Add --batch option

src/regit/__main__.py

 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Callable
+from typing import Callable, cast
+import subprocess
 import csv
 import logging
 import tempfile
+from contextlib import contextmanager
 
 import click
 import git
@@ -99,6 +101,7 @@ class BlobHandler:
     help="The file to output the csv mapping to",
     type=click.File("w", lazy=False),
 )
+@click.option("--batch/--no-batch", default=False)
 @click.option(
     "-v",
     "--verbose",
@@ -115,6 +118,7 @@ def regit(
     program: Path,
     args: tuple[str],
     verbose: int,
+    batch: bool,
 ):
     """A simple program that runs a command on every commit on a repo."""
 
@@ -132,22 +136,6 @@ def regit(
         repo = git.Repo.clone_from(url=repo, to_path=output, no_local=True)
         log.debug("Cloned repo to %s", output)
 
-    with tempfile.TemporaryDirectory() as folder:
-        folder = Path(folder)
-
-        def transformer(file: Path, content: bytes) -> bytes:
-            pargs = list(args)
-            try:
-                ix = pargs.index("{}")
-            except ValueError:
-                return utils.run_stdout([program] + pargs, input=content)
-            else:
-                with utils.tfile(folder, file.name, content) as tmp_file:
-                    pargs[ix] = str(tmp_file)
-                    utils.run([program] + pargs)
-                    with open(tmp_file, "rb") as f:
-                        return f.read()
-
     def is_relevant(file: Path):
         if pattern is None:
             return True
@@ -155,6 +143,7 @@ def regit(
         log.debug("Check if %s matched pattern %s", file, match)
         return match
 
+    with mktransformer(program, args, batch) as transformer:
         handler = BlobHandler(repo, is_relevant=is_relevant, transform=transformer)
         log.debug("Starting handler")
         with handler:
@@ -176,5 +165,67 @@ def regit(
     print(repo.working_dir)
 
 
+@contextmanager
+def mktransformer(program, args, batch):
+    with tempfile.TemporaryDirectory() as folder:
+        folder = Path(folder)
+
+        pargs = list(args)
+
+        if batch:
+            formatproc = utils.popen(
+                [program] + pargs,
+                stdin=subprocess.PIPE,
+                universal_newlines=False,
+            )
+            if formatproc.stdin is None:
+                raise RuntimeError("Could not start the formatting program")
+
+            fin = formatproc.stdin
+
+            def transformer(file: Path, content: bytes) -> bytes:
+                with utils.tfile(folder, file.name, content) as tmp_file:
+                    try:
+                        fin.write(str(tmp_file).encode("utf-8") + b"\n")  # type: ignore
+                        fin.flush()
+                    except subprocess.CalledProcessError:
+                        file = Path(file.name).with_suffix("input").absolute()
+                        log.error("Writing argument to %s", file)
+                        with open(file, "wb") as f:
+                            f.write(content)
+                        raise
+                    with open(tmp_file, "rb") as f:
+                        return f.read()
+
+            yield transformer
+
+            formatproc.stdin.close()
+            formatproc.wait()
+        elif "{}" in pargs:
+            ix = pargs.index("{}")
+
+            def transformer(file: Path, content: bytes) -> bytes:
+                with utils.tfile(folder, file.name, content) as tmp_file:
+                    pargs[ix] = str(tmp_file)
+                    try:
+                        utils.run([program] + pargs)
+                    except subprocess.CalledProcessError:
+                        file = Path(file.name).with_suffix("input").absolute()
+                        log.error("Writing argument to %s", file)
+                        with open(file, "wb") as f:
+                            f.write(content)
+                        raise
+                    with open(tmp_file, "rb") as f:
+                        return f.read()
+
+            yield transformer
+        else:
+
+            def transformer(file: Path, content: bytes) -> bytes:
+                return utils.run_stdout([program] + pargs, input=content)
+
+            yield transformer
+
+
 if __name__ == "__main__":
     regit()