//### Bezier Logic
//This is an utilety class for all major calculations related to vectorized bezier curve.
//
//License information: [ASSET STORE TERMS OF SERVICE AND EULA](https://unity3d.com/legal/as_terms)
//
//Developed by [MathArtCode](https://www.assetstore.unity3d.com/en/#!/search/page=1/sortby=popularity/query=publisher:8738) team, 2015

using System;
using System.Linq;
using Assets.Scripts.BezierCurvedParticlesFlow.Interfaces;
using UnityEngine;

namespace Assets.Scripts.BezierCurvedParticlesFlow.Utilities {
    [Serializable]
    public sealed class BezierLogic : IBezierLogic {
        [SerializeField]
        private Vector3[] _points;

        //All points are handeled inside a single array 
        //- positioning (end points) have indexes 0, 3, 6, ... 
        //- angles (control points) have indexes 1,2, 4,5, ...
        private Vector3[] Points {
            get {
                if (_points == null) {
                    Reset();
                }
                return _points;
            }
        }

        // Provides ammount of all points (end points + control pouints in AI terminolagy)
        public int ControlPointCount {
            get { return Points.Length; }
        }

        // Provides ammount of all curved segments of Bezier curve
        private int CurveCount {
            get { return (Points.Length - 1)/3; }
        }

        // Returns a coordinate point relative to curve 'time' where 0 is bezier curve beginning and 1 is end of the bezier curve (length vise)
        public Vector3 GetPoint(float t) {
            int i;
            if (t >= 1f) {
                t = 1f;
                i = _points.Length - 4;
            }
            else {
                t = Mathf.Clamp01(t)*CurveCount;
                i = (int) t;
                t -= i;
                i *= 3;
            }
            return GetPoint(_points[i], _points[i + 1], _points[i + 2], _points[i + 3], t);
        }

        // Returns a velocity point relative to curve 'time' where 0 is bezier curve beginning and 1 is end of the bezier curve (length vise)
        public Vector3 GetVelocity(float t) {
            int i;
            if (t >= 1f) {
                t = 1f;
                i = _points.Length - 4;
            }
            else {
                t = Mathf.Clamp01(t)*CurveCount;
                i = (int) t;
                t -= i;
                i *= 3;
            }
            return
                GetFirstDerivative(_points[i], _points[i + 1], _points[i + 2], _points[i + 3], t);
        }

        // Returns a normalized velocity point relative to curve 'time' where 0 is bezier curve beginning and 1 is end of the bezier curve (length vise)
        public Vector3 GetDirection(float t) {
            return GetVelocity(t).normalized;
        }

        //### Mathematical core of Bezier Logic

        private static Vector3 GetPoint(Vector3 p0, Vector3 p1, Vector3 p2, Vector3 p3, float t) {
            t = Mathf.Clamp01(t);
            var oneMinusT = 1f - t;
            return
                oneMinusT*oneMinusT*oneMinusT*p0 +
                3f*oneMinusT*oneMinusT*t*p1 +
                3f*oneMinusT*t*t*p2 +
                t*t*t*p3;
        }

        private static Vector3 GetFirstDerivative(Vector3 p0, Vector3 p1, Vector3 p2, Vector3 p3, float t) {
            t = Mathf.Clamp01(t);
            var oneMinusT = 1f - t;
            return
                3f*oneMinusT*oneMinusT*(p1 - p0) +
                6f*oneMinusT*t*(p2 - p1) +
                3f*t*t*(p3 - p2);
        }

        //Resets component to its default 2 points (forming a straight line)
        public void Reset() {
            _points = new[] {
                new Vector3(0f, 0f, 0f),
                new Vector3(2f, 0f, 0f),
                new Vector3(3f, 0f, 0f),
                new Vector3(4f, 0f, 0f)
            };
        }

        //Returns a point by its index
        //- positioning (end points) have indexes 0, 3, 6, ... 
        //- angles (control points) have indexes 1,2, 4,5, ...
        public Vector3 GetControlPoint(int index) {
            return Points[index];
        }

        //Sets a point value by its index
        //- positioning (end points) have indexes 0, 3, 6 ... 
        //- angles (control points) have indexes 1,2, 4,5, ...
        public void SetControlPoint(int index, Vector3 point) {
            if (index%3 == 0) {
                var delta = point - Points[index];

                if (index > 0) {
                    _points[index - 1] += delta;
                }
                if (index + 1 < _points.Length) {
                    _points[index + 1] += delta;
                }
            }

            Points[index] = point;
        }

        // Adds a position point + 2 angle points
        public void AddPoint() {
            var length = Points.Length;
            var point = _points[length - 1];
            var velocity = GetDirection(1f);
            Array.Resize(ref _points, length + 3);
            length = Points.Length;

            point += velocity;
            _points[length - 3] = point;
            point += velocity;
            _points[length - 2] = point;
            point += velocity;
            _points[length - 1] = point;
        }

        // Removes a position point + 2 angle points. gets an end point index as an argument
        //- positioning (end points) have indexes 0, 3, 6... 
        public void RemovePoint(int selectedIndex) {
            var points = Points.ToList();

            if (selectedIndex == _points.Length - 1) {
                points.RemoveRange(selectedIndex - 2, 3);
            }
            else {
                points.RemoveRange(selectedIndex - 1, 3);
            }
            _points = points.ToArray();
        }
    }
}