using System;

namespace AcDream.Core.Items;

public enum ExternalContainerTransitionKind
{
    Opened,
    ReplacementRequested,
    Closed,
    Reset,
}

public readonly record struct ExternalContainerTransition(
    ExternalContainerTransitionKind Kind,
    uint PreviousContainerId,
    uint ContainerId);

/// <summary>
/// Owns retail <c>ClientUISystem::groundObject</c> and the outstanding external
/// container request. ACE sends ViewContents for the requested root and then for
/// nested containers; only the expected root may become the visible ground object.
/// Retail: <c>ClientUISystem::OnViewContents @ 0x00565870</c> and
/// <c>SetGroundObject @ 0x00564510</c>.
/// </summary>
public sealed class ExternalContainerState
{
    public uint RequestedContainerId { get; private set; }
    public uint CurrentContainerId { get; private set; }

    public event Action<ExternalContainerTransition>? Changed;

    public bool RequestOpen(uint containerId)
    {
        if (containerId == 0u || RequestedContainerId == containerId)
            return false;

        uint previous = CurrentContainerId;
        RequestedContainerId = containerId;

        // ClientUISystem::SetGroundObject @ 0x00564510 retires the old
        // ground-object presentation synchronously when a different root is
        // requested. ViewContents for the new root arrives later. Keeping the
        // old root current during that interval lets its range watcher issue a
        // close Use, which ACE interprets as cancellation of the new root's
        // MoveTo chain.
        if (previous != 0u && previous != containerId)
        {
            CurrentContainerId = 0u;
            Changed?.Invoke(new ExternalContainerTransition(
                ExternalContainerTransitionKind.ReplacementRequested,
                previous,
                containerId));
        }
        return true;
    }

    public bool ApplyViewContents(uint containerId)
    {
        if (containerId == 0u || containerId != RequestedContainerId)
            return false;

        uint previous = CurrentContainerId;
        CurrentContainerId = containerId;
        RequestedContainerId = containerId;
        if (previous == containerId)
            return false;

        Changed?.Invoke(new ExternalContainerTransition(
            ExternalContainerTransitionKind.Opened,
            previous,
            containerId));
        return true;
    }

    public bool ApplyClose(uint containerId)
    {
        if (containerId == 0u || containerId != CurrentContainerId)
            return false;

        uint previous = CurrentContainerId;
        CurrentContainerId = 0u;
        RequestedContainerId = 0u;
        Changed?.Invoke(new ExternalContainerTransition(
            ExternalContainerTransitionKind.Closed,
            previous,
            0u));
        return true;
    }

    public bool ApplyUseDone(uint weenieError)
    {
        if (weenieError == 0u || RequestedContainerId == CurrentContainerId)
            return false;
        RequestedContainerId = CurrentContainerId;
        return true;
    }

    public bool Reset()
    {
        uint previous = CurrentContainerId;
        bool changed = previous != 0u || RequestedContainerId != 0u;
        CurrentContainerId = 0u;
        RequestedContainerId = 0u;

        var transition = new ExternalContainerTransition(
            ExternalContainerTransitionKind.Reset,
            previous,
            0u);
        Action<ExternalContainerTransition>? listeners = Changed;
        if (listeners is not null)
        {
            List<Exception>? failures = null;
            foreach (Action<ExternalContainerTransition> listener in listeners.GetInvocationList())
            {
                try { listener(transition); }
                catch (Exception error) { (failures ??= []).Add(error); }
            }
            if (failures is not null)
                throw new AggregateException(
                    "One or more external-container reset observers failed.",
                    failures);
        }
        return changed;
    }
}