using System;
using UnityEngine;
using Random = UnityEngine.Random;

namespace DefaultNamespace.GameOfLife
{
    public class GameOfLife : MonoBehaviour
    {
        [SerializeField] private Cell _cellPrefab;
        [SerializeField, Range(10, 999)] private int _rows = 50;
        [SerializeField, Range(10, 999)] private int _columns = 50;

        private Cell[] _cells;
        private int CalculateIndex(int x, int y) => x + y * _columns;

        private void Start()
        {
            _cells = new Cell[_rows * _columns];

            for (int x = 0; x < _columns; x++)
            {
                for (int y = 0; y < _rows; y++)
                {
                    Cell cell = Instantiate(_cellPrefab, transform);
                    cell.name = $"{x:000} / {y:000}";
                    cell.transform.localPosition = new Vector3(x, y, 0.0f);

                    _cells[CalculateIndex(x, y)] = cell;
                }
            }
        }

        private void SimulateStep()
        {
            // collect new states
            bool[] newStates = new bool[_rows * _columns];

            // changing states - apply rules
            for (int x = 0; x < _columns; x++)
            {
                for (int y = 0; y < _rows; y++)
                {
                    int index = CalculateIndex(x, y);
                    bool cellState = _cells[index].IsAlive;
                    int neighbors = CountNeighbors(x, y);

                    if (cellState)
                    {
                        // cell is alive
                        // rule 1: less than two neighbors => die
                        if (neighbors < 2) cellState = false;

                        // rule 2: equal to two or three neighbors => stay alive
                        if (neighbors is 2 or 3) cellState = true;

                        // rule 3: more than three neighbors => die
                        if (neighbors > 3) cellState = false;
                    }
                    else
                    {
                        // cell is dead
                        // rule 4: equal to three neighbors => birth
                        if (neighbors == 3) cellState = true;
                    }

                    newStates[index] = cellState;
                }
            }

            // transfer new states
            for (int i = 0; i < _cells.Length; i++)
            {
                _cells[i].IsAlive = newStates[i];
            }
        }

        private int CountNeighbors(int column, int row)
        {
            int count = 0;

            for (int dx = -1; dx <= 1; dx++)
            {
                for (int dy = -1; dy <= 1; dy++)
                {
                    // exception: own cell
                    if (dx == 0 && dy == 0) continue;

                    int currentX = column + dx;
                    int currentY = row + dy;

                    // exception: borders
                    if (currentX < 0 || currentX >= _columns) continue;
                    if (currentY < 0 || currentY >= _rows) continue;

                    if (_cells[CalculateIndex(currentX, currentY)].IsAlive) count++;
                }
            }

            return count;
        }

        public void OnFillGridRandomlyButtonClick()
        {
            for (int i = 0; i < _cells.Length; i++)
            {
                _cells[i].IsAlive = Random.value < 0.1f;
            }
        }

        public void OnSimulateStepButtonClick() => SimulateStep();

        public void OnResetGridButtonClick()
        {
            for (int i = 0; i < _cells.Length; i++)
            {
                _cells[i].IsAlive = false;
            }
            
            OnStopSimulationButtonClick();
        }
        
        public void OnStartSimulationButtonClick() => InvokeRepeating(nameof(SimulateStep), 0.0f, 0.5f);
        
        public void OnStopSimulationButtonClick() => CancelInvoke(nameof(SimulateStep));
    }
}