using UnityEngine;
using UnityEngine.Assertions;
using System.Linq;
using Unity.Netcode;

public class RopeSimulator : MonoBehaviour
{
    [Header("Solver")]
    [SerializeField] int solveIterations = 10;
    Transform ropeStart, ropeEnd;

    [Header("Rope Settings")]
    [SerializeField] int subDivision = 20;
    [SerializeField] float distBetweenRopePoints = 0.2f;

    [Header("Rope Renderer")]
    [SerializeField] LineRenderer lineRenderer;

    [SerializeField] Rope rope;

    [Header("Networking")]
    [SerializeField] CircularBuffer<RopeState> stateBuffer;
    private const int k_stateBufferSize = 128;
    private int currentTick => NetworkManager.Singleton.NetworkTickSystem.LocalTime.Tick;

    private void Awake()
    {
        stateBuffer = new CircularBuffer<RopeState>(k_stateBufferSize);

    }

    private void OnEnable()
    {
        GameManager.OnPlayersReady += Init;
    }

    private void OnDisable()
    {
        GameManager.OnPlayersReady += Init;
    }

    private void Update()
    {
        rope.points.First().position = ropeStart.position;
        rope.points.Last().position = ropeEnd.position;
        Simulate(this.rope, Time.deltaTime, this.distBetweenRopePoints, this.solveIterations);

        DisplayRope();
    }

    private void Init(GameObject[] players)
    {
        this.ropeStart = players[0].transform;
        this.ropeEnd = players[1].transform;

        this.rope = RopeSimulator.BuildRope(this.ropeStart, this.ropeEnd, this.subDivision, this.distBetweenRopePoints);
    }

    private void DisplayRope()
    {
        if (!lineRenderer) return;

        lineRenderer.positionCount = rope.points.Length;
        lineRenderer.SetPositions(rope.points.Select(point => point.position).ToArray());
    }

    public static Rope BuildRope(Transform ropeStart, Transform ropeEnd, int subDivision, float distBetweenRopePoints)
    {
        Assert.IsNotNull(ropeStart);
        Assert.IsNotNull(ropeEnd);

        RopeBuilder builder = new();
        builder.AddPoint(new Point(ropeStart.position, locked: true));

        for (int i = 0; i < subDivision; i++)
        {
            Vector3 pointPos = Vector3.Lerp(ropeStart.position, ropeEnd.position, (float) i / (float) subDivision);
            builder.AddPoint(new Point(pointPos, locked: false));
        }

        builder.AddPoint(new Point(ropeEnd.position, locked: true));

        for (int i = 0; i <= subDivision; i++)
        {
            builder.ConnectPointsWithDesiredLength(i, i + 1, desiredLength: distBetweenRopePoints);
        }

        return builder.Build();
    }

    public static void Simulate(Rope rope, float dt, float desiredLength, int solveIterations)
    {
        Assert.IsNotNull(rope);
        Assert.IsTrue(dt > 0f);

        foreach (var point in rope.points)
        {
            if (point.locked) continue;

            // Verlet
            Vector3 prevPos = point.position;
            point.position += point.position - point.prevPosition;
            point.prevPosition = prevPos;
        }

        // Stick resolution
        for (int solveIter = 0; solveIter < solveIterations; solveIter++)
        {
            for (int stickIdx = 0; stickIdx < rope.sticks.Length; stickIdx++)
            {
                var stick = rope.sticks[stickIdx];
                Vector3 stickDir = (stick.B.position - stick.A.position);
                Vector3 stickCentre = stick.A.position + stickDir / 2f;
                float length = stickDir.magnitude;
                if (length > stick.desiredLength)
                {
                    float distribution = stick.A.locked || stick.B.locked ? 1f : 2f;
                    float distanceToMove = (length - stick.desiredLength) / distribution;
                    if (!stick.A.locked)
                    {
                        Vector3 prevPos = stick.A.position;
                        stick.A.position += stickDir.normalized * distanceToMove;
                        stick.A.prevPosition = prevPos;
                    }
                    if (!stick.B.locked)
                    {
                        Vector3 prevPos = stick.B.position;
                        stick.B.position -= stickDir.normalized * distanceToMove;
                        stick.B.prevPosition = prevPos;
                    }
                }
            }
        }
    }

    private void OnDrawGizmos()
    {
        Gizmos.color = Color.green;
        foreach (var p in rope.points)
        {
            Gizmos.DrawSphere(p.position, 0.5f);
        }
    }
}