using System;
using System.Numerics;
using AcDream.App.UI.Layout;

namespace AcDream.App.UI;

/// <summary>
/// Retail <c>UIElement_Resizebar</c> (element class 9,
/// <c>UIElement_Resizebar::Register @0x0046B920</c> registers class 9 with the
/// LayoutDesc element factory). A leaf grip authored at exactly one edge or
/// corner of a window; retail authors 4 edge grips + 4 corner grips per
/// resizable window (main chat: <c>0x1000069B</c>-<c>0x100006A2</c>, minus the
/// straight top strip which is a retail <c>UIElement_Dragbar</c> move handle
/// instead — see the class doc on <see cref="AcDream.App.UI.Layout.DatWidgetFactory"/>
/// and <c>docs/research/2026-08-09-chat-retail-window-shell.md</c> §2.1/§2.3).
///
/// <para>
/// <c>UIElement_Resizebar::StartMouseResizing @0x0046B7E0</c> reads four BOOL
/// attributes off the element — <c>0x2A</c>=bottom, <c>0x2B</c>=left,
/// <c>0x2C</c>=right, <c>0x2D</c>=top — and combines them into a
/// <c>BorderLocation</c> (<c>acclient.h:4327</c>). <see cref="DecodeBorderLocation"/>
/// is a verbatim port of that branch order. acdream's engine expresses resize
/// direction as an edge-flag bitmask (<see cref="ResizeEdges"/>) rather than
/// retail's nine-case enum; <see cref="Edges"/> is the lossless projection —
/// every <see cref="Border"/> value maps to exactly one <see cref="ResizeEdges"/>
/// combination and back.
/// </para>
///
/// <para>
/// A grip is a small (5px) leaf with no children; it exists primarily as a
/// precise hit region, but it IS authored with real border/corner media (the
/// <c>0x06006129</c>-family sprites — CH6a/b REJECT-review BLOCKER 1,
/// <c>docs/research/2026-08-10-ch6ab-review-findings.md</c>: every one of the
/// seven live grips on the main chat window carries a non-zero DirectState
/// sprite, and drawing nothing left the window with only its 400×5 top strip
/// visible). A factory-built grip (<see cref="AcDream.App.UI.Layout.DatWidgetFactory.Create"/>,
/// Type 9) therefore draws its own DirectState media exactly like
/// <see cref="AcDream.App.UI.Layout.UiDatElement"/> would; a synthetic grip
/// built with the parameterless constructor (unit tests exercising only the
/// resize-drag behavior) carries no media and draws nothing, matching its
/// prior behavior. <see cref="AcDream.App.UI.UiRoot"/> gives a directly-hit
/// grip's own <see cref="Edges"/> priority over the generic proximity-based
/// <see cref="AcDream.App.UI.UiRoot.HitEdges"/> heuristic, so e.g. the chat
/// window's top-left/top-right CORNER grips resize (including the Y/top axis)
/// while the plain top EDGE strip in between remains a pure move handle.
/// </para>
/// </summary>
public sealed class UiResizeGrip : UiElement
{
    private readonly ElementInfo? _info;
    private readonly Func<uint, (uint tex, int w, int h)>? _resolve;

    /// <summary>Synthetic grip with no authored media — used by unit tests that
    /// exercise only the resize-drag hit-testing/edge behavior.</summary>
    public UiResizeGrip()
    {
    }

    /// <summary>
    /// Factory-built grip (CH6a/b REJECT-review BLOCKER 1): carries its resolved
    /// <see cref="ElementInfo"/> and sprite resolver so it draws its own
    /// authored DirectState media, the same way every other dat-imported leaf
    /// does. <see cref="UiElement.ClickThrough"/> is left at the base
    /// <see langword="false"/> default — unlike <see cref="UiDatElement"/>'s
    /// decoration default of <see langword="true"/> — because a grip must stay
    /// hit-testable to capture the resize drag.
    /// </summary>
    public UiResizeGrip(ElementInfo info, Func<uint, (uint tex, int w, int h)> resolve)
    {
        _info = info;
        _resolve = resolve;
    }

    /// <summary>
    /// This grip's authored DirectState sprite file id (0 for a synthetic grip,
    /// or an authored grip with no media). Exposed for conformance tests —
    /// BLOCKER 1's regression guard is that every one of the seven live Type-9
    /// grips resolves a non-zero value here.
    /// </summary>
    public uint SpriteFile => _info is not null && _info.StateMedia.TryGetValue("", out var media)
        ? media.File
        : 0u;

    /// <summary>
    /// Draws this grip's own DirectState media exactly like
    /// <see cref="UiDatElement.OnDraw"/> — tiled at native size (Normal), same
    /// blend for Overlay/Alphablend since the sprite shader already
    /// alpha-blends. A synthetic (parameterless-constructed) grip has no
    /// resolver and draws nothing, matching its pre-BLOCKER-1 behavior.
    /// </summary>
    protected override void OnDraw(UiRenderContext ctx)
    {
        if (_resolve is null) return;
        uint file = SpriteFile;
        if (file == 0u) return;
        var (tex, tw, th) = _resolve(file);
        if (tex == 0 || tw == 0 || th == 0) return;
        ctx.DrawSprite(tex, 0, 0, Width, Height, 0, 0, Width / tw, Height / th, Vector4.One);
    }

    /// <summary>Retail <c>BorderLocation</c> (<c>acclient.h:4327</c>):
    /// <c>BORDER_NONE=0, BORDER_UL=1, BORDER_TOP=2, BORDER_UR=3, BORDER_RIGHT=4,
    /// BORDER_LR=5, BORDER_BOTTOM=6, BORDER_LL=7, BORDER_LEFT=8</c>.</summary>
    public enum Border
    {
        None = 0,
        UpperLeft = 1,
        Top = 2,
        UpperRight = 3,
        Right = 4,
        LowerRight = 5,
        Bottom = 6,
        LowerLeft = 7,
        Left = 8,
    }

    /// <summary>Decoded retail BorderLocation for this grip.</summary>
    public Border BorderLocation { get; set; }

    /// <summary>
    /// Exact port of <c>UIElement_Resizebar::StartMouseResizing @0x0046B7E0</c>'s
    /// if/else-if chain (right beats left beats top beats bottom when more than
    /// two bools are set, which retail's authored data never does — corners set
    /// exactly two adjacent bools, edges set exactly one).
    /// </summary>
    public static Border DecodeBorderLocation(bool bottom, bool left, bool right, bool top)
    {
        if (right) return top ? Border.UpperRight : bottom ? Border.LowerRight : Border.Right;
        if (left) return top ? Border.UpperLeft : bottom ? Border.LowerLeft : Border.Left;
        if (top) return Border.Top;
        if (bottom) return Border.Bottom;
        return Border.None;
    }

    /// <summary>The <see cref="ResizeEdges"/> projection <see cref="UiRoot"/>'s resize
    /// drag state machine consumes — a lossless re-encoding of <see cref="BorderLocation"/>.</summary>
    public ResizeEdges Edges => BorderLocation switch
    {
        Border.UpperLeft => ResizeEdges.Left | ResizeEdges.Top,
        Border.Top => ResizeEdges.Top,
        Border.UpperRight => ResizeEdges.Right | ResizeEdges.Top,
        Border.Right => ResizeEdges.Right,
        Border.LowerRight => ResizeEdges.Right | ResizeEdges.Bottom,
        Border.Bottom => ResizeEdges.Bottom,
        Border.LowerLeft => ResizeEdges.Left | ResizeEdges.Bottom,
        Border.Left => ResizeEdges.Left,
        _ => ResizeEdges.None,
    };
}