using System.Collections.Generic;
using UnityEngine;

public class Rope : MonoBehaviour
{
    [SerializeField] protected int constraintIterations = 15;
    [SerializeField] protected float gravityMultiplier = 1.0f;
    [SerializeField] protected float lineWidth = 0.2f;
    [SerializeField] protected float ropeSegmentLength = 0.1f;
    [SerializeField] protected int segmentCount = 35;

    protected LineRenderer lr;
    protected DistanceJoint2D dj;
    protected GameObject player;
    protected List<RopeSegment> ropeSegments = new List<RopeSegment>();
    protected Vector3[] ropePositions;
    protected bool ropeCreated = false;

    // Start is called before the first frame update
    protected void Start()
    {
        player = GameObject.FindGameObjectWithTag("Player");
        dj = GetComponent<DistanceJoint2D>();
        lr = GetComponent<LineRenderer>();
        lr.startWidth = lineWidth;
        lr.endWidth = lineWidth;
        ropePositions = new Vector3[segmentCount];
        lr.positionCount = segmentCount;
        Vector2 ropeLoc = transform.position;

        for (int i = 0; i < segmentCount; i++)
        {
            ropeSegments.Add(new RopeSegment(ropeLoc));
            ropeLoc.y -= ropeSegmentLength;
        }
    }

    // Update is called once per frame
    protected void Update()
    {
        if (!ropeCreated)
        {
            CreateRope();
            ropeCreated = true;
        }
        else
        {

        }
        RenderLine();
        Simulate();
    }

    protected void RenderLine()
    {
        for (int i = 0; i < ropePositions.Length; i++)
        {
            ropePositions[i] = ropeSegments[i].posNow;
        }
        lr.SetPositions(ropePositions);
    }

    protected void CreateRope()
    {
        dj.connectedBody = player.GetComponent<Rigidbody2D>();
        dj.maxDistanceOnly = true;
        dj.distance = Vector2.Distance(player.transform.position, transform.position);
    }

    protected void Simulate()
    {
        Vector2 gravityForce = new Vector2(0f, -gravityMultiplier);

        for (int i = 0; i < ropeSegments.Count; i++)
        {
            RopeSegment segment = ropeSegments[i];
            Vector2 velocity = segment.posNow - segment.posOld;
            segment.posOld = segment.posNow;
            segment.posNow += velocity;
            segment.posNow += gravityForce * Time.deltaTime;
            ropeSegments[i] = segment;
        }

        for (int i = 0; i < constraintIterations; i++)
        {
            ApplyContraint();
        }
    }

    protected void ApplyContraint()
    {
        RopeSegment endSegment1 = ropeSegments[0];
        endSegment1.posNow = transform.position;
        ropeSegments[0] = endSegment1;

        RopeSegment endSegment2 = ropeSegments[ropeSegments.Count - 1];
        endSegment2.posNow = player.transform.position;
        ropeSegments[ropeSegments.Count - 1] = endSegment2;

        for (int i = 0; i < ropeSegments.Count - 1; i++)
        {
            RopeSegment segment1 = ropeSegments[i];
            RopeSegment segment2 = ropeSegments[i + 1];

            float distance = (segment1.posNow - segment2.posNow).magnitude;
            float error = distance - ropeSegmentLength;
            Vector2 normalChange = (segment1.posNow - segment2.posNow).normalized;
            Vector2 change = normalChange * error;

            if (i != 0)
            {
                segment1.posNow -= change * 0.5f;
                ropeSegments[i] = segment1;
                segment2.posNow += change * 0.5f;
                ropeSegments[i + 1] = segment2;
            }
            else
            {
                segment2.posNow += change;
                ropeSegments[i + 1] = segment2;
            }
        }
    }

    public struct RopeSegment
    {
        public Vector2 posNow;
        public Vector2 posOld;

        public RopeSegment(Vector2 pos)
        {
            this.posNow = pos;
            this.posOld = pos;
        }
    }
}