feat: Add shop buy logic (#34)

src/features/inventory/components.rs

@@ -1,4 +1,5 @@
-use crate::{features::config::components::BerrySeedConfig, prelude::*};
+use crate::features::config::components::BerrySeedConfig;
+use crate::prelude::*;
 
 #[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq, Hash)]
 pub enum ItemType {
@@ -112,6 +113,76 @@ pub struct Inventory {
     pub items: Vec<Entity>,
 }
 
+impl Inventory {
+    pub fn update_item_stack(
+        &mut self,
+        commands: &mut Commands,
+        items_query: &mut Query<&mut ItemStack>,
+        item_type_to_update: ItemType,
+        amount_delta: i32,
+    ) -> bool {
+        let mut target_entity_index: Option<usize> = None;
+        let mut current_stack_amount: u32 = 0;
+        let mut entity_id_to_update: Option<Entity> = None;
+
+        // Try to find an existing stack of the item
+        for (i, &entity) in self.items.iter().enumerate() {
+            if let Ok(stack) = items_query.get(entity) {
+                if stack.item_type == item_type_to_update {
+                    target_entity_index = Some(i);
+                    current_stack_amount = stack.amount;
+                    entity_id_to_update = Some(entity);
+                    break;
+                }
+            }
+        }
+
+        match amount_delta {
+            val if val > 0 => {
+                // Add items
+                let add_amount = amount_delta as u32;
+                if let Some(entity) = entity_id_to_update {
+                    if let Ok(mut stack) = items_query.get_mut(entity) {
+                        stack.amount += add_amount;
+                    }
+                } else {
+                    // Item not found, create a new stack
+                    let new_item_stack = ItemStack {
+                        item_type: item_type_to_update,
+                        amount: add_amount,
+                    };
+                    let id = commands.spawn(new_item_stack).id();
+                    self.items.push(id);
+                }
+                true
+            }
+            val if val < 0 => {
+                // Remove items
+                let remove_amount = amount_delta.abs() as u32;
+
+                let Some(entity) = entity_id_to_update else {
+                    return false; // Item not found for removal
+                };
+                if current_stack_amount < remove_amount {
+                    return false; // Not enough items
+                };
+
+                if let Ok(mut stack) = items_query.get_mut(entity) {
+                    stack.amount -= remove_amount;
+                    if stack.amount == 0 {
+                        commands.entity(entity).despawn();
+                        if let Some(index) = target_entity_index {
+                            self.items.remove(index);
+                        }
+                    }
+                }
+                true
+            }
+            _ => true,
+        }
+    }
+}
+
 #[derive(Component)]
 pub enum RootMarker {
     Inventory,

src/features/shop/components.rs

@@ -50,4 +50,25 @@ impl ShopOffer {
 
         offers
     }
+
+    pub fn buy(
+        &self,
+        inventory: &mut Inventory,
+        commands: &mut Commands,
+        items: &mut Query<&mut ItemStack>,
+    ) -> bool {
+        // Try to remove cost (berries)
+        if inventory.update_item_stack(commands, items, ItemType::Berry, -(self.cost as i32)) {
+            inventory.update_item_stack(
+                commands,
+                items,
+                self.item.item_type.clone(),
+                self.item.amount as i32,
+            );
+            true
+        } else {
+            false // Not enough berries
+        }
+    }
 }
+

src/features/shop/mod.rs

@@ -19,6 +19,8 @@ fn buttons(
     root_query: Query<(Entity, &RootMarker)>,
     game_config: Res<GameConfig>,
     asset_server: Res<AssetServer>,
+    mut inventory: ResMut<Inventory>,
+    mut items: Query<&mut ItemStack>,
 ) {
     for (interaction, button_type) in &mut interaction_query {
         match *interaction {
@@ -33,7 +35,18 @@ fn buttons(
                         }
                     }
                 }
-                _ => {}
+                ButtonType::ShopBuyItem(offer) => {
+                    if offer.buy(&mut inventory, &mut commands, &mut items) {
+                        // Item bought, exit the menu
+                        for (entity, root) in root_query.iter() {
+                            match *root {
+                                RootMarker::Shop => commands.entity(entity).despawn(),
+                            }
+                        }
+                    } else {
+                        // Error (e.g. not enough berries)
+                    }
+                }
             },
             _ => {}
         }