Add Document.get_location_from_index(index)

src/textual/document/_document.py

@@ -91,17 +91,27 @@ def newline(self) -> Newline:
         """Return the line separator used in the document."""
 
     @abstractmethod
-    def get_index(self, at: Location) -> int:
-        """Given a location in the document, returns the index
-        in the document seen as a flat string.
+    def get_index_from_location(self, location: Location) -> int:
+        """Given a location, returns the index from the document's text.
 
         Args:
-            at: The location in the document.
+            location: The location in the document.
 
         Returns:
-            The index in the document seen as a flat string.
+            The index in the document's text.
         """
 
+    @abstractmethod
+    def get_location_from_index(self, index: int) -> Location:
+        """Given an index in the document's text, returns the corresponding location.
+
+        Args:
+            index: The index in the document's text.
+
+        Returns:
+            The corresponding location.
+        """
+
     @abstractmethod
     def get_line(self, index: int) -> str:
         """Returns the line with the given index from the document.
@@ -332,21 +342,30 @@ def line_count(self) -> int:
         """Returns the number of lines in the document."""
         return len(self._lines)
 
-    def get_index(self, at: Location) -> int:
-        """Given a location in the document, returns the index
-        in the document seen as a flat string.
+    def get_index_from_location(self, location: Location) -> int:
+        """Given a location, returns the index from the document's text.
 
         Args:
-            at: The location in the document.
+            location: The location in the document.
 
         Returns:
-            The index in the document seen as a flat string.
+            The index in the document's text.
         """
-        row, col = at
-        idx = row * len(self.newline) + col
+        row, col = location
+        index = row * len(self.newline) + col
         for i in range(row):
-            idx += len(self.get_line(i))
-        return idx
+            index += len(self.get_line(i))
+        return index
+
+    def get_location_from_index(self, index: int) -> Location:
+        idx = 0
+        newline_len = len(self.newline)
+        for i in range(self.line_count):
+            idx += len(self.get_line(i)) + newline_len
+            if index < idx:
+                return (i, idx - index)
+            elif index == idx:
+                return (i + 1, 0)
 
     def get_line(self, index: int) -> str:
         """Returns the line with the given index from the document.