namespace BotPages.Core;

using BotPages.Core.Abstractions;
using BotPages.Core.Context;
using BotPages.Core.Logging;
using BotPages.Core.Routing;

/// <summary>
/// Основное приложение BotPages.
/// Управляет маршрутизацией, командами, middleware и страницами.
/// </summary>
public sealed class BotPagesApp
{
    private readonly IMessengerAdapterFactory _adapterFactory;
    private readonly List<IPageMiddleware> _middlewares = new();
    private readonly RoutesRegistry _routes = new();
    private readonly CommandsRegistry _commands = new();
    private readonly IStateStorage _state;
    private readonly ILogger _logger;
    private readonly NavigationService _navigation;

    /// <summary>
    /// Создать приложение BotPages.
    /// </summary>
    public BotPagesApp(IMessengerAdapterFactory adapterFactory, IStateStorage state, ILogger logger)
    {
        _adapterFactory = adapterFactory;
        _state = state;
        _logger = logger;

        _navigation = new NavigationService(_routes);
    }

    /// <summary>
    /// Установить страницу по умолчанию.
    /// </summary>
    public BotPagesApp AddDefaultPage<TPage>() where TPage : SingletonPage
    {
        _navigation.AddDefaultPage<TPage>();
        return this;
    }

    /// <summary>
    /// Добавить middleware.
    /// </summary>
    public BotPagesApp AddMiddleware<TMiddleware>(TMiddleware instance) where TMiddleware : IPageMiddleware
    {
        _middlewares.Add(instance);
        return this;
    }

    /// <summary>
    /// Зарегистрировать команду, ведущую на страницу.
    /// </summary>
    public BotPagesApp MapCommand<TPage>(string commandTemplate) where TPage : Page
    {
        _commands.Map<TPage>(commandTemplate);
        return this;
    }

    /// <summary>
    /// Зарегистрировать команду с кастомным обработчиком.
    /// </summary>
    public BotPagesApp MapCommand(string template, Func<PageContext, CancellationToken, Task> handler)
    {
        _commands.Map(template, handler);
        return this;
    }

    /// <summary>
    /// Зарегистрировать маршрут для страницы.
    /// </summary>
    public BotPagesApp MapRoute<TPage>(string template) where TPage : Page
    {
        _routes.Map<TPage>(template);
        return this;
    }

    /// <summary>
    /// Обработать входящее обновление.
    /// </summary>
    public async Task HandleUpdateAsync(UpdateContext update, CancellationToken ct)
    {
        var ctx = await CreatePageContextAsync(update, ct);

        // Команды выше событий страниц
        if (update.Kind == UpdateKind.Text && update.Text is not null && update.Text.StartsWith("/"))
        {
            if (_commands.TryDispatch(ctx, update.Text, ct, out var dispatched) && dispatched is not null)
            {
                _logger.Log(LogLevel.Info, $"Command '{update.Text}' dispatched.");
                await dispatched;
                return;
            }
        }

        // Конвейер middleware
        var pipeline = BuildPipeline(ctx, async () =>
        {
            await DispatchToPageAsync(ctx, update, ct);
        });

        await pipeline();
    }

    private Func<Task> BuildPipeline(PageContext ctx, Func<Task> terminal)
    {
        Func<Task> next = terminal;
        foreach (var mw in _middlewares.AsEnumerable().Reverse())
        {
            var prev = next;
            next = () => mw.InvokeAsync(ctx, prev, _currentCt);
        }
        return next;
    }

    // Технические поля для конвейера
    private CancellationToken _currentCt;

    /// <summary>
    /// Создать контекст страницы для текущего обновления.
    /// </summary>
    private async Task<PageContext> CreatePageContextAsync(UpdateContext update, CancellationToken ct)
    {
        _currentCt = ct;

        var sessionKey = new CompositeSessionKey(update.MessengerType, update.Chat.Id, update.User.Id);

        var ctx = new PageContext
        {
            Update = update,
            SessionKey = sessionKey,
            StateStorage = _state,
            Navigation = _navigation,
            Adapter = _adapterFactory.Resolve(update.MessengerType),
        };

        return await Task.FromResult(ctx);
    }

    /// <summary>
    /// Отправить обновление на текущую страницу.
    /// </summary>
    private async Task DispatchToPageAsync(PageContext ctx, UpdateContext update, CancellationToken ct)
    {
        var page = ResolveCurrentPage(ctx);

        if (page is null)
        {
            await ctx.Navigation.GoToHome(ctx, ct);
            return;
        }


        try
        {
            await page.OnUpdate(ctx, update, ct);

            if (update.Kind.HasFlag(UpdateKind.Text) && update.Text is not null) await page.OnText(ctx, update.Text, ct);
            if (update.Kind.HasFlag(UpdateKind.Button) && update.Text is not null) await page.OnButton(ctx, update.Text, ct);
            if (update.Kind.HasFlag(UpdateKind.File) && update.Files.Count > 0) await page.OnFile(ctx, update.Files, ct);

        }
        catch (Exception ex)
        {
            _logger.Log(LogLevel.Critical, "Unhandled page error.", ex);
            await page.OnError(ctx, ex, ct);
        }
    }

    /// <summary>
    /// Определить текущую страницу.
    /// </summary>
    private Page? ResolveCurrentPage(PageContext ctx)
        => _navigation.ResolveCurrentPage(ctx);
}