using System;
using System.Linq;

namespace AcDream.App.UI.Layout;

/// <summary>
/// Hybrid factory: behavioral element Types map to dedicated widgets (verbatim
/// algorithm ports); everything else (and unknown Types) falls back to
/// <see cref="UiDatElement"/>.
///
/// <para>
/// Type 12 (style prototype / BaseElement store) is never instantiated —
/// <see cref="Create"/> returns null and the importer skips it.
/// See docs/research/2026-06-15-layoutdesc-format.md Correction 8.
/// </para>
///
/// <para>
/// The meter's back/front 3-slice sprite ids live on grandchild image elements,
/// NOT on the meter element itself (format doc §11). <see cref="BuildMeter"/>
/// walks two layers down to extract them: the two Type-3 container children
/// ordered by <see cref="ElementInfo.ReadOrder"/> (back behind = lower, front
/// on top = higher), then within each container the image children that carry
/// a DirectState ("" key) sprite, ordered by their X position to obtain
/// left-cap / center-tile / right-cap.
/// </para>
///
/// <para>
/// The expand-detail overlay present in the front container carries ONLY named
/// states ("HideDetail"/"ShowDetail") — no "" DirectState entry — so the
/// <c>TryGetValue("")</c> filter in <see cref="SliceIds"/> excludes it
/// automatically.
/// </para>
/// </summary>
public static class DatWidgetFactory
{
    /// <summary>
    /// Creates the <see cref="UiElement"/> for <paramref name="info"/>, sets its
    /// rect (Left/Top/Width/Height) and Anchors, and returns it.
    /// </summary>
    /// <param name="info">Resolved, merged element snapshot from the LayoutDesc importer.</param>
    /// <param name="resolve">RenderSurface id → (GL tex handle, pixel width, pixel height).
    /// Returns (0,0,0) when the texture is not yet uploaded.</param>
    /// <param name="datFont">Retail UI font for the meter's "cur/max" number overlay.
    /// May be null pre-load — the meter falls back to the debug bitmap font.</param>
    /// <returns>The widget, or <c>null</c> for a Type-12 style prototype (caller skips it).</returns>
    public static UiElement? Create(ElementInfo info,
        Func<uint, (uint, int, int)> resolve, UiDatFont? datFont)
    {
        // Type 12 = zero-size style prototype / BaseElement store referenced by
        // BaseLayoutId. These are property bags, never rendered. See format doc §8
        // ("style prototypes are Type 12 which must be skipped") and Correction 8.
        if (info.Type == 12) return null;

        UiElement e = info.Type switch
        {
            7 => BuildMeter(info, resolve, datFont),  // UIElement_Meter
            _ => new UiDatElement(info, resolve),     // generic fallback for all other types
        };

        // Propagate position + size (pixel-exact from the dat).
        e.Left   = info.X;
        e.Top    = info.Y;
        e.Width  = info.Width;
        e.Height = info.Height;

        // Map the four raw edge-anchor values to the AnchorEdges bit-flag that the
        // UI layout engine uses for reflow.
        e.Anchors = ElementReader.ToAnchors(info.Left, info.Top, info.Right, info.Bottom);

        return e;
    }

    // ── Meter ────────────────────────────────────────────────────────────────

    /// <summary>
    /// Builds a <see cref="UiMeter"/> and populates its six 3-slice sprite ids by
    /// reading the meter's grandchild image elements (format doc §11).
    ///
    /// <para>
    /// Structure the importer produces for each meter (UIElement_Meter):
    /// <code>
    /// meter (Type 7)
    /// ├── back-layer container  (Type 3, lower ReadOrder — drawn first / behind)
    /// │   ├── left-cap  image   (DirectState "" → File = back-left sprite)
    /// │   ├── center    image   (DirectState "" → File = back-tile sprite)
    /// │   └── right-cap image   (DirectState "" → File = back-right sprite)
    /// ├── front-layer container (Type 3, higher ReadOrder — drawn on top)
    /// │   ├── left-cap  image   (→ front-left sprite)
    /// │   ├── center    image   (→ front-tile sprite)
    /// │   ├── right-cap image   (→ front-right sprite)
    /// │   └── expand overlay    (named "ShowDetail"/"HideDetail" only — NO DirectState — IGNORED)
    /// └── text label (Type 0)   (IGNORED — Fill/Label providers bound by VitalsController in Task 6)
    /// </code>
    /// </para>
    ///
    /// <para>
    /// <see cref="UiMeter.Fill"/> and <see cref="UiMeter.Label"/> are NOT set here.
    /// They are bound to the live stat providers in Task 6 (VitalsController).
    /// </para>
    /// </summary>
    private static UiMeter BuildMeter(ElementInfo info,
        Func<uint, (uint, int, int)> resolve, UiDatFont? datFont)
    {
        var m = new UiMeter
        {
            SpriteResolve = resolve,
            DatFont       = datFont,
        };

        // The two 3-slice containers are Type-3 children of the meter element.
        // ReadOrder determines draw order: the back track has a LOWER ReadOrder
        // (drawn first, behind the fill), the front has a HIGHER ReadOrder (on top).
        var containers = info.Children
            .Where(c => c.Type == 3)
            .OrderBy(c => c.ReadOrder)
            .ToList();

        if (containers.Count >= 1)
        {
            var (l, t, r) = SliceIds(containers[0]);
            m.BackLeft  = l;
            m.BackTile  = t;
            m.BackRight = r;
        }

        if (containers.Count >= 2)
        {
            var (l, t, r) = SliceIds(containers[1]);
            m.FrontLeft  = l;
            m.FrontTile  = t;
            m.FrontRight = r;
        }

        return m;
    }

    /// <summary>
    /// Returns the (left, tile, right) sprite ids for a 3-slice container,
    /// extracting them from the container's image children that carry a DirectState
    /// ("" key) with a non-zero file id, ordered left-to-right by their X position.
    ///
    /// <para>
    /// Children that carry ONLY named states (e.g. the expand-detail overlay with
    /// "ShowDetail"/"HideDetail" entries but no "" key) are excluded automatically
    /// because <see cref="Dictionary{TKey,TValue}.TryGetValue"/> for "" returns
    /// false.
    /// </para>
    /// </summary>
    private static (uint left, uint tile, uint right) SliceIds(ElementInfo container)
    {
        // Only children that have a non-zero DirectState image are slice candidates.
        // The expand-detail overlay has NO DirectState entry, so it's excluded here.
        var slices = container.Children
            .Where(c => c.StateMedia.TryGetValue("", out var med) && med.File != 0)
            .OrderBy(c => c.X)
            .ToList();

        static uint File(ElementInfo e)
            => e.StateMedia.TryGetValue("", out var med) ? med.File : 0u;

        uint left  = slices.Count > 0 ? File(slices[0]) : 0u;
        uint tile  = slices.Count > 1 ? File(slices[1]) : 0u;
        uint right = slices.Count > 2 ? File(slices[2]) : 0u;

        return (left, tile, right);
    }
}