1 files changed, 84 insertions, 0 deletions
diff --git a/pre_commit_hooks/file_contents_sorter.py b/pre_commit_hooks/file_contents_sorter.py
new file mode 100644
index 0000000..392e226
--- /dev/null
+++ b/pre_commit_hooks/file_contents_sorter.py
@@ -0,0 +1,84 @@
+"""
+A very simple pre-commit hook that, when passed one or more filenames
+as arguments, will sort the lines in those files.
+
+An example use case for this: you have a deploy-allowlist.txt file
+in a repo that contains a list of filenames that is used to specify
+files to be included in a docker container. This file has one filename
+per line. Various users are adding/removing lines from this file; using
+this hook on that file should reduce the instances of git merge
+conflicts and keep the file nicely ordered.
+"""
+import argparse
+from typing import Any
+from typing import Callable
+from typing import IO
+from typing import Iterable
+from typing import Optional
+from typing import Sequence
+
+PASS = 0
+FAIL = 1
+
+
+def sort_file_contents(
+    f: IO[bytes],
+    key: Optional[Callable[[bytes], Any]],
+    *,
+    unique: bool = False,
+) -> int:
+    before = list(f)
+    lines: Iterable[bytes] = (
+        line.rstrip(b'\n\r') for line in before if line.strip()
+    )
+    if unique:
+        lines = set(lines)
+    after = sorted(lines, key=key)
+
+    before_string = b''.join(before)
+    after_string = b'\n'.join(after) + b'\n'
+
+    if before_string == after_string:
+        return PASS
+    else:
+        f.seek(0)
+        f.write(after_string)
+        f.truncate()
+        return FAIL
+
+
+def main(argv: Optional[Sequence[str]] = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='+', help='Files to sort')
+    parser.add_argument(
+        '--ignore-case',
+        action='store_const',
+        const=bytes.lower,
+        default=None,
+        help='fold lower case to upper case characters',
+    )
+    parser.add_argument(
+        '--unique',
+        action='store_true',
+        help='ensure each line is unique',
+    )
+    args = parser.parse_args(argv)
+
+    retv = PASS
+
+    for arg in args.filenames:
+        with open(arg, 'rb+') as file_obj:
+            ret_for_file = sort_file_contents(
+                file_obj, key=args.ignore_case, unique=args.unique,
+            )
+
+            if ret_for_file:
+                print(f'Sorting {arg}')
+
+            retv |= ret_for_file
+
+    return retv
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())