add tree station spawning and removing

src/app.zig

@@ -224,6 +224,7 @@ const Upgrades = struct {
     minion_carry_capacity: u32 = 1,
     minion_walk: MinionWalkStats = .{},
 
+    tree_station_count: u32 = 0,
     tree_health: u32 = 10,
     tree_respawn_duration: Nanoseconds = std.time.ns_per_s,
     tree_wood_amount: u32 = 1,
@@ -309,8 +310,6 @@ pub fn init(self: *App, plt: Platform.Init) !?u8 {
         .upgrades = .{}
     };
 
-    self.spawnWoodStation(-100);
-    self.spawnWoodStation(-150);
     self.spawnBurnStation(100);
     self.spawnBurnStation(150);
 
@@ -729,6 +728,17 @@ fn removeMinion(self: *App, minion_id: EntityId) void {
     self.entities.removeAssumeExists(minion_id);
 }
 
+fn removeWoodStation(self: *App, id: EntityId) void {
+    const wood_station = self.entities.get(id) orelse return;
+    assert(wood_station.type == .wood_station);
+
+    if (wood_station.station_owned_tree) |tree_id| {
+        self.entities.removeAssumeExists(tree_id);
+    }
+
+    self.entities.removeAssumeExists(id);
+}
+
 fn getBurnMultiplier(self: *App) u32 {
     const stack_size = self.countEternalFlameStackSize();
 
@@ -786,6 +796,41 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
         }
     }
 
+    { // Spawn in or delete wood stations
+        var station_count: u32 = 0;
+        {
+            var wood_station_iter = self.initEntityIteratorByType(.wood_station);
+            while (wood_station_iter.next()) |_| {
+                station_count += 1;
+            }
+        }
+
+        const wood_station_first_pos = -100;
+        const wood_station_step = -50;
+
+        if (station_count > self.upgrades.tree_station_count) {
+            for (self.upgrades.tree_station_count..station_count) |i| {
+
+                // Remove the last wood station that was added
+                var wood_station_iter = self.initEntityIteratorByType(.wood_station);
+                while (wood_station_iter.next()) |wood_station_id| {
+                    const wood_station = self.entities.getAssumeExists(wood_station_id);
+                    const i_f32: f32 = @floatFromInt(i);
+                    const expected_x = wood_station_first_pos + wood_station_step * i_f32;
+                    if (wood_station.pos.x == expected_x) {
+                        self.removeWoodStation(wood_station_id);
+                        break;
+                    }
+                }
+            }
+        } else if (station_count < self.upgrades.tree_station_count) {
+            for (station_count..self.upgrades.tree_station_count) |i| {
+                const i_f32: f32 = @floatFromInt(i);
+                self.spawnWoodStation(wood_station_first_pos + wood_station_step * i_f32);
+            }
+        }
+    }
+
     { // Spawn trees at wood station on a cooldown
         var wood_station_iter = self.initEntityIteratorByType(.wood_station);
         while (wood_station_iter.next()) |wood_station_id| {
@@ -1164,6 +1209,7 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
 
         ImGUI.separator();
         _ = ImGUI.text("Tree upgrades", .{});
+        _ = ImGUI.inputU32("station_count", &self.upgrades.tree_station_count);
         _ = ImGUI.inputU32("health", &self.upgrades.tree_health);
         _ = ImGUI.inputU32("wood_amount", &self.upgrades.tree_wood_amount);
         _ = ImGUI.inputDuration("respawn_duration", &self.upgrades.tree_respawn_duration);