namespace MrGameEng.WorldGen;

/// <summary>
/// A dense row-major grid of height values. Plain data with indexed access — fill it from a
/// <see cref="HeightmapGenerator"/> and read it from worldgen code. Values are arbitrary until
/// <see cref="Normalize"/> rescales them into <c>[0, 1]</c>.
/// </summary>
public sealed class Heightmap
{
    /// <summary>Grid width in cells.</summary>
    public int Width { get; }

    /// <summary>Grid height in cells.</summary>
    public int Height { get; }

    /// <summary>Row-major values, length <see cref="Width"/>×<see cref="Height"/>.</summary>
    public float[] Values { get; }

    /// <summary>Creates an all-zero map of the given size.</summary>
    public Heightmap(int width, int height)
    {
        Width = width;
        Height = height;
        Values = new float[width * height];
    }

    /// <summary>Height at (<paramref name="x"/>, <paramref name="y"/>).</summary>
    public float this[int x, int y]
    {
        get => Values[y * Width + x];
        set => Values[y * Width + x] = value;
    }

    /// <summary>Rescales all values into <c>[0, 1]</c> by min–max; a flat map becomes all zeros.</summary>
    public void Normalize()
    {
        var min = float.MaxValue;
        var max = float.MinValue;
        foreach (var v in Values)
        {
            if (v < min)
            {
                min = v;
            }

            if (v > max)
            {
                max = v;
            }
        }

        var range = max - min;
        if (range <= float.Epsilon)
        {
            Array.Clear(Values);
            return;
        }

        for (var i = 0; i < Values.Length; i++)
        {
            Values[i] = (Values[i] - min) / range;
        }
    }
}