using System.ComponentModel;
using CommunityToolkit.Mvvm.ComponentModel;
using FieldLogger.Models;
using FieldLogger.Services;

namespace FieldLogger.ViewModels;

/// <summary>
/// Shared, glanceable hardware status shown above each primary workflow. The timer marks
/// position data stale even when the receiver stops sending without disconnecting.
/// </summary>
public sealed partial class AppStatusViewModel : ObservableObject
{
    private static readonly TimeSpan StaleAfter = TimeSpan.FromSeconds(2);

    private readonly DeviceConnectionManager _manager;
    private readonly MaglinkService _gps;

    [ObservableProperty]
    private ConnectionState _locatorState;

    [ObservableProperty]
    private ConnectionState _gnssState;

    [ObservableProperty]
    private string _locatorStatus = "Locator disconnected";

    [ObservableProperty]
    private string _gnssStatus = "GNSS disconnected";

    [ObservableProperty]
    private string _positionSummary = "No GNSS fix · accuracy —";

    public AppStatusViewModel(DeviceConnectionManager manager, MaglinkService gps)
    {
        _manager = manager;
        _gps = gps;

        _manager.PropertyChanged += OnConnectionPropertyChanged;
        _gps.FixReceived += OnFixReceived;
        Refresh();
    }

    private void OnConnectionPropertyChanged(object? sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName is nameof(DeviceConnectionManager.LocatorState)
            or nameof(DeviceConnectionManager.GpsState)
            or nameof(DeviceConnectionManager.LocatorName)
            or nameof(DeviceConnectionManager.GpsName))
        {
            Refresh();
        }
    }

    private void OnFixReceived(object? sender, GnssFix fix) => Refresh();

    /// <summary>Refreshes status safely from device callbacks or a UI dispatcher timer.</summary>
    public void Refresh()
    {
        var dispatcher = Application.Current?.Dispatcher;
        if (dispatcher?.IsDispatchRequired == true)
        {
            dispatcher.Dispatch(RefreshCore);
            return;
        }

        RefreshCore();
    }

    private void RefreshCore()
    {
        LocatorState = _manager.LocatorState;
        GnssState = _manager.GpsState;
        LocatorStatus = DeviceLabel("Locator", _manager.LocatorName, LocatorState);
        GnssStatus = DeviceLabel("GNSS", _manager.GpsName, GnssState);

        var fix = _gps.LatestFix;
        if (fix is null)
        {
            PositionSummary = GnssState == ConnectionState.Connected
                ? "Waiting for fix · accuracy —"
                : "No GNSS fix · accuracy —";
            return;
        }

        var stale = DateTime.UtcNow - fix.ReceivedUtc > StaleAfter;
        var staleLabel = stale ? " · STALE" : string.Empty;
        PositionSummary = $"{fix.StatusLabel}{staleLabel} · H ±{fix.Hrms:F3} m · " +
                          $"V ±{fix.Vrms:F3} m · {fix.SatellitesUsed} sats · corr {fix.CorrectionAgeSeconds:F1} s";
    }

    private static string DeviceLabel(string kind, string? name, ConnectionState state)
    {
        var stateText = state switch
        {
            ConnectionState.Connected => "connected",
            ConnectionState.Connecting => "connecting",
            _ => "disconnected",
        };

        return state == ConnectionState.Disconnected || string.IsNullOrWhiteSpace(name)
            ? $"{kind} {stateText}"
            : $"{kind} {stateText} · {name}";
    }
}