chore: import upstream snapshot with attribution

Logging/FileLogHandler.cs

@@ -0,0 +1,137 @@
+/*
+ * QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
+ * Lean Algorithmic Trading Engine v2.0. Copyright 2014 QuantConnect Corporation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+*/
+
+using System;
+using System.Globalization;
+using System.IO;
+
+namespace QuantConnect.Logging
+{
+    /// <summary>
+    /// Provides an implementation of <see cref="ILogHandler"/> that writes all log messages to a file on disk.
+    /// </summary>
+    public class FileLogHandler : ILogHandler
+    {
+        private bool _disposed;
+
+        // we need to control synchronization to our stream writer since it's not inherently thread-safe
+        private readonly object _lock = new object();
+        private readonly Lazy<TextWriter> _writer;
+        private readonly bool _useTimestampPrefix;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="FileLogHandler"/> class to write messages to the specified file path.
+        /// The file will be opened using <see cref="FileMode.Append"/>
+        /// </summary>
+        /// <param name="filepath">The file path use to save the log messages</param>
+        /// <param name="useTimestampPrefix">True to prefix each line in the log which the UTC timestamp, false otherwise</param>
+        public FileLogHandler(string filepath, bool useTimestampPrefix = true)
+        {
+            _useTimestampPrefix = useTimestampPrefix;
+            _writer = new Lazy<TextWriter>(
+                () => new StreamWriter(File.Open(filepath, FileMode.Append, FileAccess.Write, FileShare.Read))
+                );
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="FileLogHandler"/> class using 'log.txt' for the filepath.
+        /// </summary>
+        public FileLogHandler()
+            : this(Log.FilePath)
+        {
+        }
+
+        /// <summary>
+        /// Write error message to log
+        /// </summary>
+        /// <param name="text">The error text to log</param>
+        public void Error(string text)
+        {
+            WriteMessage(text, "ERROR");
+        }
+
+        /// <summary>
+        /// Write debug message to log
+        /// </summary>
+        /// <param name="text">The debug text to log</param>
+        public void Debug(string text)
+        {
+            WriteMessage(text, "DEBUG");
+        }
+
+        /// <summary>
+        /// Write debug message to log
+        /// </summary>
+        /// <param name="text">The trace text to log</param>
+        public void Trace(string text)
+        {
+            WriteMessage(text, "TRACE");
+        }
+
+        /// <summary>
+        /// Write report message to log
+        /// </summary>
+        /// <param name="text">The report text to log</param>
+        public void Report(string text)
+        {
+            WriteMessage(text, "REPORT");
+        }
+
+        /// <summary>
+        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
+        /// </summary>
+        /// <filterpriority>2</filterpriority>
+        public void Dispose()
+        {
+            lock (_lock)
+            {
+                if (_writer.IsValueCreated)
+                {
+                    _disposed = true;
+                    _writer.Value.Dispose();
+                }
+            }
+        }
+
+        /// <summary>
+        /// Creates the message to be logged
+        /// </summary>
+        /// <param name="text">The text to be logged</param>
+        /// <param name="level">The logging leel</param>
+        /// <returns></returns>
+        protected virtual string CreateMessage(string text, string level)
+        {
+            if (_useTimestampPrefix)
+            {
+                return $"{DateTime.UtcNow.ToString("o", CultureInfo.InvariantCulture)} {level}:: {text}";
+            }
+            return $"{level}:: {text}";
+        }
+
+        /// <summary>
+        /// Writes the message to the writer
+        /// </summary>
+        private void WriteMessage(string text, string level)
+        {
+            var message = CreateMessage(text, level);
+            lock (_lock)
+            {
+                if (_disposed) return;
+                _writer.Value.WriteLine(message);
+                _writer.Value.Flush();
+            }
+        }
+    }
+}