1 files changed, 85 insertions, 0 deletions
diff --git a/src/SMAPI.Toolkit/Utilities/PathUtilities.cs b/src/SMAPI.Toolkit/Utilities/PathUtilities.cs
new file mode 100644
index 00000000..8a3c2b03
--- /dev/null
+++ b/src/SMAPI.Toolkit/Utilities/PathUtilities.cs
@@ -0,0 +1,85 @@
+using System;
+using System.Diagnostics.Contracts;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+
+namespace StardewModdingAPI.Toolkit.Utilities
+{
+    /// <summary>Provides utilities for normalising file paths.</summary>
+    public static class PathUtilities
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The possible directory separator characters in a file path.</summary>
+        private static readonly char[] PossiblePathSeparators = new[] { '/', '\\', Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar }.Distinct().ToArray();
+
+        /// <summary>The preferred directory separator chaeacter in an asset key.</summary>
+        private static readonly string PreferredPathSeparator = Path.DirectorySeparatorChar.ToString();
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Get the segments from a path (e.g. <c>/usr/bin/boop</c> => <c>usr</c>, <c>bin</c>, and <c>boop</c>).</summary>
+        /// <param name="path">The path to split.</param>
+        /// <param name="limit">The number of segments to match. Any additional segments will be merged into the last returned part.</param>
+        public static string[] GetSegments(string path, int? limit = null)
+        {
+            return limit.HasValue
+                ? path.Split(PathUtilities.PossiblePathSeparators, limit.Value, StringSplitOptions.RemoveEmptyEntries)
+                : path.Split(PathUtilities.PossiblePathSeparators, StringSplitOptions.RemoveEmptyEntries);
+        }
+
+        /// <summary>Normalise path separators in a file path.</summary>
+        /// <param name="path">The file path to normalise.</param>
+        [Pure]
+        public static string NormalisePathSeparators(string path)
+        {
+            string[] parts = PathUtilities.GetSegments(path);
+            string normalised = string.Join(PathUtilities.PreferredPathSeparator, parts);
+            if (path.StartsWith(PathUtilities.PreferredPathSeparator))
+                normalised = PathUtilities.PreferredPathSeparator + normalised; // keep root slash
+            return normalised;
+        }
+
+        /// <summary>Get a directory or file path relative to a given source path.</summary>
+        /// <param name="sourceDir">The source folder path.</param>
+        /// <param name="targetPath">The target folder or file path.</param>
+        [Pure]
+        public static string GetRelativePath(string sourceDir, string targetPath)
+        {
+            // convert to URIs
+            Uri from = new Uri(sourceDir.TrimEnd(PathUtilities.PossiblePathSeparators) + "/");
+            Uri to = new Uri(targetPath.TrimEnd(PathUtilities.PossiblePathSeparators) + "/");
+            if (from.Scheme != to.Scheme)
+                throw new InvalidOperationException($"Can't get path for '{targetPath}' relative to '{sourceDir}'.");
+
+            // get relative path
+            string relative = PathUtilities.NormalisePathSeparators(Uri.UnescapeDataString(from.MakeRelativeUri(to).ToString()));
+            if (relative == "")
+                relative = "./";
+            return relative;
+        }
+
+        /// <summary>Get whether a path is relative and doesn't try to climb out of its containing folder (e.g. doesn't contain <c>../</c>).</summary>
+        /// <param name="path">The path to check.</param>
+        public static bool IsSafeRelativePath(string path)
+        {
+            if (string.IsNullOrWhiteSpace(path))
+                return true;
+
+            return
+                !Path.IsPathRooted(path)
+                && PathUtilities.GetSegments(path).All(segment => segment.Trim() != "..");
+        }
+
+        /// <summary>Get whether a string is a valid 'slug', containing only basic characters that are safe in all contexts (e.g. filenames, URLs, etc).</summary>
+        /// <param name="str">The string to check.</param>
+        public static bool IsSlug(string str)
+        {
+            return !Regex.IsMatch(str, "[^a-z0-9_.-]", RegexOptions.IgnoreCase);
+        }
+    }
+}