using System.Collections.ObjectModel;
using System.Globalization;
using AvParser.Core.Proxies;
using AvParser.Infrastructure.Proxies;
using AvParser.UI.Localization;
using Microsoft.Extensions.Logging;
using ReactiveUI;
using ReactiveUI.Primitives;
using ReactiveUI.Primitives.Concurrency;
using ReactiveUI.Primitives.Signals;
using ReactiveUI.SourceGenerators;

namespace AvParser.UI.ViewModels;

/// <summary>Health filter offered by the proxy list.</summary>
public enum ProxyHealthFilter
{
    /// <summary>No filtering.</summary>
    All,

    /// <summary>Only proxies whose last check succeeded.</summary>
    Alive,

    /// <summary>Only proxies whose last check failed.</summary>
    Dead,

    /// <summary>Only proxies that were never checked.</summary>
    Unchecked,
}

/// <summary>Manages the proxy pool: refresh from the feed, probe, and edit the custom list.</summary>
public partial class ProxiesViewModel : PageViewModel, IDisposable
{
    /// <summary>
    /// Rows rendered at once. A free feed carries a few thousand proxies, and a virtualising list
    /// still pays to build every row view model, so the view is capped and says so.
    /// </summary>
    private const int MaxDisplayedRows = 500;

    private readonly IProxyPool _pool;
    private readonly IMutableProxySource _customSource;
    private readonly ILogger<ProxiesViewModel> _logger;
    private readonly ISequencer _mainThread;
    private readonly Dictionary<string, ProxyRowViewModel> _rows = new(StringComparer.Ordinal);
    private readonly Signal<RxVoid> _poolChanged = new();

    /// <summary>Free-text filter over address and country.</summary>
    [Reactive]
    public partial string SearchText { get; set; }

    /// <summary>Protocol filter; <see cref="ProxyProtocolFilter.All"/> means no filtering.</summary>
    [Reactive]
    public partial LocalizedOption<ProxyProtocolFilter> ProtocolFilter { get; set; }

    /// <summary>Health filter.</summary>
    [Reactive]
    public partial LocalizedOption<ProxyHealthFilter> HealthFilter { get; set; }

    /// <summary>Text box contents for adding custom proxies.</summary>
    [Reactive]
    public partial string NewProxies { get; set; }

    /// <summary>Currently selected row.</summary>
    [Reactive]
    public partial ProxyRowViewModel? SelectedProxy { get; set; }

    /// <summary>Outcome of the last action; <see langword="null"/> when idle.</summary>
    [Reactive]
    public partial string? StatusMessage { get; set; }

    /// <summary>Progress of the running sweep, 0..1.</summary>
    [Reactive]
    public partial double SweepProgress { get; set; }

    /// <summary>Whether a sweep is running.</summary>
    [Reactive]
    public partial bool IsSweeping { get; set; }

    /// <summary>How many rows the filter matched before the display cap.</summary>
    [Reactive]
    public partial int MatchedCount { get; set; }

    /// <summary>Total entries in the pool.</summary>
    [Reactive]
    public partial int TotalCount { get; set; }

    /// <summary>How many entries are currently alive.</summary>
    [Reactive]
    public partial int AliveCount { get; set; }

    /// <summary>Creates the page.</summary>
    /// <param name="pool">The pool being managed.</param>
    /// <param name="customSource">The user's editable list.</param>
    /// <param name="loader">The shared startup load, joined so the page can report its outcome.</param>
    /// <param name="logger">Diagnostics.</param>
    /// <param name="mainThread">Scheduler for UI-affine updates; tests pass an immediate one.</param>
    public ProxiesViewModel(
        IProxyPool pool,
        IMutableProxySource customSource,
        IProxyPoolLoader loader,
        ILogger<ProxiesViewModel> logger,
        ISequencer? mainThread = null
    )
    {
        _pool = pool ?? throw new ArgumentNullException(nameof(pool));
        _customSource = customSource ?? throw new ArgumentNullException(nameof(customSource));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _mainThread = mainThread ?? RxSchedulers.MainThreadScheduler;
        ArgumentNullException.ThrowIfNull(loader);

        SearchText = string.Empty;
        NewProxies = string.Empty;
        ProtocolFilter = ProtocolFilters[0];
        HealthFilter = HealthFilters[0];

        var idle = this.WhenAnyValue(x => x.IsSweeping).Select(static sweeping => !sweeping);

        RefreshCommand = ReactiveCommand.CreateFromTask(RefreshAsync, idle, _mainThread);
        SweepCommand = ReactiveCommand.CreateFromTask(SweepAsync, idle, _mainThread);
        AddCustomCommand = ReactiveCommand.CreateFromTask(AddCustomAsync, idle, _mainThread);
        ClearCustomCommand = ReactiveCommand.CreateFromTask(ClearCustomAsync, idle, _mainThread);

        RemoveSelectedCommand = ReactiveCommand.CreateFromTask(
            RemoveSelectedAsync,
            this.WhenAnyValue(x => x.SelectedProxy).Select(static row => row is { IsCustom: true }),
            _mainThread
        );

        // The pool raises Changed on every single lease outcome; rebuilding the view that often
        // would make a running parse unusable, so coalesce into one refresh per burst.
        _poolChanged
            .Throttle(TimeSpan.FromMilliseconds(250), _mainThread)
            .ObserveOn(_mainThread)
            .Subscribe(_ => Rebuild());

        _pool.Changed += OnPoolChanged;

        this.WhenAnyValue(x => x.SearchText, x => x.ProtocolFilter, x => x.HealthFilter, (_, _, _) => RxVoid.Default)
            .Throttle(TimeSpan.FromMilliseconds(150), _mainThread)
            .ObserveOn(_mainThread)
            .Subscribe(_ => Rebuild());

        foreach (var command in new[] { RefreshCommand, SweepCommand, AddCustomCommand, ClearCustomCommand })
        {
            command.ThrownExceptions.Subscribe(OnCommandFailed);
        }

        RemoveSelectedCommand.ThrownExceptions.Subscribe(OnCommandFailed);

        Rebuild();

        // The pool is normally already loading by the time this page is built, but joining the
        // same operation means the page reports the outcome whether it is opened during the load
        // or long after it. Not awaited — a constructor cannot be, and the task never throws.
        _ = ReportInitialLoadAsync(loader);
    }

    /// <inheritdoc />
    public override string TitleKey => "Page.Proxies";

    /// <inheritdoc />
    public override string IconKey => "IconShield";

    /// <summary>Rows currently shown, already filtered and capped.</summary>
    public ObservableCollection<ProxyRowViewModel> Proxies { get; } = [];

    /// <summary>Protocol filter options.</summary>
    public IReadOnlyList<LocalizedOption<ProxyProtocolFilter>> ProtocolFilters { get; } =
        LocalizedOption<ProxyProtocolFilter>.For(
            ProxyProtocolFilter.All,
            ProxyProtocolFilter.Http,
            ProxyProtocolFilter.Https,
            ProxyProtocolFilter.Socks4,
            ProxyProtocolFilter.Socks5
        );

    /// <summary>Health filter options.</summary>
    public IReadOnlyList<LocalizedOption<ProxyHealthFilter>> HealthFilters { get; } =
        LocalizedOption<ProxyHealthFilter>.ForAll();

    /// <summary>Reloads every source into the pool.</summary>
    public ReactiveCommand<RxVoid, RxVoid> RefreshCommand { get; }

    /// <summary>Probes the whole pool.</summary>
    public ReactiveCommand<RxVoid, RxVoid> SweepCommand { get; }

    /// <summary>Adds the addresses typed into <see cref="NewProxies"/>.</summary>
    public ReactiveCommand<RxVoid, RxVoid> AddCustomCommand { get; }

    /// <summary>Removes the selected custom proxy.</summary>
    public ReactiveCommand<RxVoid, RxVoid> RemoveSelectedCommand { get; }

    /// <summary>Empties the custom list.</summary>
    public ReactiveCommand<RxVoid, RxVoid> ClearCustomCommand { get; }

    private async Task ReportInitialLoadAsync(IProxyPoolLoader loader)
    {
        var result = await loader.EnsureLoadedAsync().ConfigureAwait(false);
        var message = Localizer.Instance.Format(
            "Proxies.Status.Ready",
            Localizer.Instance.Plural("Proxies.Count.Proxies", result.Total),
            result.Live
        );

        // Anything the user has done since — an add, a check — is more interesting than the
        // startup count, so do not overwrite it.
        OnUi(() => StatusMessage ??= message);
    }

    private async Task RefreshAsync(CancellationToken cancellationToken)
    {
        var count = await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);
        var message = Localizer.Instance.Format(
            "Proxies.Status.PoolHolds",
            Localizer.Instance.Plural("Proxies.Count.Proxies", count)
        );

        OnUi(() => StatusMessage = message);
    }

    private async Task SweepAsync(CancellationToken cancellationToken)
    {
        OnUi(() =>
        {
            IsSweeping = true;
            SweepProgress = 0d;
            StatusMessage = null;
        });

        try
        {
            var progress = new Progress<ProxySweepProgress>(value => OnUi(() => SweepProgress = value.Fraction));
            var alive = await _pool.SweepAsync(progress, cancellationToken).ConfigureAwait(false);
            var total = _pool.Entries.Count;
            var message = Localizer.Instance.Format("Proxies.Status.Answered", Format(alive), Format(total));

            OnUi(() => StatusMessage = message);
        }
        catch (OperationCanceledException)
        {
            OnUi(() => StatusMessage = Localizer.Instance["Proxies.Status.CheckCancelled"]);
        }
        finally
        {
            OnUi(() =>
            {
                IsSweeping = false;
                SweepProgress = 0d;
            });
        }
    }

    private async Task AddCustomAsync(CancellationToken cancellationToken)
    {
        var (parsed, rejected) = CustomProxySource.ParseList(NewProxies);

        var loc = Localizer.Instance;

        if (parsed.Count == 0 && rejected.Count == 0)
        {
            OnUi(() => StatusMessage = loc["Proxies.Status.Nothing"]);
            return;
        }

        var added = await _customSource.AddAsync(parsed, cancellationToken).ConfigureAwait(false);
        await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);

        var message = loc.Format("Proxies.Status.Added", Format(added), Format(parsed.Count));
        if (rejected.Count > 0)
        {
            // Naming the first few beats "3 lines were invalid" when a paste is hundreds long.
            var sample = string.Join(", ", rejected.Take(3));
            if (rejected.Count > 3)
            {
                sample += " " + loc.Format("Proxies.Status.RejectedMore", Format(rejected.Count - 3));
            }

            message += " " + loc.Format("Proxies.Status.Rejected", sample);
        }

        OnUi(() =>
        {
            StatusMessage = message;
            if (added > 0)
            {
                NewProxies = string.Empty;
            }
        });
    }

    private async Task RemoveSelectedAsync(CancellationToken cancellationToken)
    {
        if (SelectedProxy is not { IsCustom: true } row)
        {
            return;
        }

        await _customSource.RemoveAsync(row.Entry.Endpoint, cancellationToken).ConfigureAwait(false);
        await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);

        OnUi(() => StatusMessage = Localizer.Instance.Format("Proxies.Status.Removed", row.Address));
    }

    private async Task ClearCustomAsync(CancellationToken cancellationToken)
    {
        await _customSource.ClearAsync(cancellationToken).ConfigureAwait(false);
        await _pool.RefreshAsync(cancellationToken).ConfigureAwait(false);

        OnUi(() => StatusMessage = Localizer.Instance["Proxies.Status.Cleared"]);
    }

    /// <inheritdoc />
    protected override void OnLanguageChanged()
    {
        base.OnLanguageChanged();

        // Health and source captions live on the rows, so they need the nudge individually.
        foreach (var row in _rows.Values)
        {
            row.Refresh();
        }
    }

    /// <inheritdoc />
    /// <remarks>
    /// Detaching from the pool matters: the pool is a singleton and would otherwise keep this
    /// page — and every row in it — alive for the process lifetime.
    /// </remarks>
    public void Dispose()
    {
        _pool.Changed -= OnPoolChanged;
        _poolChanged.Dispose();
        GC.SuppressFinalize(this);
    }

    private void OnPoolChanged(object? sender, EventArgs e) => _poolChanged.OnNext(RxVoid.Default);

    private void Rebuild()
    {
        var entries = _pool.Entries;

        // Reconcile rows rather than recreating them: a row rebuilt on every pool event would
        // drop the user's selection mid-sweep.
        var seen = new HashSet<string>(StringComparer.Ordinal);
        foreach (var entry in entries)
        {
            var key = entry.Endpoint.Key;
            seen.Add(key);

            if (_rows.TryGetValue(key, out var existing))
            {
                existing.Refresh();
            }
            else
            {
                _rows[key] = new ProxyRowViewModel(entry);
            }
        }

        foreach (var stale in _rows.Keys.Where(key => !seen.Contains(key)).ToArray())
        {
            _rows.Remove(stale);
        }

        var matched = _rows.Values.Where(PassesFilters).OrderBy(row => row.Address, StringComparer.Ordinal).ToArray();

        Proxies.Clear();
        foreach (var row in matched.Take(MaxDisplayedRows))
        {
            Proxies.Add(row);
        }

        MatchedCount = matched.Length;
        TotalCount = entries.Count;
        AliveCount = entries.Count(entry => entry.Health == ProxyHealthState.Alive);
    }

    private bool PassesFilters(ProxyRowViewModel row)
    {
        if (
            ProtocolFilter.Value != ProxyProtocolFilter.All
            && !ProtocolFilter.Value.HasFlag(ProxyOptions.ToFlag(row.Entry.Endpoint.Protocol))
        )
        {
            return false;
        }

        var healthOk = HealthFilter.Value switch
        {
            ProxyHealthFilter.Alive => row.Entry.Health == ProxyHealthState.Alive,
            ProxyHealthFilter.Dead => row.Entry.Health == ProxyHealthState.Dead,
            ProxyHealthFilter.Unchecked => row.Entry.Health == ProxyHealthState.Unknown,
            _ => true,
        };

        return healthOk && row.Matches(SearchText);
    }

    private void OnCommandFailed(Exception exception)
    {
        _logger.LogError(exception, "Proxy action failed");
        OnUi(() => StatusMessage = Localizer.Instance.Format("Proxies.Status.Failed", exception.Message));
    }

    private static string Format(int value) => value.ToString("N0", CultureInfo.CurrentCulture);

    private void OnUi(Action action) => _mainThread.Schedule(action);
}