using UnityEngine;

namespace Do.Spacegame
{
    public class Foliage : MonoBehaviour
    {
        [SerializeField] MeshFilter meshFilter = null;
        [SerializeField] MeshRenderer meshRenderer = null;
        [SerializeField] LayerMask layerMask = new LayerMask();
        Spring spring = new Spring();

        static readonly string LAYER = "Level";
        static readonly int LAYER_ORDER = 50;
        [SerializeField] float BEND_FACTOR = 0.5f;
        [SerializeField] float BEND_FORCE_ON_EXIT = 0.3f;
        [SerializeField] float colliderHalfWidth = 0.5f;

        float enterOffset = 0;
        float exitOffset = 0;
        bool isBending = false;
        bool isRebounding = false;

        void Awake()
        {
            meshRenderer.sortingLayerName = LAYER;
            meshRenderer.sortingOrder = LAYER_ORDER;
        }

        void LateUpdate()
        {
            if (!isRebounding)
                return;

            // apply the spring until its acceleration dies down
            if (Mathf.Abs(spring.acceleration) < Mathf.Epsilon)
            {
                setVertHorizontalOffset(0f);
                isRebounding = false;
            }
            else
                setVertHorizontalOffset(spring.simulate());
        }

        void OnTriggerEnter2D(Collider2D collider)
        {
            if ((layerMask.value & 1 << collider.gameObject.layer) == 0)
                return;

            enterOffset = collider.transform.position.x - transform.position.x;
        }

        void OnTriggerExit2D(Collider2D collider)
        {
            if ((layerMask.value & 1 << collider.gameObject.layer) == 0)
                return;

            // Apply a force in the opposite direction that we are currently bending
            if (isBending)
                spring.applyForceStartingAtPosition(BEND_FORCE_ON_EXIT * Mathf.Sign(exitOffset), exitOffset);

            isBending = false;
            isRebounding = true;
        }

        void OnTriggerStay2D(Collider2D collider)
        {
            if ((layerMask.value & 1 << collider.gameObject.layer) == 0)
                return;

            float offset = collider.transform.position.x - transform.position.x;

            if (isBending || Mathf.Sign(enterOffset) != Mathf.Sign(offset))
            {
                float radius = colliderHalfWidth + collider.bounds.size.x * 0.5f;
                exitOffset = map(offset, -radius, radius, -1f, 1f);
                setVertHorizontalOffset(exitOffset);

                isRebounding = false;
                isBending = true;
            }
        }
        void setVertHorizontalOffset(float offset)
        {
            Vector3[] vertices = meshFilter.mesh.vertices;

            vertices[2].x = -0.5f + (offset * BEND_FACTOR / transform.localScale.x);
            vertices[3].x = +0.5f + (offset * BEND_FACTOR / transform.localScale.x);

            meshFilter.mesh.vertices = vertices;
        }

        static float map(float value, float leftMin, float leftMax, float rightMin, float rightMax) => rightMin + (value - leftMin) * (rightMax - rightMin) / (leftMax - leftMin);
    }
}