refactors mapgen into chained builders

src/map_builders/distant_exit.rs

@@ -0,0 +1,49 @@
+use super::{BuilderMap, MetaMapBuilder, TileType};
+use rltk::RandomNumberGenerator;
+
+pub struct DistantExit {}
+
+impl MetaMapBuilder for DistantExit {
+    fn build_map(&mut self, rng: &mut rltk::RandomNumberGenerator, build_data: &mut BuilderMap) {
+        self.build(rng, build_data);
+    }
+}
+
+impl DistantExit {
+    #[allow(dead_code)]
+    pub fn new() -> Box<DistantExit> {
+        Box::new(DistantExit {})
+    }
+
+    fn build(&mut self, _rng: &mut RandomNumberGenerator, build_data: &mut BuilderMap) {
+        let starting_pos = build_data.starting_position.as_ref().unwrap().clone();
+        let start_idx = build_data.map.xy_idx(starting_pos.x, starting_pos.y);
+        build_data.map.populate_blocked();
+        let map_starts: Vec<usize> = vec![start_idx];
+        let dijkstra_map = rltk::DijkstraMap::new(
+            build_data.map.width as usize,
+            build_data.map.height as usize,
+            &map_starts,
+            &build_data.map,
+            1000.0,
+        );
+        let mut exit_tile = (0, 0.0f32);
+        for (i, tile) in build_data.map.tiles.iter_mut().enumerate() {
+            if *tile == TileType::Floor {
+                let distance_to_start = dijkstra_map.map[i];
+                if distance_to_start != std::f32::MAX {
+                    // If it is further away than our current exit candidate, move the exit
+                    if distance_to_start > exit_tile.1 {
+                        exit_tile.0 = i;
+                        exit_tile.1 = distance_to_start;
+                    }
+                }
+            }
+        }
+
+        // Place a staircase
+        let stairs_idx = exit_tile.0;
+        build_data.map.tiles[stairs_idx] = TileType::DownStair;
+        build_data.take_snapshot();
+    }
+}