5 files changed, 192 insertions, 0 deletions
diff --git a/src/StardewModdingAPI/Framework/LogFileManager.cs b/src/StardewModdingAPI/Framework/LogFileManager.cs
new file mode 100644
index 00000000..c2a2105b
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/LogFileManager.cs
@@ -0,0 +1,46 @@
+using System;
+using System.IO;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>Manages reading and writing to log file.</summary>
+    internal class LogFileManager : IDisposable
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The underlying stream writer.</summary>
+        private readonly StreamWriter Stream;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="path">The log file to write.</param>
+        public LogFileManager(string path)
+        {
+            // create log directory if needed
+            string logDir = Path.GetDirectoryName(path);
+            if (logDir == null)
+                throw new ArgumentException($"The log path '{path}' is not valid.");
+            Directory.CreateDirectory(logDir);
+
+            // open log file stream
+            this.Stream = new StreamWriter(path, append: false) { AutoFlush = true };
+        }
+
+        /// <summary>Write a message to the log.</summary>
+        /// <param name="message">The message to log.</param>
+        public void WriteLine(string message)
+        {
+            this.Stream.WriteLine(message);
+        }
+
+        /// <summary>Release all resources.</summary>
+        public void Dispose()
+        {
+            this.Stream.Dispose();
+        }
+    }
+}
+\ No newline at end of file
diff --git a/src/StardewModdingAPI/Framework/Monitor.cs b/src/StardewModdingAPI/Framework/Monitor.cs
new file mode 100644
index 00000000..4fe1df04
--- /dev/null
+++ b/src/StardewModdingAPI/Framework/Monitor.cs
@@ -0,0 +1,104 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace StardewModdingAPI.Framework
+{
+    /// <summary>Encapsulates monitoring and logic for a given module.</summary>
+    internal class Monitor : IMonitor
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The name of the module which logs messages using this instance.</summary>
+        private readonly string Source;
+
+        /// <summary>The log file to which to write messages.</summary>
+        private readonly LogFileManager LogFile;
+
+        /// <summary>The maximum length of the <see cref="LogLevel"/> values.</summary>
+        private static readonly int MaxLevelLength = (from level in Enumerable.Cast<LogLevel>(Enum.GetValues(typeof(LogLevel))) select level.ToString().Length).Max();
+
+        /// <summary>The console text color for each log level.</summary>
+        private static readonly Dictionary<LogLevel, ConsoleColor> Colors = new Dictionary<LogLevel, ConsoleColor>
+        {
+            [LogLevel.Trace] = ConsoleColor.DarkGray,
+            [LogLevel.Debug] = ConsoleColor.DarkGray,
+            [LogLevel.Info] = ConsoleColor.White,
+            [LogLevel.Warn] = ConsoleColor.Yellow,
+            [LogLevel.Error] = ConsoleColor.Red,
+            [LogLevel.Alert] = ConsoleColor.Magenta
+        };
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Whether to show trace messages in the console.</summary>
+        internal bool ShowTraceInConsole { get; set; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="source">The name of the module which logs messages using this instance.</param>
+        /// <param name="logFile">The log file to which to write messages.</param>
+        public Monitor(string source, LogFileManager logFile)
+        {
+            // validate
+            if (string.IsNullOrWhiteSpace(source))
+                throw new ArgumentException("The log source cannot be empty.");
+            if (logFile == null)
+                throw new ArgumentNullException(nameof(logFile), "The log file manager cannot be null.");
+
+            // initialise
+            this.Source = source;
+            this.LogFile = logFile;
+        }
+
+        /// <summary>Log a message for the player or developer.</summary>
+        /// <param name="message">The message to log.</param>
+        /// <param name="level">The log severity level.</param>
+        public void Log(string message, LogLevel level = LogLevel.Debug)
+        {
+            this.LogImpl(this.Source, message, Monitor.Colors[level], level);
+        }
+
+        /// <summary>Log a message for the player or developer, using the specified console color.</summary>
+        /// <param name="source">The name of the mod logging the message.</param>
+        /// <param name="message">The message to log.</param>
+        /// <param name="color">The console color.</param>
+        /// <param name="level">The log level.</param>
+        [Obsolete("This method is provided for backwards compatibility and otherwise should not be used. Use " + nameof(Monitor) + "." + nameof(Monitor.Log) + " instead.")]
+        internal void LegacyLog(string source, string message, ConsoleColor color, LogLevel level = LogLevel.Debug)
+        {
+            this.LogImpl(source, message, color, level);
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Write a message line to the log.</summary>
+        /// <param name="source">The name of the mod logging the message.</param>
+        /// <param name="message">The message to log.</param>
+        /// <param name="color">The console color.</param>
+        /// <param name="level">The log level.</param>
+        private void LogImpl(string source, string message, ConsoleColor color, LogLevel level)
+        {
+            // generate message
+            string levelStr = level.ToString().ToUpper().PadRight(Monitor.MaxLevelLength);
+            message = $"[{DateTime.Now:HH:mm:ss} {levelStr} {source}] {message}";
+
+            // log
+            if (this.ShowTraceInConsole || level != LogLevel.Trace)
+            {
+                Console.ForegroundColor = color;
+                Console.WriteLine(message);
+                Console.ResetColor();
+            }
+            this.LogFile.WriteLine(message);
+        }
+    }
+}
+\ No newline at end of file
diff --git a/src/StardewModdingAPI/IMonitor.cs b/src/StardewModdingAPI/IMonitor.cs
new file mode 100644
index 00000000..8d20af01
--- /dev/null
+++ b/src/StardewModdingAPI/IMonitor.cs
@@ -0,0 +1,14 @@
+namespace StardewModdingAPI
+{
+    /// <summary>Encapsulates monitoring and logging for a given module.</summary>
+    public interface IMonitor
+    {
+        /*********
+        ** Methods
+        *********/
+        /// <summary>Log a message for the player or developer.</summary>
+        /// <param name="message">The message to log.</param>
+        /// <param name="level">The log severity level.</param>
+        void Log(string message, LogLevel level = LogLevel.Debug);
+    }
+}
diff --git a/src/StardewModdingAPI/LogLevel.cs b/src/StardewModdingAPI/LogLevel.cs
new file mode 100644
index 00000000..89647876
--- /dev/null
+++ b/src/StardewModdingAPI/LogLevel.cs
@@ -0,0 +1,24 @@
+namespace StardewModdingAPI
+{
+    /// <summary>The log severity levels.</summary>
+    public enum LogLevel
+    {
+        /// <summary>Tracing info intended for developers.</summary>
+        Trace,
+
+        /// <summary>Troubleshooting info that may be relevant to the player.</summary>
+        Debug,
+
+        /// <summary>Info relevant to the player. This should be used judiciously.</summary>
+        Info,
+
+        /// <summary>An issue the player should be aware of. This should be used rarely.</summary>
+        Warn,
+
+        /// <summary>A message indicating something went wrong.</summary>
+        Error,
+
+        /// <summary>Important information to highlight for the player when player action is needed (e.g. new version available). This should be used rarely to avoid alert fatigue.</summary>
+        Alert
+    }
+}
+\ No newline at end of file
diff --git a/src/StardewModdingAPI/StardewModdingAPI.csproj b/src/StardewModdingAPI/StardewModdingAPI.csproj
index ce302b95..2d6a7c7f 100644
--- a/src/StardewModdingAPI/StardewModdingAPI.csproj
+++ b/src/StardewModdingAPI/StardewModdingAPI.csproj
@@ -195,14 +195,18 @@
     <Compile Include="Extensions.cs" />
     <Compile Include="Framework\DeprecationLevel.cs" />
     <Compile Include="Framework\DeprecationManager.cs" />
+    <Compile Include="Framework\LogFileManager.cs" />
+    <Compile Include="LogLevel.cs" />
     <Compile Include="Framework\ModRegistry.cs" />
     <Compile Include="Framework\UpdateHelper.cs" />
     <Compile Include="Framework\GitRelease.cs" />
     <Compile Include="Framework\UserSettings.cs" />
+    <Compile Include="IMonitor.cs" />
     <Compile Include="Inheritance\ChangeType.cs" />
     <Compile Include="Inheritance\ItemStackChange.cs" />
     <Compile Include="Inheritance\SObject.cs" />
     <Compile Include="Log.cs" />
+    <Compile Include="Framework\Monitor.cs" />
     <Compile Include="LogInfo.cs" />
     <Compile Include="LogWriter.cs" />
     <Compile Include="Manifest.cs" />