using System;
using System.Threading;

namespace Aivfo.OperationLog
{
    /// <summary>
    /// 进程内 traceId / parentId / operator / 设备上下文 透传（AsyncLocal，跨 async/线程切换）。
    /// 对称 Java 的 Trace（TransmittableThreadLocal）。
    /// </summary>
    public static class OperationLogContext
    {
        private static readonly AsyncLocal<string> _traceId = new AsyncLocal<string>();
        private static readonly AsyncLocal<string> _parentId = new AsyncLocal<string>();
        private static readonly AsyncLocal<string> _operator = new AsyncLocal<string>();
        private static readonly AsyncLocal<int?> _houseSn = new AsyncLocal<int?>();
        private static readonly AsyncLocal<int?> _wellSn = new AsyncLocal<int?>();

        /// <summary>当前 traceId（无则返回 null）。</summary>
        public static string TraceId
        {
            get => _traceId.Value;
            set => _traceId.Value = value;
        }

        /// <summary>当前 parentId。</summary>
        public static string ParentId
        {
            get => _parentId.Value;
            set => _parentId.Value = value;
        }

        /// <summary>当前操作者（登录用户）。可在登录后设置一次。</summary>
        public static string Operator
        {
            get => _operator.Value;
            set => _operator.Value = value;
        }

        /// <summary>当前舱号。</summary>
        public static int? HouseSn
        {
            get => _houseSn.Value;
            set => _houseSn.Value = value;
        }

        /// <summary>当前 well 号。</summary>
        public static int? WellSn
        {
            get => _wellSn.Value;
            set => _wellSn.Value = value;
        }

        /// <summary>生成一个新的 traceId（去横线的 Guid，紧凑唯一）。</summary>
        public static string NewTraceId()
        {
            return Guid.NewGuid().ToString("N");
        }

        /// <summary>
        /// 开启一次操作 scope：设置/继承 traceId，把当前 traceId 作为新 parentId。
        /// 释放时恢复原值。用 using 包裹一次完整操作。
        /// </summary>
        public static IDisposable BeginScope(string traceId = null)
        {
            var prevTrace = _traceId.Value;
            var prevParent = _parentId.Value;

            // 新 scope 的 parentId = 外层的 traceId（构成父子链）；最外层为 null。
            _parentId.Value = prevTrace;
            _traceId.Value = string.IsNullOrEmpty(traceId)
                ? (string.IsNullOrEmpty(prevTrace) ? NewTraceId() : prevTrace)
                : traceId;

            return new ScopeRestore(prevTrace, prevParent);
        }

        private sealed class ScopeRestore : IDisposable
        {
            private readonly string _prevTrace;
            private readonly string _prevParent;
            private bool _done;

            public ScopeRestore(string prevTrace, string prevParent)
            {
                _prevTrace = prevTrace;
                _prevParent = prevParent;
            }

            public void Dispose()
            {
                if (_done) return;
                _done = true;
                _traceId.Value = _prevTrace;
                _parentId.Value = _prevParent;
            }
        }
    }
}