using Godot;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// Renders a raw pass-1 height field as a HYPSOMETRIC height-gradient PNG.
	///
	/// ═══ ⚠ WHY THIS WRITES A Godot.Image DIRECTLY, AND NOT VIA THE CAPTURE PATH ═══
	///
	/// The reference captured its maps through a SubViewport + a TextureRect whose `_Draw` painted
	/// overlays — roads, town markers, river polylines — and then read the viewport texture back.
	/// That machinery exists to COMPOSITE VECTOR OVERLAYS onto a raster. It also carries a real
	/// cost: it awaits render frames, which is why unattended runs need `xvfb-run` and why
	/// `--headless` HANGS on it.
	///
	/// Phase 1 has no overlays. A heightmap is a raster and nothing else, so it is written
	/// per-pixel into an Image and saved. No viewport, no frame awaits, no display needed.
	///
	/// ⚠ DO NOT REINTRODUCE THE CAPTURE PATH BY HABIT. It becomes correct the moment something
	/// vector needs compositing on top (roads, towns, river centrelines) — and not before.
	///
	/// ═══ THE COLOUR SCHEME ═══
	///
	/// Two ramps meeting at the sea threshold, Hispaniola-style:
	///   below  — bathymetric: deep navy → shallow cyan-ish blue
	///   above  — hypsometric: shore green → lowland green → tan → brown → grey → white peak
	///
	/// ⚠⚠ THERE ARE NO BIOME WORDS HERE AND THERE MUST NOT BE. Nothing in this file knows about
	/// jungle, wasteland, snow or desert. It reads a single float per column and picks a colour on
	/// an elevation ramp. Biomes are a stage-5 CLASSIFICATION of finished shape (D-049 §2, D-056),
	/// and the whole point of the rewrite's seam is that terrain never learns their names.
	/// "White at the top" is snow-COLOURED cartography, not a snow biome.
	///
	/// ⚠ The sea threshold is a VISUALIZATION boundary only. No water is modelled: no water bodies,
	/// no ocean/lake distinction, no flooding. Phase 2 owns all of that.
	/// </summary>
	public static class HeightMapRenderer
	{
		/// <summary>
		/// FIXED ramp anchors in raw height units, deliberately NOT per-run normalized.
		///
		/// Per-run normalization would make every PNG use its full colour range, which looks better
		/// and lies: two seeds, or two rungs of the ablation ladder, would be coloured by different
		/// scales and could not be compared by eye. Fixed anchors mean the same colour is the same
		/// height in every image in a batch. Out-of-range values clamp, and the run prints the true
		/// min/max so saturation is visible as a number rather than guessed from the picture.
		/// </summary>
		public const float RampTopHeight = 1.45f;

		/// <summary>The deepest height the bathymetric ramp resolves. Below this, flat abyss colour.</summary>
		public const float RampBottomHeight = -1.00f;

		// ---- the land ramp: (t in [0,1] above sea) -> colour ----
		private static readonly (float t, Color c)[] LandRamp =
		{
			(0.00f, new Color(0.36f, 0.55f, 0.35f)),  // shore green
			(0.12f, new Color(0.47f, 0.62f, 0.36f)),  // lowland
			(0.30f, new Color(0.72f, 0.71f, 0.44f)),  // dry tan
			(0.50f, new Color(0.72f, 0.57f, 0.36f)),  // brown
			(0.70f, new Color(0.60f, 0.45f, 0.34f)),  // dark brown
			(0.86f, new Color(0.66f, 0.64f, 0.64f)),  // grey rock
			(1.00f, new Color(0.98f, 0.98f, 0.98f)),  // white peak
		};

		// ---- the sea ramp: (t in [0,1], 0 = deepest) -> colour ----
		private static readonly (float t, Color c)[] SeaRamp =
		{
			(0.00f, new Color(0.03f, 0.06f, 0.18f)),  // abyss
			(0.45f, new Color(0.06f, 0.16f, 0.36f)),  // deep
			(0.75f, new Color(0.11f, 0.30f, 0.52f)),  // mid
			(0.92f, new Color(0.20f, 0.47f, 0.66f)),  // shelf
			(1.00f, new Color(0.42f, 0.68f, 0.79f)),  // shallow, at the waterline
		};

		/// <summary>Render and save. Returns the absolute path written.</summary>
		public static string SavePng(Pass1Result result, float seaLevel, string absolutePath)
		{
			int n = result.MapSize;
			var img = Image.CreateEmpty(n, n, false, Image.Format.Rgb8);

			for (int x = 0; x < n; x++)
			{
				for (int y = 0; y < n; y++)
				{
					float h = result.Height[x, y];
					Color c;

					if (h >= seaLevel)
					{
						float t = Mathf.Clamp((h - seaLevel) / (RampTopHeight - seaLevel), 0f, 1f);
						c = Sample(LandRamp, t);
					}
					else
					{
						float t = Mathf.Clamp((h - RampBottomHeight) / (seaLevel - RampBottomHeight), 0f, 1f);
						c = Sample(SeaRamp, t);
					}

					// Image is row-major (x = column, y = row); the height field is [x, y] with y
					// increasing SOUTHWARD, matching the reference's convention. So a larger y is
					// further down the image, and "the southern sinker" sinks the bottom of the PNG.
					img.SetPixel(x, y, c);
				}
			}

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

		private static Color Sample((float t, Color c)[] ramp, float t)
		{
			for (int i = 1; i < ramp.Length; i++)
			{
				if (t <= ramp[i].t)
				{
					float span = ramp[i].t - ramp[i - 1].t;
					float local = span <= 0f ? 0f : (t - ramp[i - 1].t) / span;
					return ramp[i - 1].c.Lerp(ramp[i].c, local);
				}
			}
			return ramp[ramp.Length - 1].c;
		}

		/// <summary>
		/// Dump the raw float height field beside the PNG, little-endian float32, x-major.
		///
		/// Cheap, and it is what makes a future BYTE-LEVEL port-fidelity check possible — the kind
		/// of automatic oracle that lets taste-iteration happen without correctness being judged by
		/// eye. → `Design - Tooling - Iteration and Batching.md`, "build the oracle first".
		/// </summary>
		public static string SaveRaw(Pass1Result result, string absolutePath)
		{
			using var f = FileAccess.Open(absolutePath, FileAccess.ModeFlags.Write);
			if (f == null)
			{
				GD.PrintErr($"[HeightMapRenderer] could not open {absolutePath}: {FileAccess.GetOpenError()}");
				return absolutePath;
			}
			int n = result.MapSize;
			for (int x = 0; x < n; x++)
				for (int y = 0; y < n; y++)
					f.StoreFloat(result.Height[x, y]);
			return absolutePath;
		}
	}
}