using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using Godot;
using IslaApocalypse.Core;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// ⭐ THE FAITHFUL-CURVE BASELINE BATCH (chat2/01) — the control the reshape will be judged
	/// against, plus the instrument that decides what the reshape should be.
	///
	/// ═══ WHAT IT DOES, IN ORDER ═══
	///
	///   1. CALIBRATE — pool the LAND distribution across several seeds and take
	///      P60/73/83/88/96/99. Those quantiles ARE the curve's knots, which is what makes the band
	///      shares 60/13/10/5/8/3/1 exact by construction. Reports them against the reference's
	///      shipped literals: that delta is the port-fidelity evidence.
	///   2. VARIANTS — per seed, `curve_off` (the control) and `curve_on` (the faithful baseline).
	///      Grayscale + raw `.f32` + relief, because a pretty render alone cannot be argued with.
	///   3. HISTOGRAMS — raw and shaped land distributions for the showpiece seed, with the knots and
	///      the output anchors overlaid, plus the per-band mass table.
	///   4. ORACLE — the four automatic checks, run before anything is looked at.
	///   5. SHOWPIECE — one render at a larger profile for the judging plate.
	///
	/// ═══ ⚠ CALIBRATE SMALL, CONFIRM BIG ═══
	///
	/// Knots are measured at the iteration profile (2K) and used at every profile. That rests on the
	/// land distribution's SHAPE being scale-invariant — which Phase 1 established by construction
	/// (every frequency and distance is a fraction of MapSize). The tool does not take that on trust:
	/// the showpiece re-measures its own quantiles and reports the delta, so the assumption is
	/// evidence rather than a footnote.
	///
	/// ═══ RUNNING IT ═══
	///
	///   xvfb-run -a Godot_v4.7.2-stable_mono_linux.x86_64 \
	///     --path ~/celerNexus/islaApocalypse-v2 res://Tools/Scenes/CurveBaselineTool.tscn
	///
	/// (`--headless` also works — this tool awaits no render frames — but `xvfb-run` is correct in
	/// both cases and costs nothing. → Tools/README.md §1.)
	///
	///   ISLA_TASK           authoring task number         (default 1)
	///   ISLA_BATCH          descriptor, NO prefix         (default "curve_baseline")
	///   ISLA_MAPSIZE        calibration/variant profile   (default 2048)
	///   ISLA_SEEDS          comma-separated positive      (default: the 6 pinned below)
	///   ISLA_SHOWPIECE_SIZE larger confirmation profile   (default 8192)
	///   ISLA_SHOWPIECE      "0" to skip the big render
	///   ISLA_VARIANTS       "0" to skip the per-seed variants (calibration-only probe)
	///   ISLA_PHASE1_SOURCE  batch holding Phase-1 .f32    (default "02_pass1_port")
	///   ISLA_SKIP_RAW       "1" to skip the .f32 dumps
	/// </summary>
	public partial class CurveBaselineTool : Node
	{
		/// <summary>
		/// PINNED POSITIVE SEEDS — the four Phase-1 seeds plus two, for a six-seed calibration pool.
		/// Pinned, not random: a calibration you cannot reproduce is a magic number with a good story.
		/// </summary>
		private static readonly int[] DefaultSeeds = { 1063685222, 20260819, 777001, 424242, 90210, 31337 };

		private const int DefaultMapSize = 2048;
		private const int DefaultShowpieceSize = 8192;

		/// <summary>
		/// Band-share tolerance, percentage points. The knots come from the SAME histogram the shares
		/// are measured on, so the only error is in-bin interpolation — tenths, not units. A loose
		/// tolerance here would make check (d) unfalsifiable.
		/// </summary>
		private const double ShareTolerancePp = 0.25;

		public override void _Ready()
		{
			// ⚠ An exception out of _Ready does NOT stop Godot — it logs and the process sits there
			// with no main loop to end it, so a misconfigured run HANGS instead of failing. A hang
			// looks like slow work, which is worse than a crash. Catch, say what was refused, exit 2.
			try { Run(); }
			catch (Exception e)
			{
				GD.PrintErr("==================================================================");
				GD.PrintErr($"  REFUSED: {e.Message}");
				GD.PrintErr("==================================================================");
				GetTree().Quit(2);
			}
		}

		private void Run()
		{
			ToolingPaths.Configure(OS.GetUserDataDir());

			int task        = EnvInt("ISLA_TASK", 1);
			string descr    = EnvStr("ISLA_BATCH", "curve_baseline");
			int mapSize     = EnvInt("ISLA_MAPSIZE", DefaultMapSize);
			int[] seeds     = EnvSeeds("ISLA_SEEDS", DefaultSeeds);
			int showSize    = EnvInt("ISLA_SHOWPIECE_SIZE", DefaultShowpieceSize);
			bool showpiece  = EnvStr("ISLA_SHOWPIECE", "1") == "1";
			bool variants   = EnvStr("ISLA_VARIANTS", "1") == "1";
			string p1Source = EnvStr("ISLA_PHASE1_SOURCE", "02_pass1_port");
			bool skipRaw    = EnvStr("ISLA_SKIP_RAW", "0") == "1";

			// ⚠ Composed by BatchRoot, never free-form — it refuses a descriptor carrying its own
			// numeric prefix, which is how the counter drifted once already.
			string batchRoot = ToolingPaths.BatchRoot(task, descr);
			string scratch   = ToolingPaths.BatchScratch(batchRoot);
			DirAccess.MakeDirRecursiveAbsolute(batchRoot);
			DirAccess.MakeDirRecursiveAbsolute(scratch);

			var scale = new GenerationScale(mapSize);
			var anchors = CurveAnchors.Default;
			float sea = 0.15f;

			GD.Print("==================================================================");
			GD.Print("  CURVE BASELINE — faithful redistribution port + the histogram");
			GD.Print("==================================================================");
			GD.Print($"MapSize      : {mapSize}   (scaleFactor {scale.ScaleFactor:F3})");
			GD.Print($"yardstick    : {WorldScale.Describe()}");
			GD.Print($"anchors      : {anchors.DescribeMetres()}");
			GD.Print($"seeds        : {string.Join(", ", seeds)}");
			GD.Print($"batch        : {batchRoot}");
			GD.Print("------------------------------------------------------------------");
			GD.Print(ToolingPaths.Describe());
			GD.Print("==================================================================");

			// ═══════════════════════════════════════════════════════════════════
			//  1. CALIBRATE — the knots ARE percentiles of the pooled land CDF
			// ═══════════════════════════════════════════════════════════════════
			GD.Print("\n--- 1. CALIBRATION POOL ---");

			var rawPool = new LandHistogram(sea);
			var pass1 = new Dictionary<int, Pass1Result>();
			var perSeedKnots = new List<CurveKnots>();

			foreach (int seed in seeds)
			{
				var cfg = new TerrainGenConfig { MapSize = mapSize, Seed = seed };
				Pass1Result p1 = Topography.Generate(cfg);
				pass1[seed] = p1;
				rawPool.Accumulate(p1.Height, mapSize);

				// Each seed's OWN knots too — the pool is the calibration, but the SPREAD across
				// seeds is what tells us how much of any later delta is scale and how much is just
				// which seed you happened to look at. Without it, the scale-invariance check below
				// compares a 6-seed pool against one seed and calls the difference "scale".
				var solo = new LandHistogram(sea);
				solo.Accumulate(p1.Height, mapSize);
				perSeedKnots.Add(MeasureKnots(solo, $"seed_{seed}"));

				GD.Print($"  pooled seed {seed,-11} h[{p1.HMinSeed,7:F3} .. {p1.HMaxSeed,6:F3}]  {p1.ElapsedMs,5} ms");
			}
			GD.Print($"  {rawPool}");

			float seedSpread = KnotSpread(perSeedKnots);
			GD.Print($"  per-seed knot spread at {mapSize}: max range across the 6 seeds = " +
					 $"{seedSpread:F6} raw ({WorldScale.MetresFromRaw(seedSpread):F2} m)");

			CurveKnots measured = MeasureKnots(rawPool, "v2_balanced");
			GD.Print("\n  MEASURED KNOTS vs THE REFERENCE'S SHIPPED LITERALS");
			GD.Print("  knot  pct     v2 measured   reference     delta      delta (m)");
			for (int i = 0; i < 6; i++)
			{
				float v2 = measured[i], rf = CurveKnots.Reference[i];
				GD.Print($"  K{i + 1}    P{CurveKnots.Percentiles[i],-5:F0}  {v2,11:F6}   {rf,11:F6}   " +
						 $"{v2 - rf,+9:F6}  {WorldScale.MetresFromRaw(v2 - rf),+8:F2}");
			}

			double[] shares = ShapingOracle.RealizedShares(rawPool, measured);
			GD.Print("\n  REALIZED LAND SHARES (target 60/13/10/5/8/3/1)");
			for (int i = 0; i < 7; i++)
				GD.Print($"    {CurveKnots.BandNames[i],-16} {shares[i],6:F2} %   (target {CurveKnots.BandShareTargets[i],4:F0} %)");

			// ═══════════════════════════════════════════════════════════════════
			//  2. THE SHAPED POOL — what the curve actually produces
			// ═══════════════════════════════════════════════════════════════════
			GD.Print("\n--- 2. SHAPED POOL (curve on, detail on) ---");

			var shapedPool = new LandHistogram(sea);
			var shapedResults = new Dictionary<int, Pass2Result>();

			foreach (int seed in seeds)
			{
				var cfg = OnConfig(mapSize, seed, measured, anchors);
				Pass2Result p2 = Shaping.Shape(pass1[seed], cfg);
				shapedResults[seed] = p2;
				shapedPool.Accumulate(p2.Height, mapSize);
				if (seed == seeds[0]) foreach (string n in p2.Notes) GD.Print("  " + n);
				GD.Print($"  shaped seed {seed,-11} h[{p2.HMin,7:F3} .. {p2.HMax,6:F3}]  {p2.ElapsedMs,5} ms");
			}
			GD.Print($"  {shapedPool}");

			GD.Print("\n  SHAPED LAND PERCENTILES (what the palette would need to be placed on)");
			double[] paletteP = { 10, 25, 50, 75, 90, 95, 99, 99.9 };
			var sb2 = new StringBuilder("   ");
			foreach (double p in paletteP) sb2.Append($" p{p:G}={shapedPool.Quantile(p):F3}");
			GD.Print(sb2.ToString());
			GD.Print($"    shaped max {shapedPool.MaxLand:F4}   (peak cap {anchors.PeakCap:F4})");

			// ⚠ THE PALETTE WAS CALIBRATED ON THE *RAW* DISTRIBUTION (Phase 1, chat1/03) and the
			// curve moves that distribution wholesale. This is reported, NOT fixed: re-placing the
			// stops now would make the render look more dramatic while the terrain is genuinely
			// lower — i.e. it would disguise the exact finding the histograms exist to deliver.
			// Whether to recalibrate is a PRESENTATION call the developer makes AFTER deciding
			// whether this elevation profile is the one they want.
			double rawLow = raw3Stop(rawPool), shapedLow = raw3Stop(shapedPool);
			double rawSat = 1.0 - rawPool.FractionBelow(1.450f), shapedSat = 1.0 - shapedPool.FractionBelow(1.450f);
			GD.Print("\n  PALETTE FIT (CostaRica stops were placed on the RAW distribution)");
			GD.Print($"    land below stop 3 (0.310 raw):  raw {rawLow * 100:F1} %  ->  shaped {shapedLow * 100:F1} %");
			GD.Print($"    land above top stop (1.450):    raw {rawSat * 100:F3} %  ->  shaped {shapedSat * 100:F3} %  (clamps to white)");

			// ═══════════════════════════════════════════════════════════════════
			//  3. THE ORACLE — before a single render is looked at
			// ═══════════════════════════════════════════════════════════════════
			GD.Print("\n--- 3. ORACLE ---");
			var checks = new List<ShapingOracle.Check>();

			int primary = seeds[0];
			Pass1Result pp1 = pass1[primary];

			Pass2Result offPrimary = Shaping.Shape(pp1, OffConfig(mapSize, primary));
			checks.Add(ShapingOracle.RegressionCurveOff(pp1, offPrimary));

			string dumpPath = Path.Combine(ToolingPaths.BatchesRoot, p1Source, $"{primary}_full", "height.f32");
			float[,] phase1Dump = HeightField.Load(dumpPath, mapSize);
			checks.Add(ShapingOracle.RegressionAgainstDump(pp1.Height, phase1Dump, mapSize, dumpPath));

			checks.Add(ShapingOracle.ClassifyFidelity(pp1, shapedResults[primary]));
			checks.Add(ShapingOracle.Monotonicity(shapedResults[primary]));
			checks.Add(ShapingOracle.BandShares(rawPool, measured, ShareTolerancePp));

			// Every seed's classify field, not just the showpiece's — the invariant is per-seed.
			long classifyDrift = 0;
			foreach (int seed in seeds)
			{
				var c = ShapingOracle.ClassifyFidelity(pass1[seed], shapedResults[seed]);
				if (!c.Passed) { classifyDrift++; GD.PrintErr($"  classify drift on seed {seed}: {c.Detail}"); }
			}

			foreach (var c in checks) GD.Print("  " + c);
			bool oracleOk = checks.TrueForAll(c => c.Passed) && classifyDrift == 0;
			GD.Print($"  ORACLE: {(oracleOk ? "ALL PASS" : "FAILURES PRESENT")}  " +
					 $"(classify checked on all {seeds.Length} seeds: {seeds.Length - classifyDrift} clean)");

			// ═══════════════════════════════════════════════════════════════════
			//  4. VARIANTS — plain data beside the pretty render
			// ═══════════════════════════════════════════════════════════════════
			var rows = new List<string>();
			if (variants)
			{
				GD.Print("\n--- 4. VARIANTS (curve_off / curve_on) ---");
				foreach (int seed in seeds)
				{
					rows.Add(WriteVariant(batchRoot, pass1[seed], OffConfig(mapSize, seed), skipRaw, sea, 1.45f));
					rows.Add(WriteVariant(batchRoot, pass1[seed], OnConfig(mapSize, seed, measured, anchors),
						skipRaw, sea, anchors.PeakCap));
				}
			}
			else GD.Print("\n--- variants skipped (ISLA_VARIANTS=0) ---");

			// ═══════════════════════════════════════════════════════════════════
			//  5. HISTOGRAMS — the diagnostic, for the showpiece seed
			// ═══════════════════════════════════════════════════════════════════
			GD.Print("\n--- 5. HISTOGRAMS ---");
			var rawSeed = new LandHistogram(sea);
			rawSeed.Accumulate(pass1[primary].Height, mapSize);
			var shapedSeed = new LandHistogram(sea);
			shapedSeed.Accumulate(shapedResults[primary].Height, mapSize);

			DrawRawHistogram(rawSeed, measured, primary, mapSize, batchRoot);
			DrawShapedHistogram(shapedSeed, rawSeed, measured, anchors, primary, mapSize, batchRoot);

			// ═══════════════════════════════════════════════════════════════════
			//  6. SHOWPIECE — the judging plate, and the scale-invariance check
			// ═══════════════════════════════════════════════════════════════════
			string showNote = "skipped (ISLA_SHOWPIECE=0)";
			if (showpiece)
			{
				GD.Print($"\n--- 6. SHOWPIECE at {showSize} ---");
				showNote = WriteShowpiece(batchRoot, primary, showSize, measured, anchors, sea, skipRaw, rows, seedSpread);
			}
			else GD.Print("\n--- showpiece skipped (ISLA_SHOWPIECE=0) ---");

			WriteIndex(batchRoot, mapSize, showSize, scale, seeds, primary, measured, anchors,
				rawPool, shapedPool, shares, checks, rows, oracleOk, showNote, variants, seedSpread);

			GD.Print("\n==================================================================");
			GD.Print($"  DONE — {batchRoot}");
			GD.Print($"  ORACLE {(oracleOk ? "ALL PASS" : "*** FAILURES — see the table ***")}");
			GD.Print("==================================================================");
			GetTree().Quit(oracleOk ? 0 : 3);
		}

		// ---- configs --------------------------------------------------------

		private static TerrainGenConfig OffConfig(int mapSize, int seed) =>
			new TerrainGenConfig { MapSize = mapSize, Seed = seed, VariantLabel = "curve_off", Curve = false, ShelfDetail = false };

		private static TerrainGenConfig OnConfig(int mapSize, int seed, CurveKnots k, CurveAnchors a) =>
			new TerrainGenConfig
			{
				MapSize = mapSize, Seed = seed, VariantLabel = "curve_on",
				Curve = true, ShelfDetail = true, Knots = k, Anchors = a,
			};

		/// <summary>
		/// Fraction of land below the CostaRica palette's third stop (0.310 raw). A blunt
		/// "how much of the island is painted with the first two colours" number — the palette's own
		/// stops are at measured RAW percentiles, so this is how far the curve moved the picture.
		/// </summary>
		private static double raw3Stop(LandHistogram h) => h.FractionBelow(0.310f);

		/// <summary>
		/// The widest max−min range of any single knot across a set of measurements — "how much does
		/// K_n move if you just change which seed you looked at". The yardstick every other knot
		/// delta in this batch has to be judged against.
		/// </summary>
		private static float KnotSpread(List<CurveKnots> sets)
		{
			float worst = 0f;
			for (int i = 0; i < 6; i++)
			{
				float lo = float.MaxValue, hi = float.MinValue;
				foreach (CurveKnots s in sets) { lo = MathF.Min(lo, s[i]); hi = MathF.Max(hi, s[i]); }
				worst = MathF.Max(worst, hi - lo);
			}
			return worst;
		}

		/// <summary>The knots ARE the quantiles. This one method is the whole calibration.</summary>
		private static CurveKnots MeasureKnots(LandHistogram pool, string name) => new CurveKnots(
			2, name,
			pool.Quantile(CurveKnots.Percentiles[0]), pool.Quantile(CurveKnots.Percentiles[1]),
			pool.Quantile(CurveKnots.Percentiles[2]), pool.Quantile(CurveKnots.Percentiles[3]),
			pool.Quantile(CurveKnots.Percentiles[4]), pool.Quantile(CurveKnots.Percentiles[5]));

		// ---- output ---------------------------------------------------------

		private static string WriteVariant(string batchRoot, Pass1Result p1, TerrainGenConfig cfg,
			bool skipRaw, float sea, float legendTop)
		{
			Pass2Result p2 = Shaping.Shape(p1, cfg);

			string dir = Path.Combine(batchRoot, $"{cfg.Seed}_{cfg.VariantLabel}");
			DirAccess.MakeDirRecursiveAbsolute(dir);

			// ⭐ PLAIN DATA BESIDE THE PRETTY RENDER, always — the point is judging the terrain, and
			// you cannot judge a distribution through a palette.
			var (gMin, gMax) = GrayscaleRenderer.SavePng(p2.Height, p2.MapSize, Path.Combine(dir, "grayscale.png"));
			if (!skipRaw) HeightField.Save(p2.Height, p2.MapSize, Path.Combine(dir, "height.f32"));

			var look = new LookConfig
			{
				Name = "gradient_flat", Palette = ReliefPalette.Kind.CostaRica,
				HillshadeStrength = 0f, SeaLevel = sea,
			};
			Image map = ReliefRenderer.Render(p2.Height, p2.MapSize, look);
			Image withLegend = LegendRenderer.WithLegend(map, look.Palette, sea, legendTop,
				cfg.VariantLabel.ToUpperInvariant());
			withLegend.SavePng(Path.Combine(dir, "relief.png"));

			float land = p2.LandFraction(sea);
			GD.Print($"  {cfg.VariantLabel,-10} seed {cfg.Seed,-11} h[{p2.HMin,7:F3} .. {p2.HMax,6:F3}] " +
					 $" land {land * 100,5:F1}%  {p2.ElapsedMs,5} ms");

			return $"| `{cfg.Seed}_{cfg.VariantLabel}` | {cfg.Seed} | {cfg.VariantLabel} | " +
				   $"{p2.HMin:F3} | {p2.HMax:F3} | {land * 100:F1}% | {gMin:F3}..{gMax:F3} | {p2.ElapsedMs} ms |";
		}

		private static void DrawRawHistogram(LandHistogram raw, CurveKnots k, int seed, int mapSize, string batchRoot)
		{
			// Coarse enough to draw, fine enough to keep the shape: ~360 bins across the range.
			float top = MathF.Ceiling(raw.MaxLand * 20f) / 20f;
			var display = raw.Rebin((top - raw.SeaLevel) / 360f);

			var o = new HistogramRenderer.Options
			{
				Title = $"RAW LAND HEIGHTS - SEED {seed}",
				Subtitle = "PRE-CURVE. THE KNOTS ARE PERCENTILES OF THIS DISTRIBUTION.",
				XAxisLabel = "RAW HEIGHT (PRE-CURVE)",
				XTop = top,
				Footer = $"{raw.TotalLand} LAND COLUMNS AT MAPSIZE {mapSize} - BIN {display.BinWidth:F4} RAW",
			};

			float[] edges = { raw.SeaLevel, k.K1, k.K2, k.K3, k.K4, k.K5, k.K6, top };
			for (int i = 0; i < 7; i++)
				o.Bands.Add(new HistogramRenderer.Band
				{
					Lo = edges[i], Hi = edges[i + 1],
					Label = CurveKnots.BandNames[i],
					SharePercent = i < 6
						? raw.FractionBetween(edges[i], edges[i + 1]) * 100.0
						: Math.Max(0.0, (1.0 - raw.FractionBelow(k.K6)) * 100.0),
				});

			for (int i = 0; i < 6; i++)
				o.Markers.Add(new HistogramRenderer.Marker
				{
					Value = k[i], Label = $"K{i + 1} P{CurveKnots.Percentiles[i]:F0}", Strong = true,
				});

			HistogramRenderer.SavePng(display, o, Path.Combine(batchRoot, "histogram_raw.png"));
			GD.Print($"  histogram_raw.png   ({raw.TotalLand:N0} land columns, max {raw.MaxLand:F4})");
		}

		private static void DrawShapedHistogram(LandHistogram shaped, LandHistogram raw, CurveKnots k,
			CurveAnchors a, int seed, int mapSize, string batchRoot)
		{
			float top = MathF.Ceiling(shaped.MaxLand * 20f) / 20f;
			var display = shaped.Rebin((top - shaped.SeaLevel) / 360f);

			var o = new HistogramRenderer.Options
			{
				Title = $"SHAPED LAND HEIGHTS - SEED {seed}",
				Subtitle = "POST-CURVE. BANDS SIT AT THE STORM-LADDER OUTPUT ANCHORS.",
				XAxisLabel = "RAW HEIGHT (POST-CURVE)",
				XTop = top,
				Footer = $"{shaped.TotalLand} LAND COLUMNS AT MAPSIZE {mapSize} - BIN {display.BinWidth:F4} RAW",
			};

			// The OUTPUT bands: each input band's share, drawn where the curve puts it.
			float benchTop = a.BenchBase + a.ShelfSpanMin;
			float plateauTop = a.PlateauBase + a.ShelfSpanMin;
			float[] outEdges = { a.Sea, a.OrangeCeil, a.RedCeil, a.BenchBase, benchTop, a.PlateauBase, plateauTop, top };
			float[] inEdges = { raw.SeaLevel, k.K1, k.K2, k.K3, k.K4, k.K5, k.K6 };

			for (int i = 0; i < 7; i++)
				o.Bands.Add(new HistogramRenderer.Band
				{
					Lo = outEdges[i], Hi = outEdges[i + 1],
					Label = CurveKnots.BandNames[i],
					SharePercent = i < 6
						? raw.FractionBetween(inEdges[i], inEdges[i + 1]) * 100.0
						: Math.Max(0.0, (1.0 - raw.FractionBelow(k.K6)) * 100.0),
				});

			o.Markers.Add(new HistogramRenderer.Marker { Value = a.OrangeCeil,  Label = "ORANGE" });
			o.Markers.Add(new HistogramRenderer.Marker { Value = a.RedCeil,     Label = "RED" });
			o.Markers.Add(new HistogramRenderer.Marker { Value = a.BenchBase,   Label = "BENCH" });
			o.Markers.Add(new HistogramRenderer.Marker { Value = a.PlateauBase, Label = "PLATEAU" });
			o.Markers.Add(new HistogramRenderer.Marker { Value = a.PeakCap,     Label = "CAP 420M" });

			HistogramRenderer.SavePng(display, o, Path.Combine(batchRoot, "histogram_shaped.png"));
			GD.Print($"  histogram_shaped.png ({shaped.TotalLand:N0} land columns, max {shaped.MaxLand:F4})");
		}

		private static string WriteShowpiece(string batchRoot, int seed, int showSize, CurveKnots k,
			CurveAnchors a, float sea, bool skipRaw, List<string> rows, float seedSpread)
		{
			var cfg = OnConfig(showSize, seed, k, a);
			cfg.VariantLabel = "curve_on_showpiece";

			Pass1Result p1 = Topography.Generate(cfg);
			GD.Print($"  pass1 {showSize}: h[{p1.HMinSeed:F3} .. {p1.HMaxSeed:F3}]  {p1.ElapsedMs} ms");

			// ⭐ THE SCALE-INVARIANCE CHECK. Knots were measured at the iteration profile; if the
			// land distribution's shape really is scale-free, this profile's own quantiles land on
			// the same numbers. Measured, not assumed.
			var bigPool = new LandHistogram(sea);
			bigPool.Accumulate(p1.Height, showSize);
			var bigKnots = MeasureKnots(bigPool, $"at_{showSize}");

			var deltas = new StringBuilder();
			float worst = 0f;
			for (int i = 0; i < 6; i++)
			{
				float d = bigKnots[i] - k[i];
				if (MathF.Abs(d) > MathF.Abs(worst)) worst = d;
				deltas.Append($" K{i + 1}{d:+0.0000;-0.0000}");
			}
			// ⚠ THE COMPARISON IS CONFOUNDED, AND SAYING SO IS THE POINT. This is ONE seed at the
			// big profile against a SIX-SEED POOL at the small one, so the delta mixes scale effects
			// with seed-to-seed variation. `seedSpread` is how far a knot moves from seed choice
			// alone at a fixed size — if the delta sits inside it, scale is not what moved.
			bool withinSeedNoise = MathF.Abs(worst) <= seedSpread;
			GD.Print($"  scale-invariance: knots re-measured at {showSize} differ by{deltas}");
			GD.Print($"    worst {worst:+0.000000;-0.000000} raw = {WorldScale.MetresFromRaw(worst):+0.00;-0.00} m  " +
					 $"vs per-seed spread {seedSpread:F6} raw ({WorldScale.MetresFromRaw(seedSpread):F2} m) " +
					 $"-> {(withinSeedNoise ? "WITHIN seed variation" : "EXCEEDS seed variation")}");

			rows.Add(WriteVariant(batchRoot, p1, cfg, skipRaw, sea, a.PeakCap));

			return $"seed {seed} at {showSize}; knots re-measured there differ by at most " +
				   $"{MathF.Abs(worst):F6} raw ({MathF.Abs(WorldScale.MetresFromRaw(worst)):F2} m), " +
				   $"{(withinSeedNoise ? "within" : "beyond")} the {WorldScale.MetresFromRaw(seedSpread):F2} m per-seed spread";
		}

		// ---- the index ------------------------------------------------------

		private static void WriteIndex(string batchRoot, int mapSize, int showSize, GenerationScale scale,
			int[] seeds, int primary, CurveKnots k, CurveAnchors a, LandHistogram rawPool,
			LandHistogram shapedPool, double[] shares, List<ShapingOracle.Check> checks,
			List<string> rows, bool oracleOk, string showNote, bool variants, float seedSpread)
		{
			var sb = new StringBuilder();
			sb.AppendLine("# Batch 01 — the faithful curve baseline");
			sb.AppendLine();
			sb.AppendLine("The redistribution curve and shelf detail, ported faithfully and **re-calibrated against");
			sb.AppendLine("v2's own pass-1 output**. This is the CONTROL every later reshape is judged against —");
			sb.AppendLine("not a taste gate. No erosion, no rivers, no water, no crater, no coast shelf, no islets.");
			sb.AppendLine();
			sb.AppendLine("## ⭐ Open this first");
			sb.AppendLine();
			sb.AppendLine($"1. **`{primary}_curve_on_showpiece/relief.png`** — the judging plate ({showNote}).");
			sb.AppendLine($"2. **`histogram_raw.png`** and **`histogram_shaped.png`** — the diagnostic that says");
			sb.AppendLine("   *why* the upper terrain looks the way it does. Read them before forming an opinion.");
			sb.AppendLine($"3. **`{primary}_curve_off/relief.png`** vs **`{primary}_curve_on/relief.png`** — the A/B.");
			sb.AppendLine();
			sb.AppendLine("## Disposability");
			sb.AppendLine();
			sb.AppendLine("| Artifact | Keep? |");
			sb.AppendLine("|---|---|");
			sb.AppendLine("| `relief.png` | **keep** — the judging plates |");
			sb.AppendLine("| `histogram_*.png` | **keep** — the finding |");
			sb.AppendLine("| `INDEX.md` | **keep** |");
			sb.AppendLine("| `grayscale.png` | ♻ **regenerable** from the `.f32` — safe to clear |");
			sb.AppendLine("| `height.f32` | ♻ **regenerable** from seed + code — safe to clear, but it is the byte-level oracle |");
			sb.AppendLine("| `scratch/` | persistent by rule; never cleaned |");
			sb.AppendLine();
			sb.AppendLine("## Setup");
			sb.AppendLine();
			sb.AppendLine($"- **Calibration/variant profile:** {mapSize} (scaleFactor {scale.ScaleFactor:F3})");
			sb.AppendLine($"- **Showpiece profile:** {showSize}");
			sb.AppendLine($"- **Seeds (pooled as one calibration set):** {string.Join(", ", seeds)}");
			sb.AppendLine($"- **Yardstick:** {WorldScale.Describe()}");
			sb.AppendLine($"- **Output anchors:** {a.DescribeMetres()}");
			sb.AppendLine($"- **Curve:** v{HeightCurve.Version} · **detail:** v{TerrainDetailPass.Version}");
			sb.AppendLine();
			sb.AppendLine("## ⭐ The re-measured knots");
			sb.AppendLine();
			sb.AppendLine($"Pooled land CDF: **{rawPool.TotalLand:N0} samples** from {rawPool.FieldsPooled} seeds, ");
			sb.AppendLine($"range [{rawPool.MinLand:F4} .. {rawPool.MaxLand:F4}] raw, bin {rawPool.BinWidth:G3}.");
			sb.AppendLine();
			sb.AppendLine("| Knot | Percentile | v2 measured | reference literal | delta (raw) | delta (m) |");
			sb.AppendLine("|---|---|---|---|---|---|");
			for (int i = 0; i < 6; i++)
			{
				float v2 = k[i], rf = CurveKnots.Reference[i];
				sb.AppendLine($"| K{i + 1} | P{CurveKnots.Percentiles[i]:F0} | `{v2:F6}` | `{rf:F6}` | " +
							  $"{v2 - rf:+0.000000;-0.000000} | {WorldScale.MetresFromRaw(v2 - rf):+0.00;-0.00} |");
			}
			sb.AppendLine();
			sb.AppendLine("> **This delta is the port-fidelity check.** Near-identical means v2's pass-1 height");
			sb.AppendLine("> distribution matches the reference's — the crown-jewel port is faithful. A large gap");
			sb.AppendLine("> would mean pass 1 diverged, and would be the finding rather than a nuisance.");
			sb.AppendLine();
			sb.AppendLine($"**Scale for judging any knot delta:** across the six seeds at {mapSize}, a single knot");
			sb.AppendLine($"moves by up to **{seedSpread:F6} raw ({WorldScale.MetresFromRaw(seedSpread):F2} m)** from seed choice alone.");
			sb.AppendLine("Anything smaller than that is seed noise, not a difference.");
			sb.AppendLine();
			sb.AppendLine($"**Scale invariance:** {showNote}.");
			sb.AppendLine();
			sb.AppendLine("## Realized land shares");
			sb.AppendLine();
			sb.AppendLine("| Band | Realized | Target | Output lands at |");
			sb.AppendLine("|---|---|---|---|");
			float benchTop = a.BenchBase + a.ShelfSpanMin, plateauTop = a.PlateauBase + a.ShelfSpanMin;
			string[] lands =
			{
				$"{WorldScale.MetresFromRaw(a.Sea - a.Sea):F0}–{WorldScale.MetresFromRaw(a.OrangeCeil - a.Sea):F0} m",
				$"{WorldScale.MetresFromRaw(a.OrangeCeil - a.Sea):F0}–{WorldScale.MetresFromRaw(a.RedCeil - a.Sea):F0} m",
				$"{WorldScale.MetresFromRaw(a.RedCeil - a.Sea):F0}–{WorldScale.MetresFromRaw(a.BenchBase - a.Sea):F0} m",
				$"~{WorldScale.MetresFromRaw(a.BenchBase - a.Sea):F0} m (bench)",
				$"{WorldScale.MetresFromRaw(benchTop - a.Sea):F0}–{WorldScale.MetresFromRaw(a.PlateauBase - a.Sea):F0} m",
				$"~{WorldScale.MetresFromRaw(a.PlateauBase - a.Sea):F0} m (plateau)",
				$"{WorldScale.MetresFromRaw(plateauTop - a.Sea):F0}–{WorldScale.MetresFromRaw(a.PeakCap - a.Sea):F0} m",
			};
			for (int i = 0; i < 7; i++)
				sb.AppendLine($"| {CurveKnots.BandNames[i]} | {shares[i]:F2} % | {CurveKnots.BandShareTargets[i]:F0} % | {lands[i]} |");
			sb.AppendLine();
			sb.AppendLine($"Shaped land range: **[{shapedPool.MinLand:F4} .. {shapedPool.MaxLand:F4}] raw** " +
						  $"= {WorldScale.MetresFromRaw(shapedPool.MinLand - a.Sea):F0}–{WorldScale.MetresFromRaw(shapedPool.MaxLand - a.Sea):F0} m above sea.");
			sb.AppendLine();
			sb.AppendLine("## ⭐ The elevation profile this produces");
			sb.AppendLine();
			sb.AppendLine("Land height percentiles, before and after the curve — **this is the finding**:");
			sb.AppendLine();
			sb.AppendLine("| Percentile | raw | shaped | shaped, metres above sea |");
			sb.AppendLine("|---|---|---|---|");
			foreach (double p in new[] { 10.0, 25.0, 50.0, 75.0, 90.0, 95.0, 99.0, 99.9 })
			{
				float r = rawPool.Quantile(p), s = shapedPool.Quantile(p);
				sb.AppendLine($"| p{p:G} | {r:F3} | {s:F3} | **{WorldScale.MetresFromRaw(s - a.Sea):F0} m** |");
			}
			sb.AppendLine();
			double belowBench   = shapedPool.FractionBelow(a.BenchBase) * 100.0;
			double belowPlateau = shapedPool.FractionBelow(a.PlateauBase) * 100.0;
			sb.AppendLine($"- **{belowBench:F1} %** of land sits below the bench " +
						  $"({WorldScale.MetresFromRaw(a.BenchBase - a.Sea):F0} m).");
			sb.AppendLine($"- **{belowPlateau:F1} %** of land sits below the plateau " +
						  $"({WorldScale.MetresFromRaw(a.PlateauBase - a.Sea):F0} m).");
			// ⚠ Do NOT state the RAW median in metres. Raw pre-curve height has no metre meaning —
			// the yardstick applies to CURVED output, which is what the storm-ladder anchors define.
			// Converting the raw median would invent a "before" elevation the world never had.
			sb.AppendLine($"- The median land column ends up **{WorldScale.MetresFromRaw(shapedPool.Quantile(50) - a.Sea):F0} m** " +
						  $"above sea: the curve maps raw {rawPool.Quantile(50):F3} → {shapedPool.Quantile(50):F3}.");
			sb.AppendLine();
			sb.AppendLine("> ⚠ **Read `histogram_shaped.png` before concluding the terrain is broken.** The curve is");
			sb.AppendLine("> doing exactly what its share targets say: 60 % of land into the bottom band, 73 % below");
			sb.AppendLine("> the red ceiling, 4 % above the plateau. If the island reads flat, that is a decision");
			sb.AppendLine("> showing up in a render — not a bug. Changing it is the RESHAPE, and the reshape is a");
			sb.AppendLine("> later task with its own gate.");
			sb.AppendLine();
			sb.AppendLine("## ⚠ Palette fit — reported, not fixed");
			sb.AppendLine();
			sb.AppendLine("The CostaRica stops were placed on **measured percentiles of the RAW distribution**");
			sb.AppendLine("(Phase 1). The curve moves that distribution, so the ramp no longer sits where the land is:");
			sb.AppendLine();
			sb.AppendLine("| | raw | shaped |");
			sb.AppendLine("|---|---|---|");
			sb.AppendLine($"| land below palette stop 3 (0.310 raw) | {raw3Stop(rawPool) * 100:F1} % | **{raw3Stop(shapedPool) * 100:F1} %** |");
			sb.AppendLine($"| land above the top stop (1.450, clamps white) | {(1.0 - rawPool.FractionBelow(1.450f)) * 100:F3} % | {(1.0 - shapedPool.FractionBelow(1.450f)) * 100:F3} % |");
			sb.AppendLine();
			sb.AppendLine("**Deliberately left alone.** Re-placing the stops now would make the render look more");
			sb.AppendLine("dramatic while the terrain is genuinely lower — it would disguise the very finding above.");
			sb.AppendLine("Recalibrating the palette is a presentation call to make *after* the elevation profile is");
			sb.AppendLine("settled, not before.");
			sb.AppendLine();
			sb.AppendLine("## The oracle");
			sb.AppendLine();
			sb.AppendLine(ShapingOracle.ToMarkdownTable(checks));
			sb.AppendLine($"**{(oracleOk ? "ALL PASS" : "⚠⚠ FAILURES PRESENT — do not judge this batch until they are resolved")}**");
			sb.AppendLine();
			if (variants)
			{
				sb.AppendLine("## Results");
				sb.AppendLine();
				sb.AppendLine("| Folder | Seed | Variant | h min | h max | land % | grayscale range | time |");
				sb.AppendLine("|---|---|---|---|---|---|---|---|");
				foreach (string row in rows) sb.AppendLine(row);
				sb.AppendLine();
			}
			sb.AppendLine("`scratch/` is persistent and is never cleaned.");

			string index = Path.Combine(batchRoot, "INDEX.md");
			using var f = Godot.FileAccess.Open(index, Godot.FileAccess.ModeFlags.Write);
			if (f == null) { GD.PrintErr($"could not write {index}"); return; }
			f.StoreString(sb.ToString());
		}

		// ---- env helpers ----------------------------------------------------

		private static string EnvStr(string k, string fallback)
		{
			string v = System.Environment.GetEnvironmentVariable(k);
			return string.IsNullOrWhiteSpace(v) ? fallback : v;
		}

		private static int EnvInt(string k, int fallback)
			=> int.TryParse(EnvStr(k, null) ?? "", out int v) ? v : fallback;

		private static int[] EnvSeeds(string k, int[] fallback)
		{
			string v = EnvStr(k, null);
			if (v == null) return fallback;
			var outp = new List<int>();
			foreach (string part in v.Split(',', StringSplitOptions.RemoveEmptyEntries))
				if (int.TryParse(part.Trim(), out int s) && s > 0) outp.Add(s);
			return outp.Count > 0 ? outp.ToArray() : fallback;
		}
	}
}