
+                self.value[: self._cursor_position - 1]
+                + self.value[self._cursor_position :]
+            )
+            self._cursor_position -= 1
+            self._update_offset_left()
+
+    def _key_delete(self):
+        """Handle key press Delete"""
+        if self._cursor_position < len(self.value):
+            self.value = (
+                self.value[: self._cursor_position]
+                + self.value[self._cursor_position + 1 :]
+            )
+
+    def _key_printable(self, event: events.Key):
+        """Handle all printable keys"""
+        self.value = (
+            self.value[: self._cursor_position]
+            + event.key
+            + self.value[self._cursor_position :]
+        )
+
+        if not self._cursor_position > len(self.value):
+            self._cursor_position += 1
+            self._update_offset_right()
+
     async def on_key(self, event: events.Key) -> None:
-        if event.key == "left":
-            if self._cursor_position == 0:
-                self._cursor_position = 0
-            else:
-                self._cursor_position -= 1
+        """Handle key events
 
+        Args:
+            event (events.Key): A Textual Key event
+        """
+        BACKSPACE = "ctrl+h"
+        if event.key == "left":
+            self._cursor_left()
         elif event.key == "right":
-            if self._cursor_position != len(self.value):
-                self._cursor_position = self._cursor_position + 1
-
+            self._cursor_right()
         elif event.key == "home":
-            self._cursor_position = 0
-
+            self._cursor_home()
         elif event.key == "end":
-            self._cursor_position = len(self.value)
-
-        elif event.key == "ctrl+h":  # Backspace
-            if self._cursor_position == 0:
-                return
-            elif len(self.value) == 1:
-                self.value = ""
-                self._cursor_position = 0
-            elif len(self.value) == 2:
-                if self._cursor_position == 1:
-                    self.value = self.value[1]
-                    self._cursor_position = 0
-                else:
-                    self.value = self.value[0]
-                    self._cursor_position = 1
-            else:
-                if self._cursor_position == 1:
-                    self.value = self.value[1:]
-                    self._cursor_position = 0
-                elif self._cursor_position == len(self.value):
-                    self.value = self.value[:-1]
-                    self._cursor_position -= 1
-                else:
-                    self.value = (
-                        self.value[: self._cursor_position - 1]
-                        + self.value[self._cursor_position :]
-                    )
-                    self._cursor_position -= 1
-
+            self._cursor_end()
+        elif event.key == BACKSPACE:
+            self._key_backspace()
             await self._emit_on_change(event)
-
         elif event.key == "delete":
-            if self._cursor_position == len(self.value):
-                return
-            elif len(self.value) == 1:
-                self.value = ""
-            elif len(self.value) == 2:
-                if self._cursor_position == 1:
-                    self.value = self.value[0]
-                else:
-                    self.value = self.value[1]
-            else:
-                if self._cursor_position == 0:
-                    self.value = self.value[1:]
-                else:
-                    self.value = (
-                        self.value[: self._cursor_position]
-                        + self.value[self._cursor_position + 1 :]
-                    )
+            self._key_delete()
             await self._emit_on_change(event)
-
         elif len(event.key) == 1 and event.key.isprintable():
-            if self._cursor_position == 0:
-                self.value = event.key + self.value
-            elif self._cursor_position == len(self.value):
-                self.value = self.value + event.key
-            else:
-                self.value = (
-                    self.value[: self._cursor_position]
-                    + event.key
-                    + self.value[self._cursor_position :]
-                )
-
-            if not self._cursor_position > len(self.value):
-                self._cursor_position += 1
-
+            self._key_printable(event)
             await self._emit_on_change(event)
 
     async def _emit_on_change(self, event: events.Key) -> None:
+        """Emit custom message class on Change events"""
         event.stop()
         await self.emit(self._on_change_message_class(self))
 
     async def _emit_on_focus(self) -> None:
+        """Emit custom message class on Focus events"""
         await self.emit(self._on_focus_message_class(self))