BABA_YAGA/Assets/Scripts/GameSetup/Maze/PrimsAlgorithm.cs

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

namespace Hallucinate.GameSetup.Maze
{
    public class PrimsAlgorithm : IMazeAlgorithm
    {
        private const int InitialX = 2;
        private const int InitialZ = 2;
        private const int MaxIterations = 10000;
        private const int TargetCorridorNeighbours = 1;

        public void Generate(MazeGrid grid)
        {
            int x = InitialX;
            int z = InitialZ;
            grid.SetCell(x, z, MazeCellType.Corridor);

            List<MapLocation> walls = GetNeighbouringWalls(grid, x, z);

            int iterations = 0;
            while (walls.Count > 0 && iterations < MaxIterations)
            {
                int rIndex = Random.Range(0, walls.Count);
                MapLocation w = walls[rIndex];
                walls.RemoveAt(rIndex);

                if (grid.CountSquareNeighbours(w.x, w.z, MazeCellType.Corridor) == TargetCorridorNeighbours)
                {
                    grid.SetCell(w.x, w.z, MazeCellType.Corridor);
                    
                    foreach (var nw in GetNeighbouringWalls(grid, w.x, w.z))
                    {
                        if (!walls.Contains(nw)) walls.Add(nw);
                    }
                }
                iterations++;
            }
        }

        public IEnumerator GenerateStepByStep(MazeGrid grid, float interval)
        {
            int x = InitialX;
            int z = InitialZ;
            grid.SetCell(x, z, MazeCellType.Corridor);
            yield return new WaitForSeconds(interval);

            List<MapLocation> walls = GetNeighbouringWalls(grid, x, z);
            foreach(var w in walls) grid.SetCell(w.x, w.z, MazeCellType.Processing);

            int iterations = 0;
            while (walls.Count > 0 && iterations < MaxIterations)
            {
                int rIndex = Random.Range(0, walls.Count);
                MapLocation w = walls[rIndex];
                walls.RemoveAt(rIndex);

                if (grid.CountSquareNeighbours(w.x, w.z, MazeCellType.Corridor) == TargetCorridorNeighbours)
                {
                    grid.SetCell(w.x, w.z, MazeCellType.Corridor);
                    if (interval > 0) yield return new WaitForSeconds(interval);

                    foreach (var nw in GetNeighbouringWalls(grid, w.x, w.z))
                    {
                        if (grid.GetCell(nw.x, nw.z) == MazeCellType.Wall)
                        {
                            grid.SetCell(nw.x, nw.z, MazeCellType.Processing);
                            walls.Add(nw);
                        }
                    }
                }
                else
                {
                    // If it's no longer a candidate, turn it back to Wall
                    grid.SetCell(w.x, w.z, MazeCellType.Wall);
                }
                iterations++;
            }
        }

        private List<MapLocation> GetNeighbouringWalls(MazeGrid grid, int x, int z)
        {
            List<MapLocation> neighbours = new List<MapLocation>();
            foreach (var dir in MapLocation.Directions)
            {
                int nx = x + dir.x;
                int nz = z + dir.z; 
                
                // Correction
                nx = x + dir.x;
                nz = z + dir.z;

                if (grid.IsInBounds(nx, nz))
                {
                    MazeCellType type = grid.GetCell(nx, nz);
                    if (type == MazeCellType.Wall || type == MazeCellType.Processing)
                    {
                        neighbours.Add(new MapLocation(nx, nz));
                    }
                }
            }
            return neighbours;
        }
    }
}