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

namespace IslaApocalypse.Server
{
	/// <summary>
	/// One straight stretch of road, plus which tier it belongs to. The tier is what
	/// decides how wide and how smoothly it gets carved (D-022) — before this existed,
	/// every road was bulldozed to the same dimensions regardless of what it was.
	/// </summary>
	public struct RoadSegment
	{
		public Vector2 A;
		public Vector2 B;
		public RoadTier Tier;

		public RoadSegment(Vector2 a, Vector2 b, RoadTier tier)
		{
			A = a;
			B = b;
			Tier = tier;
		}
	}

	public partial class ServerChunkManager : Node
	{
		private WorldBlueprint _blueprint;
		private Dictionary<Vector2I, ChunkData> _activeChunks = new Dictionary<Vector2I, ChunkData>();
		public int chunkSize = 24;

		// Water-at-rest diagnostics (task 13), summed across the chunks generated.
		private long _waterColumnsRendered = 0;
		private int _chunksWithWater = 0;
		private float _waterMinY = float.MaxValue, _waterMaxY = float.MinValue, _waterMaxDepth = 0f;

		public override void _Ready()
		{

			// 1. LOAD CONFIGURATION and the seed-based blueprint data from the MapDataParser!
			ConfigManager.LoadConfig();
			chunkSize = ConfigManager.ChunkRadius; // Update chunk radius from config file
			_blueprint = MapDataParser.LoadMapData(ConfigManager.WorldSeed.ToString());

			if (_blueprint != null)
			{
				// Params cross-check (v2 blueprints only): the file carries its resolved
				// generation inputs, so a config edited after generation is detectable —
				// canon H7's silent desync becomes loud. Warning, not an abort: the world
				// still loads; the developer decides what to do about the mismatch.
				if (_blueprint.Params != null)
				{
					var p = _blueprint.Params;
					if (p.WorldSeed != BlueprintFormat.SENTINEL_WORLD_SEED && p.WorldSeed != ConfigManager.WorldSeed)
						GD.PrintErr($"[Server] ⚠⚠ BLUEPRINT/CONFIG DESYNC: blueprint was generated with seed " +
							$"{p.WorldSeed} but ServerConfig.json says {ConfigManager.WorldSeed}. " +
							"The world you load is not the world this config describes.");
					if (p.MapSize != ConfigManager.MapSize)
						GD.PrintErr($"[Server] ⚠⚠ BLUEPRINT/CONFIG DESYNC: blueprint MapSize {p.MapSize} " +
							$"vs config MapSize {ConfigManager.MapSize}.");
				}

				GD.Print("[Server] Blueprint loaded. Locating Capitol City...");

				// 2. Find the Capitol in the parsed data
				
				Vector2 capitolPos = new Vector2(2048, 2048); // Safe fallback center
				foreach (var town in _blueprint.Towns) {
					if (town.Tier == TownTier.Capitol) {
						capitolPos = town.Position;
						break;
					}
				}

				// Old original png map coords
				// Vector2 capitolPos = new Vector2(2405, 3296); // hardcoded for now since we know exactly where it is in this seed, which is the "paradise" biome hub
				// New Manual Test point
				// Vector2 capitolPos = new Vector2(4487, 4424);

				GD.Print($"[Server] Capitol found at {capitolPos}. Generating chunks...");

				// 3. Convert pixel coordinates to Chunk coordinates
				int capitolChunkX = (int)(capitolPos.X / Constants.CHUNK_SIZE_X);
				int capitolChunkZ = (int)(capitolPos.Y / Constants.CHUNK_SIZE_Z);

				int radius = ConfigManager.ChunkRadius;

				for (int x = capitolChunkX - radius; x < capitolChunkX + radius; x++)
				{
					for (int z = capitolChunkZ - radius; z < capitolChunkZ + radius; z++)
					{
						GenerateChunk(new Vector2I(x, z));
					}
				}

				// Say what was actually drawn. The water is the blueprint's, not the
				// runtime's, so if this reads zero the question is which of the two
				// sides went quiet — and this line answers it without a debugger.
				GD.Print($"[Server] Water at rest: {_waterColumnsRendered} water columns across " +
					$"{_chunksWithWater} of {_activeChunks.Count} chunks" +
					(_waterColumnsRendered > 0
						? $"; surface Y {_waterMinY:F1}..{_waterMaxY:F1} m, depth up to {_waterMaxDepth:F1} m."
						: " — nothing to draw here (check the blueprint carries WBID/WSRF)."));

				// 5. Teleport the Camera to look down at our creation!
				Camera3D cam = GetNodeOrNull<Camera3D>("Camera3D");
				if (cam != null)
				{
					// Put the camera 120 meters in the air above the Capitol
					cam.GlobalPosition = new Vector3(capitolPos.X, 120f, capitolPos.Y);
					// Point it straight down at the ground
					cam.LookAt(new Vector3(capitolPos.X, 0, capitolPos.Y)); 
				}
			}
		}

		public void GenerateChunk(Vector2I chunkCoord)
		{
			if (_activeChunks.ContainsKey(chunkCoord)) return; 

			ChunkData newChunk = new ChunkData(chunkCoord);

			int startX = chunkCoord.X * Constants.CHUNK_SIZE_X;
			int startZ = chunkCoord.Y * Constants.CHUNK_SIZE_Z; 

// --- SPATIAL CULLING FOR ROADS ---
			// Bounding box for this chunk, padded so a road running just outside it still
			// carves its shoulder in. The pad comes from the widest shoulder any tier has
			// (plus a margin), so widening a road can't silently outgrow this and clip
			// roads off at chunk edges.
			float roadPad = Constants.MAX_SHOULDER_RADIUS + Constants.ROAD_CULL_MARGIN;
			Rect2 chunkBounds = new Rect2(
				startX - roadPad, startZ - roadPad,
				Constants.CHUNK_SIZE_X + roadPad * 2, Constants.CHUNK_SIZE_Z + roadPad * 2);

			List<RoadSegment> localRoadSegments = new List<RoadSegment>();

			// Keep only the segments that actually reach this chunk, and remember which
			// TIER each came from — that is what decides how wide and smooth it carves.
			void CollectSegments(List<Vector2[]> paths, RoadTier tier)
			{
				foreach (var path in paths) {
					for (int i = 0; i < path.Length - 1; i++) {
						Vector2 a = path[i];
						Vector2 b = path[i+1];
						Rect2 segBounds = new Rect2(Mathf.Min(a.X, b.X), Mathf.Min(a.Y, b.Y), Mathf.Abs(b.X - a.X), Mathf.Abs(b.Y - a.Y));
						if (chunkBounds.Intersects(segBounds.Grow(1.0f))) {
							localRoadSegments.Add(new RoadSegment(a, b, tier));
						}
					}
				}
			}

			// All four tiers now carve. Rugged and Trail are the county roads — they were
			// generated and saved all along, but nothing ever consumed them.
			CollectSegments(_blueprint.Highways,    RoadTier.Highway);
			CollectSegments(_blueprint.BranchRoads, RoadTier.Branch);
			CollectSegments(_blueprint.RuggedRoads, RoadTier.Rugged);
			CollectSegments(_blueprint.TrailRoads,  RoadTier.Trail);
			// ---------------------------------------

			for (int x = 0; x <= Constants.CHUNK_SIZE_X; x++)
			{
				for (int z = 0; z <= Constants.CHUNK_SIZE_Z; z++)
				{
					int globalX = startX + x;
					int globalZ = startZ + z;

					if (globalX >= _blueprint.MapSize || globalZ >= _blueprint.MapSize || globalX < 0 || globalZ < 0)
						continue;

					float GetExactSurface(int gX, int gZ, out byte roadMaterial)
					{
						roadMaterial = BlockRegistry.AIR; // 0 == "not a road"
						if (gX >= _blueprint.MapSize) gX = _blueprint.MapSize - 1;
						if (gZ >= _blueprint.MapSize) gZ = _blueprint.MapSize - 1;
						
						float raw = _blueprint.HeightMap[gX, gZ];
						float baseHeight = Mathf.Clamp(raw * (Constants.CHUNK_HEIGHT - 5), 2.0f, Constants.CHUNK_HEIGHT - 2.0f);
						
						// If no roads are in this chunk, skip the heavy math entirely!
						if (localRoadSegments.Count == 0) return baseHeight;

						float finalHeight = baseHeight;
						Vector2 currentPos = new Vector2(gX, gZ);

						// Details of the nearest road that actually REACHES us. Each tier has
						// its own reach, so "nearest" alone isn't enough — a footpath two
						// metres away must not shadow a highway whose shoulder still covers
						// us. We therefore ignore any road we're outside the shoulder of, and
						// take the closest of what's left.
						bool foundRoad = false;
						float bestDist = float.MaxValue;
						float bestRoadElevation = baseHeight;
						RoadProfile bestProfile = default;

						foreach (var seg in localRoadSegments)
						{
							RoadProfile profile = Constants.GetRoadProfile(seg.Tier);

							// 'alongT' tells us HOW FAR ALONG this segment the nearest point is
							// (0 = at the start point, 1 = at the end point).
							float dist = DistanceToLineSegment(currentPos, seg.A, seg.B, out float alongT);

							if (dist > profile.ShoulderRadius) continue; // this road doesn't reach us
							if (dist >= bestDist) continue;              // a closer one already won

							// F2 FIX — the road elevation is taken at the point on the segment
							// CLOSEST TO US, not at the segment's midpoint.
							//
							// The old code gave every column near a segment that segment's
							// single midpoint height, so each stretch of road was one flat
							// plank and consecutive planks stepped up/down like a staircase.
							//
							// Two honest ways to read the height at our closest point:
							//   rampElevation - a straight line between this segment's two
							//                   end points. Holds a grade; cuts and fills.
							//   landElevation - the actual terrain under that point.
							//                   Hugs the land; inherits its bumps.
							// The tier's GradeSmoothing dials between them (D-021 / D-022):
							// a highway holds its grade, a trail follows the ground.
							//
							// Either way it varies CONTINUOUSLY as we move along the road,
							// which is what kills the steps. And because neighbouring
							// segments share an end point, the height matches exactly where
							// one segment hands over to the next — no seam at the joins.
							float rampElevation = Mathf.Lerp(HeightAtPixel(seg.A), HeightAtPixel(seg.B), alongT);
							float landElevation = HeightAtPixel(seg.A.Lerp(seg.B, alongT));

							foundRoad = true;
							bestDist = dist;
							bestProfile = profile;
							bestRoadElevation = Mathf.Lerp(landElevation, rampElevation, profile.GradeSmoothing);
						}

						// THE BULLDOZER: Carve the terrain, using the winning road's own dimensions.
						if (foundRoad)
						{
							if (bestDist <= bestProfile.RoadRadius) {
								finalHeight = bestRoadElevation; // Flatten it completely!
								roadMaterial = bestProfile.SurfaceMaterial;
							} else {
								// Smoothly interpolate from the flat road up/down to the natural mountain height
								float t = (bestDist - bestProfile.RoadRadius) / (bestProfile.ShoulderRadius - bestProfile.RoadRadius);
								t = t * t * (3f - 2f * t); // SmoothStep equation for a beautiful curved slope
								finalHeight = Mathf.Lerp(bestRoadElevation, baseHeight, t);
							}
						}

						return finalHeight;
					}

					// Pass the road surface out for the main voxel so we can paint it!
					// 0 (AIR) means this column is not part of any road.
					byte roadSurface = BlockRegistry.AIR;
					float exactSurfaceY = GetExactSurface(globalX, globalZ, out roadSurface);
					
					// We discard the 'out' variable for the normals using an underscore '_'
					float surfaceRight = GetExactSurface(globalX + 1, globalZ, out _);
					float surfaceFwd = GetExactSurface(globalX, globalZ + 1, out _);

					Biome columnBiome = _blueprint.BiomeMap[globalX, globalZ];

					// Hand the renderer the TRUE surface height for this column, plus the
					// biome and road flag that go with it. The BlockIDs below still use the
					// rounded height (unchanged) — but the colour no longer has to.
					newChunk.SurfaceHeights[x, z] = exactSurfaceY;
					newChunk.ColumnBiomes[x, z] = columnBiome;
					newChunk.ColumnRoadMaterial[x, z] = roadSurface;

					// --- WATER AT REST (task 13) ---------------------------------
					// The blueprint is the AUTHORITY on where water is; the runtime
					// only draws it. WBID decides presence (it is the water stage's
					// own classification output, the same set the biome grid's
					// Ocean/Lake pixels form by construction), WSRF gives the level
					// per pixel, and the WBTB body table is the fallback if a column
					// is flagged wet but carries the WSRF no-water sentinel.
					if (_blueprint.WaterBodyIds != null)
					{
						ushort bodyId = _blueprint.WaterBodyIds[globalX, globalZ];
						if (bodyId != 0)
						{
							float levelRaw = -1f;
							if (_blueprint.WaterSurfaceQ != null)
							{
								ushort q = _blueprint.WaterSurfaceQ[globalX, globalZ];
								if (q != 0) levelRaw = BlueprintFormat.DecodeWaterLevel(q);
							}
							if (levelRaw < 0f) levelRaw = BodyLevel(bodyId);

							if (levelRaw >= 0f)
							{
								// Same mapping as the terrain, so the sheet and the
								// seabed cannot drift apart.
								newChunk.WaterSurfaceY[x, z] = Mathf.Clamp(
									levelRaw * Constants.HEIGHT_SCALE, 2.0f, Constants.CHUNK_HEIGHT - 2.0f);
								// TRUE depth, from blueprint units — see ChunkData.
								newChunk.WaterDepthM[x, z] =
									Mathf.Max(0f, (levelRaw - _blueprint.HeightMap[globalX, globalZ]) * Constants.HEIGHT_SCALE);
								newChunk.HasAnyWater = true;

								_waterColumnsRendered++;
								float wy = newChunk.WaterSurfaceY[x, z];
								if (wy < _waterMinY) _waterMinY = wy;
								if (wy > _waterMaxY) _waterMaxY = wy;
								if (newChunk.WaterDepthM[x, z] > _waterMaxDepth) _waterMaxDepth = newChunk.WaterDepthM[x, z];
							}
						}
					}

					float hRight = surfaceRight - exactSurfaceY;
					float hFwd = surfaceFwd - exactSurfaceY;
					float slopeX = hRight / Constants.VOXEL_SCALE;
					float slopeZ = hFwd / Constants.VOXEL_SCALE;

					float len = Mathf.Sqrt(slopeX * slopeX + 1.0f + slopeZ * slopeZ);

					for (int y = 0; y <= Constants.CHUNK_HEIGHT; y++)
					{
						float verticalDist = y - exactSurfaceY; 
						float density = verticalDist / len;
						
						newChunk.Densities[x, y, z] = density;

						int blockY = Mathf.RoundToInt(exactSurfaceY);
						
						// THE PAINT: Pass the road surface into the Biome Palette!
						newChunk.BlockIDs[x, y, z] = BiomePalette.GetVoxelID(columnBiome, blockY, y, roadSurface);
					}
				} // End of Z loop
			} // End of X loop

			if (newChunk.HasAnyWater) _chunksWithWater++;
			_activeChunks.Add(chunkCoord, newChunk);

			var renderer = new IslaApocalypse.Client.ChunkRenderer();
			AddChild(renderer);
			renderer.RenderChunk(newChunk);
		}

		/// <summary>
		/// A water body's flat surface level, from the blueprint's WBTB table. Only
		/// used as the fallback when a column is flagged wet by WBID but its WSRF
		/// entry is the no-water sentinel — WSRF is the per-pixel authority, this is
		/// the per-body one. Returns -1 if the body is unknown, which the caller
		/// reads as "leave this column dry" rather than guessing a level.
		/// </summary>
		private float BodyLevel(ushort bodyId)
		{
			if (_blueprint.WaterBodies == null) return -1f;
			foreach (var body in _blueprint.WaterBodies)
				if (body.Id == bodyId) return body.SurfaceLevel;
			return -1f;
		}

		/// <summary>
		/// Turns a map-pixel position into a world surface height, with bounds clamping.
		/// Same mapping used everywhere else: raw 0-1 heightmap value scaled into the
		/// usable vertical band of the chunk.
		///
		/// The position handed in is usually FRACTIONAL (road path points land between
		/// heightmap cells), so we read the four cells around it and blend — bilinear
		/// interpolation — rather than snapping to whichever cell we happen to land in.
		///
		/// Why that matters: snapping made the height jump by a whole cell's worth the
		/// instant a point crossed a cell boundary, and hold perfectly flat until it did.
		/// Along a road whose points sit less than a metre apart, that produced a fine
		/// metre-scale staircase — the "washboard". Blending makes the height vary
		/// continuously as the position moves, so the staircase has nothing to stand on.
		/// </summary>
		private float HeightAtPixel(Vector2 pixel)
		{
			int max = _blueprint.MapSize - 1;

			// The four heightmap cells surrounding this position.
			// At the very edge of the map x1/y1 clamp back onto x0/y0, which makes the
			// blend a harmless no-op instead of reading out of bounds.
			int x0 = Mathf.Clamp(Mathf.FloorToInt(pixel.X), 0, max);
			int y0 = Mathf.Clamp(Mathf.FloorToInt(pixel.Y), 0, max);
			int x1 = Mathf.Clamp(x0 + 1, 0, max);
			int y1 = Mathf.Clamp(y0 + 1, 0, max);

			// How far between those cells we actually are, 0 to 1 on each axis.
			// Clamped so a position outside the map can't push the blend past its corners.
			float fx = Mathf.Clamp(pixel.X - x0, 0.0f, 1.0f);
			float fy = Mathf.Clamp(pixel.Y - y0, 0.0f, 1.0f);

			// Blend across X on the near row and the far row, then blend those two down Y.
			float nearRow = Mathf.Lerp(_blueprint.HeightMap[x0, y0], _blueprint.HeightMap[x1, y0], fx);
			float farRow  = Mathf.Lerp(_blueprint.HeightMap[x0, y1], _blueprint.HeightMap[x1, y1], fx);
			float raw     = Mathf.Lerp(nearRow, farRow, fy);

			return Mathf.Clamp(raw * (Constants.CHUNK_HEIGHT - 5), 2.0f, Constants.CHUNK_HEIGHT - 2.0f);
		}

		/// <summary>
		/// Calculates the shortest distance from a point to a line segment defined by v and w.
		/// </summary>
		private float DistanceToLineSegment(Vector2 point, Vector2 v, Vector2 w)
		{
			return DistanceToLineSegment(point, v, w, out _);
		}

		/// <summary>
		/// Same as above, but also reports WHERE along the segment the nearest point falls:
		/// <paramref name="t"/> is 0 at v, 1 at w. The road carving needs this so it can read
		/// the height at the spot next to us instead of at the segment's midpoint.
		/// </summary>
		private float DistanceToLineSegment(Vector2 point, Vector2 v, Vector2 w, out float t)
		{
			float l2 = v.DistanceSquaredTo(w);
			if (l2 == 0) // v == w case
			{
				t = 0f;
				return point.DistanceTo(v);
			}

			// Consider the line extending the segment, parameterized as v + t (w - v).
			// We find projection of point p onto the line.
			// It falls where t = [(p-v) . (w-v)] / |w-v|^2
			t = Mathf.Max(0, Mathf.Min(1, (point - v).Dot(w - v) / l2));

			// Projection falls on the segment
			Vector2 projection = v + t * (w - v);
			return point.DistanceTo(projection);
		}

	}
}