using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Threading;
using System.Threading.Tasks;
using Avalonia.Threading;
using CommunityToolkit.Mvvm.Input;
using Junction.Core.Monitoring;
using Junction.Domain.Models;
using Junction.Domain.Persistence;
using Microsoft.Extensions.Logging;

namespace Junction.App.ViewModels
{
    /// <summary>
    /// Live machine dashboard. Loads configured machines from the repository, seeds each row from
    /// the monitor's latest-snapshot cache, and refreshes rows as <see cref="IMachineMonitor.SnapshotUpdated"/>
    /// fires. Snapshot events arrive on poll-loop threads and are marshalled onto the UI thread.
    /// </summary>
    public sealed partial class DashboardViewModel : ViewModelBase, IDisposable
    {
        private readonly IMachineRepository _repository;
        private readonly IMachineMonitor _monitor;
        private readonly ILogger<DashboardViewModel> _logger;
        private readonly Dictionary<Guid, MachineRowViewModel> _rowsById = new Dictionary<Guid, MachineRowViewModel>();
        private bool _subscribed;
        private bool _disposed;

        public string Title => "Junction — Machines";

        /// <summary>
        /// Shell reference, set by <see cref="MainWindowViewModel"/> after construction (breaks the
        /// otherwise-circular DI graph). Used to open a machine's detail screen on row click.
        /// </summary>
        public MainWindowViewModel? Navigator { get; set; }

        public ObservableCollection<MachineRowViewModel> Machines { get; } = new ObservableCollection<MachineRowViewModel>();

        public DashboardViewModel(IMachineRepository repository, IMachineMonitor monitor, ILogger<DashboardViewModel> logger)
        {
            _repository = repository;
            _monitor = monitor;
            _logger = logger;
        }

        /// <summary>Loads machines, seeds latest snapshots, and subscribes to live updates.</summary>
        public async Task LoadAsync()
        {
            // Subscribe first so no update slips through between load and subscribe;
            // rows are looked up by id, unknown ids are ignored.
            if (!_subscribed)
            {
                _monitor.SnapshotUpdated += OnSnapshotUpdated;
                _subscribed = true;
            }

            var result = await _repository.GetAllAsync(CancellationToken.None).ConfigureAwait(true);
            if (!result.IsSuccess)
            {
                var detail = result.Errors.Count > 0 ? result.Errors[0].Message : "unknown error";
                _logger.LogError("Dashboard load failed: {Detail}", detail);
                return;
            }

            Machines.Clear();
            _rowsById.Clear();

            var latest = _monitor.LatestSnapshots;
            foreach (var machine in result.Value)
            {
                var row = new MachineRowViewModel(machine, OpenDetail);
                if (latest.TryGetValue(machine.Id, out var snapshot))
                {
                    row.Apply(snapshot);
                }

                _rowsById[machine.Id] = row;
                Machines.Add(row);
            }

            _logger.LogInformation("Dashboard loaded {Count} machine(s).", Machines.Count);
        }

        /// <summary>Header action: opens the add-machine config screen via the shell.</summary>
        [RelayCommand]
        private void AddMachine() => Navigator?.ShowConfig(null);

        /// <summary>Row-click handler: routes to the machine-detail screen via the shell.</summary>
        private void OpenDetail(MachineRowViewModel row)
        {
            if (row == null)
            {
                return;
            }

            Navigator?.ShowDetail(row.MachineId, row.Name);
        }

        private void OnSnapshotUpdated(object? sender, MachineSnapshot snapshot)
        {
            if (snapshot == null)
            {
                return;
            }

            // Event fires on a poll-loop thread → marshal all observable mutations to the UI thread.
            Dispatcher.UIThread.Post(() =>
            {
                if (_disposed)
                {
                    return;
                }

                if (_rowsById.TryGetValue(snapshot.MachineId, out var row))
                {
                    row.Apply(snapshot);
                }
            });
        }

        public void Dispose()
        {
            if (_disposed)
            {
                return;
            }

            _disposed = true;
            if (_subscribed)
            {
                _monitor.SnapshotUpdated -= OnSnapshotUpdated;
                _subscribed = false;
            }
        }
    }
}