// ClassicalSharp copyright 2014-2016 UnknownShadow200 | Licensed under MIT
using System;
using ClassicalSharp.Map;
using ClassicalSharp.Physics;
using OpenTK;

namespace ClassicalSharp {
	public static class Picking {	
		
		static RayTracer t = new RayTracer();
		
		/// <summary> Determines the picked block based on the given origin and direction vector.<br/>
		/// Marks pickedPos as invalid if a block could not be found due to going outside map boundaries
		/// or not being able to find a suitable candiate within the given reach distance. </summary>
		public static void CalculatePickedBlock( Game game, Vector3 origin, Vector3 dir,
		                                        float reach, PickedPos pos ) {
			if( !RayTrace( game, origin, dir, reach, pos, false ) ) {
				pos.SetAsInvalid();
			}
		}
		
		static bool PickBlock( Game game, PickedPos pos ) {
			if( !game.CanPick( t.Block ) ) return false;
			
			// This cell falls on the path of the ray. Now perform an additional bounding box test,
			// since some blocks do not occupy a whole cell.
			float t0, t1;
			if( !Intersection.RayIntersectsBox( t.Origin, t.Dir, t.Min, t.Max, out t0, out t1 ) )
				return false;
			Vector3 I = t.Origin + t.Dir * t0;
			pos.SetAsValid( t.X, t.Y, t.Z, t.Min, t.Max, t.Block, I );
			return true;
		}
		
		public static void ClipCameraPos( Game game, Vector3 origin, Vector3 dir,
		                                 float reach, PickedPos pos ) {
			if( !game.CameraClipping || !RayTrace( game, origin, dir, reach, pos, true ) ) {
				pos.SetAsInvalid();
				pos.Intersect = origin + dir * reach;
			}
		}
		
		static bool CameraClip( Game game, PickedPos pos ) {
			BlockInfo info = game.BlockInfo;
			if( info.IsAir[t.Block] || info.Collide[t.Block] != CollideType.Solid )
				return false;
			
			float t0, t1;
			const float adjust = 0.1f;
			if( !Intersection.RayIntersectsBox( t.Origin, t.Dir, t.Min, t.Max, out t0, out t1 ) )
				return false;
			Vector3 I = t.Origin + t.Dir * t0;
			pos.SetAsValid( t.X, t.Y, t.Z, t.Min, t.Max, t.Block, I );
			
			switch (pos.BlockFace) {
				case BlockFace.XMin: pos.Intersect.X -= adjust; break;
				case BlockFace.XMax: pos.Intersect.X += adjust; break;
				case BlockFace.YMin: pos.Intersect.Y -= adjust; break;
				case BlockFace.YMax: pos.Intersect.Y += adjust; break;
				case BlockFace.ZMin: pos.Intersect.Z -= adjust; break;
				case BlockFace.ZMax: pos.Intersect.Z += adjust; break;
			}
			return true;
		}


		static bool RayTrace( Game game, Vector3 origin, Vector3 dir, float reach,
		                     PickedPos pos, bool clipMode ) {
			t.SetVectors( origin, dir );
			BlockInfo info = game.BlockInfo;
			float reachSq = reach * reach;
			Vector3I pOrigin = Vector3I.Floor( origin );

			for( int i = 0; i < 10000; i++ ) {
				int x = t.X, y = t.Y, z = t.Z;
				t.Block = GetBlock( game.World, x, y, z, pOrigin );
				Vector3 min = new Vector3( x, y, z ) + info.MinBB[t.Block];
				Vector3 max = new Vector3( x, y, z ) + info.MaxBB[t.Block];
				if( info.IsLiquid( t.Block ) ) { min.Y -= 1.5f/16; max.Y -= 1.5f/16; }
				
				float dx = Math.Min( Math.Abs( origin.X - min.X ), Math.Abs( origin.X - max.X ) );
				float dy = Math.Min( Math.Abs( origin.Y - min.Y ), Math.Abs( origin.Y - max.Y ) );
				float dz = Math.Min( Math.Abs( origin.Z - min.Z ), Math.Abs( origin.Z - max.Z ) );
				if( dx * dx + dy * dy + dz * dz > reachSq ) return false;
				
				t.Min = min; t.Max = max;
				bool intersect = clipMode ? CameraClip( game, pos ) : PickBlock( game, pos );
				if( intersect ) return true;
				t.Step();
			}
			
			throw new InvalidOperationException( "did over 10000 iterations in CalculatePickedBlock(). " +
			                                    "Something has gone wrong. (dir: " + dir + ")" );
		}

		const byte border = Block.Bedrock;
		static byte GetBlock( World map, int x, int y, int z, Vector3I origin ) {
			bool sides = map.Env.SidesBlock != Block.Air;
			int height = Math.Max( 1, map.Env.SidesHeight );
			bool insideMap = map.IsValidPos( origin );
			
			// handling of blocks inside the map, above, and on borders
			if( x >= 0 && z >= 0 && x < map.Width && z < map.Length ) {
				if( y >= map.Height ) return 0;
				if( sides && y == -1 && insideMap ) return border;
				if( sides && y == 0 && origin.Y < 0 ) return border;
				
				if( sides && x == 0 && y >= 0 && y < height && origin.X < 0 ) return border;
				if( sides && z == 0 && y >= 0 && y < height && origin.Z < 0 ) return border;
				if( sides && x == (map.Width - 1) && y >= 0 && y < height && origin.X >= map.Width )
					return border;
				if( sides && z == (map.Length - 1) && y >= 0 && y < height && origin.Z >= map.Length )
					return border;
				if( y >= 0 ) return map.GetBlock( x, y, z );
			}
			
			// pick blocks on the map boundaries (when inside the map)
			if( !sides || !insideMap ) return 0;
			if( y == 0 && origin.Y < 0 ) return border;
			bool validX = (x == -1 || x == map.Width) && (z >= 0 && z < map.Length);
			bool validZ = (z == -1 || z == map.Length) && (x >= 0 && x < map.Width);
			if( y >= 0 && y < height && (validX || validZ) ) return border;
			return 0;
		}
	}
}