1 files changed, 88 insertions, 0 deletions
diff --git a/pre_commit_hooks/mixed_line_ending.py b/pre_commit_hooks/mixed_line_ending.py
new file mode 100644
index 0000000..4e07ed9
--- /dev/null
+++ b/pre_commit_hooks/mixed_line_ending.py
@@ -0,0 +1,88 @@
+import argparse
+import collections
+from typing import Dict
+from typing import Optional
+from typing import Sequence
+
+
+CRLF = b'\r\n'
+LF = b'\n'
+CR = b'\r'
+# Prefer LF to CRLF to CR, but detect CRLF before LF
+ALL_ENDINGS = (CR, CRLF, LF)
+FIX_TO_LINE_ENDING = {'cr': CR, 'crlf': CRLF, 'lf': LF}
+
+
+def _fix(filename: str, contents: bytes, ending: bytes) -> None:
+    new_contents = b''.join(
+        line.rstrip(b'\r\n') + ending for line in contents.splitlines(True)
+    )
+    with open(filename, 'wb') as f:
+        f.write(new_contents)
+
+
+def fix_filename(filename: str, fix: str) -> int:
+    with open(filename, 'rb') as f:
+        contents = f.read()
+
+    counts: Dict[bytes, int] = collections.defaultdict(int)
+
+    for line in contents.splitlines(True):
+        for ending in ALL_ENDINGS:
+            if line.endswith(ending):
+                counts[ending] += 1
+                break
+
+    # Some amount of mixed line endings
+    mixed = sum(bool(x) for x in counts.values()) > 1
+
+    if fix == 'no' or (fix == 'auto' and not mixed):
+        return mixed
+
+    if fix == 'auto':
+        max_ending = LF
+        max_lines = 0
+        # ordering is important here such that lf > crlf > cr
+        for ending_type in ALL_ENDINGS:
+            # also important, using >= to find a max that prefers the last
+            if counts[ending_type] >= max_lines:
+                max_ending = ending_type
+                max_lines = counts[ending_type]
+
+        _fix(filename, contents, max_ending)
+        return 1
+    else:
+        target_ending = FIX_TO_LINE_ENDING[fix]
+        # find if there are lines with *other* endings
+        # It's possible there's no line endings of the target type
+        counts.pop(target_ending, None)
+        other_endings = bool(sum(counts.values()))
+        if other_endings:
+            _fix(filename, contents, target_ending)
+        return other_endings
+
+
+def main(argv: Optional[Sequence[str]] = None) -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        '-f', '--fix',
+        choices=('auto', 'no') + tuple(FIX_TO_LINE_ENDING),
+        default='auto',
+        help='Replace line ending with the specified. Default is "auto"',
+    )
+    parser.add_argument('filenames', nargs='*', help='Filenames to fix')
+    args = parser.parse_args(argv)
+
+    retv = 0
+    for filename in args.filenames:
+        if fix_filename(filename, args.fix):
+            if args.fix == 'no':
+                print(f'{filename}: mixed line endings')
+            else:
+                print(f'{filename}: fixed mixed line endings')
+            retv = 1
+    return retv
+
+
+if __name__ == '__main__':
+    raise SystemExit(main())