using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(LineRenderer))]
public class PhysicLineSegment : MonoBehaviour
{
    public float segmentSpacing = 0.1f;
    public int k = 30;

    public List<VerletParticle> particles = new();
    private List<VerletStick> sticks = new();
    [HideInInspector]
    public LineRenderer lineRenderer;
    private int segmentCount;
    public float gravity = -9.8f;

    private float originalLength;

    public void Initialize(Vector3 start, Vector3 end)
    {
        particles.Clear();
        sticks.Clear();
        if (lineRenderer != null)
        {
            lineRenderer.positionCount = 0;
        }

        originalLength = Vector3.Distance(start, end);

        segmentCount = Mathf.RoundToInt(originalLength / segmentSpacing);
        lineRenderer = GetComponent<LineRenderer>();

        // Initialize particles
        for (int i = 0; i < segmentCount; i++)
        {
            var particle = new VerletParticle(Vector3.Lerp(start, end, i / (float)segmentCount));
            particles.Add(particle);
        }

        // Initialize sticks
        for (int i = 0; i < segmentCount - 1; i++)
        {
            sticks.Add(new VerletStick(particles[i], particles[i + 1], segmentSpacing));
        }

        // Lock the first particle
        particles[0].isLocked = true;

        lineRenderer.positionCount = segmentCount;
    }

    void FixedUpdate()
    {
        UpdateLine();
        for (int i = 0; i < segmentCount; i++)
        {
            if (lineRenderer != null)
            {
                lineRenderer.SetPosition(i, particles[i].position);
            }
        }
    }

    void UpdateLine()
    {
        // Apply gravity to particles
        for (int i = 1; i < particles.Count; i++)
        {
            particles[i].ApplyForce(Vector3.up * gravity * Time.deltaTime);
            particles[i].UpdatePosition();
        }

        // Update sticks
        for (int ik = 0; ik < k; ik++)
        {
            foreach (var stick in sticks)
            {
                stick.UpdateStick();
            }
        }
    }
    
    public void UpdatePlug(Transform plug)
    {
        if (plug && particles.Count > 1)
        {
            Vector3 plugPosition = particles[^1].position;
            float plugLength = plug.GetComponent<SpriteRenderer>().bounds.size.y;
            Vector3 direction = particles[^1].position - particles[^2].position;
            float angle = Mathf.Atan2(direction.y, direction.x) * Mathf.Rad2Deg;
            plug.rotation = Quaternion.Euler(0, 0, angle - 90f);
            plug.position = plugPosition + direction.normalized * (plugLength / 2);
        }
    }

    public void UpdateStart(Vector3 newStartPosition)
    {
        if (particles.Count > 0)
        {
            particles[0].position = newStartPosition;
        }
    }
}