1 files changed, 139 insertions, 0 deletions
diff --git a/src/SMAPI.Toolkit/Utilities/CaseInsensitivePathLookup.cs b/src/SMAPI.Toolkit/Utilities/CaseInsensitivePathLookup.cs
new file mode 100644
index 00000000..12fad008
--- /dev/null
+++ b/src/SMAPI.Toolkit/Utilities/CaseInsensitivePathLookup.cs
@@ -0,0 +1,139 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace StardewModdingAPI.Toolkit.Utilities
+{
+    /// <summary>Provides an API for case-insensitive relative path lookups within a root directory.</summary>
+    internal class CaseInsensitivePathLookup
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The root directory path for relative paths.</summary>
+        private readonly string RootPath;
+
+        /// <summary>A case-insensitive lookup of file paths within the <see cref="RootPath"/>. Each path is listed in both file path and asset name format, so it's usable in both contexts without needing to re-parse paths.</summary>
+        private readonly Lazy<Dictionary<string, string>> RelativePathCache;
+
+        /// <summary>The case-insensitive path caches by root path.</summary>
+        private static readonly Dictionary<string, CaseInsensitivePathLookup> CachedRoots = new(StringComparer.OrdinalIgnoreCase);
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="rootPath">The root directory path for relative paths.</param>
+        /// <param name="searchOption">Which directories to scan from the root.</param>
+        public CaseInsensitivePathLookup(string rootPath, SearchOption searchOption = SearchOption.AllDirectories)
+        {
+            this.RootPath = rootPath;
+            this.RelativePathCache = new(() => this.GetRelativePathCache(searchOption));
+        }
+
+        /// <summary>Get the exact capitalization for a given relative file path.</summary>
+        /// <param name="relativePath">The relative path.</param>
+        /// <remarks>Returns the resolved path in file path format, else the normalized <paramref name="relativePath"/>.</remarks>
+        public string GetFilePath(string relativePath)
+        {
+            return this.GetImpl(PathUtilities.NormalizePath(relativePath));
+        }
+
+        /// <summary>Get the exact capitalization for a given asset name.</summary>
+        /// <param name="relativePath">The relative path.</param>
+        /// <remarks>Returns the resolved path in asset name format, else the normalized <paramref name="relativePath"/>.</remarks>
+        public string GetAssetName(string relativePath)
+        {
+            return this.GetImpl(PathUtilities.NormalizeAssetName(relativePath));
+        }
+
+        /// <summary>Add a relative path that was just created by a SMAPI API.</summary>
+        /// <param name="relativePath">The relative path. This must already be normalized in asset name or file path format.</param>
+        public void Add(string relativePath)
+        {
+            // skip if cache isn't created yet (no need to add files manually in that case)
+            if (!this.RelativePathCache.IsValueCreated)
+                return;
+
+            // skip if already cached
+            if (this.RelativePathCache.Value.ContainsKey(relativePath))
+                return;
+
+            // make sure path exists
+            relativePath = PathUtilities.NormalizePath(relativePath);
+            if (!File.Exists(Path.Combine(this.RootPath, relativePath)))
+                throw new InvalidOperationException($"Can't add relative path '{relativePath}' to the case-insensitive cache for '{this.RootPath}' because that file doesn't exist.");
+
+            // cache path
+            this.CacheRawPath(this.RelativePathCache.Value, relativePath);
+        }
+
+        /// <summary>Get a cached dictionary of relative paths within a root path, for case-insensitive file lookups.</summary>
+        /// <param name="rootPath">The root path to scan.</param>
+        public static CaseInsensitivePathLookup GetCachedFor(string rootPath)
+        {
+            rootPath = PathUtilities.NormalizePath(rootPath);
+
+            if (!CaseInsensitivePathLookup.CachedRoots.TryGetValue(rootPath, out CaseInsensitivePathLookup? cache))
+                CaseInsensitivePathLookup.CachedRoots[rootPath] = cache = new CaseInsensitivePathLookup(rootPath);
+
+            return cache;
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get the exact capitalization for a given relative path.</summary>
+        /// <param name="relativePath">The relative path. This must already be normalized into asset name or file path format (i.e. using <see cref="PathUtilities.NormalizeAssetName"/> or <see cref="PathUtilities.NormalizePath"/> respectively).</param>
+        /// <remarks>Returns the resolved path in the same format if found, else returns the path as-is.</remarks>
+        private string GetImpl(string relativePath)
+        {
+            // invalid path
+            if (string.IsNullOrWhiteSpace(relativePath))
+                return relativePath;
+
+            // already cached
+            if (this.RelativePathCache.Value.TryGetValue(relativePath, out string? resolved))
+                return resolved;
+
+            // keep capitalization as-is
+            if (File.Exists(Path.Combine(this.RootPath, relativePath)))
+            {
+                // file exists but isn't cached for some reason
+                // cache it now so any later references to it are case-insensitive
+                this.CacheRawPath(this.RelativePathCache.Value, relativePath);
+            }
+            return relativePath;
+        }
+
+        /// <summary>Get a case-insensitive lookup of file paths (see <see cref="RelativePathCache"/>).</summary>
+        /// <param name="searchOption">Which directories to scan from the root.</param>
+        private Dictionary<string, string> GetRelativePathCache(SearchOption searchOption)
+        {
+            Dictionary<string, string> cache = new(StringComparer.OrdinalIgnoreCase);
+
+            foreach (string path in Directory.EnumerateFiles(this.RootPath, "*", searchOption))
+            {
+                string relativePath = path.Substring(this.RootPath.Length + 1);
+
+                this.CacheRawPath(cache, relativePath);
+            }
+
+            return cache;
+        }
+
+        /// <summary>Add a raw relative path to the cache.</summary>
+        /// <param name="cache">The cache to update.</param>
+        /// <param name="relativePath">The relative path to cache, with its exact filesystem capitalization.</param>
+        private void CacheRawPath(IDictionary<string, string> cache, string relativePath)
+        {
+            string filePath = PathUtilities.NormalizePath(relativePath);
+            string assetName = PathUtilities.NormalizeAssetName(relativePath);
+
+            cache[filePath] = filePath;
+            cache[assetName] = assetName;
+        }
+    }
+}