#region File Description
//-----------------------------------------------------------------------------
// A node is the basic container in the scene graph. Its basically a point in
// transformations that can contain child nodes (and inherit transformations), 
// and contain renderable entities to draw inside.
//
// Author: Ronen Ness.
// Since: 2017.
//-----------------------------------------------------------------------------
#endregion
using Microsoft.Xna.Framework;
using System.Collections.Generic;

namespace MonoGameSceneGraph
{
    /// <summary>
    /// A node with transformations, you can attach renderable entities to it, or append
    /// child nodes to inherit transformations.
    /// </summary>
    public class Node
    {
        /// <summary>
        /// Parent node.
        /// </summary>
        protected Node _parent = null;

        /// <summary>
        /// Node's transformations.
        /// </summary>
        protected Transformations _transformations = new Transformations();

        /// <summary>
        /// Is this node currently visible?
        /// </summary>
        public virtual bool Visible { get; set; }

        /// <summary>
        /// Optional identifier we can give to nodes.
        /// </summary>
        public string Identifier;

        /// <summary>
        /// Optional user data we can attach to nodes.
        /// </summary>
        public object UserData;

        /// <summary>
        /// Const return value for null bounding box.
        /// </summary>
        private static readonly BoundingBox EmptyBoundingBox = new BoundingBox();

        /// <summary>
        /// The order in which we apply transformations when building the matrix for this node.
        /// </summary>
        protected TransformOrder _transformationsOrder = TransformOrder.ScaleRotationPosition;

        /// <summary>
        /// The order in which we apply rotation when building the matrix for this node.
        /// </summary>
        protected RotationOrder _rotationOrder = RotationOrder.RotateYXZ;

        /// <summary>
        /// Local transformations matrix, eg the result of the current local transformations.
        /// </summary>
        protected Matrix _localTransform = Matrix.Identity;

        /// <summary>
        /// World transformations matrix, eg the result of the local transformations multiplied with parent transformations.
        /// </summary>
        protected Matrix _worldTransform = Matrix.Identity;

        /// <summary>
        /// Child nodes under this node.
        /// </summary>
        protected List<Node> _childNodes = new List<Node>();

        /// <summary>
        /// Child entities under this node.
        /// </summary>
        protected List<IEntity> _childEntities = new List<IEntity>();

        /// <summary>
        /// Turns true when the transformations of this node changes.
        /// </summary>
        protected bool _isDirty = true;

        /// <summary>
        /// This number increment every time we update transformations.
        /// We use it to check if our parent's transformations had been changed since last
        /// time this node was rendered, and if so, we re-apply parent updated transformations.
        /// </summary>
        protected uint _transformVersion = 0;

        /// <summary>
        /// The last transformations version we got from our parent.
        /// </summary>
        protected uint _parentLastTransformVersion = 0;

        /// <summary>
        /// Get parent node.
        /// </summary>
        public Node Parent { get { return _parent; } }

        /// <summary>
        /// Transformation version is a special identifier that changes whenever the world transformations
        /// of this node changes. Its not necessarily a sequence, but if you check this number for changes every
        /// frame its a good indication of transformation change.
        /// </summary>
        public uint TransformVersion { get { return _transformVersion; } }

        /// <summary>
        /// Create the new node.
        /// </summary>
        public Node()
        {
            Visible = true;
        }

        /// <summary>
        /// Draw the node and its children.
        /// </summary>
        public virtual void Draw()
        {
            // not visible? skip
            if (!Visible)
            {
                return;
            }

            // update transformations (only if needed, testing logic is inside)
            UpdateTransformations();

            // draw all child nodes
            foreach (Node node in _childNodes)
            {
                node.Draw();
            }

            // draw all child entities
            foreach (IEntity entity in _childEntities)
            {
                entity.Draw(this, _localTransform, _worldTransform);
            }
        }

        /// <summary>
        /// Add an entity to this node.
        /// </summary>
        /// <param name="entity">Entity to add.</param>
        public void AddEntity(IEntity entity)
        {
            _childEntities.Add(entity);
        }

        /// <summary>
        /// Remove an entity from this node.
        /// </summary>
        /// <param name="entity">Entity to add.</param>
        public void RemoveEntity(IEntity entity)
        {
            _childEntities.Remove(entity);
        }

        /// <summary>
        /// Add a child node to this node.
        /// </summary>
        /// <param name="node">Node to add.</param>
        public void AddChildNode(Node node)
        {
            // node already got a parent?
            if (node._parent != null)
            {
                throw new System.Exception("Can't add a node that already have a parent.");
            }

            // add node to children list
            _childNodes.Add(node);

            // set self as node's parent
            node.SetParent(this);
        }

        /// <summary>
        /// Remove a child node from this node.
        /// </summary>
        /// <param name="node">Node to add.</param>
        public void RemoveChildNode(Node node)
        {
            // make sure the node is a child of this node
            if (node._parent != this)
            {
                throw new System.Exception("Can't remove a node that don't belong to this parent.");
            }

            // remove node from children list
            _childNodes.Remove(node);

            // clear node parent
            node.SetParent(null);
        }

        /// <summary>
        /// Find and return first child node by identifier.
        /// </summary>
        /// <param name="identifier">Node identifier to search for.</param>
        /// <param name="searchInChildren">If true, will also search recurisvely in children.</param>
        /// <returns>Node with given identifier or null if not found.</returns>
        public Node FindChildNode(string identifier, bool searchInChildren = true)
        {
            foreach (Node node in _childNodes)
            {
                // search in direct children
                if (node.Identifier == identifier)
                {
                    return node;
                }

                // recursive search
                if (searchInChildren)
                {
                    Node foundInChild = node.FindChildNode(identifier, searchInChildren);
                    if (foundInChild != null)
                    {
                        return foundInChild;
                    }
                }
            }

            // if got here it means we didn't find any child node with given identifier
            return null;
        }

        /// <summary>
        /// Remove this node from its parent.
        /// </summary>
        public void RemoveFromParent()
        {
            // don't have a parent?
            if (_parent == null)
            {
                throw new System.Exception("Can't remove an orphan node from parent.");
            }

            // remove from parent
            _parent.RemoveChildNode(this);
        }

        /// <summary>
        /// Called when the world matrix of this node is actually recalculated (invoked after the calculation).
        /// </summary>
        protected virtual void OnWorldMatrixChange()
        {
            // update transformations version
            _transformVersion++;
            
            // notify parent
            if (_parent != null)
            {
                _parent.OnChildWorldMatrixChange(this);
            }
        }

        /// <summary>
        /// Called when local transformations are set, eg when Position, Rotation, Scale etc. is changed.
        /// We use this to set this node as "dirty", eg that we need to update local transformations.
        /// </summary>
        protected virtual void OnTransformationsSet()
        {
            _isDirty = true;
        }

        /// <summary>
        /// Set the parent of this node.
        /// </summary>
        /// <param name="newParent">New parent node to set, or null for no parent.</param>
        protected virtual void SetParent(Node newParent)
        {
            // set parent
            _parent = newParent;

            // set our parents last transformations version to make sure we'll update world transformations next frame.
            _parentLastTransformVersion = newParent != null ? newParent._transformVersion - 1 : 1;
        }

        /// <summary>
        /// Calc final transformations for current frame.
        /// This uses an indicator to know if an update is needed, so no harm is done if you call it multiple times.
        /// </summary>
        protected virtual void UpdateTransformations()
        {
            // if local transformations are dirty, we need to update them
            if (_isDirty)
            {
                _localTransform = _transformations.BuildMatrix(_transformationsOrder, _rotationOrder);
            }
            
            // if local transformations are dirty, or parent transformations are out-of-date, update world transformations
            if (_isDirty || 
                (_parent != null && _parentLastTransformVersion != _parent._transformVersion) ||
                (_parent == null && _parentLastTransformVersion != 0))
            {
                // if we got parent, apply its transformations
                if (_parent != null)
                {
                    _worldTransform = _localTransform * _parent._worldTransform;
                    _parentLastTransformVersion = _parent._transformVersion;
                }
                // if not, world transformations are the same as local, and reset parent last transformations version
                else
                {
                    _worldTransform = _localTransform;
                    _parentLastTransformVersion = 0;
                }

                // called the function that mark world matrix change (increase transformation version etc)
                OnWorldMatrixChange();
            }

            // no longer dirty
            _isDirty = false;
        }

        /// <summary>
        /// Return local transformations matrix (note: will recalculate if needed).
        /// </summary>
        public Matrix LocalTransformations
        {
            get { UpdateTransformations(); return _localTransform; }
        }

        /// <summary>
        /// Return world transformations matrix (note: will recalculate if needed).
        /// </summary>
        public Matrix WorldTransformations
        {
            get { UpdateTransformations(); return _worldTransform; }
        }

        /// <summary>
        /// Reset all local transformations.
        /// </summary>
        public void ResetTransformations()
        {
            _transformations = new Transformations();
            OnTransformationsSet();
        }

        /// <summary>
        /// Get / Set the order in which we apply local transformations in this node.
        /// </summary>
        public TransformOrder TransformationsOrder
        {
            get { return _transformationsOrder; }
            set { _transformationsOrder = value;  OnTransformationsSet(); }
        }

        /// <summary>
        /// Get / Set the order in which we apply local rotation in this node.
        /// </summary>
        public RotationOrder RotationOrder
        {
            get { return _rotationOrder; }
            set { _rotationOrder = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Get / Set node local position.
        /// </summary>
        public Vector3 Position
        {
            get { return _transformations.Position; }
            set { _transformations.Position = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Get / Set node local scale.
        /// </summary>
        public Vector3 Scale
        {
            get { return _transformations.Scale; }
            set { _transformations.Scale = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Get / Set node local rotation.
        /// </summary>
        public Vector3 Rotation
        {
            get { return _transformations.Rotation; }
            set { _transformations.Rotation = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access rotation X directly.
        /// </summary>
        public float RotationX
        {
            get { return _transformations.Rotation.X; }
            set { _transformations.Rotation.X = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access rotation Y directly.
        /// </summary>
        public float RotationY
        {
            get { return _transformations.Rotation.Y; }
            set { _transformations.Rotation.Y = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access rotation Z directly.
        /// </summary>
        public float RotationZ
        {
            get { return _transformations.Rotation.Z; }
            set { _transformations.Rotation.Z = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access scale X directly.
        /// </summary>
        public float ScaleX
        {
            get { return _transformations.Scale.X; }
            set { _transformations.Scale.X = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access scale Y directly.
        /// </summary>
        public float ScaleY
        {
            get { return _transformations.Scale.Y; }
            set { _transformations.Scale.Y = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access scale Z directly.
        /// </summary>
        public float ScaleZ
        {
            get { return _transformations.Scale.Z; }
            set { _transformations.Scale.Z = value; OnTransformationsSet(); }
        }


        /// <summary>
        /// Alias to access position X directly.
        /// </summary>
        public float PositionX
        {
            get { return _transformations.Position.X; }
            set { _transformations.Position.X = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access position Y directly.
        /// </summary>
        public float PositionY
        {
            get { return _transformations.Position.Y; }
            set { _transformations.Position.Y = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Alias to access position Z directly.
        /// </summary>
        public float PositionZ
        {
            get { return _transformations.Position.Z; }
            set { _transformations.Position.Z = value; OnTransformationsSet(); }
        }

        /// <summary>
        /// Move position by vector.
        /// </summary>
        /// <param name="moveBy">Vector to translate by.</param>
        public void Translate(Vector3 moveBy)
        {
            _transformations.Position += moveBy;
            OnTransformationsSet();
        }

        /// <summary>
        /// Called every time one of the child nodes recalculate world transformations.
        /// </summary>
        /// <param name="node">The child node that updated.</param>
        public virtual void OnChildWorldMatrixChange(Node node)
        {
        }

        /// <summary>
        /// Return true if this node is empty.
        /// </summary>
        public bool Empty
        {
            get { return _childEntities.Count == 0 && _childNodes.Count == 0; }
        }

        /// <summary>
        /// Get bounding box of this node and all its child nodes.
        /// </summary>
        /// <param name="includeChildNodes">If true, will include bounding box of child nodes. If false, only of entities directly attached to this node.</param>
        /// <returns>Bounding box of the node and its children.</returns>
        public virtual BoundingBox GetBoundingBox(bool includeChildNodes = true)
        {
            // if empty skip
            if (Empty)
            {
                return EmptyBoundingBox;
            }

            // make sure transformations are up-to-date
            UpdateTransformations();

            // list of points to build bounding box from
            List<Vector3> corners = new List<Vector3>();

            // apply all child nodes bounding boxes
            if (includeChildNodes)
            {
                foreach (Node child in _childNodes)
                {
                    // skip invisible nodes
                    if (!child.Visible)
                    {
                        continue;
                    }

                    // get bounding box
                    BoundingBox currBox = child.GetBoundingBox();
                    if (currBox.Min != currBox.Max)
                    {
                        corners.Add(currBox.Min);
                        corners.Add(currBox.Max);
                    }
                }
            }

            // apply all entities directly under this node
            foreach (IEntity entity in _childEntities)
            {
                // skip invisible entities
                if (!entity.Visible)
                {
                    continue;
                }

                // get entity bounding box
                BoundingBox currBox = entity.GetBoundingBox(this, _localTransform, _worldTransform);
                if (currBox.Min != currBox.Max)
                {
                    corners.Add(currBox.Min);
                    corners.Add(currBox.Max);
                }
            }

            // nothing in this node?
            if (corners.Count == 0)
            {
                return EmptyBoundingBox;
            }

            // return final bounding box
            return BoundingBox.CreateFromPoints(corners);
        }
    }
}