add --shebang option

3 files changed, 50 insertions, 10 deletions

diff --git a/patchtree/cli.py b/patchtree/cli.py
index 2535256..8e923dd 100644
--- a/patchtree/cli.py
+++ b/patchtree/cli.py
@@ -39,6 +39,12 @@ def parse_arguments(config: Config) -> Context:
         help="lines of context in output diff",
         type=int,
     )
+    parser.add_argument(
+        "-s",
+        "--shebang",
+        help="output shebang in resulting patch",
+        action="store_true",
+    )
     parser.add_argument("target", help="target directory or archive")
     parser.add_argument("patch", help="patch input glob(s)", nargs="+")
 
@@ -47,8 +53,11 @@ def parse_arguments(config: Config) -> Context:
     if options.context is not None:
         config.diff_context = options.context
 
+    if options.shebang:
+        config.output_shebang = True
+
     try:
-        return config.context(options)
+        return config.context(config, options)
     except Exception as e:
         parser.error(str(e))
 
@@ -70,7 +79,7 @@ def main():
         print("no files to patch!", file=stderr)
         return 0
 
-    config.header(context)
+    config.header(config, context)
 
     for file in files:
         patch = config.patch(config, file)
diff --git a/patchtree/config.py b/patchtree/config.py
index 743307b..196ecb1 100644
--- a/patchtree/config.py
+++ b/patchtree/config.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from dataclasses import dataclass, field
 from argparse import ArgumentParser
 from importlib import metadata
@@ -21,17 +23,32 @@ DEFAULT_DIFFS: dict[str, type[Diff]] = {
 
 
 class Header:
+    config: Config
     context: Context
+
     name = "patchtree"
     license = None
 
-    def __init__(self, context: Context):
+    def __init__(self, config: Config, context: Context):
+        self.config = config
         self.context = context
 
+        self.write_shebang()
         self.write_version()
         self.write_version_extra()
         self.write_license()
 
+    def write_shebang(self):
+        if not self.config.output_shebang:
+            return
+        cmd = [
+            "/usr/bin/env",
+            "-S",
+            *self.context.get_apply_cmd(),
+        ]
+        cmdline = " ".join(cmd)
+        self.context.output.write(f"#!{cmdline}\n")
+
     def write_version(self):
         version = metadata.version("patchtree")
         self.context.output.write(f"{self.name} output (version {version})\n")
@@ -59,6 +76,7 @@ class Config:
     )
     header: type[Header] = Header
     diff_context: int = 3
+    output_shebang: bool = False
 
     def __post_init__(self):
         self.processors = {**DEFAULT_PROCESSORS, **self.processors}
diff --git a/patchtree/context.py b/patchtree/context.py
index 554d09e..0ff769a 100644
--- a/patchtree/context.py
+++ b/patchtree/context.py
@@ -1,5 +1,7 @@
+from __future__ import annotations
+from typing import TYPE_CHECKING, IO, cast
+
 from argparse import Namespace
-from typing import IO, cast
 from pathlib import Path
 from zipfile import ZipInfo, is_zipfile
 from tempfile import TemporaryFile
@@ -9,6 +11,9 @@ from subprocess import run
 from zipfile import ZipFile
 from stat import S_IFDIR, S_IFREG
 
+if TYPE_CHECKING:
+    from .config import Config
+
 ZIP_CREATE_SYSTEM_UNX = 3
 
 
@@ -107,10 +112,14 @@ class ZipFS(FS):
 class Context:
     fs: FS
     output: IO
+
+    config: Config
     options: Namespace
 
-    def __init__(self, options: Namespace):
+    def __init__(self, config: Config, options: Namespace):
+        self.config = config
         self.options = options
+
         self.fs = self.get_fs()
         self.output = self.get_output()
 
@@ -166,16 +175,20 @@ class Context:
 
         return stdout
 
-    def apply(self, reverse: bool) -> None:
-        location = cast(DiskFS, self.fs).path
-        cache = location.joinpath(".patchtree.diff")
-
+    def get_apply_cmd(self) -> list[str]:
         cmd = [
             "git",
             "apply",
-            "--unidiff-zero",
             "--allow-empty",
         ]
+        if self.config.diff_context == 0:
+            cmd.append("--unidiff-zero")
+        return cmd
+
+    def apply(self, reverse: bool) -> None:
+        location = cast(DiskFS, self.fs).path
+        cache = location.joinpath(".patchtree.diff")
+        cmd = self.get_apply_cmd()
 
         if reverse:
             if not cache.exists():