Add a class ID migration script for REAPER

tools/migration/README.md

@@ -11,4 +11,7 @@ before that commit will no longer be compatible. As a temporary migration path,
 there are a few scripts here that you can use to convert old project files to
 the new format.
 
-TODO: Document further once we add the actual scripts
+These scripts won't overwrite any existing files, but remember to always make
+more backups than you really need!
+
+TODO: Document further once we finish the Bitwig, Ardour and Renoise scripts

tools/migration/migrate-reaper.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python3
+
+import argparse
+import os
+import re
+import textwrap
+
+
+# Yes, you shouldn't try to parse these kinds of things with regular
+# expressions. But writing a proper parser takes effort, and this approach will
+# catch all VST3 plugins just fine even if the developer somehow included
+# quotes in their vendor or plugin names. This regexp will find VST3 plugins in
+# a .RPP file and capture its name and class ID.
+REAPER_VST3_RE = re.compile(rb'<VST "(VST3.+?)" .+\{([0-9a-zA-Z]{32})\}')
+
+
+parser = argparse.ArgumentParser(
+    description="Migrate old yabridge VST3 plugin instances in REAPER project files."
+)
+parser.add_argument("filename", type=str, help="The .RPP project file to migrate.")
+
+# As a safety measure we want to limit the file names we accept
+args = parser.parse_args()
+
+filename = args.filename
+file_stem, file_extension = os.path.splitext(filename)
+if file_extension.lower() != ".rpp":
+    print("For safety reasons, only '*.RPP' files are accepted")
+    exit(1)
+if file_stem.endswith("-migrated"):
+    print("This project file has already been migrated to the new format")
+    exit(1)
+
+migrated_filename = file_stem + "-migrated" + file_extension
+if os.path.exists(migrated_filename):
+    print(
+        f"'{migrated_filename}' already exists, back it up and move it elsewhere "
+        "if you want to redo the migration"
+    )
+    exit(1)
+
+print(
+    "\n".join(
+        textwrap.wrap(
+            f"This script will go through '{filename}' to migrate old yabridge VST3 plugin instances. "
+            f"The output will be saved to '{migrated_filename}', but make sure to still create a backup of the original file in case something does go wrong. "
+            f"For every VST3 plugin found you will be prompted with the question if you want to migrate it. "
+            f"Answer 'yes' for all old yabridge VST3 plugin instances, and 'no' for any other VST3 plugin."
+            f"Make sure to test whether the new project works immediately after migration.",
+            width=80,
+        )
+    )
+)
+print()
+
+# We'll search through the original file, and prompt to replace all VST3 class
+# IDs we come across. See `WineUID` in yabridge's source code for an
+# explanation of this conversion.
+with open(filename, "rb") as f_input, open(migrated_filename, "xb") as f_output:
+    migrated_file = []
+    for line in f_input.readlines():
+        # Sadly can't use the walrus operator here since old distros might
+        # still ship with Python 3.6
+        matches = REAPER_VST3_RE.search(line)
+        if matches is not None:
+            plugin_name = matches.group(1).decode("utf-8")
+
+            wine_uid_start, wine_uid_end = matches.span(2)
+            wine_uid = bytearray.fromhex(matches.group(2).decode("ascii"))
+            converted_uid = bytearray.fromhex(matches.group(2).decode("ascii"))
+
+            converted_uid[0] = wine_uid[3]
+            converted_uid[1] = wine_uid[2]
+            converted_uid[2] = wine_uid[1]
+            converted_uid[3] = wine_uid[0]
+
+            converted_uid[4] = wine_uid[5]
+            converted_uid[5] = wine_uid[4]
+            converted_uid[6] = wine_uid[7]
+            converted_uid[7] = wine_uid[6]
+
+            migrated_line = (
+                line[:wine_uid_start]
+                + converted_uid.hex().encode("ascii").upper()
+                + line[wine_uid_end:]
+            )
+
+            while True:
+                answer = input(
+                    f"Found '{plugin_name}' with class ID '{wine_uid.hex().upper()}'\nShould this plugin be migrated? [yes/no] "
+                ).lower()
+                if answer == "yes":
+                    migrated_file.append(migrated_line)
+                    break
+                elif answer == "no":
+                    migrated_file.append(line)
+                    break
+                else:
+                    print("Please answer only 'yes' or 'no'")
+        else:
+            migrated_file.append(line)
+
+    print(f"\nMigration successful, writing the results to '{migrated_filename}'")
+    f_output.writelines(migrated_file)