added file-name input option

Author: KiraPC

README.md

@@ -12,6 +12,7 @@ pip install fastapi-openapi-generator
 ### How to use
 ```
 fastapi-openapi-gen main:app \
-    --app-dir= # The path to mounth in the python path to import the module \
-    --output-dir= # The path where store the openapi template
+    --app-dir= # The path to mounth in the python path to import the module. \
+    --output-dir= # The path where store the openapi template. \
+    --file-name= # The name the openapi file will assume.
 ```

generator/main.py

@@ -22,16 +22,24 @@
     show_default=True,
     help="The folder where the swagger is stored."
 )
-def main(app, app_dir, output_dir):
+@click.option(
+    "--file-name",
+    "file_name",
+    default="openapi.json",
+    show_default=True,
+    help="The name the openapi file will assume."
+)
+def main(app, app_dir, output_dir, file_name):
     sys.path.insert(0, app_dir)
 
     fastapi: FastAPI = import_from_string(app)
 
     if not isinstance(fastapi, FastAPI):
         raise NotFastAPIException('The given object is not a FastAPI application')
 
-    with open('{}/openapi.json'.format(output_dir), 'w+') as openapi:
+    with open('{}/{}'.format(output_dir, file_name), 'w+') as openapi:
         openapi.write(json.dumps(fastapi.openapi(), indent=2))
+        openapi.close()
 
 if __name__ == "__main__":
     main()