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);

    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)
    {
        ctx.DrawRect(0, 0, Width, Height, BgColor);

        float? pct = Fill();
        if (pct is float p)
        {
            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);
        }
    }
}