Allow going back a level

src/main.rs

@@ -77,6 +77,7 @@ pub enum RunState {
     },
     SaveGame,
     NextLevel,
+    PreviousLevel,
     ShowRemoveItem,
     GameOver,
     MagicMapReveal {
@@ -345,6 +346,11 @@ impl GameState for State {
                 self.goto_next_level();
                 newrunstate = RunState::PreRun;
             }
+            RunState::PreviousLevel => {
+                self.goto_previous_level();
+                self.mapgen_next_state = Some(RunState::PreRun);
+                newrunstate = RunState::MapGeneration;
+            }
             RunState::MagicMapReveal { row } => {
                 let mut map = self.ecs.fetch_mut::<Map>();
                 for x in 0..map.width {
@@ -429,6 +435,29 @@ impl State {
         gamelog.append("You descend to the next level.");
     }
 
+    fn goto_previous_level(&mut self) {
+        // Delete entities that aren't the palyer or their equipment
+        let to_delete = self.entities_to_remove_on_level_change();
+        for target in to_delete {
+            self.ecs
+                .delete_entity(target)
+                .expect("failed to delete entity");
+        }
+
+        // Build a new map and place the player
+        #[allow(unused_assignments)]
+        let current_depth;
+        {
+            let worldmap_resource = self.ecs.fetch::<Map>();
+            current_depth = worldmap_resource.depth;
+        }
+        self.generate_world_map(current_depth - 1);
+
+        // Notify the player
+        let mut gamelog = self.ecs.fetch_mut::<GameLog>();
+        gamelog.append("You ascend to the previous level.");
+    }
+
     fn game_over_cleanup(&mut self) {
         // Delete everything
         let mut to_delete = Vec::new();

src/player.rs

@@ -119,6 +119,22 @@ pub fn try_next_level(ecs: &mut World) -> bool {
     }
 }
 
+pub fn try_previous_level(ecs: &mut World) -> bool {
+    let player_pos = ecs.fetch::<Point>();
+    let map = ecs.fetch::<Map>();
+    let player_idx = map.xy_idx(player_pos.x, player_pos.y);
+
+    if map.tiles[player_idx] == TileType::UpStairs {
+        true
+    } else {
+        let mut gamelog = ecs.fetch_mut::<GameLog>();
+        gamelog
+            .entries
+            .push("There is no way up from here.".to_string());
+        false
+    }
+}
+
 fn get_item(ecs: &mut World) {
     let player_pos = ecs.fetch::<Point>();
     let player_entity = ecs.fetch::<Entity>();
@@ -316,6 +332,11 @@ pub fn player_input(gs: &mut State, ctx: &mut Rltk) -> RunState {
                     return RunState::NextLevel;
                 }
             }
+            VirtualKeyCode::Comma => {
+                if try_previous_level(&mut gs.ecs) {
+                    return RunState::PreviousLevel;
+                }
+            }
 
             // Item management
             VirtualKeyCode::G => get_item(&mut gs.ecs),