Add type checking, rework parsing, fix bugs

1 files changed, 9 insertions, 3 deletions

diff --git a/rebreak_lines.py b/rebreak_lines.py
index 41594a3..54473e2 100755
--- a/rebreak_lines.py
+++ b/rebreak_lines.py
@@ -13,7 +13,7 @@ import click
 import parse_srt
 import math
 import sys
-from typing import List
+import typing
 
 # May still be exceeded if there are no word boundaries to wrap at
 MAX_LINE_LENGTH = 42
@@ -33,21 +33,27 @@ def main(in_file_path: str):
 
 
 def rebreak(text: str) -> str:
-    get_target_line_num = lambda length: math.ceil(length / MAX_LINE_LENGTH)
+    get_target_line_num: typing.Callable[[int], int] = lambda length: math.ceil(
+        length / MAX_LINE_LENGTH
+    )
     text = " ".join(text.split("\n"))
     target_line_num = get_target_line_num(len(text))
 
-    lines: List[str] = []
+    lines: list[str] = []
     for _ in range(target_line_num):
         partition_at = round(len(text) / target_line_num) - 1
 
         # Move to a word boundary
+        steps_backward = 0
         for steps_backward, c in enumerate(text[partition_at::-1]):
             if c.isspace():
                 break
         if partition_at - steps_backward != 0:
             partition_at -= steps_backward
         else:
+            # Moving the partition backward would give us an empty line, so
+            # move forward instead to ensure we always make progress.
+            steps_forward = 0
             for steps_forward, c in enumerate(text[partition_at:]):
                 if c.isspace():
                     break