namespace Lumi.Companion.Overlay;

public enum OverlayItemState { Queued, Entering, Visible, Exiting, Removed }

public sealed class OverlayQueueItem(string id, string kind, object payload, DateTimeOffset queuedAt)
{
    public string Id { get; } = id;
    public string Kind { get; } = kind;
    public object Payload { get; } = payload;
    public DateTimeOffset QueuedAt { get; } = queuedAt;
    public DateTimeOffset StateAt { get; internal set; } = queuedAt;
    public OverlayItemState State { get; internal set; } = OverlayItemState.Queued;
}

public sealed class OverlayLifecycleQueue(Func<OverlayContainerSettings> settings, Func<DateTimeOffset>? now = null)
{
    private readonly List<OverlayQueueItem> _items = [];
    private readonly Func<DateTimeOffset> _now = now ?? (() => DateTimeOffset.UtcNow);
    public IReadOnlyList<OverlayQueueItem> Items => _items;
    public event Action? Changed;

    public bool Add(string id, string kind, object payload)
    {
        if (_items.Any(item => item.Id == id && item.State != OverlayItemState.Removed)) return false;
        var value = settings();
        if (_items.Count(item => item.State != OverlayItemState.Removed) >= Math.Max(value.QueueLimit + 1, value.QueueLimit * 2))
            return false;
        var active = _items.Where(item => item.State is not OverlayItemState.Exiting and not OverlayItemState.Removed).ToList();
        while (active.Count >= value.QueueLimit)
        {
            var oldest = active[0];
            oldest.State = OverlayItemState.Exiting;
            oldest.StateAt = _now();
            active.RemoveAt(0);
        }
        var created = new OverlayQueueItem(id, kind, payload, _now()) { State = OverlayItemState.Entering, StateAt = _now() };
        _items.Add(created);
        Changed?.Invoke();
        return true;
    }

    public void Advance()
    {
        var current = _now();
        var value = settings();
        var changed = false;
        foreach (var item in _items)
        {
            var elapsed = current - item.StateAt;
            if (item.State == OverlayItemState.Entering && elapsed.TotalMilliseconds >= value.EntryDurationMs)
            {
                item.State = OverlayItemState.Visible; item.StateAt = current; changed = true;
            }
            else if (item.State == OverlayItemState.Visible && elapsed.TotalMilliseconds >= value.LifetimeMs)
            {
                item.State = OverlayItemState.Exiting; item.StateAt = current; changed = true;
            }
            else if (item.State == OverlayItemState.Exiting && elapsed.TotalMilliseconds >= value.ExitDurationMs)
            {
                item.State = OverlayItemState.Removed; changed = true;
            }
        }
        if (_items.RemoveAll(item => item.State == OverlayItemState.Removed) > 0) changed = true;
        if (changed) Changed?.Invoke();
    }

    public void Clear()
    {
        var current = _now();
        foreach (var item in _items.Where(item => item.State is not OverlayItemState.Exiting and not OverlayItemState.Removed))
        {
            item.State = OverlayItemState.Exiting;
            item.StateAt = current;
        }
        Changed?.Invoke();
    }

    public void ExitWhere(Func<OverlayQueueItem, bool> predicate)
    {
        var current = _now();
        var changed = false;
        foreach (var item in _items.Where(item => item.State is not OverlayItemState.Exiting and not OverlayItemState.Removed && predicate(item)))
        {
            item.State = OverlayItemState.Exiting;
            item.StateAt = current;
            changed = true;
        }
        if (changed) Changed?.Invoke();
    }
}