REF: Refactor plugin.py to use modular dataclasses in tree-like structure to represent parsed data (#121)

Refactor plugin to parse input into data-class based hierarchical structure

src/betterproto/plugin/main.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+import sys
+import os
+
+from google.protobuf.compiler import plugin_pb2 as plugin
+
+from betterproto.plugin.parser import generate_code
+
+
+def main():
+    """The plugin's main entry point."""
+    # Read request message from stdin
+    data = sys.stdin.buffer.read()
+
+    # Parse request
+    request = plugin.CodeGeneratorRequest()
+    request.ParseFromString(data)
+
+    dump_file = os.getenv("BETTERPROTO_DUMP")
+    if dump_file:
+        dump_request(dump_file, request)
+
+    # Create response
+    response = plugin.CodeGeneratorResponse()
+
+    # Generate code
+    generate_code(request, response)
+
+    # Serialise response message
+    output = response.SerializeToString()
+
+    # Write to stdout
+    sys.stdout.buffer.write(output)
+
+
+def dump_request(dump_file: str, request: plugin.CodeGeneratorRequest):
+    """
+    For developers: Supports running plugin.py standalone so its possible to debug it.
+    Run protoc (or generate.py) with BETTERPROTO_DUMP="yourfile.bin" to write the request to a file.
+    Then run plugin.py from your IDE in debugging mode, and redirect stdin to the file.
+    """
+    with open(str(dump_file), "wb") as fh:
+        sys.stderr.write(f"\033[31mWriting input from protoc to: {dump_file}\033[0m\n")
+        fh.write(request.SerializeToString())
+
+
+if __name__ == "__main__":
+    main()