using Godot;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// ⭐ THE BEAUTY RENDER — hypsometric tint blended with shaded relief. The Phase-1 finish line.
	///
	/// ⚠ PRESENTATION ONLY (→ `Design - Rendering - Roughness Is Presentation.md`). This file
	/// changes how height is SHOWN, never how it is MADE. It cannot: it is handed a height field
	/// and has no way to produce one.
	///
	/// ═══ ⚠ WHY THIS WRITES A Godot.Image DIRECTLY, AND NOT VIA THE CAPTURE PATH ═══
	///
	/// The reference captured maps through a SubViewport + a TextureRect._Draw, because it
	/// composited VECTOR OVERLAYS — roads, town markers, river polylines — onto the raster. That
	/// machinery awaits render frames, which is why unattended runs need `xvfb-run` and why
	/// `--headless` hangs on it. Phase 1 has no overlays, so this is a raster and nothing else.
	/// **Do not reintroduce the capture path by habit** — it becomes correct the moment something
	/// vector needs compositing, and not before.
	///
	/// ═══ THE BLEND — the difference between a colour ramp and a map you would frame ═══
	///
	/// The naive composite is <c>tint × hillshade</c>. It looks wrong, for a reason worth stating:
	/// hillshade on FLAT ground is <c>sin(altitude)</c> ≈ 0.71 at a 45° sun, so a plain multiply
	/// darkens the entire map by 29% before any slope is involved, and the carefully-placed
	/// hypsometric tints are never actually seen.
	///
	/// So the shade is NORMALIZED BY ITS FLAT-GROUND VALUE first:
	///
	///     lum    = shade / sin(altitude)          → 1.0 on flat ground, &lt;1 shadowed, &gt;1 lit
	///     factor = lerp(1, lum, strength)         → strength dials relief without touching hue
	///
	/// Flat terrain therefore keeps its true tint, and ONLY SLOPE moves the colour. Then the two
	/// sides are treated differently, because multiplying both ways blows the highlights to paper:
	///
	///     factor ≤ 1  →  MULTIPLY  : c = tint × factor            (shadows deepen, hue held)
	///     factor &gt; 1  →  SCREEN   : c = tint + (1−tint)×(factor−1)×gain   (lit slopes lift toward
	///                                                              white, gently, never clipping)
	///
	/// That asymmetry is the whole trick. Shadows want to keep the tint's hue; highlights want to
	/// desaturate toward sunlight, exactly as they do on a printed relief plate.
	///
	/// ⚠ NO BIOME WORDS. Continuous height ramp + slope. Nothing here classifies anything.
	/// </summary>
	public static class ReliefRenderer
	{
		/// <summary>Render a height field to a shaded-relief PNG. Returns the path written.</summary>
		public static string SavePng(float[,] height, int mapSize, LookConfig look, string absolutePath)
		{
			Image img = Render(height, mapSize, look);
			Error err = img.SavePng(absolutePath);
			if (err != Error.Ok) GD.PrintErr($"[ReliefRenderer] SavePng failed ({err}) for {absolutePath}");
			return absolutePath;
		}

		/// <summary>
		/// Render to an in-memory image, so a caller can composite onto it (a legend, say) before
		/// saving. ⚠ With <c>HillshadeStrength = 0</c> this is a FLAT hypsometric tint and no relief
		/// at all — which is the intended hero render, not a degenerate case.
		/// </summary>
		public static Image Render(float[,] height, int mapSize, LookConfig look)
		{
			var img = Image.CreateEmpty(mapSize, mapSize, false, Image.Format.Rgb8);

			var (lx, ly, lz) = Hillshade.LightVector(look.LightAzimuth, look.LightAltitude);
			float neutral = Hillshade.Neutral(look.LightAltitude);
			float invNeutral = neutral > 0.0001f ? 1f / neutral : 1f;

			for (int x = 0; x < mapSize; x++)
			{
				for (int y = 0; y < mapSize; y++)
				{
					float h = height[x, y];
					Color tint = ReliefPalette.Tint(look.Palette, h, look.SeaLevel);

					float shade = Hillshade.At(height, mapSize, x, y, look.ZExaggeration, lx, ly, lz);

					// Relief is dialled back below sea, AND FADED OUT WITH DEPTH.
					//
					// ⚠ The depth fade is not just taste. The deep floor is dominated by the
					// TRENCH — a synthetic additive wall (falloff += (dist-0.90)*15) whose gradient
					// is ~1.5x the p99 LAND gradient. Shading it faithfully draws a bright rim
					// around the whole map and lights up the abyss with base-noise mottle: relief
					// on terrain that was never meant to be looked at. Fading with depth puts the
					// relief where the bathymetry is real — the near-shore shelf — and lets the
					// abyss lie flat, which is also the cartographic convention.
					//
					// Uses the same compressed depth index as the palette, so the tint and the
					// shading fade together instead of drifting apart.
					float strength;
					if (h >= look.SeaLevel)
					{
						strength = look.HillshadeStrength;
					}
					else
					{
						float depth = look.SeaLevel - h;
						float dt = depth / (depth + ReliefPalette.SeaCompression);   // 0 shore → 1 abyss
						strength = look.HillshadeStrength * look.SeaHillshadeFactor * (1f - dt);
					}

					float lum = shade * invNeutral;
					float factor = 1f + (lum - 1f) * strength;

					Color c;
					if (factor <= 1f)
					{
						c = new Color(tint.R * factor, tint.G * factor, tint.B * factor);
					}
					else
					{
						float lift = (factor - 1f) * look.HighlightGain;
						c = new Color(
							tint.R + (1f - tint.R) * lift,
							tint.G + (1f - tint.G) * lift,
							tint.B + (1f - tint.B) * lift);
					}

					img.SetPixel(x, y, new Color(
						Mathf.Clamp(c.R, 0f, 1f), Mathf.Clamp(c.G, 0f, 1f), Mathf.Clamp(c.B, 0f, 1f)));
				}
			}

			return img;
		}
	}
}