using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using DiscordChatExporter.Core.Discord;
using DiscordChatExporter.Core.Discord.Data;
using DiscordChatExporter.Core.Exceptions;
using DiscordChatExporter.Core.Exporting;
using DiscordChatExporter.Core.Utils.Extensions;
using DiscordChatExporter.Gui.Services;
using DiscordChatExporter.Gui.Utils;
using DiscordChatExporter.Gui.ViewModels.Dialogs;
using DiscordChatExporter.Gui.ViewModels.Framework;
using Gress;
using MaterialDesignThemes.Wpf;
using Stylet;

namespace DiscordChatExporter.Gui.ViewModels;

public class RootViewModel : Screen
{
    private readonly IViewModelFactory _viewModelFactory;
    private readonly DialogManager _dialogManager;
    private readonly SettingsService _settingsService;
    private readonly UpdateService _updateService;

    private DiscordClient? _discord;

    public ISnackbarMessageQueue Notifications { get; } = new SnackbarMessageQueue(TimeSpan.FromSeconds(5));

    public IProgressManager ProgressManager { get; } = new ProgressManager();

    public bool IsBusy { get; private set; }

    public bool IsProgressIndeterminate { get; private set; }

    public string? Token { get; set; }

    private IReadOnlyDictionary<Guild, IReadOnlyList<Channel>>? GuildChannelMap { get; set; }

    public IReadOnlyList<Guild>? AvailableGuilds => GuildChannelMap?.Keys.ToArray();

    public Guild? SelectedGuild { get; set; }

    public IReadOnlyList<Channel>? AvailableChannels => SelectedGuild is not null
        ? GuildChannelMap?[SelectedGuild]
        : null;

    public IReadOnlyList<Channel>? SelectedChannels { get; set; }

    public RootViewModel(
        IViewModelFactory viewModelFactory,
        DialogManager dialogManager,
        SettingsService settingsService,
        UpdateService updateService)
    {
        _viewModelFactory = viewModelFactory;
        _dialogManager = dialogManager;
        _settingsService = settingsService;
        _updateService = updateService;

        DisplayName = $"{App.Name} v{App.VersionString}";

        // Update busy state when progress manager changes
        ProgressManager.Bind(o => o.IsActive, (_, _) =>
            IsBusy = ProgressManager.IsActive
        );

        ProgressManager.Bind(o => o.IsActive, (_, _) =>
            IsProgressIndeterminate = ProgressManager.IsActive && ProgressManager.Progress is <= 0 or >= 1
        );

        ProgressManager.Bind(o => o.Progress, (_, _) =>
            IsProgressIndeterminate = ProgressManager.IsActive && ProgressManager.Progress is <= 0 or >= 1
        );
    }

    private async ValueTask CheckForUpdatesAsync()
    {
        try
        {
            var updateVersion = await _updateService.CheckForUpdatesAsync();
            if (updateVersion is null)
                return;

            Notifications.Enqueue($"Downloading update to {App.Name} v{updateVersion}...");
            await _updateService.PrepareUpdateAsync(updateVersion);

            Notifications.Enqueue(
                "Update has been downloaded and will be installed when you exit",
                "INSTALL NOW", () =>
                {
                    _updateService.FinalizeUpdate(true);
                    RequestClose();
                }
            );
        }
        catch
        {
            // Failure to update shouldn't crash the application
            Notifications.Enqueue("Failed to perform application update");
        }
    }

    protected override async void OnViewLoaded()
    {
        base.OnViewLoaded();

        _settingsService.Load();

        if (_settingsService.LastToken is not null)
        {
            Token = _settingsService.LastToken;
        }

        if (_settingsService.IsDarkModeEnabled)
        {
            App.SetDarkTheme();
        }
        else
        {
            App.SetLightTheme();
        }

        await CheckForUpdatesAsync();
    }

    protected override void OnClose()
    {
        base.OnClose();

        _settingsService.Save();
        _updateService.FinalizeUpdate(false);
    }

    public async void ShowSettings()
    {
        var dialog = _viewModelFactory.CreateSettingsViewModel();
        await _dialogManager.ShowDialogAsync(dialog);
    }

    public void ShowHelp() => ProcessEx.StartShellExecute(App.GitHubProjectWikiUrl);

    public bool CanPopulateGuildsAndChannels =>
        !IsBusy && !string.IsNullOrWhiteSpace(Token);

    public async void PopulateGuildsAndChannels()
    {
        using var operation = ProgressManager.CreateOperation();

        try
        {
            var token = Token?.Trim('"', ' ');
            if (string.IsNullOrWhiteSpace(token))
                return;

            _settingsService.LastToken = token;

            var discord = new DiscordClient(token);

            var guildChannelMap = new Dictionary<Guild, IReadOnlyList<Channel>>();
            await foreach (var guild in discord.GetUserGuildsAsync())
            {
                var channels = await discord.GetGuildChannelsAsync(guild.Id);
                guildChannelMap[guild] = channels.Where(c => c.IsTextChannel).ToArray();
            }

            _discord = discord;
            GuildChannelMap = guildChannelMap;
            SelectedGuild = guildChannelMap.Keys.FirstOrDefault();
        }
        catch (DiscordChatExporterException ex) when (!ex.IsFatal)
        {
            Notifications.Enqueue(ex.Message.TrimEnd('.'));
        }
        catch (Exception ex)
        {
            var dialog = _viewModelFactory.CreateMessageBoxViewModel(
                "Error pulling guilds and channels",
                ex.ToString()
            );

            await _dialogManager.ShowDialogAsync(dialog);
        }
    }

    public bool CanExportChannels =>
        !IsBusy &&
        _discord is not null &&
        SelectedGuild is not null &&
        SelectedChannels is not null &&
        SelectedChannels.Any();

    public async void ExportChannels()
    {
        try
        {
            if (_discord is null || SelectedGuild is null || SelectedChannels is null || !SelectedChannels.Any())
                return;

            var dialog = _viewModelFactory.CreateExportSetupViewModel(SelectedGuild, SelectedChannels);
            if (await _dialogManager.ShowDialogAsync(dialog) != true)
                return;

            var exporter = new ChannelExporter(_discord);

            var operations = ProgressManager.CreateOperations(dialog.Channels!.Count);
            var successfulExportCount = 0;

            await Parallel.ForEachAsync(
                dialog.Channels.Zip(operations),
                new ParallelOptions
                {
                    MaxDegreeOfParallelism = Math.Max(1, _settingsService.ParallelLimit)
                },
                async (tuple, cancellationToken) =>
                {
                    var (channel, operation) = tuple;

                    try
                    {
                        var request = new ExportRequest(
                            dialog.Guild!,
                            channel,
                            dialog.OutputPath!,
                            dialog.SelectedFormat,
                            dialog.After?.Pipe(Snowflake.FromDate),
                            dialog.Before?.Pipe(Snowflake.FromDate),
                            dialog.PartitionLimit,
                            dialog.MessageFilter,
                            dialog.ShouldDownloadMedia,
                            _settingsService.ShouldReuseMedia,
                            _settingsService.DateFormat
                        );

                        await exporter.ExportChannelAsync(request, operation, cancellationToken);

                        Interlocked.Increment(ref successfulExportCount);
                    }
                    catch (DiscordChatExporterException ex) when (!ex.IsFatal)
                    {
                        Notifications.Enqueue(ex.Message.TrimEnd('.'));
                    }
                    finally
                    {
                        operation.Dispose();
                    }
                }
            );

            // Notify of overall completion
            if (successfulExportCount > 0)
                Notifications.Enqueue($"Successfully exported {successfulExportCount} channel(s)");
        }
        catch (Exception ex)
        {
            var dialog = _viewModelFactory.CreateMessageBoxViewModel(
                "Error exporting channel(s)",
                ex.ToString()
            );

            await _dialogManager.ShowDialogAsync(dialog);
        }
    }
}