Add missing system for completing chapter 2

src/systems/gameplay_state_sytem.rs

@@ -0,0 +1,44 @@
+use specs::{Join, ReadStorage, System, Write};
+use std::collections::HashMap;
+
+use crate::{
+    components::{Box, BoxSpot, Position},
+    resources::{Gameplay, GameplayState},
+};
+
+pub struct GameplayStateSystem {}
+
+impl<'a> System<'a> for GameplayStateSystem {
+    // Data
+    type SystemData = (
+        Write<'a, Gameplay>,
+        ReadStorage<'a, Position>,
+        ReadStorage<'a, Box>,
+        ReadStorage<'a, BoxSpot>,
+    );
+
+    fn run(&mut self, data: Self::SystemData) {
+        let (mut gameplay_state, positions, boxes, box_spots) = data;
+
+        // get all boxes indexed by position
+        let boxes_by_position: HashMap<(u8, u8), &Box> = (&positions, &boxes)
+            .join()
+            .map(|t| ((t.0.x, t.0.y), t.1))
+            .collect();
+
+        // loop through all box spots and check if there is a corresponding
+        // box at that position
+        for (_box_spot, position) in (&box_spots, &positions).join() {
+            if boxes_by_position.contains_key(&(position.x, position.y)) {
+                // continue
+            } else {
+                gameplay_state.state = GameplayState::Playing;
+                return;
+            }
+        }
+
+        // If we made it this far, then all box spots have boxes on them, and the
+        // game has been won
+        gameplay_state.state = GameplayState::Won;
+    }
+}