using System.Linq;

namespace NexusReader.UI.Shared.Services;

public class ReaderNavigationService : IReaderNavigationService
{
    public int CurrentChapterIndex { get; private set; } = 0;
    public int TotalChapters { get; private set; } = 1;
    public string ChapterTitle { get; private set; } = "Loading...";

    public event Func<Task>? OnNavigationChanged;

    public async Task GoToChapter(int index)
    {
        if (index < 0 || index >= TotalChapters) return;
        
        CurrentChapterIndex = index;
        await NotifyNavigationChangedAsync();
    }

    public async Task GoToNextChapter()
    {
        if (CurrentChapterIndex < TotalChapters - 1)
        {
            await GoToChapter(CurrentChapterIndex + 1);
        }
    }

    public async Task GoToPreviousChapter()
    {
        if (CurrentChapterIndex > 0)
        {
            await GoToChapter(CurrentChapterIndex - 1);
        }
    }

    public void UpdateMetadata(int currentIndex, int totalChapters, string title)
    {
        bool changed = false;
        if (CurrentChapterIndex != currentIndex) { CurrentChapterIndex = currentIndex; changed = true; }
        if (TotalChapters != totalChapters) { TotalChapters = totalChapters; changed = true; }
        if (ChapterTitle != title) { ChapterTitle = title; changed = true; }
        
        if (changed)
        {
            // Note: UpdateMetadata remains void, so we trigger notification fire-and-forget here
            // but usually this is called during a render cycle where metadata is updated from a load.
            _ = NotifyNavigationChangedAsync();
        }
    }

    private async Task NotifyNavigationChangedAsync()
    {
        var handlers = OnNavigationChanged?.GetInvocationList();
        if (handlers != null)
        {
            foreach (var handler in handlers.Cast<Func<Task>>())
            {
                await handler();
            }
        }
    }
}