using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using SharpGLTF.Transforms;

using XFORM = System.Numerics.Matrix4x4;

namespace SharpGLTF.Runtime
{
    /// <summary>
    /// Represents a specific and independent state of a <see cref="SceneTemplate"/>.
    /// </summary>
    public sealed class SceneInstance
    {
        #region lifecycle

        internal SceneInstance(NodeTemplate[] nodeTemplates, DrawableTemplate[] drawables, Collections.NamedList<float> tracks)
        {
            _AnimationTracks = tracks;

            _NodeTemplates = nodeTemplates;
            _NodeInstances = new NodeInstance[_NodeTemplates.Length];

            for (var i = 0; i < _NodeInstances.Length; ++i)
            {
                var n = _NodeTemplates[i];
                var pidx = _NodeTemplates[i].ParentIndex;

                if (pidx >= i) throw new ArgumentException("invalid parent index", nameof(nodeTemplates));

                var p = pidx < 0 ? null : _NodeInstances[pidx];

                _NodeInstances[i] = new NodeInstance(n, p);
            }

            _DrawableReferences = drawables;
            _DrawableTransforms = new IGeometryTransform[_DrawableReferences.Length];

            for (int i = 0; i < _DrawableTransforms.Length; ++i)
            {
                _DrawableTransforms[i] = _DrawableReferences[i].CreateGeometryTransform();
            }
        }

        #endregion

        #region data

        private readonly NodeTemplate[] _NodeTemplates;
        private readonly NodeInstance[] _NodeInstances;

        private readonly DrawableTemplate[] _DrawableReferences;
        private readonly IGeometryTransform[] _DrawableTransforms;

        private readonly Collections.NamedList<float> _AnimationTracks;

        #endregion

        #region properties

        /// <summary>
        /// Gets a list of all the <see cref="NodeInstance"/> nodes used by this <see cref="SceneInstance"/>.
        /// </summary>
        public IReadOnlyList<NodeInstance> LogicalNodes => _NodeInstances;

        /// <summary>
        /// Gets all the <see cref="NodeInstance"/> roots used by this <see cref="SceneInstance"/>.
        /// </summary>
        public IEnumerable<NodeInstance> VisualNodes => _NodeInstances.Where(item => item.VisualParent == null);

        /// <summary>
        /// Gets all the names of the animations tracks.
        /// </summary>
        public IEnumerable<String> AnimationTracks => _AnimationTracks.Names;

        /// <summary>
        /// Gets the number of drawable references.
        /// </summary>
        [Obsolete("Use DrawableInstancesCount")]
        public int DrawableReferencesCount => _DrawableTransforms.Length;

        /// <summary>
        /// Gets the number of drawable instances.
        /// </summary>
        public int DrawableInstancesCount => _DrawableTransforms.Length;

        /// <summary>
        /// Gets a collection of drawable references, where:
        /// <list type="bullet">
        /// <item>
        /// <term>MeshIndex</term>
        /// <description>The logical Index of a <see cref="Schema2.Mesh"/> in <see cref="Schema2.ModelRoot.LogicalMeshes"/>.</description>
        /// </item>
        /// <item>
        /// <term>Transform</term>
        /// <description>An <see cref="IGeometryTransform"/> that can be used to transform the <see cref="Schema2.Mesh"/> into world space.</description>
        /// </item>
        /// </list>
        /// </summary>
        [Obsolete("Use DrawableInstances.")]
        public IEnumerable<(int MeshIndex, IGeometryTransform Transform)> DrawableReferences
        {
            get
            {
                for (int i = 0; i < _DrawableTransforms.Length; ++i)
                {
                    yield return GetDrawableReference(i);
                }
            }
        }

        public IEnumerable<DrawableInstance> DrawableInstances
        {
            get
            {
                for (int i = 0; i < _DrawableTransforms.Length; ++i)
                {
                    yield return GetDrawableInstance(i);
                }
            }
        }

        #endregion

        #region API

        public void SetLocalMatrix(string name, XFORM localMatrix)
        {
            var n = LogicalNodes.FirstOrDefault(item => item.Name == name);
            if (n == null) return;
            n.LocalMatrix = localMatrix;
        }

        public void SetWorldMatrix(string name, XFORM worldMatrix)
        {
            var n = LogicalNodes.FirstOrDefault(item => item.Name == name);
            if (n == null) return;
            n.WorldMatrix = worldMatrix;
        }

        public void SetPoseTransforms()
        {
            foreach (var n in _NodeInstances) n.SetPoseTransform();
        }

        public float GetAnimationDuration(int trackLogicalIndex)
        {
            if (trackLogicalIndex < 0) return 0;
            if (trackLogicalIndex >= _AnimationTracks.Count) return 0;

            return _AnimationTracks[trackLogicalIndex];
        }

        public float GetAnimationDuration(string trackName)
        {
            return GetAnimationDuration(_AnimationTracks.IndexOf(trackName));
        }

        public void SetAnimationFrame(int trackLogicalIndex, float time, bool looped = true)
        {
            if (looped)
            {
                var duration = GetAnimationDuration(trackLogicalIndex);
                if (duration > 0) time = time % duration;
            }

            foreach (var n in _NodeInstances) n.SetAnimationFrame(trackLogicalIndex, time);
        }

        public void SetAnimationFrame(string trackName, float time, bool looped = true)
        {
            SetAnimationFrame(_AnimationTracks.IndexOf(trackName), time, looped);
        }

        public void SetAnimationFrame(params (int TrackIdx, float Time, float Weight)[] blended)
        {
            SetAnimationFrame(_NodeInstances, blended);
        }

        public static void SetAnimationFrame(IEnumerable<NodeInstance> nodes, params (int TrackIdx, float Time, float Weight)[] blended)
        {
            Guard.NotNull(nodes, nameof(nodes));

            Span<int> tracks = stackalloc int[blended.Length];
            Span<float> times = stackalloc float[blended.Length];
            Span<float> weights = stackalloc float[blended.Length];

            float w = blended.Sum(item => item.Weight);

            w = w == 0 ? 1 : 1 / w;

            for (int i = 0; i < blended.Length; ++i)
            {
                tracks[i] = blended[i].TrackIdx;
                times[i] = blended[i].Time;
                weights[i] = blended[i].Weight * w;
            }

            foreach (var n in nodes) n.SetAnimationFrame(tracks, times, weights);
        }

        /// <summary>
        /// Gets a drawable reference pair, where:
        /// - MeshIndex is the logical Index of a <see cref="Schema2.Mesh"/> in <see cref="Schema2.ModelRoot.LogicalMeshes"/>.
        /// - Transform is an <see cref="IGeometryTransform"/> that can be used to transform the <see cref="Schema2.Mesh"/> into world space.
        /// </summary>
        /// <param name="index">The index of the drawable reference, from 0 to <see cref="DrawableReferencesCount"/></param>
        /// <returns>A drawable reference</returns>
        [Obsolete("Use GetDrawableInstance")]
        public (int MeshIndex, IGeometryTransform Transform) GetDrawableReference(int index)
        {
            var dref = _DrawableReferences[index];

            dref.UpdateGeometryTransform(_DrawableTransforms[index], _NodeInstances);

            return (dref.LogicalMeshIndex, _DrawableTransforms[index]);
        }

        /// <summary>
        /// Gets a <see cref="DrawableInstance"/> object, where:
        /// - Name is the name of this drawable instance. Originally, it was the name of <see cref="Schema2.Node"/>.
        /// - MeshIndex is the logical Index of a <see cref="Schema2.Mesh"/> in <see cref="Schema2.ModelRoot.LogicalMeshes"/>.
        /// - Transform is an <see cref="IGeometryTransform"/> that can be used to transform the <see cref="Schema2.Mesh"/> into world space.
        /// </summary>
        /// <param name="index">The index of the drawable reference, from 0 to <see cref="DrawableInstancesCount"/></param>
        /// <returns><see cref="DrawableInstance"/> object.</returns>
        public DrawableInstance GetDrawableInstance(int index)
        {
            var dref = _DrawableReferences[index];

            dref.UpdateGeometryTransform(_DrawableTransforms[index], _NodeInstances);

            return new DrawableInstance(dref, _DrawableTransforms[index]);
        }

        #endregion
    }
}