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

namespace IslaApocalypse.Tools
{
	/// <summary>
	/// ⭐⭐ THE CANDIDATE SET — one implementation, shared by every task that ranks rivers.
	///
	/// Extracted from `RiverPromotionTool` at rivers/03, unchanged in behaviour, because routing needs
	/// exactly the same promoted set the count gate was judged on. **Two copies of this enumeration
	/// would be two answers to "which rivers does the island have", and the epic rests on there being
	/// one.** `RiverPromotionTool` now delegates here; its plates are byte-identical across the change.
	///
	/// ═══ WHAT IT DOES, AND WHAT IT DELIBERATELY DOES NOT ═══
	///
	/// It derives the COMPLETE candidate set from the arrays `DrainageAnalysis.Plan` exposes —
	/// `Dir` / `Acc` / `BasinId` / `BasinInflow` / `FullFilled` — rather than from `Plan.Trunks` /
	/// `Plan.Giants`, which are already truncated by the analysis's lean reporting caps. Ranking over
	/// the truncated lists would measure the caps rather than the terrain.
	///
	/// ⚠ **`DrainageAnalysis` is reused, never rebuilt.** Every derived quantity here is a
	/// reconstruction of a value the analysis computed internally, from state it exposes. Nothing the
	/// analysis owns is reimplemented — least of all stem tracing, which is BOUND from the analysis's
	/// own `Trunk` / `Giant` (see <see cref="BindCourses"/>).
	/// </summary>
	public static class RiverCandidates
	{
		/// <summary>The enumeration's full result: the ranking, plus what the separation rule cost.</summary>
		public sealed class Enumeration
		{
			/// <summary>Separated and above the floor, descending by <c>DrainagePx</c>, `Rank` assigned.</summary>
			public List<RiverCandidate> Ranked;
			public long LandCells, SeaReachingCells, EndorheicCells, UnroutedCells;
			public int TerminalBasins, SeaOutletsAll;
			/// <summary>Sea outlets dropped by the separation rule — ALL of them, incl. one-cell trickles.</summary>
			public int SuppressedCount;
			public long SuppressedPx;
			/// <summary>⭐ The two that matter: only outlets clearing the floor could ever have been promoted.</summary>
			public int SuppressedAboveFloor;
			public long SuppressedAboveFloorPx;
			/// <summary>Of those, suppressed by an outlet on a DIFFERENT landmass — not a delta mouth by any definition.</summary>
			public int SuppressedCrossLandmass;
			public long SuppressedCrossLandmassPx;
			public List<long> SuppressedAboveFloorAccs = new();

			public int SeaCount { get { int s = 0; foreach (var c in Ranked) if (c.IsSea) s++; return s; } }
		}

		/// <summary>
		/// Enumerate every candidate major drainage, cap-free.
		///
		///   SEA        every cell with <c>Dir == D_SEA</c>, carrying <c>Acc</c> there, then the
		///              analysis's own greedy <c>MinOutletSeparationPx</c> rule so three mouths of one
		///              delta are not three rivers.
		///   ENDORHEIC  every terminal basin in <c>BasinId</c>, carrying <c>BasinInflow[id]</c>, with
		///              terminal cell / area / depth re-derived from the exposed surfaces.
		///
		/// ⚠⚠ Throws unless the metric-comparability identity holds exactly — see below.
		/// </summary>
		public static Enumeration Enumerate(DrainageAnalysis.Plan plan, float[,] height, int n,
			long floorPx, int separationPx, RegionLabels regions)
		{
			int total = n * n;
			var r = new Enumeration
			{
				LandCells = plan.LandCells, SeaReachingCells = plan.SeaReachingCells,
				EndorheicCells = plan.EndorheicCells, UnroutedCells = plan.UnroutedCells,
				TerminalBasins = plan.TerminalBasinCount,
			};

			// ---- SEA: every outlet, then the separation rule ----
			var outlets = new List<(int cell, long acc)>();
			long seaSum = 0;
			for (int i = 0; i < total; i++)
				if (plan.Dir[i] == DrainageAnalysis.D_SEA) { outlets.Add((i, plan.Acc[i])); seaSum += plan.Acc[i]; }
			outlets.Sort((a, b) => b.acc.CompareTo(a.acc));
			r.SeaOutletsAll = outlets.Count;

			var sea = new List<RiverCandidate>();
			var kept = new List<int>();
			foreach (var (cell, acc) in outlets)
			{
				int cx = cell / n, cy = cell % n;
				bool far = true; int suppressor = -1;
				foreach (int pcell in kept)
				{
					float ddx = cx - pcell / n, ddy = cy - pcell % n;
					if (ddx * ddx + ddy * ddy < (float)separationPx * separationPx) { far = false; suppressor = pcell; break; }
				}
				var c = new RiverCandidate { IsSea = true, Cell = cell, X = cx, Y = cy, TermX = cx, TermY = cy, DrainagePx = acc, SuppressedBySeparation = !far };
				if (far) kept.Add(cell);
				else
				{
					r.SuppressedCount++; r.SuppressedPx += acc;
					if (acc >= floorPx)
					{
						r.SuppressedAboveFloor++; r.SuppressedAboveFloorPx += acc; r.SuppressedAboveFloorAccs.Add(acc);
						// ⚠⚠ IS THE SUPPRESSOR EVEN ON THE SAME LANDMASS? The separation rule is a plain
						// Euclidean distance test — it has no idea what land a coastline belongs to. On
						// this deliberately fragmented archipelago (→ D-063) an ISLAND's only river can
						// be suppressed by a mainland mouth 400 px away ACROSS WATER. Measured, not
						// argued; the rule itself is NOT changed (it belongs to the analysis).
						if (regions != null && suppressor >= 0)
						{
							int a = regions.Id[cell], b = regions.Id[suppressor];
							if (a != 0 && b != 0 && a != b) { r.SuppressedCrossLandmass++; r.SuppressedCrossLandmassPx += acc; }
						}
					}
				}
				if (acc >= floorPx) sea.Add(c);
			}

			// ---- ENDORHEIC: every terminal basin, metrics re-derived ----
			// After the analysis's reversion, BasinId is non-zero ONLY on terminal-basin cells, and
			// Filled == the original height there — so FullFilled − height IS the fill depth, and the
			// basin minimum is the argmin of height over the basin's cells. Both reconstruct exactly
			// what the analysis computed internally as basinMinCell / basinDepthM / basinAreaPx.
			int maxId = 0;
			for (int i = 0; i < total; i++) if (plan.BasinId[i] > maxId) maxId = plan.BasinId[i];
			var area = new long[maxId + 1];
			var minCell = new int[maxId + 1];
			var minH = new float[maxId + 1];
			var depth = new float[maxId + 1];
			for (int id = 0; id <= maxId; id++) { minCell[id] = -1; minH[id] = float.MaxValue; }
			for (int i = 0; i < total; i++)
			{
				int id = plan.BasinId[i];
				if (id == 0) continue;
				area[id]++;
				float h = height[i / n, i % n];
				if (h < minH[id]) { minH[id] = h; minCell[id] = i; }
				float d = WorldScale.MetresFromRaw(plan.FullFilled[i] - h);
				if (d > depth[id]) depth[id] = d;
			}

			var endo = new List<RiverCandidate>();
			long endoSum = 0;
			for (int id = 1; id <= maxId; id++)
			{
				if (minCell[id] < 0) continue;
				long inflow = id < plan.BasinInflow.Length ? plan.BasinInflow[id] : 0;
				endoSum += inflow;
				if (inflow < floorPx) continue;
				endo.Add(new RiverCandidate
				{
					IsSea = false, Cell = minCell[id], X = minCell[id] / n, Y = minCell[id] % n,
					TermX = minCell[id] / n, TermY = minCell[id] % n,   // replaced at bind time by the stem's pooling point
					DrainagePx = inflow, BasinId = id, BasinAreaPx = area[id], BasinDepthM = depth[id],
				});
			}

			// ═══ ⚠⚠ THE COMPARABILITY ASSERTION — the whole unified ranking rests on this ═══
			//
			// Both metrics are counts of contributing LAND CELLS on the same D8 field, and every land
			// cell has exactly one destination — so the two populations partition the land exactly.
			// If this identity ever fails, the two numbers are not the same unit and ranking them in
			// one list is meaningless. It is asserted per seed rather than argued in a comment.
			long partition = seaSum + endoSum + plan.UnroutedCells;
			if (seaSum != plan.SeaReachingCells || endoSum != plan.EndorheicCells || partition != plan.LandCells)
				throw new InvalidOperationException(
					"[RiverCandidates] METRIC COMPARABILITY VIOLATION — the unified ranking is not sound on this field.\n" +
					$"    Σ Acc over sea outlets = {seaSum:N0}, expected SeaReachingCells = {plan.SeaReachingCells:N0}\n" +
					$"    Σ BasinInflow          = {endoSum:N0}, expected EndorheicCells   = {plan.EndorheicCells:N0}\n" +
					$"    sum + unrouted         = {partition:N0}, expected LandCells       = {plan.LandCells:N0}\n" +
					"Sea-outlet drainage area and endorheic credited inflow must be the same unit over the same " +
					"population for one ranking to mean anything. Refusing to rank. (rivers/02 Part 0 §2.)");
			GD.Print($"  ✅ comparability: Σ sea Acc {seaSum:N0} + Σ BasinInflow {endoSum:N0} + unrouted {plan.UnroutedCells:N0} == land {plan.LandCells:N0} — same unit, exact partition");

			// ---- the unified ranking: one list, both termini, descending by contributing cells ----
			var ranked = new List<RiverCandidate>();
			foreach (var c in sea) if (!c.SuppressedBySeparation) ranked.Add(c);
			ranked.AddRange(endo);
			ranked.Sort((a, b) => b.DrainagePx.CompareTo(a.DrainagePx));
			for (int i = 0; i < ranked.Count; i++) ranked[i].Rank = i + 1;
			r.Ranked = ranked;
			return r;
		}

		/// <summary>
		/// Bind each candidate in <paramref name="need"/> to the <c>Trunk</c> / <c>Giant</c> the
		/// analysis already traced, so plates draw REAL upland stems rather than anything reimplemented
		/// here. Sea binds by outlet cell (identical greedy pick, identical order); endorheic binds by
		/// BASIN ID — not by terminal coordinates, because a flat basin floor can have several cells at
		/// the minimum height and the analysis's DFS tie-break need not match a row-major scan.
		///
		/// ⚠ Also transfers the analysis's own <see cref="RiverCandidate.Kind"/> and
		/// <see cref="RiverCandidate.TerminalInClassifyWater"/> for endorheic candidates — rivers/03
		/// needs the reference's routed/lake-ender verdict to compare against its own.
		/// </summary>
		public static void BindCourses(DrainageAnalysis.Plan plan, int n, List<RiverCandidate> need, string what)
		{
			var byOutlet = new Dictionary<int, DrainageAnalysis.Trunk>();
			foreach (var t in plan.Trunks) byOutlet[(int)t.Outlet.x * n + (int)t.Outlet.y] = t;
			var byBasin = new Dictionary<int, DrainageAnalysis.Giant>();
			foreach (var g in plan.Giants)
			{
				int cell = (int)g.Terminal.x * n + (int)g.Terminal.y;
				int id = plan.BasinId[cell];
				if (id > 0 && !byBasin.ContainsKey(id)) byBasin[id] = g;
			}

			int missing = 0;
			foreach (var c in need)
			{
				if (c.Course != null) continue;
				if (c.IsSea)
				{
					if (byOutlet.TryGetValue(c.Cell, out var t)) { c.Course = t.Course; c.TermX = (int)t.Outlet.x; c.TermY = (int)t.Outlet.y; }
				}
				else
				{
					// ⚠ Take the RIVER's terminus from the Giant, not the basin minimum this candidate
					// is keyed on — see RiverCandidate.TermX. They differ on a flat basin floor, and
					// marking the wrong one draws every endorheic stem detached from its own endpoint.
					if (byBasin.TryGetValue(c.BasinId, out var g))
					{
						c.Course = g.Course; c.TermX = (int)g.Terminal.x; c.TermY = (int)g.Terminal.y;
						c.AnalysisKind = g.Kind;
						c.TerminalInClassifyWater = g.TerminalInClassifyWater;
					}
				}
				if (c.Course == null) missing++;
			}
			if (missing > 0)
				throw new InvalidOperationException(
					$"[RiverCandidates] {missing} of {need.Count} candidates in {what} have no traced stem. The analysis's " +
					"reporting caps are what produce the courses, so they must cover every candidate being drawn — " +
					"raise ISLA_PROMOTE_MAX. Refusing to render a plate with rivers drawn as bare markers.");
		}
	}
}