using System.Collections.Generic;
using DatReaderWriter;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Types;

namespace AcDream.App.UI.Layout;

/// <summary>
/// Resolves the empty-slot background sprite for a UIElement_ItemList's cells the way retail
/// does. Retail ref: UIElement_ItemList::InternalCreateItem (acclient_2013_pseudo_c.txt:231486 /
/// 0x004e3570): GetAttribute_Enum(this, 0x1000000e, &amp;id) -> GetByEnum(0x10000038,5,0x23) [the
/// shared UIItem catalog LayoutDesc, = 0x21000037] -> CreateChildElement(catalog, id); the cloned
/// prototype's ItemSlot_Empty (state 0x1000001c) media is the empty-cell background.
/// </summary>
public static class ItemListCellTemplate
{
    /// <summary>The shared UIItem cell-template catalog. Hardcoded: retail resolves it via
    /// GetByEnum(0x10000038,5,0x23) through a master enum-map DAT object (no code literal);
    /// 0x21000037 is the only LayoutDesc that is a catalog of standalone UIItem (0x10000032)
    /// prototypes. Validated by the real-dat test (the resolved sprite must be a real 0x06 surface).</summary>
    public const uint CatalogLayoutId = 0x21000037u;

    private const uint CellTemplateAttr = 0x1000000eu;        // UIElement attribute: cell-template element id
    private const uint IconChildId      = 0x1000033Bu;        // m_elem_Icon sub-element (carries ItemSlot_Empty)
    private const string ItemSlotEmpty  = "ItemSlot_Empty";   // UIStateId.ToString() for state 0x1000001c

    /// <summary>
    /// Resolve the empty-slot sprite (a 0x06xxxxxx RenderSurface id) for the cells of item-list
    /// element <paramref name="listElementId"/> in LayoutDesc <paramref name="listLayoutId"/>.
    /// Returns 0 when the layout/element/attribute/prototype/media is absent (the caller keeps
    /// the <see cref="UiItemSlot"/> default).
    /// </summary>
    public static uint ResolveEmptySprite(DatCollection dats, uint listLayoutId, uint listElementId)
    {
        var listLd = dats.Get<LayoutDesc>(listLayoutId);
        if (listLd is null) return 0;
        var listElem = FindDesc(listLd, listElementId);
        if (listElem is null) return 0;

        uint protoId = ReadCellTemplateId(listElem);          // attr 0x1000000e
        if (protoId == 0) return 0;

        var catalog = dats.Get<LayoutDesc>(CatalogLayoutId);
        if (catalog is null) return 0;
        var proto = FindDesc(catalog, protoId);
        if (proto is null) return 0;

        // The empty-slot BACKGROUND is the m_elem_Icon's ItemSlot_Empty media, resolved THROUGH
        // BaseElement inheritance: the 36x36 container prototype (0x1000033F) nests its icon behind
        // an inner wrapper (0x10000340 -> base 0x1000033E -> 0x1000033B -> 0x06000F6E), so a raw
        // child search alone returns nothing for containers. We deliberately do NOT use the
        // prototype's DirectState child overlay: on the container prototype that child is the
        // open/selected-container TRIANGLE indicator (0x06005D9C), which retail draws ONLY on the
        // selected container (a deferred container-selection feature) — never as empty-cell art.
        // (Live visual gate 2026-06-22: frame-first stamped the triangle onto every empty cell.)
        return FindIconEmpty(catalog, proto, new HashSet<uint>());
    }

    // ── attribute 0x1000000e: stored as EnumBaseProperty in the dat (Value is the prototype id) ──
    // Note: the spec anticipated DataIdBaseProperty/ArrayBaseProperty based on the font-DID pattern,
    // but the live dat uses EnumBaseProperty.Value (uint) — confirmed by runtime reflection.
    private static uint ReadCellTemplateId(ElementDesc elem)
    {
        uint id = ReadIdFromState(elem.StateDesc);
        if (id != 0) return id;
        foreach (var s in elem.States)
        {
            id = ReadIdFromState(s.Value);
            if (id != 0) return id;
        }
        return 0;
    }

    private static uint ReadIdFromState(StateDesc? sd)
    {
        if (sd?.Properties is null) return 0;
        return sd.Properties.TryGetValue(CellTemplateAttr, out var raw) ? ReadId(raw) : 0;
    }

    private static uint ReadId(BaseProperty raw)
    {
        if (raw is ArrayBaseProperty arr && arr.Value.Count > 0) return ReadId(arr.Value[0]);
        if (raw is DataIdBaseProperty did) return did.Value;
        if (raw is EnumBaseProperty ep) return ep.Value;   // 0x1000000e is EnumBaseProperty in the live dat
        return 0;
    }

    // ── prototype media: the m_elem_Icon (0x1000033B) ItemSlot_Empty, resolved through inheritance ──
    // Find the icon child's empty media within `element`'s subtree, following BaseElement edges
    // within the same catalog (cycle-guarded by `baseSeen`). The 32x32 contents prototype carries
    // 0x1000033B as a direct child; the 36x36 container prototype reaches it only via an inherited
    // base (0x10000340 -> 0x1000033E), so a raw child search alone returns nothing for containers.
    private static uint FindIconEmpty(LayoutDesc catalog, ElementDesc element, HashSet<uint> baseSeen)
    {
        if (element.ElementId == IconChildId)
        {
            uint e = IconEmptyState(element);
            if (e != 0) return e;
        }
        foreach (var kv in element.Children)
        {
            uint e = FindIconEmpty(catalog, kv.Value, baseSeen);
            if (e != 0) return e;
        }
        if (element.BaseElement != 0 && element.BaseLayoutId == CatalogLayoutId && baseSeen.Add(element.BaseElement))
        {
            var baseDesc = FindDesc(catalog, element.BaseElement);
            if (baseDesc is not null)
            {
                uint e = FindIconEmpty(catalog, baseDesc, baseSeen);
                if (e != 0) return e;
            }
        }
        return 0;
    }

    private static uint IconEmptyState(ElementDesc icon)
    {
        foreach (var s in icon.States)
            if (s.Key.ToString() == ItemSlotEmpty)
            {
                uint f = StateImage(s.Value);
                if (f != 0) return f;
            }
        return DirectStateImage(icon);   // some icons carry empty media on the DirectState
    }

    private static uint DirectStateImage(ElementDesc d)
        => d.StateDesc is null ? 0u : StateImage(d.StateDesc);

    private static uint StateImage(StateDesc sd)
    {
        foreach (var m in sd.Media)
            if (m is MediaDescImage img && img.File != 0) return img.File;
        return 0;
    }

    // ── depth-first element search by id (LayoutImporter.FindDesc is private there) ──
    private static ElementDesc? FindDesc(LayoutDesc ld, uint id)
    {
        foreach (var kv in ld.Elements)
        {
            var f = FindDescIn(kv.Value, id);
            if (f is not null) return f;
        }
        return null;
    }

    private static ElementDesc? FindDescIn(ElementDesc d, uint id)
    {
        if (d.ElementId == id) return d;
        foreach (var kv in d.Children)
        {
            var f = FindDescIn(kv.Value, id);
            if (f is not null) return f;
        }
        return null;
    }
}