Check for SPDX headers using pre-commit

Signed-off-by: Russell Bryant <[email protected]>

.pre-commit-config.yaml

@@ -91,3 +91,8 @@ repos:
     language: system
     verbose: true
     pass_filenames: false
+  - id: check-spdx-header
+    name: Check SPDX headers
+    entry: python tools/check_spdx_header.py
+    language: python
+    types: [python]

tools/check_spdx_header.py

@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: Apache-2.0
+
+import sys
+
+SPDX_HEADER = "# SPDX-License-Identifier: Apache-2.0"
+SPDX_HEADER_PREFIX = "# SPDX-License-Identifier:"
+
+
+def check_spdx_header(file_path):
+    with open(file_path, encoding='UTF-8') as file:
+        lines = file.readlines()
+        if not lines:
+            # not necessary for an empty file like __init__.py
+            return True
+        if not lines[0].strip().startswith(SPDX_HEADER_PREFIX):
+            return False
+    return True
+
+
+def add_header(file_path):
+    with open(file_path, 'r+', encoding='UTF-8') as file:
+        lines = file.readlines()
+        file.seek(0, 0)
+        file.write(SPDX_HEADER + '\n\n' + ''.join(lines))
+
+
+def main():
+    files_with_missing_header = []
+    for file_path in sys.argv[1:]:
+        if not check_spdx_header(file_path):
+            files_with_missing_header.append(file_path)
+
+    if files_with_missing_header:
+        print("The following files are missing the SPDX header:")
+        for file_path in files_with_missing_header:
+            print(f"  {file_path}")
+            add_header(file_path)
+
+    sys.exit(1 if files_with_missing_header else 0)
+
+
+if __name__ == "__main__":
+    main()