using System.Numerics;
using AcDream.App.Rendering.Gpu;

namespace AcDream.App.UI;

/// <summary>Leaf widget for dat Type 0xD (UIElement_Viewport). Blits the texture produced by its
/// IUiViewportRenderer (run in the pre-UI hook) as a single sprite at its own rect. The 3-D render
/// does NOT happen here (OnDraw only has a 2-D context).</summary>
public sealed class UiViewport : UiElement
{
    public override bool ConsumesDatChildren => true;

    /// <summary>Optional click action. Non-null makes the viewport handle the press
    /// itself instead of it being captured as a window move.</summary>
    public System.Action? Clicked { get; set; }
    /// <summary>Position-aware variant with viewport-local pixel coordinates.</summary>
    public System.Action<int, int>? ClickedAt { get; set; }

    public override bool HandlesClick => Clicked is not null || ClickedAt is not null;

    public override bool OnEvent(in UiEvent e)
    {
        if (Clicked is null && ClickedAt is null) return base.OnEvent(e);
        switch (e.Type)
        {
            case UiEventType.MouseDown: return true;   // consume the press; act on Click
            case UiEventType.Click:
                Clicked?.Invoke();
                ClickedAt?.Invoke(e.Data1, e.Data2);
                return true;
        }
        return base.OnEvent(e);
    }

    /// <summary>Renderer that produces the off-screen texture. Set by GameWindow wiring (later task).</summary>
    public IUiViewportRenderer? Renderer { get; set; }

    /// <summary>
    /// Campaign V slice V4a: the off-screen FBO colour texture produced by the
    /// pre-UI hook, registered into the device's texture table by the
    /// pre-approved paperdoll/appraisal transitional seam
    /// (<c>GlGpuDevice.RegisterExternalColorTexture</c>, campaign doc §7.1) —
    /// its owning renderer (<c>PrivateEntityViewportRenderer</c>) stays raw GL
    /// until V4g. <see cref="GpuTextureSlot.Unassigned"/> = nothing to blit.
    /// internal, not public: <see cref="GpuTextureSlot"/> is an internal type
    /// (the pinned RHI contract); UiViewport stays public.
    /// </summary>
    internal GpuTextureSlot TextureSlot { get; set; } = GpuTextureSlot.Unassigned;

    protected override void OnDraw(UiRenderContext ctx)
    {
        if (!Visible || !TextureSlot.IsAssigned) return;
        uint textureHandle = AcDream.App.Rendering.TextRenderer.ResolveExternalTextureSlot(TextureSlot);
        if (textureHandle == 0) return;
        // Local origin is already at this widget's Left/Top (PushTransform applied by DrawSelfAndChildren).
        //
        // V depends on the backend that produced the texture, and slice V6l is
        // where that stopped being a constant. A GL off-screen FBO colour texture
        // has a BOTTOM-LEFT origin while the UI sprite convention is top-left, so
        // its V is flipped (v0=1, v1=0) — without that the doll renders
        // upside-down, which is what the line this replaces had always said. A
        // Vulkan render target has a top-left origin and needs no flip; applying
        // one drew the doll on its head in the first Vulkan capture. The renderer
        // that made the texture is the one that knows.
        bool bottomUp = Renderer?.TextureIsBottomUp ?? true;
        float v0 = bottomUp ? 1f : 0f;
        float v1 = bottomUp ? 0f : 1f;
        ctx.DrawSprite(textureHandle, 0f, 0f, Width, Height, 0f, v0, 1f, v1, Vector4.One);
    }
}