Rewrite the update license script

The old script duplicated license headers for me, instead of
updating them.

tools/update-license.py

@@ -0,0 +1,58 @@
+import argparse
+import os
+from typing import *
+
+T = TypeVar('T')
+
+SOURCE_FILES_SEARCH_DIRECTORIES = ['src', 'test']
+LICENSE_HEADER_END = ' * along with this program. If not, see http://gnu.org/licenses'
+
+def is_source_file(file: str) -> bool:
+    return file.endswith('.cpp') or file.endswith('.h')
+
+
+def find_all_source_files(directories: list[str]) -> str:
+    for directory in directories:
+        for root, found_dirs, found_files in os.walk(directory):
+            for file in found_files:
+                if is_source_file(file):
+                    path = os.path.join(root, file)
+                    yield path
+
+
+def find_license_header_end(lines: list[str]) -> Optional[int]:
+    for idx, line in enumerate(lines):
+        if LICENSE_HEADER_END in line:
+            return idx + 2 # One more line with '*/' and idx past end
+    return None
+
+
+def remove_range(a_list: list[T], begin: int, end: int) -> list[str]:
+    return a_list[0:begin] + a_list[end:]
+
+
+def remove_license_header(lines: list[str]) -> list[str]:
+    return remove_range(lines, begin=0, end=find_license_header_end(lines))
+
+
+def add_license_header_at_beginning(lines: list[str], new_license_header: list[str]) -> list[str]:
+    return new_license_header + lines
+
+
+def update_license_header(lines: list[str], new_license_header: list[str]) -> list[str]:
+    return add_license_header_at_beginning(remove_license_header(lines), new_license_header)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('license_header', help='Path to the new license header file', type=str)
+    args = parser.parse_args()
+    new_license_header = open(args.license_header).readlines()
+    for source_file in find_all_source_files(SOURCE_FILES_SEARCH_DIRECTORIES):
+        print(source_file)
+        lines = update_license_header(open(source_file).readlines(), new_license_header)
+        open(source_file, 'w', newline='\n').writelines(lines)
+
+
+if __name__ == '__main__':
+    main()

tools/update-license.sh

@@ -1,12 +0,0 @@
-#!/bin/bash
-# Replaces license text with contents of file provided as an argument
-if [ ! $# -eq 1 ]; then
-	echo "Usage: $0 [file with new license header]"
-	exit 1
-fi
-find . -name "*.cpp" -or -name "*.h" | while read file; do
-	echo $file
-	sed '/\/\/ \* This.*/,/If not\, see.*/d' $file > $file.tmp
-	cat $1 $file.tmp > $file
-	rm $file.tmp
-done