added logging for startup issues

Oqtane.Server/Infrastructure/Logging/FileLogger.cs

@@ -0,0 +1,72 @@
+using System;
+using System.IO;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Oqtane.Infrastructure
+{
+    public class FileLogger : ILogger
+    {
+        protected readonly FileLoggerProvider _FileLoggerProvider;
+        private readonly IWebHostEnvironment _environment;
+        private readonly IConfigManager _configManager;
+
+        public FileLogger(FileLoggerProvider FileLoggerProvider, IWebHostEnvironment environment,IConfigManager configManager)
+        {
+            _FileLoggerProvider = FileLoggerProvider;
+            _environment = environment;
+            _configManager = configManager;
+        }
+
+        public IDisposable BeginScope<TState>(TState state)
+        {
+            return null;
+        }
+
+        public bool IsEnabled(LogLevel logLevel)
+        {
+            return logLevel != LogLevel.None;
+        }
+
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+        {
+            if (_configManager.GetSetting("Logging:FileLogger:LogLevel:Default", "") == "")
+            {
+                _configManager.AddOrUpdateSetting("Logging:FileLogger:LogLevel:Default", "Error", true);
+                if (logLevel < LogLevel.Error)
+                {
+                    return;
+                }
+            }
+
+            if (!IsEnabled(logLevel))
+            {
+                return;
+            }
+
+            string folder = Path.Combine(_environment.ContentRootPath, "Content", "Log");
+
+            // ensure directory exists
+            if (!Directory.Exists(folder))
+            {
+                Directory.CreateDirectory(folder);
+            }
+
+            var filepath = Path.Combine(folder, "error.log");
+
+            var logentry = string.Format("{0} [{1}] {2} {3}", "[" + DateTimeOffset.UtcNow.ToString("yyyy-MM-dd HH:mm:ss+00:00") + "]", logLevel.ToString(), formatter(state, exception), exception != null ? exception.StackTrace : "");
+
+            try
+            {
+                using (var streamWriter = new StreamWriter(filepath, true))
+                {
+                    streamWriter.WriteLine(logentry);
+                }
+            }
+            catch
+            {
+                // error occurred
+            }
+        }
+    }
+}