1 files changed, 171 insertions, 0 deletions
diff --git a/src/StardewModdingAPI/SemanticVersion.cs b/src/StardewModdingAPI/SemanticVersion.cs
new file mode 100644
index 00000000..daefda51
--- /dev/null
+++ b/src/StardewModdingAPI/SemanticVersion.cs
@@ -0,0 +1,171 @@
+using System;
+using System.Text.RegularExpressions;
+
+namespace StardewModdingAPI
+{
+    /// <summary>A semantic version with an optional release tag.</summary>
+    public class SemanticVersion : ISemanticVersion
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>A regular expression matching a semantic version string.</summary>
+        /// <remarks>Derived from https://github.com/maxhauser/semver.</remarks>
+        private static readonly Regex Regex = new Regex(@"^(?<major>\d+)(\.(?<minor>\d+))?(\.(?<patch>\d+))?(?<build>.*)$", RegexOptions.CultureInvariant | RegexOptions.ExplicitCapture);
+
+        /// <summary>The backing field for <see cref="Build"/>.</summary>
+        private string _build;
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The major version incremented for major API changes.</summary>
+        public int MajorVersion { get; set; }
+
+        /// <summary>The minor version incremented for backwards-compatible changes.</summary>
+        public int MinorVersion { get; set; }
+
+        /// <summary>The patch version for backwards-compatible bug fixes.</summary>
+        public int PatchVersion { get; set; }
+
+        /// <summary>An optional build tag.</summary>
+        public string Build
+        {
+            get { return this._build; }
+            set { this._build = this.GetNormalisedTag(value); }
+        }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="major">The major version incremented for major API changes.</param>
+        /// <param name="minor">The minor version incremented for backwards-compatible changes.</param>
+        /// <param name="patch">The patch version for backwards-compatible bug fixes.</param>
+        /// <param name="build">An optional build tag.</param>
+        public SemanticVersion(int major, int minor, int patch, string build = null)
+        {
+            this.MajorVersion = major;
+            this.MinorVersion = minor;
+            this.PatchVersion = patch;
+            this.Build = build;
+        }
+
+        /// <summary>Construct an instance.</summary>
+        /// <param name="version">The semantic version string.</param>
+        /// <exception cref="FormatException">The <paramref name="version"/> is not a valid semantic version.</exception>
+        internal SemanticVersion(string version)
+        {
+            var match = SemanticVersion.Regex.Match(version);
+            if (!match.Success)
+                throw new FormatException($"The input '{version}' is not a valid semantic version.");
+
+            this.MajorVersion = int.Parse(match.Groups["major"].Value);
+            this.MinorVersion = match.Groups["minor"].Success ? int.Parse(match.Groups["minor"].Value) : 0;
+            this.PatchVersion = match.Groups["patch"].Success ? int.Parse(match.Groups["patch"].Value) : 0;
+            this.Build = match.Groups["build"].Success ? match.Groups["build"].Value : null;
+        }
+
+        /// <summary>Get an integer indicating whether this version precedes (less than 0), supercedes (more than 0), or is equivalent to (0) the specified version.</summary>
+        /// <param name="other">The version to compare with this instance.</param>
+        /// <remarks>The implementation is defined by Semantic Version 2.0 (http://semver.org/).</remarks>
+        public int CompareTo(ISemanticVersion other)
+        {
+            const int same = 0;
+            const int curNewer = 1;
+            const int curOlder = -1;
+
+            // compare stable versions
+            if (this.MajorVersion != other.MajorVersion)
+                return this.MajorVersion.CompareTo(other.MajorVersion);
+            if (this.MinorVersion != other.MinorVersion)
+                return this.MinorVersion.CompareTo(other.MinorVersion);
+            if (this.PatchVersion != other.PatchVersion)
+                return this.PatchVersion.CompareTo(other.PatchVersion);
+            if (this.Build == other.Build)
+                return same;
+
+            // stable supercedes pre-release
+            bool curIsStable = string.IsNullOrWhiteSpace(this.Build);
+            bool otherIsStable = string.IsNullOrWhiteSpace(other.Build);
+            if (curIsStable)
+                return curNewer;
+            if (otherIsStable)
+                return curOlder;
+
+            // compare two pre-release tag values
+            string[] curParts = this.Build.Split('.');
+            string[] otherParts = other.Build.Split('.');
+            for (int i = 0; i < curParts.Length; i++)
+            {
+                // longer prerelease tag supercedes if otherwise equal
+                if (otherParts.Length <= i)
+                    return curNewer;
+
+                // compare if different
+                if (curParts[i] != otherParts[i])
+                {
+                    // compare numerically if possible
+                    {
+                        int curNum, otherNum;
+                        if (int.TryParse(curParts[i], out curNum) && int.TryParse(otherParts[i], out otherNum))
+                            return curNum.CompareTo(otherNum);
+                    }
+
+                    // else compare lexically
+                    return string.Compare(curParts[i], otherParts[i], StringComparison.OrdinalIgnoreCase);
+                }
+            }
+
+            // fallback (this should never happen)
+            return string.Compare(this.ToString(), other.ToString(), StringComparison.InvariantCultureIgnoreCase);
+        }
+
+        /// <summary>Get whether this version is older than the specified version.</summary>
+        /// <param name="other">The version to compare with this instance.</param>
+        public bool IsOlderThan(ISemanticVersion other)
+        {
+            return this.CompareTo(other) < 0;
+        }
+
+        /// <summary>Get whether this version is newer than the specified version.</summary>
+        /// <param name="other">The version to compare with this instance.</param>
+        public bool IsNewerThan(ISemanticVersion other)
+        {
+            return this.CompareTo(other) > 0;
+        }
+
+        /// <summary>Get a string representation of the version.</summary>
+        public override string ToString()
+        {
+            // version
+            string result = this.PatchVersion != 0
+                ? $"{this.MajorVersion}.{this.MinorVersion}.{this.PatchVersion}"
+                : $"{this.MajorVersion}.{this.MinorVersion}";
+
+            // tag
+            string tag = this.Build;
+            if (tag != null)
+                result += $"-{tag}";
+            return result;
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Get a normalised build tag.</summary>
+        /// <param name="tag">The tag to normalise.</param>
+        private string GetNormalisedTag(string tag)
+        {
+            tag = tag?.Trim().Trim('-', '.');
+            if (string.IsNullOrWhiteSpace(tag))
+                return null;
+            if (tag == "0")
+                return null; // from incorrect examples in old SMAPI documentation
+            return tag;
+        }
+    }
+}