Unity asset GUIDs regenerator

UnityGuidRegenerator.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using UnityEditor;

namespace UnityGuidRegenerator {
    public class UnityGuidRegeneratorMenu {
        [MenuItem("Tools/Regenerate All GUIDs")]
        public static void RegenerateGuids() {
            if (EditorUtility.DisplayDialog("Regenerate All GUIDs",
                "You are going to start the process of GUID regeneration. This may have unexpected results and may break unsaved changes. Are you sure you want to do this?",
                "Regenerate GUIDs", "Cancel")) {
                try {
                    AssetDatabase.StartAssetEditing();

                    string path = Path.GetFullPath(".") + Path.DirectorySeparatorChar + "Assets";
                    UnityGuidRegenerator regenerator = new UnityGuidRegenerator(path);
                    regenerator.RegenerateGuids();
                }
                finally {
                    AssetDatabase.StopAssetEditing();
                    EditorUtility.ClearProgressBar();
                    AssetDatabase.Refresh();
                }
            }
        }
    }

    internal class UnityGuidRegenerator {
        private static readonly string[] kDefaultFileExtensions = {
            "*.meta",
            "*.mat",
            "*.anim",
            "*.prefab",
            "*.unity",
            "*.asset",
            "*.guiskin",
            "*.fontsettings",
            "*.controller",
        };

        private readonly string _assetsPath;

        public UnityGuidRegenerator(string assetsPath) {
            _assetsPath = assetsPath;
        }

        public void RegenerateGuids(string[] regeneratedExtensions = null) {
            if (regeneratedExtensions == null) {
                regeneratedExtensions = kDefaultFileExtensions;
            }

            // Get list of working files
            List<string> filesPaths = new List<string>();
            foreach (string extension in regeneratedExtensions) {
                filesPaths.AddRange(
                    Directory.GetFiles(_assetsPath, extension, SearchOption.AllDirectories)
                    );
            }

            // Create dictionary to hold old-to-new GUID map
            Dictionary<string, string> guidOldToNewMap = new Dictionary<string, string>();
            Dictionary<string, List<string>> guidsInFileMap = new Dictionary<string, List<string>>();

            // We must only replace GUIDs for Resources present in Assets. 
            // Otherwise built-in resources (shader, meshes etc) get overwritten.
            HashSet<string> ownGuids = new HashSet<string>();

            // Traverse all files, remember which GUIDs are in which files and generate new GUIDs
            int counter = 0;
            foreach (string filePath in filesPaths) {
                if (!EditorUtility.DisplayCancelableProgressBar("Scanning Assets folder", MakeRelativePath(_assetsPath, filePath),
                    counter / (float) filesPaths.Count)) {
                    string contents = File.ReadAllText(filePath);

                    IEnumerable<string> guids = GetGuids(contents);
                    bool isFirstGuid = true;
                    foreach (string oldGuid in guids) {
                        // First GUID in .meta file is always the GUID of the asset itself
                        if (isFirstGuid && Path.GetExtension(filePath) == ".meta") {
                            ownGuids.Add(oldGuid);
                            isFirstGuid = false;
                        }
                        // Generate and save new GUID if we haven't added it before
                        if (!guidOldToNewMap.ContainsKey(oldGuid)) {
                            string newGuid = Guid.NewGuid().ToString("N");
                            guidOldToNewMap.Add(oldGuid, newGuid);
                        }

                        if (!guidsInFileMap.ContainsKey(filePath))
                            guidsInFileMap[filePath] = new List<string>();

                        if (!guidsInFileMap[filePath].Contains(oldGuid)) {
                            guidsInFileMap[filePath].Add(oldGuid);
                        }
                    }

                    counter++;
                } else {
                    UnityEngine.Debug.LogWarning("GUID regeneration canceled");
                    return;
                }
            }

            // Traverse the files again and replace the old GUIDs
            counter = -1;
            int guidsInFileMapKeysCount = guidsInFileMap.Keys.Count;
            foreach (string filePath in guidsInFileMap.Keys) {
                EditorUtility.DisplayProgressBar("Regenerating GUIDs", MakeRelativePath(_assetsPath, filePath), counter / (float) guidsInFileMapKeysCount);
                counter++;

                string contents = File.ReadAllText(filePath);
                foreach (string oldGuid in guidsInFileMap[filePath]) {
                    if (!ownGuids.Contains(oldGuid))
                        continue;

                    string newGuid = guidOldToNewMap[oldGuid];
                    if (string.IsNullOrEmpty(newGuid))
                        throw new NullReferenceException("newGuid == null");

                    contents = contents.Replace("guid: " + oldGuid, "guid: " + newGuid);
                }
                File.WriteAllText(filePath, contents);
            }

            EditorUtility.ClearProgressBar();
        }

        private static IEnumerable<string> GetGuids(string text) {
            const string guidStart = "guid: ";
            const int guidLength = 32;
            int textLength = text.Length;
            int guidStartLength = guidStart.Length;
            List<string> guids = new List<string>();

            int index = 0;
            while (index + guidStartLength + guidLength < textLength) {
                index = text.IndexOf(guidStart, index, StringComparison.Ordinal);
                if (index == -1)
                    break;

                index += guidStartLength;
                string guid = text.Substring(index, guidLength);
                index += guidLength;

                if (IsGuid(guid)) {
                    guids.Add(guid);
                }
            }

            return guids;
        }

        private static bool IsGuid(string text) {
            for (int i = 0; i < text.Length; i++) {
                char c = text[i];
                if (
                    !((c >= '0' && c <= '9') ||
                      (c >= 'a' && c <= 'z'))
                    )
                    return false;
            }

            return true;
        }

        private static string MakeRelativePath(string fromPath, string toPath) {
            Uri fromUri = new Uri(fromPath);
            Uri toUri = new Uri(toPath);

            Uri relativeUri = fromUri.MakeRelativeUri(toUri);
            string relativePath = Uri.UnescapeDataString(relativeUri.ToString());

            return relativePath;
        }
    }
}