using System.ComponentModel;
using System.Globalization;
using System.IO;
using System.Net.Http;
using System.Text.Json;
using System.Windows.Data;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using CursorLang.Core.Models;
using CursorLang.Core.Services;

namespace CursorLang.Settings.ViewModels;

/// <summary>
/// The updates section of the settings window.
/// </summary>
/// <remarks>
/// The section always says where things stand: a check flies off the moment the window
/// appears, and its outcome — including an unreachable network — stays written in the
/// status line. Nothing here is silent, and nothing disappears: a user who opened the
/// window is told about updates whether they came looking for them or not.
/// </remarks>
public sealed partial class UpdateViewModel : ObservableObject, IDisposable
{
    private readonly IUpdateService _updates;
    private readonly ILocalizationService _localization;

    private CancellationTokenSource? _work;
    private ReleaseInfo? _release;
    private string? _packagePath;

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(StatusText))]
    [NotifyPropertyChangedFor(nameof(IsBusy))]
    [NotifyPropertyChangedFor(nameof(CanCheck))]
    [NotifyPropertyChangedFor(nameof(IsProgressUnknown))]
    [NotifyPropertyChangedFor(nameof(IsDownloadOffered))]
    [NotifyPropertyChangedFor(nameof(IsInstallOffered))]
    [NotifyPropertyChangedFor(nameof(IsProgressShown))]
    [NotifyPropertyChangedFor(nameof(IsReleaseLinkShown))]
    private UpdateStatus _status = UpdateStatus.Idle;

    /// <summary>The downloaded fraction: from 0 to 1.</summary>
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(IsProgressUnknown))]
    private double _progress;

    public UpdateViewModel(IUpdateService updates, ILocalizationService localization)
    {
        _updates = updates;
        _localization = localization;

        _localization.PropertyChanged += OnLocalizationChanged;
    }

    /// <summary>Whether to show the updates section at all.</summary>
    public bool IsSupported => _updates.IsSupported;

    public string CurrentVersion => _updates.CurrentVersion.ToString();

    /// <summary>A request or a download is in flight — the buttons freeze for that time.</summary>
    public bool IsBusy => Status is UpdateStatus.Checking or UpdateStatus.Downloading;

    public bool CanCheck => !IsBusy;

    /// <summary>
    /// The package size is unknown, and the bar shows only the fact of the download.
    /// Its start looks the same until the first report arrives.
    /// </summary>
    public bool IsProgressUnknown => Status == UpdateStatus.Downloading && Progress <= 0;

    public bool IsDownloadOffered => Status == UpdateStatus.Available;

    public bool IsInstallOffered => Status == UpdateStatus.Ready;

    public bool IsProgressShown => Status == UpdateStatus.Downloading;

    public bool IsReleaseLinkShown => _release?.PageUrl is not null && Status is not UpdateStatus.Checking;

    /// <summary>The release page: the release notes live there too.</summary>
    public Uri? ReleaseUrl => _release?.PageUrl;

    /// <summary>
    /// What the section says. There is a line for every state, the one before the
    /// first check included: the status is never an empty spot in the window.
    /// </summary>
    public string StatusText => Status switch
    {
        UpdateStatus.Checking => _localization["UpdateChecking"],
        UpdateStatus.UpToDate => _localization["UpdateUpToDate"],
        UpdateStatus.Available => Format("UpdateAvailable", _release?.Tag),
        UpdateStatus.Downloading => _localization["UpdateDownloading"],
        UpdateStatus.Ready => _localization["UpdateReady"],
        UpdateStatus.Failed => _localization["UpdateFailed"],
        _ => _localization["UpdateNotChecked"],
    };

    /// <summary>
    /// Asks about new versions. Called once, when the window has just appeared.
    /// </summary>
    /// <remarks>
    /// It used to be called when the application started, which back then meant when
    /// the machine was switched on. The background half is a separate process now and
    /// does not go to the network at all — nothing in it could show the answer — so the
    /// question is asked when there is a window to answer into.
    ///
    /// And it is asked every time that window appears: opening it is a deliberate act
    /// of the user, rare enough that a request costs nothing, and the answer is what
    /// the section exists for. A remembered answer from yesterday is worth less than
    /// today's, so nothing is remembered.
    /// </remarks>
    public Task StartAsync() => CheckAsync();

    public void Dispose()
    {
        _localization.PropertyChanged -= OnLocalizationChanged;

        _work?.Cancel();
        _work?.Dispose();
        _work = null;
    }

    [RelayCommand]
    private async Task CheckAsync()
    {
        if (!IsSupported)
        {
            return;
        }

        CancellationToken token = StartWork();
        Status = UpdateStatus.Checking;

        try
        {
            _release = await _updates.CheckAsync(token);
            _packagePath = null;

            Status = _release is null ? UpdateStatus.UpToDate : UpdateStatus.Available;
        }
        catch (OperationCanceledException) when (token.IsCancellationRequested)
        {
            // The check was cancelled by the next piece of work: it has already set its own state
            return;
        }
        catch (Exception e) when (IsExpected(e))
        {
            Status = UpdateStatus.Failed;
        }

        OnPropertyChanged(nameof(ReleaseUrl));
        OnPropertyChanged(nameof(IsReleaseLinkShown));
    }

    [RelayCommand]
    private async Task DownloadAsync()
    {
        if (_release is not { } release)
        {
            return;
        }

        CancellationToken token = StartWork();
        Progress = 0;
        Status = UpdateStatus.Downloading;

        try
        {
            var progress = new Progress<double>(value => Progress = value);
            _packagePath = await _updates.DownloadAsync(release, progress, token);
            Status = UpdateStatus.Ready;
        }
        catch (OperationCanceledException) when (token.IsCancellationRequested)
        {
            // The download was interrupted by the next piece of work: it has already set its own state
        }
        catch (Exception e) when (IsExpected(e))
        {
            Status = UpdateStatus.Failed;
        }
    }

    [RelayCommand]
    private void Install()
    {
        if (_packagePath is null || !File.Exists(_packagePath))
        {
            // The file was removed by the temp folder cleanup — downloading it again is what is left
            Status = _release is null ? UpdateStatus.Idle : UpdateStatus.Available;
            return;
        }

        try
        {
            _updates.Install(_packagePath);
        }
        catch (Exception e) when (IsExpected(e))
        {
            Status = UpdateStatus.Failed;
        }
    }

    /// <summary>
    /// The errors that simply leave the update undone: an unreachable network, an
    /// unexpected response, a file in use. Everything else is a reason to crash.
    /// </summary>
    /// <remarks>
    /// <c>OperationCanceledException</c> means an expired request deadline here:
    /// cancellation by the application itself is caught by a separate handler above.
    /// </remarks>
    private static bool IsExpected(Exception e) =>
        e is HttpRequestException or JsonException or IOException or UnauthorizedAccessException
            or NotSupportedException or InvalidOperationException or Win32Exception
            or OperationCanceledException;

    /// <summary>
    /// Starts a new piece of work, cancelling the previous one: the user may have
    /// pressed "Check" in the middle of a download.
    /// </summary>
    private CancellationToken StartWork()
    {
        _work?.Cancel();
        _work?.Dispose();
        _work = new CancellationTokenSource();
        return _work.Token;
    }

    private string Format(string key, string? argument) =>
        string.Format(CultureInfo.CurrentCulture, _localization[key], argument);

    private void OnLocalizationChanged(object? sender, PropertyChangedEventArgs e)
    {
        if (e.PropertyName == Binding.IndexerName)
        {
            OnPropertyChanged(nameof(StatusText));
        }
    }
}