// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Diagnostics;
using DiagnosticsTraceSource = System.Diagnostics.TraceSource;

namespace Microsoft.Extensions.Logging.TraceSource
{
    /// <summary>
    /// A logger that writes a trace source log message.
    /// </summary>
    internal sealed class TraceSourceLogger : ILogger
    {
        private readonly DiagnosticsTraceSource _traceSource;

        /// <summary>
        /// Initializes a new instance of the <see cref="TraceSourceLogger"/> class.
        /// </summary>
        /// <param name="traceSource">trace source</param>
        public TraceSourceLogger(DiagnosticsTraceSource traceSource)
        {
            _traceSource = traceSource;
        }

        /// <inheritdoc />
        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
        {
            if (!IsEnabled(logLevel))
            {
                return;
            }

            string message = string.Empty;

            if (formatter != null)
            {
                message = formatter(state, exception);
            }
            else if (state != null)
            {
                message += state;
            }

            if (exception != null)
            {
                string exceptionDelimiter = string.IsNullOrEmpty(message) ? string.Empty : " ";
                message += exceptionDelimiter + exception;
            }

            if (!string.IsNullOrEmpty(message))
            {
                _traceSource.TraceEvent(GetEventType(logLevel), eventId.Id, message);
            }
        }

        public bool IsEnabled(LogLevel logLevel)
        {
            if (logLevel == LogLevel.None)
            {
                return false;
            }

            TraceEventType traceEventType = GetEventType(logLevel);
            return _traceSource.Switch.ShouldTrace(traceEventType);
        }

        private static TraceEventType GetEventType(LogLevel logLevel)
        {
            switch (logLevel)
            {
                case LogLevel.Critical: return TraceEventType.Critical;
                case LogLevel.Error: return TraceEventType.Error;
                case LogLevel.Warning: return TraceEventType.Warning;
                case LogLevel.Information: return TraceEventType.Information;
                case LogLevel.Trace:
                default: return TraceEventType.Verbose;
            }
        }

        public IDisposable BeginScope<TState>(TState state) where TState : notnull
        {
            return new TraceSourceScope(state);
        }
    }
}