using Godot;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// A plain grayscale render: normalize a float field to its own [min, max] and map to
	/// [black, white]. No colour, no hillshade, no interpretation.
	///
	/// ═══ WHY THIS EXISTS ═══
	///
	/// Because you cannot judge noise through a palette. A hypsometric ramp and a hillshade are both
	/// opinionated transforms — one bends the value distribution onto chosen stops, the other adds
	/// shape the data does not contain. Both are the right thing for a map and the wrong thing for
	/// asking "is the noise itself good?". This mode answers that question and no other.
	///
	/// ⚠ THIS IS THE ONE PLACE PER-IMAGE NORMALIZATION IS CORRECT. Everywhere else the palette
	/// anchors are fixed so images can be compared. Here the point is to see the full structure of
	/// ONE field at full contrast, so it is normalized to its own range — and the range used is
	/// printed and written into the INDEX, so a shade reads back to a height.
	/// </summary>
	public static class GrayscaleRenderer
	{
		/// <summary>Render to grayscale. Returns the (min, max) used for the normalization.</summary>
		public static (float min, float max) SavePng(float[,] field, int mapSize, string absolutePath)
		{
			float min = float.MaxValue, max = float.MinValue;
			for (int x = 0; x < mapSize; x++)
				for (int y = 0; y < mapSize; y++)
				{
					float v = field[x, y];
					if (v < min) min = v;
					if (v > max) max = v;
				}

			float span = max - min;
			float inv = span > 1e-9f ? 1f / span : 0f;

			var img = Image.CreateEmpty(mapSize, mapSize, false, Image.Format.Rgb8);
			for (int x = 0; x < mapSize; x++)
				for (int y = 0; y < mapSize; y++)
				{
					float g = (field[x, y] - min) * inv;
					img.SetPixel(x, y, new Color(g, g, g));
				}

			Error err = img.SavePng(absolutePath);
			if (err != Error.Ok) GD.PrintErr($"[GrayscaleRenderer] SavePng failed ({err}) for {absolutePath}");
			return (min, max);
		}
	}
}