rust-roguelike-tutorial/chapter-29-mazes/src/map_builders/maze.rs

use super::{MapBuilder, Map,  
    TileType, Position, spawner, SHOW_MAPGEN_VISUALIZER,
    remove_unreachable_areas_returning_most_distant, generate_voronoi_spawn_regions};
use rltk::RandomNumberGenerator;
use specs::prelude::*;
use std::collections::HashMap;

pub struct MazeBuilder {
    map : Map,
    starting_position : Position,
    depth: i32,
    history: Vec<Map>,
    noise_areas : HashMap<i32, Vec<usize>>
}

impl MapBuilder for MazeBuilder {
    fn get_map(&self) -> Map {
        self.map.clone()
    }

    fn get_starting_position(&self) -> Position {
        self.starting_position.clone()
    }

    fn get_snapshot_history(&self) -> Vec<Map> {
        self.history.clone()
    }

    fn build_map(&mut self)  {
        self.build();
    }

    fn spawn_entities(&mut self, ecs : &mut World) {
        for area in self.noise_areas.iter() {
            spawner::spawn_region(ecs, area.1, self.depth);
        }
    }

    fn take_snapshot(&mut self) {
        if SHOW_MAPGEN_VISUALIZER {
            let mut snapshot = self.map.clone();
            for v in snapshot.revealed_tiles.iter_mut() {
                *v = true;
            }
            self.history.push(snapshot);
        }
    }
}

impl MazeBuilder {
    pub fn new(new_depth : i32) -> MazeBuilder {
        MazeBuilder{
            map : Map::new(new_depth),
            starting_position : Position{ x: 0, y : 0 },
            depth : new_depth,
            history: Vec::new(),
            noise_areas : HashMap::new()
        }
    }

    #[allow(clippy::map_entry)]
    fn build(&mut self) {
        let mut rng = RandomNumberGenerator::new();

        // Maze gen
        let mut maze = Grid::new((self.map.width / 2)-2, (self.map.height / 2)-2, &mut rng);
        maze.generate_maze(self);

        // Find a starting point; start at the middle and walk left until we find an open tile
        self.starting_position = Position{ x: 2, y : 2 };
        let start_idx = self.map.xy_idx(self.starting_position.x, self.starting_position.y);
        self.take_snapshot();

        // Find all tiles we can reach from the starting point
        let exit_tile = remove_unreachable_areas_returning_most_distant(&mut self.map, start_idx);
        self.take_snapshot();

        // Place the stairs
        self.map.tiles[exit_tile] = TileType::DownStairs;
        self.take_snapshot();

        // Now we build a noise map for use in spawning entities later
        self.noise_areas = generate_voronoi_spawn_regions(&self.map, &mut rng);
    }
}

/* Maze code taken under MIT from https://github.com/cyucelen/mazeGenerator/ */

const TOP : usize = 0;
const RIGHT : usize = 1;
const BOTTOM : usize = 2;
const LEFT : usize = 3;

#[derive(Copy, Clone)]
struct Cell {
    row: i32,
    column: i32,
    walls: [bool; 4],
    visited: bool,
}

impl Cell {
    fn new(row: i32, column: i32) -> Cell {
        Cell{
            row,
            column,
            walls: [true, true, true, true],
            visited: false
        }
    }

    unsafe fn remove_walls(&mut self, next : *mut Cell) {
        let x = self.column - (*(next)).column;
        let y = self.row - (*(next)).row;

        if x == 1 {
            self.walls[LEFT] = false;
            (*(next)).walls[RIGHT] = false;
        }
        else if x == -1 {
            self.walls[RIGHT] = false;
            (*(next)).walls[LEFT] = false;
        }
        else if y == 1 {
            self.walls[TOP] = false;
            (*(next)).walls[BOTTOM] = false;
        }
        else if y == -1 {
            self.walls[BOTTOM] = false;
            (*(next)).walls[TOP] = false;
        }
    }
}

struct Grid<'a> {
    width: i32,
    height: i32,
    cells: Vec<Cell>,
    backtrace: Vec<usize>,
    current: usize,
    rng : &'a mut RandomNumberGenerator
}

impl<'a> Grid<'a> {
    fn new(width: i32, height:i32, rng: &mut RandomNumberGenerator) -> Grid {
        let mut grid = Grid{
            width,
            height,
            cells: Vec::new(),
            backtrace: Vec::new(),
            current: 0,
            rng
        };

        for row in 0..height {
            for column in 0..width {
                grid.cells.push(Cell::new(row, column));
            }
        }

        grid
    }

    fn calculate_index(&self, row: i32, column: i32) -> i32 {
        if row < 0 || column < 0 || column > self.width-1 || row > self.height-1 {
            -1
        } else {
            column + (row * self.width)
        }
    }

    fn get_available_neighbors(&self) -> Vec<usize> {
        let mut neighbors : Vec<usize> = Vec::new();

        let current_row = self.cells[self.current].row;
        let current_column = self.cells[self.current].column;

        let neighbor_indices : [i32; 4] = [
            self.calculate_index(current_row -1, current_column),
            self.calculate_index(current_row, current_column + 1),
            self.calculate_index(current_row + 1, current_column),
            self.calculate_index(current_row, current_column - 1)
        ];

        for i in neighbor_indices.iter() {
            if *i != -1 && !self.cells[*i as usize].visited {
                neighbors.push(*i as usize);
            }
        }

        neighbors
    }

    fn find_next_cell(&mut self) -> Option<usize> {
        let neighbors = self.get_available_neighbors();
        if !neighbors.is_empty() {
            if neighbors.len() == 1 {
                return Some(neighbors[0]);
            } else {
                return Some(neighbors[(self.rng.roll_dice(1, neighbors.len() as i32)-1) as usize]);
            }
        }
        None
    }

    fn generate_maze(&mut self, generator : &mut MazeBuilder) {
        let mut i = 0;
        loop {
            self.cells[self.current].visited = true;
            let next = self.find_next_cell();

            match next {
                Some(next) => {
                    self.cells[next].visited = true;
                    self.backtrace.insert(0, self.current);
                    unsafe {
                        let next_cell : *mut Cell = &mut self.cells[next];
                        let current_cell = &mut self.cells[self.current];
                        current_cell.remove_walls(next_cell);
                    }
                    self.current = next;
                }
                None => {
                    if !self.backtrace.is_empty() {
                        self.current = self.backtrace[0];
                        self.backtrace.remove(0);
                    } else {
                        break;
                    }
                }
            }

            if i % 50 == 0 {
                self.copy_to_map(&mut generator.map);
                generator.take_snapshot();    
            }
            i += 1;
        }
    }

    fn copy_to_map(&self, map : &mut Map) {
        // Clear the map
        for i in map.tiles.iter_mut() { *i = TileType::Wall; }

        for cell in self.cells.iter() {
            let x = cell.column + 1;
            let y = cell.row + 1;
            let idx = map.xy_idx(x * 2, y * 2);

            map.tiles[idx] = TileType::Floor;
            if !cell.walls[TOP] { map.tiles[idx - map.width as usize] = TileType::Floor }
            if !cell.walls[RIGHT] { map.tiles[idx + 1] = TileType::Floor }
            if !cell.walls[BOTTOM] { map.tiles[idx + map.width as usize] = TileType::Floor }
            if !cell.walls[LEFT] { map.tiles[idx - 1] = TileType::Floor }
        }
    }
}