using System;

using System.IO;

using Delta.Engine;

using Delta.Utilities;

using Delta.Utilities.Datatypes;

using Delta.Utilities.Helpers;



namespace Delta.Rendering.Cameras

{

	/// <summary>

	/// Path camera represent a camera witch moves on a given path.

	/// A path consist of many positions in a 3D space. The camera stops moving,

	/// when it reached the last position in the given path.

	/// The UP-Vector is implemented in the base camera in the UpdateViewMatrix

	/// method. Which is the UnitZ-Vector.

	/// <para />

	/// </summary>

	public class PathCamera : LookAtCamera

	{

		#region Constants

		/// <summary>

		/// The current version of the implementation of this Camera class.

		/// </summary>

		private const int ImplementationVersion = 1;



		/// <summary>

		/// Camera default speed.

		/// </summary>

		private const float DefaultSpeed = 10f;

		#endregion



		#region LoadColladaCameraPath (Static)

		/// <summary>

		/// Loads the exported camera path (view) matrices from a Collada (file)

		/// data string.

		/// </summary>

		/// <param name="colladaMatricesString">Collada matrices string.</param>

		/// <returns>Return the loaded array of matrices.</returns>

		public static Matrix[] LoadColladaCameraPath(string colladaMatricesString)

		{

			float[] rawMatricesValues =

				colladaMatricesString.ToFloatArray();



			// Build the matrices path from the raw path data

			int matricesCount = rawMatricesValues.Length / 16;

			Matrix[] matricesPath = new Matrix[matricesCount];

			// we have to scale down the exported matrix by the engine scaling

			// 1m = 0.01 max units (cm)

			Matrix correctionScaleMatrix = Matrix.CreateScale(0.01f);

			for (int index = 0; index < matricesCount; index++)

			{

				// The view matrix is in Collada exported as inverse view matrix,

				// probably because of optimization reasons of 3DsMax's viewport render

				Matrix deltaViewMatrix =

					LoadColladaMatrix(rawMatricesValues, index * 16).Inverse;



				Matrix.Multiply(ref deltaViewMatrix, ref correctionScaleMatrix,

					ref matricesPath[index]);

			}



			return matricesPath;

		}

		#endregion



		#region LoadColladaMatrix (Static)

		/// <summary>

		/// Create matrix from collada float value array. The matrices in collada

		/// are stored differently from the xna format (row based instead of

		/// columns).

		/// </summary>

		/// <param name="mat">Array of floats containing this matrix, but

		/// not exclusively. Can contain many more matrices by using the offset

		/// parameter.</param>

		/// <param name="offset">The offset index inside the mat array.</param>

		/// <returns>Delta Matrix created from collada matrix data.</returns>

		public static Matrix LoadColladaMatrix(float[] mat, int offset)

		{

			return new Matrix(

				mat[offset + 0], mat[offset + 4], mat[offset + 8], mat[offset + 12],

				mat[offset + 1], mat[offset + 5], mat[offset + 9], mat[offset + 13],

				mat[offset + 2], mat[offset + 6], mat[offset + 10], mat[offset + 14],

				mat[offset + 3], mat[offset + 7], mat[offset + 11], mat[offset + 15]);

		}

		#endregion



		#region LookDirection (Public)

		/// <summary>

		/// Look direction

		/// </summary>

		public override Vector LookDirection

		{

			get

			{

				return target - position;

			}

			set

			{

				// Ignored anyway

				lookDirection = value;

			}

		}

		#endregion



		#region IsFinished (Public)

		/// <summary>

		/// Has the camera reached the last node of the path?

		/// </summary>

		public bool IsFinished

		{

			get;

			private set;

		}

		#endregion



		#region Speed (Public)

		/// <summary>

		/// The speed of the camera, default is 10f.

		/// </summary>

		public float Speed

		{

			get;

			set;

		}

		#endregion



		#region Private



		#region pathByMatrices (Private)

		/// <summary>

		/// Interpolated positions and direction as a matrix.

		/// We get all the data from a Collada file.

		/// </summary>

		private readonly Matrix[] pathByMatrices;

		#endregion



		#region pathByPoints (Private)

		/// <summary>

		/// Path of the camera by position points.

		/// </summary>

		private readonly Vector[] pathByPoints;

		#endregion



		#region positionDistances (Private)

		/// <summary>

		/// Precalculated distances from the start to the current position,

		/// to speed up the calculations on moving along the path.

		/// </summary>

		private readonly float[] positionDistances;

		#endregion



		#region targetPath (Private)

		/// <summary>

		/// The camera target positions path related to the camera

		/// positions path.

		/// This path can also be longer or shorter than the positions

		/// path, because the current distance on the target path will be

		/// calculated relatively to the length of the positions path.

		/// </summary>

		private readonly Vector[] targetPath;

		#endregion



		#region targetDistances (Private)

		/// <summary>

		/// Precalculated distances from the start to the current target

		/// position, to speed up the calculations on moving along the path.

		/// </summary>

		private readonly float[] targetDistances;

		#endregion



		#region elapsedDistance (Private)

		/// <summary>

		/// The elapsed distance on the path.

		/// </summary>

		private float elapsedDistance;

		#endregion



		#region targetDistanceFactor (Private)

		/// <summary>

		/// The relative factor between the length of the camera path and

		/// the length of the target path.

		/// </summary>

		private readonly float targetDistanceFactor;

		#endregion



		#endregion



		#region Constructors

		/// <summary>

		/// Create path camera with a list of matrices.

		/// </summary>

		/// <param name="setPath">Matrix array containing path data.</param>

		public PathCamera(Matrix[] setPath)

			: this()

		{

			// Set the camera path (which is always valid)

			pathByMatrices = setPath != null

			                 	? setPath

			                 	: new Matrix[0];



			if (pathByMatrices.Length < 1)

			{

				Log.Warning("There is no camera path. We can't move any path " +

				            "without at least 1 matrix.");

				UpdateViewMatrix();

				UpdateScreenProperties();

			}



			positionDistances = new float[pathByMatrices.Length];

			float distanceCount = 0f;

			for (int index = 1; index < pathByMatrices.Length; index++)

			{

				Matrix inv1 = Matrix.Invert(pathByMatrices[index]);

				Matrix inv2 = Matrix.Invert(pathByMatrices[index - 1]);



				distanceCount += (inv1.Translation -

				                  inv2.Translation).Length;



				positionDistances[index] = distanceCount;

			}

		}



		/// <summary>

		/// Create path camera with a list of vectors (positions) and

		/// a list of target vectors (if available).

		/// </summary>

		/// <param name="setPath">Vector array containing

		/// path points data.</param>

		/// <param name="setPath">Vector array containing

		/// target path points data.</param>

		public PathCamera(Vector[] setPath, Vector[] setTargetPath = null)

			: this()

		{

			// Set the camera path (which is always valid)

			pathByPoints = (setPath != null)

			               	? setPath

			               	: new Vector[0];



			positionDistances = new float[pathByPoints.Length];

			float distanceCount = 0f;

			for (int index = 1; index < pathByPoints.Length; index++)

			{

				distanceCount += (pathByPoints[index] -

				                  pathByPoints[index - 1]).Length;

				positionDistances[index] = distanceCount;

			}



			if (pathByPoints.Length < 2)

			{

				Log.Warning("There is no camera path. We can't move any path " +

				            "without at least 2 positions.");

				UpdateViewMatrix();

				UpdateScreenProperties();

			}



			// Set the target path (if valid)

			if (setTargetPath != null)

			{

				if (setTargetPath.Length == 0)

				{

					Log.Warning("The target path needs at least one position!");

				}

				else

				{

					targetPath = setTargetPath;



					targetDistances = new float[targetPath.Length];

					distanceCount = 0f;

					for (int index = 1; index < targetPath.Length; index++)

					{

						distanceCount += (targetPath[index] -

						                  targetPath[index - 1]).Length;

						targetDistances[index] = distanceCount;

					}



					targetDistanceFactor =

						targetDistances[targetDistances.Length - 1] /

						positionDistances[positionDistances.Length - 1];

				}

			}

		}



		/// <summary>

		/// Private helper constructor to set the default values for

		/// all other constructors above.

		/// </summary>

		private PathCamera()

			: base(DefaultLookAtCamPosition, DefaultTargetPosition)

		{

			// Set the default values

			Speed = DefaultSpeed;

			IsFinished = false;

		}

		#endregion



		#region Save (Public)

		/// <summary>

		/// Override saving data from BinaryStream.

		/// </summary>

		/// <param name="dataWriter">Binary writer used for writing data.</param>

		public override void Save(BinaryWriter dataWriter)

		{

			base.Save(dataWriter);



			// Save the implementation version first

			dataWriter.Write(ImplementationVersion);



			//throw new NotImplementedException("TODO");

			//dataWriter.Write(TargetPath.Length);

			//for (int index = 0; index < TargetPath.Length; index++)

			//{

			//  TargetPath[index].Save(dataWriter);

			//}

		}

		#endregion



		#region Load (Public)

		/// <summary>

		/// Override loading data from BinaryStream.

		/// </summary>

		/// <param name="reader">Binary reader used for reading data.</param>

		public override void Load(BinaryReader reader)

		{

			base.Load(reader);



			// First read the implementation version

			int version = reader.ReadInt32();

			switch (version)

			{

					// Version 1

				case 1:

					//throw new NotImplementedException("TODO");

					//int length = reader.ReadInt32();

					//TargetPath = new Vector[length];



					//for (int index = 0; index < length; index++)

					//{

					//  TargetPath[index].Load(reader);

					//}

					break;



				default:

					Log.InvalidVersionWarning(GetType().Name + ": " + Name,

						version, ImplementationVersion);

					break;

			}

		}

		#endregion



		#region Methods (Private)



		#region InternalRun

		/// <summary>

		/// Internal run

		/// </summary>

		protected override void InternalRun()

		{

			elapsedDistance += Time.Delta * Speed;



			if (pathByMatrices != null)

			{

				UpdateMatrixPath();

			}

			else if (pathByPoints != null)

			{

				UpdatePointsPath();

			}

		}

		#endregion



		#region UpdateMatrixPath

		/// <summary>

		/// Update the path camera according to the matrices.

		/// </summary>

		private void UpdateMatrixPath()

		{

			Matrix currentMatrix = Matrix.Identity;

			if (elapsedDistance <= 0f)

			{

				currentMatrix = pathByMatrices[0];

			}

			else if (elapsedDistance >=

			         positionDistances[positionDistances.Length - 1])

			{

				IsFinished = true;

				currentMatrix = pathByMatrices[pathByMatrices.Length - 1];

			}

			else

			{

				int currentIndex = 0;

				for (int index = 0; index < positionDistances.Length - 1; index++)

				{

					if (elapsedDistance >= positionDistances[index] &&

					    elapsedDistance < positionDistances[index + 1])

					{

						currentIndex = index;

						break;

					}

				}



				currentMatrix = pathByMatrices[currentIndex];

			}



			viewMatrix = currentMatrix;

			UpdateScreenProperties();

		}

		#endregion



		#region UpdatePointsPath

		/// <summary>

		/// Update the path camera according to the vector positions and target

		/// positions (if available).

		/// </summary>

		private void UpdatePointsPath()

		{

			Vector direction;

			Vector position = GetPointPosition(pathByPoints, positionDistances,

				elapsedDistance, out direction);



			Vector target = Vector.Zero;

			if (targetPath != null)

			{

				if (targetPath.Length == 1)

				{

					target = targetPath[0];

				}

				else

				{

					target = GetPointPosition(targetPath, targetDistances,

						elapsedDistance * targetDistanceFactor, out direction);

				}

			}

			else

			{

				target = position + direction;

			}



			if (elapsedDistance >= positionDistances[positionDistances.Length - 1])

			{

				IsFinished = true;

			}



			viewMatrix = Matrix.CreateLookAt(position,

				target, UpVector);

			UpdateScreenProperties();

		}

		#endregion



		#region GetPointPosition

		/// <summary>

		/// Get a vector position by an array of positions, precalculated

		/// distances (for performance) and a current distance.

		/// <para />

		/// Basically the logic of a 2d graph but with a 3d vector as the

		/// result.

		/// </summary>

		private Vector GetPointPosition(Vector[] positions,

			float[] distances, float distance, out Vector direction)

		{

			int currentIndex = 0;



			if (distance >= distances[distances.Length - 1])

			{

				direction = positions[positions.Length - 1] -

				            positions[positions.Length - 2];

				return positions[positions.Length - 1];

			}

			else if (distance <= 0f)

			{

				direction = positions[1] - positions[0];

				return positions[0];

			}

			else

			{

				for (int index = 0; index < distances.Length - 1; index++)

				{

					if (distance >= distances[index] &&

					    distance < distances[index + 1])

					{

						currentIndex = index;

						break;

					}

				}

			}



			float relativeDistance = distance - distances[currentIndex];

			direction = positions[currentIndex + 1] - positions[currentIndex];

			direction.Normalize();

			return positions[currentIndex] + (relativeDistance * direction);

		}

		#endregion



		#endregion

	}

}