using System.Numerics;

namespace AcDream.App.UI;

/// <summary>
/// A horizontal vital bar (retail HP/Stamina/Mana style): a background rect, a
/// partial-width solid fill, and an optional centered "current/max" numeric
/// overlay. <see cref="Fill"/> returns 0..1 (null = no data → empty bar);
/// <see cref="Label"/> returns the overlay text (null = no number).
///
/// <para>
/// Solid-color fill + debug font for Spec 1. The retail gradient bar sprite
/// (glassy center highlight) and the retail dat font are a later polish pass —
/// retail's vitals are bars exactly like this, just sprited.
/// </para>
/// </summary>
public sealed class UiMeter : UiElement
{
    /// <summary>Fill fraction provider; a null result draws an empty bar.</summary>
    public Func<float?> Fill { get; set; } = () => 0f;
    /// <summary>Centered overlay text provider (e.g. "291/291"); null = none.</summary>
    public Func<string?> Label { get; set; } = () => null;
    public Vector4 BarColor { get; set; } = new(1f, 0f, 0f, 1f);
    public Vector4 BgColor { get; set; } = new(0f, 0f, 0f, 0.5f);
    public Vector4 LabelColor { get; set; } = new(1f, 1f, 1f, 1f);

    /// <summary>Resolver from a RenderSurface DataId to (GL handle, w, h). When set
    /// with the 9-slice ids below, the bar draws the retail sprites instead of solid color.</summary>
    public Func<uint, (uint tex, int w, int h)>? SpriteResolve { get; set; }

    // Retail vital bars are a horizontal 3-slice: a fixed-width bevelled left-cap,
    // a stretched gradient middle, and a fixed-width right-cap. The "back" slice is
    // the empty track (drawn full width); the "front" slice is the coloured fill
    // (drawn from the left, grown to the fill fraction — the track owns the right
    // end, so the fill omits its own right-cap). Ids come from the vitals LayoutDesc
    // (0x21000014) via tools/dump-vitals-bars; 0 = none.
    /// <summary>Empty-track left-cap RenderSurface id.</summary>
    public uint BackLeft { get; set; }
    /// <summary>Empty-track middle (stretched gradient) RenderSurface id.</summary>
    public uint BackTile { get; set; }
    /// <summary>Empty-track right-cap RenderSurface id.</summary>
    public uint BackRight { get; set; }
    /// <summary>Coloured-fill left-cap RenderSurface id.</summary>
    public uint FrontLeft { get; set; }
    /// <summary>Coloured-fill middle (stretched gradient) RenderSurface id.</summary>
    public uint FrontTile { get; set; }
    /// <summary>Coloured-fill right-cap RenderSurface id.</summary>
    public uint FrontRight { get; set; }

    public UiMeter() { ClickThrough = true; }

    /// <summary>Clamp <paramref name="pct"/> to [0,1] and return the fill rect
    /// (local px) for a bar of <paramref name="w"/> x <paramref name="h"/>.</summary>
    public static (float x, float y, float w, float h) ComputeFillRect(
        float pct, float w, float h)
    {
        if (pct < 0f) pct = 0f;
        if (pct > 1f) pct = 1f;
        return (0f, 0f, w * pct, h);
    }

    protected override void OnDraw(UiRenderContext ctx)
    {
        float? pct = Fill();
        float p = pct is float pf ? (pf < 0f ? 0f : pf > 1f ? 1f : pf) : 0f;

        if (SpriteResolve is { } resolve && (BackLeft != 0 || BackTile != 0 || FrontTile != 0))
        {
            // Empty track: full-width 3-slice (left-cap + stretched gradient + right-cap).
            DrawHBar(ctx, resolve, BackLeft, BackTile, BackRight, 0, 0, Width, Height, withRightCap: true);
            // Coloured fill: grows from the left to the value, no right-cap of its own.
            if (pct is not null && p > 0f)
                DrawHBar(ctx, resolve, FrontLeft, FrontTile, FrontRight, 0, 0, Width * p, Height, withRightCap: false);
        }
        else
        {
            // Placeholder solid-color fallback.
            ctx.DrawRect(0, 0, Width, Height, BgColor);
            if (pct is not null && p > 0f)
            {
                var (fx, fy, fw, fh) = ComputeFillRect(p, Width, Height);
                if (fw > 0f) ctx.DrawRect(fx, fy, fw, fh, BarColor);
            }
        }

        string? label = Label();
        if (!string.IsNullOrEmpty(label) && ctx.DefaultFont is { } font)
        {
            float tw = font.MeasureWidth(label);
            float tx = (Width - tw) * 0.5f;
            float ty = (Height - font.LineHeight) * 0.5f;
            ctx.DrawString(label, tx, ty, LabelColor);
        }
    }

    /// <summary>
    /// Draws a horizontal 3-slice into <paramref name="w"/> x <paramref name="h"/> at
    /// (<paramref name="x"/>,<paramref name="y"/>): a native-width left-cap, a stretched
    /// middle, and (when <paramref name="withRightCap"/>) a native-width right-cap. Caps
    /// are clamped so a narrow bar never overdraws. A 0 id skips that slice.
    /// </summary>
    private static void DrawHBar(
        UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve,
        uint leftId, uint tileId, uint rightId,
        float x, float y, float w, float h, bool withRightCap)
    {
        if (w <= 0f) return;
        var (lt, lw, _) = resolve(leftId);
        var (tt, _,  _) = resolve(tileId);
        var (rt, rw, _) = resolve(rightId);

        float rcap = withRightCap && rt != 0 ? MathF.Min(rw, w) : 0f;
        float lcap = lt != 0 ? MathF.Min(lw, w - rcap) : 0f;

        if (lt != 0 && lcap > 0f)
            ctx.DrawSprite(lt, x, y, lcap, h, 0, 0, 1, 1, Vector4.One);

        float midX = x + lcap;
        float midW = w - lcap - rcap;
        if (tt != 0 && midW > 0f)
            ctx.DrawSprite(tt, midX, y, midW, h, 0, 0, 1, 1, Vector4.One);

        if (rcap > 0f)
            ctx.DrawSprite(rt, x + w - rcap, y, rcap, h, 0, 0, 1, 1, Vector4.One);
    }
}