using Godot;
using IslaApocalypse.Core;

namespace IslaApocalypse.Client
{
	// Notice this inherits from MeshInstance3D, which is Godot's visual 3D node!
	public partial class ChunkRenderer : MeshInstance3D
	{
		public void RenderChunk(ChunkData data)
		{
			// 1. Pass the BlockIDs array to the generator, plus the per-column
			//    surface/biome/road data it needs to fade colours smoothly.
			Mesh = MarchingCubes.GenerateMesh(
				data.Densities, data.BlockIDs,
				data.SurfaceHeights, data.ColumnBiomes, data.ColumnRoadMaterial,
				Constants.ISO_LEVEL, Constants.VOXEL_SCALE);


			StandardMaterial3D mat = new StandardMaterial3D();

			// 2. THE FIX: Tell the material to use the colors we paint on the vertices!
			mat.VertexColorUseAsAlbedo = true;
			mat.Roughness = 0.8f;
			mat.CullMode = BaseMaterial3D.CullModeEnum.Disabled;

			MaterialOverride = mat;

			Position = new Vector3(
				data.ChunkPosition.X * Constants.CHUNK_SIZE_X * Constants.VOXEL_SCALE,
				0,
				data.ChunkPosition.Y * Constants.CHUNK_SIZE_Z * Constants.VOXEL_SCALE
			);

			// 3. Water at rest (task 13) — its own mesh, its own material.
			BuildWaterSurface(data);
		}

		/// <summary>
		/// The water sheet, as a SEPARATE MeshInstance3D child.
		///
		/// Why separate rather than a block in the terrain field: the terrain is a
		/// Marching-Cubes iso-surface over ChunkData.Densities. Writing water into
		/// that field would not lay a sheet on top of the seabed — it would move the
		/// iso-surface, fusing the water into the terrain as if the sea were solid
		/// ground. A second surface is the only way to have water sit AT its own
		/// level, independent of the ground beneath it.
		///
		/// It also makes translucency nearly free, which is why this task ships it
		/// rather than deferring: a distinct MeshInstance3D carries its own
		/// StandardMaterial3D, so alpha is one flag and Godot sorts transparent
		/// surfaces after opaque ones on its own. No mesher change at all.
		///
		/// Water at rest is FLAT — one level per cell, taken from the blueprint's own
		/// body levels. No waves, no displacement, no animation (those are C2+).
		/// </summary>
		private void BuildWaterSurface(ChunkData data)
		{
			if (!data.HasAnyWater) return;   // most inland chunks: nothing to build

			var st = new SurfaceTool();
			st.Begin(Mesh.PrimitiveType.Triangles);

			int cellsX = Constants.CHUNK_SIZE_X;
			int cellsZ = Constants.CHUNK_SIZE_Z;
			bool any = false;

			for (int x = 0; x < cellsX; x++)
			{
				for (int z = 0; z < cellsZ; z++)
				{
					// A cell is drawn if ANY of its four corners is wet, and it is drawn
					// FLAT at the deepest-standing level among those wet corners.
					//
					// Drawing on a partly-dry cell is deliberate: it carries the sheet
					// right up under the shoreline, where the opaque terrain in front of
					// it hides the submerged part. The alternative — only fully-wet
					// cells — retreats the waterline a metre from shore and leaves a
					// visible dry gap all the way around every coast and lake.
					float level = Constants.NO_WATER;
					float d00 = data.WaterSurfaceY[x, z];
					float d10 = data.WaterSurfaceY[x + 1, z];
					float d01 = data.WaterSurfaceY[x, z + 1];
					float d11 = data.WaterSurfaceY[x + 1, z + 1];
					if (d00 > level) level = d00;
					if (d10 > level) level = d10;
					if (d01 > level) level = d01;
					if (d11 > level) level = d11;
					if (level <= Constants.NO_WATER) continue;

					// Depth for colour: the deepest wet corner of the cell, so a shelving
					// coast reads as a gradient rather than a staircase of flat tiles.
					float depth = Mathf.Max(
						Mathf.Max(data.WaterDepthM[x, z], data.WaterDepthM[x + 1, z]),
						Mathf.Max(data.WaterDepthM[x, z + 1], data.WaterDepthM[x + 1, z + 1]));

					Color c = DepthColor(depth);
					float s = Constants.VOXEL_SCALE;

					var p00 = new Vector3(x * s, level, z * s);
					var p10 = new Vector3((x + 1) * s, level, z * s);
					var p01 = new Vector3(x * s, level, (z + 1) * s);
					var p11 = new Vector3((x + 1) * s, level, (z + 1) * s);

					// Two triangles, wound so the surface faces up.
					AddVert(st, c, p00); AddVert(st, c, p01); AddVert(st, c, p11);
					AddVert(st, c, p00); AddVert(st, c, p11); AddVert(st, c, p10);
					any = true;
				}
			}

			if (!any) return;

			var water = new MeshInstance3D();
			water.Mesh = st.Commit();

			var mat = new StandardMaterial3D();
			mat.VertexColorUseAsAlbedo = true;
			// Vertex alpha is only honoured when the material is actually transparent.
			mat.Transparency = BaseMaterial3D.TransparencyEnum.Alpha;
			// Lighting note: the scene's environment is minimal (one default
			// DirectionalLight3D, a blue ambient), so a metallic surface reads almost
			// black — metal shows its surroundings, and there is little to show. Water
			// is therefore non-metallic with moderate roughness: albedo stays visible
			// under weak ambient, and it still catches a highlight when a light does
			// hit it. Left deliberately in the same lighting world as the terrain so
			// the two improve together when the scene gets proper lighting.
			mat.Roughness = 0.35f;
			mat.Metallic = 0.0f;
			// Both faces: the camera starts above, but a player will swim under it.
			mat.CullMode = BaseMaterial3D.CullModeEnum.Disabled;
			water.MaterialOverride = mat;

			// Child of this chunk renderer, so it inherits the chunk's world offset
			// and dies with the chunk.
			AddChild(water);
			water.Position = Vector3.Zero;
			water.Name = "Water";
		}

		private static void AddVert(SurfaceTool st, Color c, Vector3 p)
		{
			// SetColor/SetNormal must be set immediately before AddVertex — same rule
			// the terrain mesher follows.
			st.SetColor(c);
			st.SetNormal(Vector3.Up);
			st.AddVertex(p);
		}

		/// <summary>
		/// Shallow teal to deep navy, with alpha closing up as it deepens, so the
		/// shelved coast stays readable and open ocean does not.
		/// </summary>
		private static Color DepthColor(float depthMeters)
		{
			float t = Mathf.Clamp(depthMeters / Constants.WATER_DEEP_METERS, 0f, 1f);
			t = t * t * (3f - 2f * t);   // smoothstep: hold the shallows, then fall away
			Color c = Constants.WATER_SHALLOW.Lerp(Constants.WATER_DEEP, t);
			c.A = Mathf.Lerp(Constants.WATER_ALPHA_SHALLOW, Constants.WATER_ALPHA_DEEP, t);
			return c;
		}
	}
}