using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(LineRenderer))]
public class Cable : MonoBehaviour
{
    public Transform start;
    public Transform end;
    public int resolution = 10;
    public float dstMin = 0.1f;
    public float dstMax = 1.0f;
    public float forceMin = 0.1f;
    public float forceMax = 1.0f;
    public int k = 10;

    private LineRenderer lineRenderer;
    private Vector3[] points;

    private void Start()
    {
        lineRenderer = GetComponent<LineRenderer>();
        points = new Vector3[resolution];
        for (int i = 0; i < resolution; i++)
        {
            float t = i / (float)(resolution - 1);
            points[i] = Vector3.Lerp(start.position, end.position, t);
        }

        lineRenderer.positionCount = resolution;
    }

    private void FixedUpdate()
    {
        UpdateRope();
        for (int i = 0; i < resolution; i++)
        {
            lineRenderer.SetPosition(i, points[i] + Vector3.forward * -.3f);
        }
    }

    void UpdateRope()
    {
        float t = Mathf.InverseLerp(dstMin, dstMax, (start.position - end.position).magnitude);
        float F = Mathf.Lerp(forceMin, forceMax, t);
        points[0] = start.position;
        points[points.Length - 1] = end.position;

        for (int ik = 0; ik < k; ik++)
        {
            for (int i = 1; i < points.Length - 1; i++)
            {
                Vector3 offsetPrev = (points[i - 1] - points[i]);
                Vector3 offsetNext = points[i + 1] - points[i];
                Vector3 velocity = offsetPrev.normalized * offsetPrev.magnitude * F +
                                   offsetNext.normalized * offsetNext.magnitude * F;
                points[i] += velocity * Time.deltaTime / k;
            }

            for (int i = 1; i < points.Length - 1; i++)
            {
                points[i] += Vector3.down * 9.8f * Time.deltaTime / k;
            }
        }
    }
}