using System;
using System.Numerics;

namespace AcDream.App.UI;

/// <summary>
/// Generic scrollbar. Ports retail <c>UIElement_Scrollbar</c>
/// (RegisterElementClass(0xb) @ acclient_2013_pseudo_c.txt:124137);
/// thumb size = trackLen * ThumbRatio (min 8px); step ±1 line.
/// </summary>
/// <remarks>
/// Dat element ids (chat LayoutDesc 0x21000006): track 0x10000012 (X=474 Y=6 W=16 H=68),
/// thumb 0x1000048C. The track is instanced from base layout 0x2100003E which contains
/// the full scrollbar widget with distinct up/down button children:
///   Up button   element 0x10000071 — Y=0,  16×16, Normal sprite 0x06004C69.
///   Down button element 0x10000072 — Y=32, 16×16, Normal sprite 0x06004C6C.
/// Track body sprite: 0x06004C5F (48px tall in the base template; stretched to H=68 in chat).
/// Thumb is a 3-slice: top cap 0x06004C60, middle 0x06004C63, bottom cap 0x06004C66.
/// For Task H wiring: up/down regions occupy the top and bottom ButtonH (16px) of the
/// rendered scrollbar's height; the widget responds to those regions directly via hit
/// comparison in OnEvent without requiring separate child elements.
/// </remarks>
public sealed class UiScrollbar : UiElement
{
    /// <summary>The scroll model this bar reflects + drives (shared with the transcript).</summary>
    public UiScrollable? Model { get; set; }

    /// <summary>
    /// Optional scalar mode used by retail's horizontal stack-split control. When set,
    /// the bar reflects/drives one normalized value rather than a <see cref="UiScrollable"/>.
    /// </summary>
    public float ScalarPosition { get; private set; }
    public Action<float>? ScalarChanged { get; set; }
    public bool Horizontal { get; set; }

    /// <summary>
    /// Optional fill rendered beneath the scalar thumb. Retail's combat power
    /// control is a horizontal scrollbar containing a meter child; the importer
    /// folds that authored child into these properties because scrollbars consume
    /// their DAT children.
    /// </summary>
    public Func<float?> ScalarFill { get; set; } = () => null;
    public uint ScalarFillSprite { get; set; }
    /// <summary>
    /// Optional authored texture beneath the live scalar fill. gmCombatUI's
    /// dark-red interior media comes from element <c>0x100005EF</c>.
    /// </summary>
    public uint ScalarRangeSprite { get; set; }
    public float ScalarRangeLeft { get; set; }
    public float ScalarRangeWidth { get; set; } = float.PositiveInfinity;
    /// <summary>
    /// Authored layout policy for a consumed range child. This preserves the
    /// child's own DAT edge modes even though the scrollbar draws it procedurally.
    /// </summary>
    public UiLayoutPolicy? ScalarRangeLayoutPolicy { get; set; }
    /// <summary>
    /// Draw the scalar meter from the power end (right) toward the speed end
    /// (left). This is the authored gmCombatUI power meter direction.
    /// </summary>
    public bool ScalarFillFromRight { get; set; }

    /// <summary>Programmatically set retail scrollbar attribute 0x86 without broadcasting.</summary>
    public void SetScalarPosition(float position)
        => ScalarPosition = Math.Clamp(position, 0f, 1f);

    /// <summary>RenderSurface id → (GL tex, w, h). 0 id = skip.</summary>
    public Func<uint, (uint tex, int w, int h)>? SpriteResolve { get; set; }

    /// <summary>Track background sprite id (0x06004C5F from layout 0x2100003E element 0x10000455).</summary>
    public uint TrackSprite { get; set; }

    /// <summary>Thumb 3-slice MIDDLE tile sprite id (0x06004C63), tiled between the caps.</summary>
    public uint ThumbSprite { get; set; }

    /// <summary>Thumb 3-slice TOP cap sprite id (0x06004C60, 3px tall).</summary>
    public uint ThumbTopSprite { get; set; }

    /// <summary>Thumb 3-slice BOTTOM cap sprite id (0x06004C66, 3px tall).</summary>
    public uint ThumbBotSprite { get; set; }

    /// <summary>Up-arrow button sprite id (0x06004C69 Normal state, element 0x10000071).</summary>
    public uint UpSprite { get; set; }

    /// <summary>Down-arrow button sprite id (0x06004C6C Normal state, element 0x10000072).</summary>
    public uint DownSprite { get; set; }

    /// <summary>Retail attribute 0x89 floor: minimum thumb height in pixels.</summary>
    private const float MinThumb = 8f;

    /// <summary>Thumb cap height (native sprite height from base layout 0x2100003E).</summary>
    private const float CapH = 3f;

    /// <summary>Up/down button height in pixels. Matches element height 16px from
    /// the up/down button children in base layout 0x2100003E.</summary>
    private const float ButtonH = 16f;

    private bool _draggingThumb;
    private float _dragOffsetY;
    private float _dragOffsetX;

    public UiScrollbar() { CapturesPointerDrag = true; }

    /// <summary>The scrollbar draws its own track/thumb/arrows; its dat up/down button
    /// children are reproduced procedurally, so the importer must not build them.</summary>
    public override bool ConsumesDatChildren => true;

    /// <summary>
    /// Computes the thumb rectangle (local y origin and height) within the track area
    /// between the two end buttons. Ports retail <c>UIElement_Scrollbar::UpdateLayout
    /// @0x4710d0</c>: thumb height = max(MinThumb, trackLen * ThumbRatio); thumb top
    /// offset = trackTop + (trackLen - thumbH) * PositionRatio.
    /// </summary>
    /// <param name="m">The scroll model.</param>
    /// <param name="trackTop">Y of the top of the usable track area (below up-button).</param>
    /// <param name="trackLen">Pixel length of the usable track area (between up and down buttons).</param>
    /// <returns>Local Y of the thumb's top edge, and its pixel height.</returns>
    public static (float y, float h) ThumbRect(UiScrollable m, float trackTop, float trackLen)
    {
        float h = MathF.Max(MinThumb, trackLen * m.ThumbRatio);
        float travel = trackLen - h;
        float y = trackTop + travel * m.PositionRatio;
        return (y, h);
    }

    /// <summary>Returns the clipped scalar-meter span in local pixels.</summary>
    public static (float x, float width) ScalarFillRect(
        float totalWidth, float fill, bool fromRight)
        => ScalarFillRect(0f, totalWidth, fill, fromRight);

    /// <summary>Returns a clipped scalar-meter span inside an authored sub-range.</summary>
    public static (float x, float width) ScalarFillRect(
        float rangeLeft, float rangeWidth, float fill, bool fromRight)
    {
        float safeWidth = MathF.Max(0f, rangeWidth);
        float visibleWidth = safeWidth * Math.Clamp(fill, 0f, 1f);
        return (fromRight ? rangeLeft + safeWidth - visibleWidth : rangeLeft, visibleWidth);
    }

    protected override void OnDraw(UiRenderContext ctx)
    {
        if (SpriteResolve is not { } resolve) return;
        if (Horizontal)
        {
            DrawTiled(ctx, resolve, TrackSprite, 0f, 0f, Width, Height);
            (float rangeLeft, float rangeWidth) = ScalarRangeRect();
            if (ScalarRangeSprite != 0)
                DrawTiled(ctx, resolve, ScalarRangeSprite,
                    rangeLeft, 0f, rangeWidth, Height);
            float thumbWidth = ScalarThumbWidth(resolve);
            if (ScalarFill() is float fill && ScalarFillSprite != 0)
            {
                // The authored charge child spans the entire scrollbar; it does
                // not share the dark range child's inset geometry.
                var (fillX, visibleWidth) = ScalarFillRect(
                    Width, fill, ScalarFillFromRight);
                DrawTiledClipped(ctx, resolve, ScalarFillSprite,
                    0f, fillX, visibleWidth, Height);
            }
            float travel = MathF.Max(0f, Width - thumbWidth);
            float x = travel * ScalarPosition;
            DrawSprite(ctx, resolve, ThumbSprite, x, 0f, thumbWidth, Height);
            return;
        }

        if (Model is not { } m) return;

        // Track background — TILED vertically (retail DrawMode=Normal). The native track
        // sprite (~16×32) repeats to fill the element height instead of stretch-distorting.
        DrawTiled(ctx, resolve, TrackSprite, 0f, 0f, Width, Height);

        // Decrement/up button — top ButtonH rows (inherited element 0x10000071).
        DrawSprite(ctx, resolve, UpSprite, 0f, 0f, Width, ButtonH);

        // Increment/down button — bottom ButtonH rows (inherited element 0x10000072).
        DrawSprite(ctx, resolve, DownSprite, 0f, Height - ButtonH, Width, ButtonH);

        // Thumb — only when content overflows the view. Retail 3-slice: top cap +
        // tiled middle + bottom cap (base layout 0x2100003E thumb sub-elements
        // 0x10000364/65/66). Falls back to a single tiled middle if the caps are unset
        // or the thumb is too short to hold both caps.
        if (m.HasOverflow)
        {
            float trackTop = ButtonH;
            float trackLen = Height - 2f * ButtonH;
            var (ty, th) = ThumbRect(m, trackTop, trackLen);
            if (ThumbTopSprite != 0 && ThumbBotSprite != 0 && th >= 2f * CapH)
            {
                DrawSprite(ctx, resolve, ThumbTopSprite, 0f, ty, Width, CapH);
                DrawTiled(ctx, resolve, ThumbSprite, 0f, ty + CapH, Width, th - 2f * CapH);
                DrawSprite(ctx, resolve, ThumbBotSprite, 0f, ty + th - CapH, Width, CapH);
            }
            else
            {
                DrawTiled(ctx, resolve, ThumbSprite, 0f, ty, Width, th);
            }
        }
    }

    /// <summary>Draw a sprite stretched 1:1 to the dest rect.</summary>
    private void DrawSprite(UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve,
        uint id, float x, float y, float w, float h)
    {
        if (id == 0 || w <= 0f || h <= 0f) return;
        var (tex, _, _) = resolve(id);
        if (tex == 0) return;
        ctx.DrawSprite(tex, x, y, w, h, 0f, 0f, 1f, 1f, Vector4.One);
    }

    /// <summary>Draw a sprite TILED to fill the dest rect (UV-repeat at native size on
    /// both axes — the UI texture is GL_REPEAT-wrapped). A native-width axis gives 1:1.</summary>
    private void DrawTiled(UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve,
        uint id, float x, float y, float w, float h)
    {
        if (id == 0 || w <= 0f || h <= 0f) return;
        var (tex, tw, th) = resolve(id);
        if (tex == 0 || tw == 0 || th == 0) return;
        ctx.DrawSprite(tex, x, y, w, h, 0f, 0f, w / tw, h / th, Vector4.One);
    }

    /// <summary>
    /// Draws a clipped portion of a tiled range without restarting the texture
    /// phase at the clip edge. This mirrors retail meter child clipping.
    /// </summary>
    private void DrawTiledClipped(
        UiRenderContext ctx,
        Func<uint, (uint tex, int w, int h)> resolve,
        uint id,
        float rangeLeft,
        float x,
        float w,
        float h)
    {
        if (id == 0 || w <= 0f || h <= 0f) return;
        var (tex, tw, th) = resolve(id);
        if (tex == 0 || tw == 0 || th == 0) return;
        float u0 = (x - rangeLeft) / tw;
        float u1 = u0 + w / tw;
        ctx.DrawSprite(tex, x, 0f, w, h, u0, 0f, u1, h / th, Vector4.One);
    }

    internal (float left, float width) ScalarRangeRect()
    {
        float configuredLeft = ScalarRangeLeft;
        float configuredWidth = ScalarRangeWidth;
        if (ScalarRangeLayoutPolicy is { } policy)
        {
            UiPixelRect currentParent = UiPixelRect.FromPositionAndSize(
                0, 0, (int)Width, (int)Height);
            UiPixelRect range = policy.Apply(policy.OriginalChild, currentParent);
            configuredLeft = range.X0;
            configuredWidth = range.Width;
        }
        float left = Math.Clamp(configuredLeft, 0f, Width);
        float requestedWidth = float.IsPositiveInfinity(configuredWidth)
            ? Width - left
            : MathF.Max(0f, configuredWidth);
        float width = Math.Clamp(requestedWidth, 0f, Width - left);
        return (left, width);
    }

    public override bool OnEvent(in UiEvent e)
    {
        if (Horizontal && ScalarChanged is not null)
            return OnScalarEvent(e);

        if (Model is not { } m) return false;

        switch (e.Type)
        {
            case UiEventType.MouseDown:
            {
                // e.Data1 = local X, e.Data2 = local Y (int pixel coords, see UiRoot hit dispatch).
                float ly = e.Data2;

                // Up-button region: top ButtonH rows.
                if (ly <= ButtonH) { m.ScrollByLines(-1); return true; }

                // Down-button region: bottom ButtonH rows.
                if (ly >= Height - ButtonH) { m.ScrollByLines(1); return true; }

                // Track interior: start a thumb drag or page-scroll.
                float trackTop = ButtonH;
                float trackLen = Height - 2f * ButtonH;
                var (ty, th) = ThumbRect(m, trackTop, trackLen);

                if (ly >= ty && ly <= ty + th)
                {
                    // Clicked inside the thumb — begin drag with offset from thumb top.
                    _draggingThumb = true;
                    _dragOffsetY = ly - ty;
                }
                else
                {
                    // Clicked above or below thumb — page scroll (HandleButtonClick page case).
                    m.ScrollByPage(ly < ty ? -1 : 1);
                }
                return true;
            }

            case UiEventType.MouseMove when _draggingThumb:
            {
                // Map current local Y (minus drag offset from thumb top) back to a
                // position ratio across the available travel distance.
                float trackTop = ButtonH;
                float trackLen = Height - 2f * ButtonH;
                float thumbH = MathF.Max(MinThumb, trackLen * m.ThumbRatio);
                float travel = MathF.Max(1f, trackLen - thumbH);
                float newRatio = ((float)e.Data2 - _dragOffsetY - trackTop) / travel;
                m.SetPositionRatio(newRatio);
                return true;
            }

            case UiEventType.MouseUp:
                _draggingThumb = false;
                return true;
        }

        return false;
    }

    private bool OnScalarEvent(in UiEvent e)
    {
        switch (e.Type)
        {
            case UiEventType.MouseDown:
            {
                float thumbWidth = ScalarThumbWidth(SpriteResolve);
                float travel = MathF.Max(1f, Width - thumbWidth);
                float thumbX = travel * ScalarPosition;
                float x = e.Data1;
                if (x >= thumbX && x <= thumbX + thumbWidth)
                {
                    _dragOffsetX = x - thumbX;
                }
                else
                {
                    _dragOffsetX = thumbWidth * 0.5f;
                    ChangeScalarPosition((x - _dragOffsetX) / travel);
                }
                _draggingThumb = true;
                return true;
            }

            case UiEventType.MouseMove when _draggingThumb:
            {
                float thumbWidth = ScalarThumbWidth(SpriteResolve);
                float travel = MathF.Max(1f, Width - thumbWidth);
                ChangeScalarPosition(((float)e.Data1 - _dragOffsetX) / travel);
                return true;
            }

            case UiEventType.MouseUp:
                _draggingThumb = false;
                return true;
        }

        return false;
    }

    private float ScalarThumbWidth(Func<uint, (uint tex, int w, int h)>? resolve)
    {
        if (resolve is not null && ThumbSprite != 0)
        {
            var (_, width, _) = resolve(ThumbSprite);
            if (width > 0) return MathF.Min(width, Width);
        }
        return MathF.Min(16f, Width);
    }

    private void ChangeScalarPosition(float position)
    {
        SetScalarPosition(position);
        ScalarChanged?.Invoke(ScalarPosition);
    }
}