fix the way tabs are used

The previous code just assumed a tab was 4 spaces wide.
This is not true, because a tab can be between 1 and 4 spaces wide.

line.py

@@ -16,9 +16,12 @@ class Line:
     def line(self) -> str:
         return self._line
 
-    def length(self) -> int:
+    def length_in_charaters(self) -> int:
         return len(self._line)
 
+    def length_in_columns(self) -> int:
+        return self.char_to_column(len(self._line))
+
     def char_index_to_byte(self, char_in_line: int) -> int:
         return len(self.prefix(char_in_line).encode("utf8"))
 
@@ -27,26 +30,46 @@ class Line:
         prefix_chars = prefix_bytes.decode("utf8", errors="ignore")
         return len(prefix_chars)
 
+    def line_tabs_replaced(self):
+        line = self._line;
+        i = 0
+        offset = 0
+        result = ""
+        length = len(line)
+        while True:
+            tab_index = line.find("\t", offset)
+            if tab_index < 0:
+                break
+            result = result + line[offset:tab_index]
+            result = result + " " * (constants.tab_width - len(result) % constants.tab_width)
+            offset = tab_index + 1
+
+        result = result + line[offset:]
+
+        return result
+
     def column_to_char(self, column_in_line: int) -> int:
         i = 0
         result = 0
         while i < column_in_line:
             char = self._line[result]
             if char == "\t":
-                i = i + constants.tab_width - 1  # jump the additional 7 columns of the tab width
-                if i >= column_in_line:
+                i = i + constants.tab_width - i % constants.tab_width  # jump the additional columns to complete the tab
+                if i > column_in_line:
                     break;
-            i = i + 1
+            else:
+                i = i + 1
             result = result + 1
 
         return result
 
+    # todo this method is slow
     def char_to_column(self, char_in_line: int) -> int:
         result = 0
         i = 0
         while i < char_in_line:
             if i < len(self._line) and self._line[i] == "\t":
-                result = result + constants.tab_width
+                result = result + constants.tab_width - result % constants.tab_width
             else:
                 result = result + 1
             i = i + 1