From 4a204558382cd478629eaf8569e634f1a9417d0f Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Thu, 28 Apr 2022 13:26:29 +0100
Subject: [PATCH] moved layout

---
 src/textual/_layout.py | 40 ++++++++++++++++++++++++++++++++++++++++
 src/textual/app.py     |  3 ++-
 src/textual/widget.py  |  5 +++--
 3 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 src/textual/_layout.py

diff --git a/src/textual/_layout.py b/src/textual/_layout.py
new file mode 100644
index 000000000..ea459a3e0
--- /dev/null
+++ b/src/textual/_layout.py
@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import ClassVar, NamedTuple, TYPE_CHECKING
+
+
+from .geometry import Region, Offset, Size
+
+
+if TYPE_CHECKING:
+    from .widget import Widget
+
+
+class WidgetPlacement(NamedTuple):
+    """The position, size, and relative order of a widget within its parent."""
+
+    region: Region
+    widget: Widget | None = None  # A widget of None means empty space
+    order: int = 0
+
+
+class Layout(ABC):
+    """Responsible for arranging Widgets in a view and rendering them."""
+
+    name: ClassVar[str] = ""
+
+    @abstractmethod
+    def arrange(
+        self, parent: Widget, size: Size, scroll: Offset
+    ) -> tuple[list[WidgetPlacement], set[Widget]]:
+        """Generate a layout map that defines where on the screen the widgets will be drawn.
+
+        Args:
+            parent (Widget): Parent widget.
+            size (Size): Size of container.
+            scroll (Offset): Offset to apply to the Widget placements.
+
+        Returns:
+            Iterable[WidgetPlacement]: An iterable of widget location
+        """
diff --git a/src/textual/app.py b/src/textual/app.py
index c0be02030..2341f2c6b 100644
--- a/src/textual/app.py
+++ b/src/textual/app.py
@@ -182,7 +182,8 @@ class App(Generic[ReturnType], DOMNode):
         self._return_value = result
         self.close_messages_no_wait()
 
-    def compose(self) -> Iterable[Widget]:
+    def compose(self) -> ComposeResult:
+        """Yield child widgets for a container."""
         return
         yield
 
diff --git a/src/textual/widget.py b/src/textual/widget.py
index 161169958..e2a4b53c7 100644
--- a/src/textual/widget.py
+++ b/src/textual/widget.py
@@ -39,7 +39,7 @@ from .renderables.opacity import Opacity
 
 
 if TYPE_CHECKING:
-    from .app import App
+    from .app import App, ComposeResult
     from .scrollbar import (
         ScrollBar,
         ScrollTo,
@@ -115,7 +115,8 @@ class Widget(DOMNode):
         self.app.register(self, *anon_widgets, **widgets)
         self.screen.refresh()
 
-    def compose(self) -> Iterable[Widget]:
+    def compose(self) -> ComposeResult:
+        """Yield child widgets for a container."""
         return
         yield