using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using ZB.MOM.WW.LmxOpcUa.Host.Domain;

namespace ZB.MOM.WW.LmxOpcUa.Tests.Helpers
{
    /// <summary>
    /// In-memory IMxAccessClient used by tests to drive connection, read, write, and subscription scenarios without COM runtime dependencies.
    /// </summary>
    public class FakeMxAccessClient : IMxAccessClient
    {
        /// <summary>
        /// Gets or sets the connection state returned to the system under test.
        /// </summary>
        public ConnectionState State { get; set; } = ConnectionState.Connected;

        /// <summary>
        /// Gets the number of active subscriptions currently stored by the fake client.
        /// </summary>
        public int ActiveSubscriptionCount => _subscriptions.Count;

        /// <summary>
        /// Gets or sets the reconnect count exposed to health and dashboard tests.
        /// </summary>
        public int ReconnectCount { get; set; }

        /// <summary>
        /// Occurs when tests explicitly simulate a connection-state transition.
        /// </summary>
        public event EventHandler<ConnectionStateChangedEventArgs>? ConnectionStateChanged;

        /// <summary>
        /// Occurs when tests publish a simulated runtime value change.
        /// </summary>
        public event Action<string, Vtq>? OnTagValueChanged;

        private readonly ConcurrentDictionary<string, Action<string, Vtq>> _subscriptions = new(StringComparer.OrdinalIgnoreCase);

        /// <summary>
        /// Gets the in-memory tag-value table returned by fake reads.
        /// </summary>
        public ConcurrentDictionary<string, Vtq> TagValues { get; } = new(StringComparer.OrdinalIgnoreCase);

        /// <summary>
        /// Gets the values written through the fake client so tests can assert write behavior.
        /// </summary>
        public List<(string Tag, object Value)> WrittenValues { get; } = new();

        /// <summary>
        /// Gets or sets the result returned by fake writes to simulate success or failure.
        /// </summary>
        public bool WriteResult { get; set; } = true;

        /// <summary>
        /// Simulates establishing a healthy runtime connection.
        /// </summary>
        /// <param name="ct">A cancellation token that is ignored by the in-memory fake.</param>
        public Task ConnectAsync(CancellationToken ct = default)
        {
            State = ConnectionState.Connected;
            return Task.CompletedTask;
        }

        /// <summary>
        /// Simulates disconnecting from the runtime.
        /// </summary>
        public Task DisconnectAsync()
        {
            State = ConnectionState.Disconnected;
            return Task.CompletedTask;
        }

        /// <summary>
        /// Stores a subscription callback so later simulated data changes can target it.
        /// </summary>
        /// <param name="fullTagReference">The Galaxy attribute reference to monitor.</param>
        /// <param name="callback">The callback that should receive simulated value changes.</param>
        public Task SubscribeAsync(string fullTagReference, Action<string, Vtq> callback)
        {
            _subscriptions[fullTagReference] = callback;
            return Task.CompletedTask;
        }

        /// <summary>
        /// Removes a stored subscription callback for the specified tag reference.
        /// </summary>
        /// <param name="fullTagReference">The Galaxy attribute reference to stop monitoring.</param>
        public Task UnsubscribeAsync(string fullTagReference)
        {
            _subscriptions.TryRemove(fullTagReference, out _);
            return Task.CompletedTask;
        }

        /// <summary>
        /// Returns the current in-memory VTQ for a tag reference or a bad-quality placeholder when none has been seeded.
        /// </summary>
        /// <param name="fullTagReference">The Galaxy attribute reference to read.</param>
        /// <param name="ct">A cancellation token that is ignored by the in-memory fake.</param>
        /// <returns>The seeded VTQ value or a bad not-connected VTQ when the tag was not populated.</returns>
        public Task<Vtq> ReadAsync(string fullTagReference, CancellationToken ct = default)
        {
            if (TagValues.TryGetValue(fullTagReference, out var vtq))
                return Task.FromResult(vtq);
            return Task.FromResult(Vtq.Bad(Quality.BadNotConnected));
        }

        /// <summary>
        /// Records a write request, optionally updates the in-memory tag table, and returns the configured write result.
        /// </summary>
        /// <param name="fullTagReference">The Galaxy attribute reference being written.</param>
        /// <param name="value">The value supplied by the code under test.</param>
        /// <param name="ct">A cancellation token that is ignored by the in-memory fake.</param>
        /// <returns>A completed task returning the configured write outcome.</returns>
        public Task<bool> WriteAsync(string fullTagReference, object value, CancellationToken ct = default)
        {
            WrittenValues.Add((fullTagReference, value));
            if (WriteResult)
                TagValues[fullTagReference] = Vtq.Good(value);
            return Task.FromResult(WriteResult);
        }

        /// <summary>
        /// Publishes a simulated tag-value change to both the event stream and any stored subscription callback.
        /// </summary>
        /// <param name="address">The Galaxy attribute reference whose value changed.</param>
        /// <param name="vtq">The value, timestamp, and quality payload to publish.</param>
        public void SimulateDataChange(string address, Vtq vtq)
        {
            OnTagValueChanged?.Invoke(address, vtq);
            if (_subscriptions.TryGetValue(address, out var callback))
                callback(address, vtq);
        }

        /// <summary>
        /// Raises a simulated connection-state transition for health and reconnect tests.
        /// </summary>
        /// <param name="prev">The previous connection state.</param>
        /// <param name="curr">The new connection state.</param>
        public void RaiseConnectionStateChanged(ConnectionState prev, ConnectionState curr)
        {
            State = curr;
            ConnectionStateChanged?.Invoke(this, new ConnectionStateChangedEventArgs(prev, curr));
        }

        /// <summary>
        /// Releases the fake client. No unmanaged resources are held.
        /// </summary>
        public void Dispose() { }
    }
}