using System.Collections.Generic;
using UnityEngine;

namespace CreatureControl {

    /// <summary>
    /// A leg of a creature
    /// </summary>
    [System.Serializable]
    public class Leg {
        [SerializeField]
        private Transform _coxa;
        /// <summary>
        /// The hip bone
        /// </summary>
        public Transform coxa {
            get => this._coxa;
            set {
                this._coxa = value;
                this._femurLength = 0;
            }
        }

        [SerializeField]
        private Transform _femur;
        /// <summary>
        /// The upper leg or thigh bone
        /// </summary>
        public Transform femur {
            get => this._femur;
            set {
                this._femur = value;
                this._femurLength = 0;
            }
        }

        [SerializeField]
        private Transform _tibia;
        /// <summary>
        /// The lower leg or shank bone
        /// </summary>
        public Transform tibia {
            get => this._tibia;
            set {
                this._tibia = value;
                this._femurLength = 0;
                this._tibiaLength = 0;
            }
        }

        [SerializeField]
        private Transform _tarsus;
        /// <summary>
        /// The foot bone
        /// </summary>
        public Transform tarsus {
            get => this._tarsus;
            set {
                this._tarsus = value;
                this._tibiaLength = 0;
                this._tarsusLength = 0;
            }
        }

        [SerializeField]
        private Transform _phalanges;
        /// <summary>
        /// The toes
        /// </summary>
        public Transform phalanges {
            get => this._phalanges;
            set {
                this._phalanges = value;
                this._tarsusLength = 0;
                this._phalangesLength = 0;
            }
        }

        [SerializeField]
        private Transform _end;
        /// <summary>
        /// The end of the leg
        /// </summary>
        public Transform end {
            get => this._end;
            set {
                this._end = value;
                this._phalangesLength = 0;
            }
        }

        #region Bones

        [SerializeField]
        private float _femurLength;
        /// <summary>
        /// The length of the femur bone
        /// </summary>
        public float femurLength {
            get {
                if (_femurLength <= 0 && this.femur != null && this.tibia != null)
                    _femurLength = Vector3.Distance(this.femur.position, this.tibia.position);
                return _femurLength;
            }
        }

        [SerializeField]
        private float _tibiaLength;
        /// <summary>
        /// The length of the tibia bone
        /// </summary>
        public float tibiaLength {
            get {
                if (_tibiaLength <= 0 && this.tibia != null && this.tarsus != null)
                    _tibiaLength = Vector3.Distance(this.tibia.position, this.tarsus.position);
                return _tibiaLength;
            }
        }

        [SerializeField]
        private float _tarsusLength;
        /// <summary>
        /// The length of the tarsus bone
        /// </summary>
        public float tarsusLength {
            get {
                if (_tarsusLength <= 0 && this.tarsus != null && this.phalanges != null)
                    _tarsusLength = Vector3.Distance(this.tarsus.position, this.phalanges.position);
                return _tarsusLength;
            }
        }

        [SerializeField]
        private float _phalangesLength;
        /// <summary>
        /// The length of the phalanges
        /// </summary>
        public float phalangesLength {
            get {
                if (_phalangesLength <= 0 && this.phalanges != null && this.end != null)
                    _phalangesLength = Vector3.Distance(this.phalanges.position, this.end.position);
                return _phalangesLength;
            }
        }

        /// <summary>
        /// The length of the leg from hip to foot
        /// </summary>
        /// This consists of the femur and tibia
        public float length => femurLength + tibiaLength;

        /// <summary>
        /// The size of the foot
        /// </summary>
        /// This consists of the tarsus and phalanges
        public float footLength => tarsusLength + phalangesLength;

        public void ResetLengths() {
            _femurLength = 0;
            _tibiaLength = 0;
            _tarsusLength = 0;
            _phalangesLength = 0;
        }

        /// <summary>
        /// Try to determine the leg bones
        /// </summary>
        /// <param name="firstLegBone">the first bone of the leg (could be coxa or femur depending on chain length)</param>        
        public void DetectBones(Transform root) {
            if (root == null)
                return;
            coxa = femur = tibia = tarsus = phalanges = end = null;

            // gather a straight chain following single-child links
            List<Transform> chain = new();
            Transform current = root;
            chain.Add(current);
            while (current.childCount == 1) {
                current = current.GetChild(0);
                chain.Add(current);
            }

            // the detected end bone is the last element in the collected chain
            end = chain[^1];

            // map chain length to bone roles according to rules:
            // 1 => femur
            // 2 => femur, tibia
            // 3 => femur, tibia, tarsus
            // 4 => femur, tibia, tarsus, phalanges
            // 5+ => coxa, femur, tibia, tarsus, phalanges (first 5)
            int count = chain.Count;
            if (count == 1)
                femur = chain[0];
            else if (count == 2) {
                femur = chain[0];
                tibia = chain[1];
            }
            else if (count == 3) {
                femur = chain[0];
                tibia = chain[1];
                tarsus = chain[2];
            }
            else if (count == 4) {
                femur = chain[0];
                tibia = chain[1];
                tarsus = chain[2];
                phalanges = chain[3];
            }
            else // count >= 5
            {
                coxa = chain[0];
                femur = chain[1];
                tibia = chain[2];
                tarsus = chain[3];
                phalanges = chain[4];
            }
        }

        #endregion Bones

        /// <summary>
        /// Check if all bones of the legs have been configured
        /// </summary>
        /// <returns>True when all bones are configured</returns>
        public bool isConfigured =>
            this.femur != null &&
            this.tibia != null &&
            this.tarsus != null &&
            this.phalanges != null &&
            this.end != null;

        public Side side;
        public bool isLeft => side == Side.Left;
        public bool isRight => side == Side.Right;

        private Vector3 _kneeAxis = Vector3.zero;
        public Vector3 kneeAxis {
            get {
                if (this._kneeAxis.sqrMagnitude == 0) {
                    Vector3 femurWorldDirection = (this.tibia.position - this.femur.position).normalized;
                    Vector3 tibiaWorldDirection = (this.tarsus.position - this.tibia.position).normalized;
                    Vector3 kneeWorldAxis = Vector3.Cross(femurWorldDirection, tibiaWorldDirection);
                    Vector3 kneeLocalAxis = this.femur.InverseTransformDirection(kneeWorldAxis);
                    this._kneeAxis = kneeLocalAxis;
                }
                return this._kneeAxis;
            }
        }
    }

}