using System;
using System.Collections.Generic;
using Godot;

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// Draws a <see cref="LandHistogram"/> as a labelled plot — the picture the developer reads
	/// before deciding what the curve should become.
	///
	/// ═══ WHY A PLOT AND NOT JUST THE TABLE ═══
	///
	/// The per-band mass table is the EVIDENCE; this is what makes the evidence obvious at a glance.
	/// The three candidate causes of flat upper terrain have three different SHAPES here, and the
	/// shape is recognisable in a second where a column of numbers takes a minute:
	///
	///   • curve squashing     — the SHAPED plot spikes hard at the bench and plateau anchors.
	///                           Mass that was spread out arrives stacked.
	///   • noise empty up high — the RAW plot's right-hand tail is a long, flat, almost-invisible
	///                           sliver. There is nothing above P96 to redistribute.
	///   • share allocation    — neither plot is odd, and the band overlays simply show that the
	///                           top two bands were only ever allotted 4 % of the land.
	///
	/// ⚠ LINEAR Y, DELIBERATELY. A log axis would make the upper tail look substantial — which is
	/// precisely the question being asked. If the top of the distribution is a sliver, the plot must
	/// show a sliver. The peak bin count is printed so the vertical scale is never a mystery.
	///
	/// ⚠ Presentation only, and it cannot be otherwise: it is handed a histogram and returns a PNG.
	/// It has no access to a height field and no way to produce one.
	///
	/// Text is <see cref="TinyFont"/> (5×7 bitmap), specifically so this does not drag in the
	/// SubViewport capture path — which awaits render frames and is why `--headless` hangs.
	/// ⚠ The font is uppercase, digits and <c>. - : / ( )</c> only. Unsupported characters render as
	/// blanks, so labels here say "PCT" rather than "%" and avoid commas.
	/// </summary>
	public static class HistogramRenderer
	{
		/// <summary>A vertical reference line — a knot, or an output anchor.</summary>
		public sealed class Marker
		{
			public float Value;
			public string Label;
			/// <summary>Strong markers get a brighter line; use for the ones that carry the argument.</summary>
			public bool Strong = true;
		}

		/// <summary>A shaded span between two values, labelled underneath. The curve's bands.</summary>
		public sealed class Band
		{
			public float Lo, Hi;
			public string Label;
			/// <summary>Share of land in this band, in percent. Drawn under the label.</summary>
			public double SharePercent;
		}

		public sealed class Options
		{
			public string Title = "LAND HEIGHT DISTRIBUTION";
			public string Subtitle = "";
			public string Footer = "";
			public string XAxisLabel = "RAW HEIGHT";
			/// <summary>Right edge of the x axis, raw. Defaults to the histogram's max land height.</summary>
			public float XTop = 0f;
			public int Width = 1800;
			public int Height = 1000;
			public List<Marker> Markers = new();
			public List<Band> Bands = new();
		}

		// A dark plate, so these sit beside the relief renders rather than glaring next to them.
		private static readonly Color Paper     = new(0.098f, 0.106f, 0.125f);
		private static readonly Color Ink       = new(0.941f, 0.949f, 0.961f);
		private static readonly Color Faint     = new(0.565f, 0.596f, 0.643f);
		private static readonly Color Grid      = new(0.192f, 0.208f, 0.243f);
		private static readonly Color BarColor   = new(0.380f, 0.760f, 0.780f);   // the distribution itself
		private static readonly Color MarkStrong = new(0.980f, 0.720f, 0.300f);  // knots — the argument
		private static readonly Color MarkSoft   = new(0.620f, 0.560f, 0.780f);  // anchors — context
		private static readonly Color BandA      = new(0.145f, 0.161f, 0.196f);
		private static readonly Color BandB      = new(0.118f, 0.129f, 0.157f);
		private static readonly Color OverColor  = new(0.980f, 0.560f, 0.290f);  // bars that exceed the clipped axis

		/// <summary>
		/// The clipped y-axis ceiling: 3× the 90th-percentile non-empty bin, so ordinary structure
		/// fills the plot while a single dominating spike is cut off and MARKED.
		///
		/// ⚠ Returns <paramref name="peak"/> unchanged when nothing dominates — a plot is only
		/// clipped when clipping actually buys legibility, never as a default. The threshold is on
		/// the bin DISTRIBUTION rather than a fixed number so it adapts to whatever is handed in.
		/// </summary>
		private static long ClipCap(LandHistogram h, long peak)
		{
			var nonEmpty = new List<long>();
			for (int i = 0; i < h.BinCount; i++)
				if (h.BinCountAt(i) > 0) nonEmpty.Add(h.BinCountAt(i));

			if (nonEmpty.Count < 8) return peak;
			nonEmpty.Sort();

			long p90 = nonEmpty[(int)(nonEmpty.Count * 0.90)];
			long cap = Math.Max(1, p90 * 3);
			// Only worth clipping if the spike really is off the scale of everything else. On a
			// well-spread distribution (the RAW plot) this is false and the axis stays true.
			return cap * 2 < peak ? cap : peak;
		}

		/// <summary>Render and save. Returns the path written.</summary>
		public static string SavePng(LandHistogram h, Options o, string absolutePath)
		{
			Image img = Render(h, o);
			Error err = img.SavePng(absolutePath);
			if (err != Error.Ok) GD.PrintErr($"[HistogramRenderer] SavePng failed ({err}) for {absolutePath}");
			return absolutePath;
		}

		public static Image Render(LandHistogram h, Options o)
		{
			int W = o.Width, H = o.Height;
			var img = Image.CreateEmpty(W, H, false, Image.Format.Rgb8);
			img.Fill(Paper);

			// ---- layout, derived from text metrics rather than guessed fractions ----
			const int titleScale = 4, labelScale = 2, tickScale = 2;
			int marginL = 130, marginR = 50;
			// Room for: title, subtitle, the clip banner, and TWO staggered rows of marker labels.
			int marginT = 40 + TinyFont.Height(titleScale) + 18 + TinyFont.Height(labelScale) + 20
						+ (TinyFont.Height(labelScale) + 5) * 3;
			// Room for: x ticks, then TWO staggered rows of two-line band labels.
			int marginB = 30 + TinyFont.Height(tickScale) + 14
						+ ((TinyFont.Height(labelScale) + 4) * 2 + 6) * 2 + 16;

			int plotX = marginL, plotY = marginT;
			int plotW = W - marginL - marginR;
			int plotH = H - marginT - marginB;
			if (plotW < 64 || plotH < 64) return img;   // absurd canvas — a broken plot is worse than none

			float xLo = h.SeaLevel;
			float xHi = o.XTop > xLo ? o.XTop : (h.MaxLand > xLo ? h.MaxLand : xLo + 1f);
			float xSpan = xHi - xLo;

			int Px(float v) => plotX + (int)MathF.Round((v - xLo) / xSpan * (plotW - 1));

			// ---- band shading, behind everything ----
			bool alt = false;
			foreach (Band b in o.Bands)
			{
				int x0 = Math.Clamp(Px(b.Lo), plotX, plotX + plotW - 1);
				int x1 = Math.Clamp(Px(b.Hi), plotX, plotX + plotW - 1);
				Color c = alt ? BandA : BandB;
				alt = !alt;
				for (int x = x0; x <= x1; x++)
					for (int y = plotY; y < plotY + plotH; y++)
						img.SetPixel(x, y, c);
			}

			// ---- horizontal grid at quarters ----
			for (int i = 1; i < 4; i++)
			{
				int gy = plotY + plotH - (int)(plotH * (i / 4.0));
				for (int x = plotX; x < plotX + plotW; x++) img.SetPixel(x, gy, Grid);
			}

			// ---- the bars ----
			//
			// ⚠ THE VERTICAL SCALE IS CLIPPED, AND THE CLIP IS DRAWN. The curve piles 60 % of land
			// into a 14 m band, so one bin can be 20× its neighbours; at full scale every other
			// feature — the bench bump, the plateau bump, the whole upper tail — flattens to the
			// axis and the plot shows one spike and nothing else. Clipping makes the rest readable;
			// COLOURING the clipped part and printing both numbers is what keeps it honest. A
			// silently truncated axis would be a lie told in the most trusted artefact in the batch.
			long peak = h.PeakBinCount();
			long cap = ClipCap(h, peak);
			bool clipped = cap < peak;

			if (cap > 0)
			{
				for (int i = 0; i < h.BinCount; i++)
				{
					long c = h.BinCountAt(i);
					if (c == 0) continue;

					float lo = h.BinLow(i), hi = lo + h.BinWidth;
					if (hi < xLo || lo > xHi) continue;

					int x0 = Math.Clamp(Px(lo), plotX, plotX + plotW - 1);
					int x1 = Math.Clamp(Px(hi), plotX, plotX + plotW - 1);
					if (x1 < x0) x1 = x0;

					bool over = c > cap;
					int barH = (int)MathF.Round((float)(Math.Min(c, cap) / (double)cap) * (plotH - 1));
					// A non-empty bin always paints at least one pixel — otherwise the thin upper
					// tail vanishes entirely and the plot argues the opposite of the data.
					if (barH < 1) barH = 1;

					Color c1 = over ? OverColor : BarColor;
					for (int x = x0; x <= x1; x++)
						for (int y = plotY + plotH - barH; y < plotY + plotH; y++)
							img.SetPixel(x, y, c1);
				}
			}

			// ---- axes ----
			for (int x = plotX; x < plotX + plotW; x++) img.SetPixel(x, plotY + plotH, Faint);
			for (int y = plotY; y <= plotY + plotH; y++) img.SetPixel(plotX, y, Faint);

			// ---- markers (knots / anchors), over the bars ----
			// ⚠ Same two-row stagger as the band labels, for the same reason: K3 and K4 are five
			// percentiles apart and their labels would otherwise overprint into a false reading.
			// The LINE is always drawn even when its label is staggered — the position is the data;
			// the text is the convenience.
			var mRowRight = new[] { int.MinValue, int.MinValue };
			int mRowH = TinyFont.Height(labelScale) + 5;

			for (int mi = 0; mi < o.Markers.Count; mi++)
			{
				Marker m = o.Markers[mi];
				if (m.Value < xLo || m.Value > xHi) continue;
				int mx = Math.Clamp(Px(m.Value), plotX, plotX + plotW - 1);
				Color c = m.Strong ? MarkStrong : MarkSoft;

				for (int y = plotY; y <= plotY + plotH; y++)
				{
					// Dashed for the soft ones, so a dense cluster stays readable.
					if (!m.Strong && ((y / 6) & 1) == 0) continue;
					img.SetPixel(mx, y, c);
				}

				int lw = TinyFont.Width(m.Label, labelScale);
				int lx = mx - lw / 2;
				int row = 0;
				if (lx <= mRowRight[0] + 8)
				{
					row = 1;
					if (lx <= mRowRight[1] + 8) continue;   // both rows taken — the line still stands
				}
				lx = Math.Clamp(lx, plotX, plotX + plotW - lw);
				TinyFont.Draw(img, m.Label, lx, plotY - TinyFont.Height(labelScale) - 6 - (1 - row) * mRowH,
					labelScale, c);
				mRowRight[row] = lx + lw;
			}

			// ---- band labels + shares, under the axis ----
			//
			// ⚠ STAGGERED ACROSS TWO ROWS, AND A COLLIDING LABEL IS DROPPED RATHER THAN OVERPRINTED.
			// The curve's bench and plateau bands are ~6 m wide, so at map scale their labels sit
			// almost on top of their neighbours: the first cut rendered "TOE/ORANGERED" and
			// "59.9 PCT19 PCT", which is worse than no label because it reads as a value.
			// A leader line ties each surviving label to its band, so a dropped one is visibly
			// dropped rather than silently mis-attributed.
			int bandLabelY = plotY + plotH + 12 + TinyFont.Height(tickScale) + 10;
			int rowH = (TinyFont.Height(labelScale) + 4) * 2 + 6;
			var rowRight = new[] { int.MinValue, int.MinValue };

			for (int bi = 0; bi < o.Bands.Count; bi++)
			{
				Band b = o.Bands[bi];
				int cx = (Px(b.Lo) + Px(b.Hi)) / 2;
				string l1 = b.Label.ToUpperInvariant();
				string l2 = $"{b.SharePercent:F1} PCT";
				int w = Math.Max(TinyFont.Width(l1, labelScale), TinyFont.Width(l2, labelScale));

				int row = bi & 1;                    // stagger: alternate rows first
				int left = cx - w / 2;
				if (left <= rowRight[row] + 8)       // still colliding on that row? try the other
				{
					row ^= 1;
					if (left <= rowRight[row] + 8) continue;   // both taken — drop it, do not overprint
				}

				left = Math.Clamp(left, 2, W - w - 2);
				int y = bandLabelY + row * rowH;

				// Leader line from the band's centre down to its label.
				for (int ly = plotY + plotH + 2; ly < y - 2; ly++)
					if ((ly & 1) == 0) img.SetPixel(Math.Clamp(cx, 0, W - 1), ly, Grid);

				TinyFont.Draw(img, l1, left, y, labelScale, Faint);
				TinyFont.Draw(img, l2, left, y + TinyFont.Height(labelScale) + 4, labelScale, Ink);
				rowRight[row] = left + w;
			}

			// ---- x ticks ----
			int tickCount = 8;
			for (int i = 0; i <= tickCount; i++)
			{
				float v = xLo + xSpan * i / tickCount;
				int tx = Px(v);
				for (int t = 0; t < 6; t++) img.SetPixel(tx, plotY + plotH + t, Faint);
				string lab = v.ToString("0.00");
				int lw = TinyFont.Width(lab, tickScale);
				TinyFont.Draw(img, lab, Math.Clamp(tx - lw / 2, 2, W - lw - 2), plotY + plotH + 10, tickScale, Faint);
			}

			// ---- y axis: the scale, and the clip if there is one ----
			TinyFont.Draw(img, Thousands(cap), 8, plotY - 4, tickScale, clipped ? OverColor : Faint);
			TinyFont.Draw(img, "0", 8, plotY + plotH - TinyFont.Height(tickScale), tickScale, Faint);
			TinyFont.Draw(img, "COUNT", 8, plotY + plotH / 2, tickScale, Faint);
			if (clipped)
			{
				// Said twice, on the image, in the clip's own colour — because a reader who misses
				// this misreads the whole plot.
				TinyFont.Draw(img, "CLIPPED", 8, plotY + 6 + TinyFont.Height(tickScale), tickScale, OverColor);
				TinyFont.Draw(img, $"TRUE PEAK {Thousands(peak)} - AMBER BARS EXCEED THE CLIPPED AXIS",
					plotX, plotY - TinyFont.Height(labelScale) - 6 - mRowH * 2 - 6, labelScale, OverColor);
			}

			// ---- titles ----
			TinyFont.Draw(img, o.Title, marginL, 40, titleScale, Ink);
			if (!string.IsNullOrEmpty(o.Subtitle))
				TinyFont.Draw(img, o.Subtitle, marginL, 40 + TinyFont.Height(titleScale) + 14, labelScale, Faint);

			// ---- footer ----
			if (!string.IsNullOrEmpty(o.Footer))
				TinyFont.Draw(img, o.Footer, marginL, H - TinyFont.Height(labelScale) - 20, labelScale, Faint);

			TinyFont.Draw(img, o.XAxisLabel, plotX + plotW - TinyFont.Width(o.XAxisLabel, labelScale),
				H - TinyFont.Height(labelScale) - 20, labelScale, Faint);

			return img;
		}

		/// <summary>
		/// Group digits with spaces. ⚠ Not commas: the font has no comma glyph, so "1,234" would
		/// render as "1 234" anyway — better to mean it than to have it happen.
		/// </summary>
		private static string Thousands(long v)
		{
			string s = v.ToString();
			var sb = new System.Text.StringBuilder();
			for (int i = 0; i < s.Length; i++)
			{
				if (i > 0 && (s.Length - i) % 3 == 0) sb.Append(' ');
				sb.Append(s[i]);
			}
			return sb.ToString();
		}
	}
}