using System;
using System.IO;
using System.Text;

namespace WxOrder.Framework.Helpers
{
	/// <summary> 日志消息级别。 </summary>
	public enum LogMessageLevel
	{
		Trace = 0,
		Debug = 1,
		Info = 2,
		Warn = 3,
		Error = 4,
		Fatal = 5,
		None = 6
	}

	/// <summary>
	/// 调试输出桥接。默认输出到 System.Diagnostics.Debug，
	/// 可在外部重新赋值 DebugPrint 以接管控件台/UI 输出。
	/// </summary>
	public static class DebugLog
	{
		/// <summary> 调试输出回调。默认写到 Debug 输出窗口。 </summary>
		public static Action<string>? DebugPrint { get; set; }
			= msg => System.Diagnostics.Debug.WriteLine(msg);
	}

	/// <summary>
	/// 默认日志逻辑类（不依赖任何第三方日志库）。
	/// 日志文件按日期分目录存放，并在跨天时自动切换：
	/// {logDirectory}/yyyy-MM/yyyy-MM-dd.log，例如 log/2022-12/2022-12-12.log
	/// </summary>
	public sealed class NLogger : IDisposable, ILogger
	{
		private const string DefaultName = "App";

		private static readonly object _lock = new object();
		private static NLogger? _instance;

		/// <summary>
		/// 同一进程内所有实例共用的写入锁。
		/// 多个实例（不同 Name）会写入同一个按日期命名的文件，需要串行化写入。
		/// </summary>
		private static readonly object _fileLock = new object();

		/// <summary> 获取 NLogger 的唯一单例实例（线程安全）。 </summary>
		public static NLogger Instance
		{
			get
			{
				if (_instance == null)
				{
					lock (_lock)
					{
						if (_instance == null)
							_instance = new NLogger(DefaultName);
					}
				}
				return _instance;
			}
		}

		/// <summary> 静态工厂：根据名称创建日志实例。 </summary>
		public static NLogger Create(string name, string? logDirectory = null)
		{
			if (string.IsNullOrWhiteSpace(name))
				throw new ArgumentException("日志名称不能为空。", nameof(name));

			return new NLogger(name, logDirectory);
		}

		/// <summary> 静态工厂：创建使用默认名称的日志实例。 </summary>
		public static NLogger Create() => new NLogger(DefaultName);

		/// <summary> 日志名称（写入每行日志中，用于区分来源，不再决定文件名）。 </summary>
		public string Name { get; }

		public bool IsDebugEnabled { get; set; } = false;

		public bool IsDebugWriteLineEnabled { get; set; } = false;

		public LogMessageLevel MinimumLevel { get; set; } = LogMessageLevel.Trace;

		/// <summary> 日志根目录。 </summary>
		public string LogDirectory { get; }

		private string? _currentFilePath;
		private StreamWriter? _writer;
		private bool _disposed;

		private NLogger(string name, string? logDirectory = null)
		{
			Name = name;
			LogDirectory = logDirectory ?? Path.Combine(AppContext.BaseDirectory, "log");
			// 文件在第一次写入时按当前日期惰性创建，构造阶段不打开文件。
		}

		#region 日志方法

		public void Trace(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Trace, message, exception);

		public void Debug(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Debug, message, exception);

		public void Info(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Info, message, exception);

		public void Warn(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Warn, message, exception);

		public void Error(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Error, message, exception);

		public void Fatal(string message, Exception? exception = null)
			=> Execute(LogMessageLevel.Fatal, message, exception);

		public void Log(string message, LogMessageLevel level, Exception? exception = null)
			=> Execute(level, message, exception);

		#endregion

		#region 内部逻辑

		private bool CheckEnabled(LogMessageLevel level)
		{
			if (level == LogMessageLevel.None)
				return false;

			if (level < MinimumLevel)
				return false;

			if (level == LogMessageLevel.Trace || level == LogMessageLevel.Debug)
				return IsDebugEnabled;

			return true;
		}

		private void Execute(LogMessageLevel level, string message, Exception? exception)
		{
			if (CheckEnabled(level))
			{
				WriteToFile(level, message, exception);
			}

			if (IsDebugWriteLineEnabled)
			{
				string logOutput = "[" + level + "] " + message;
				if (exception != null)
				{
					logOutput += Environment.NewLine + exception;
				}

				Action<string>? handler = DebugLog.DebugPrint;
				if (handler != null)
				{
					handler(logOutput);
				}
			}
		}

		/// <summary> 根据日期生成日志文件路径：{根目录}/yyyy-MM/yyyy-MM-dd.log </summary>
		private string GetLogFilePath(DateTime time)
		{
			return Path.Combine(
				LogDirectory,
				time.ToString("yyyy-MM"),
				time.ToString("yyyy-MM-dd") + ".log");
		}

		/// <summary> 写入当天的日志文件，跨天时自动切换到新文件。 </summary>
		private void WriteToFile(LogMessageLevel level, string message, Exception? exception)
		{
			DateTime now = DateTime.Now;

			var sb = new StringBuilder();
			sb.Append('[')
			  .Append(now.ToString("yyyy-MM-dd HH:mm:ss.fff"))
			  .Append("] [")
			  .Append(level)
			  .Append("] [")
			  .Append(Name)
			  .Append("] ")
			  .AppendLine(message);

			if (exception != null)
			{
				sb.AppendLine(exception.ToString());
			}

			string line = sb.ToString();

			lock (_fileLock)
			{
				if (_disposed) return;

				try
				{
					EnsureWriter(GetLogFilePath(now));
					_writer!.Write(line);
					_writer.Flush();
				}
				catch
				{
					// 日志写入失败不应影响主流程，这里吞掉异常。
					// 重置写入器，下次写入时重新尝试打开文件。
					CloseWriter();
				}
			}
		}

		/// <summary> 确保写入器指向指定路径；路径变化（跨天/跨月）时关闭旧文件并打开新文件。 </summary>
		private void EnsureWriter(string path)
		{
			if (_writer != null && string.Equals(_currentFilePath, path, StringComparison.Ordinal))
				return;

			CloseWriter();

			string? dir = Path.GetDirectoryName(path);
			if (!string.IsNullOrEmpty(dir))
			{
				Directory.CreateDirectory(dir);
			}

			var fs = new FileStream(
				path,
				FileMode.Append,
				FileAccess.Write,
				FileShare.ReadWrite);

			_writer = new StreamWriter(fs, new UTF8Encoding(false))
			{
				AutoFlush = false
			};
			_currentFilePath = path;
		}

		private void CloseWriter()
		{
			try
			{
				if (_writer != null)
				{
					_writer.Flush();
					_writer.Dispose();
				}
			}
			catch { /* ignore */ }
			finally
			{
				_writer = null;
				_currentFilePath = null;
			}
		}

		#endregion

		#region IDisposable

		public void Dispose()
		{
			lock (_fileLock)
			{
				if (_disposed) return;
				_disposed = true;
				CloseWriter();
			}
		}

		#endregion
	}
}