@@ -0,0 +1,129 @@
+package store.model.product;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import store.dto.request.ProductInputDto;
+import store.exception.ExceptionMessage;
+import store.exception.ExceptionUtils;
+
+public class ProductManager {
+    private final PromotionTypeManager promotionTypeManager;
+    private final List<Stock> stocks = new ArrayList<>();
+
+    public ProductManager(PromotionTypeManager promotionTypeManager, List<ProductInputDto> productInputDtos) {
+        this.promotionTypeManager = promotionTypeManager;
+        addProductStock(productInputDtos);
+        addRegularProductsIfOnlyPromotions();
+    }
+
+    public List<Stock> getStocks() {
+        return List.copyOf(stocks);
+    }
+
+    public List<Product> findMatchingProducts(String productName) {
+        return stocks.stream()
+                .filter(stock -> stock.isNameEqual(productName))
+                .map(Stock::getProduct)
+                .toList();
+    }
+
+    public int getProductTotalQuantity(String productName) {
+        return stocks.stream()
+                .filter(stock -> stock.isNameEqual(productName))
+                .mapToInt(Stock::getQuantity)
+                .sum();
+    }
+
+    public int getPromotionProductQuantity(String productName) {
+        return stocks.stream()
+                .filter(stock -> stock.isNameEqual(productName))
+                .filter(stock -> stock.isPromotionStock())
+                .mapToInt(Stock::getQuantity)
+                .sum();
+    }
+
+    public List<Stock> findStocksByProductName(String productName) {
+        return stocks.stream()
+                .filter(stock -> stock.isNameEqual(productName))
+                .sorted()
+                .toList();
+    }
+
+    private void addProductStock(List<ProductInputDto> productsInputDto) {
+        if (productsInputDto == null) {
+            ExceptionUtils.throwIllegalArgumentException(ExceptionMessage.NULL_VALUE_ERROR);
+        }
+        for (ProductInputDto productInput : productsInputDto) {
+            processProductInput(productInput);
+        }
+    }
+
+    private void processProductInput(ProductInputDto productInput) {
+        Optional<PromotionType> matchingPromotionType = promotionTypeManager.getValidPromotionType(
+                productInput.promotion());
+        List<Product> matchingProducts = findMatchingProducts(productInput.name());
+
+        if (matchingProducts.isEmpty()) {
+            createProductAndStock(productInput, matchingPromotionType);
+            return;
+        }
+        handleExistingProducts(productInput, matchingProducts, matchingPromotionType);
+    }
+
+    private void handleExistingProducts(ProductInputDto productInput, List<Product> matchingProducts,
+                                        Optional<PromotionType> matchingPromotionType) {
+        ProductManagerValidator.validateProductPrice(productInput.price(), matchingProducts);
+
+        if (promotionTypeManager.isPromotionTypeMatched(productInput.name(), productInput.promotion(),
+                matchingProducts)) {
+            addStockQuantity(productInput);
+            return;
+        }
+        ProductManagerValidator.validateProductVariety(matchingProducts, productInput.promotion());
+        createProductAndStock(productInput, matchingPromotionType);
+    }
+
+    private void addStockQuantity(ProductInputDto productInput) {
+        List<Stock> samePromotionStocks = stocks.stream()
+                .filter(stock -> stock.getProduct().isSamePromotionType(productInput.name(), productInput.promotion()))
+                .toList();
+        samePromotionStocks.getFirst().addQuantity(productInput.quantity());
+    }
+
+    private void createProductAndStock(ProductInputDto productInput, Optional<PromotionType> matchingPromotionType) {
+        Product product = new Product(productInput.name(), productInput.price(),
+                matchingPromotionType.orElse(null));
+        stocks.add(new Stock(product, productInput.quantity()));
+    }
+
+    private void addRegularProductsIfOnlyPromotions() {
+        stocks.stream()
+                .collect(Collectors.groupingBy(stock -> stock.getProduct().getName()))
+                .values()
+                .stream()
+                .filter(stockList -> hasPromotionOnly(stockList) && !hasRegularProduct(stockList))
+                .forEach(stockList -> {
+                    Product regularProduct = createRegularProductFromFirstPromotion(stockList);
+                    stocks.add(new Stock(regularProduct, 0));
+                });
+    }
+
+    private boolean hasPromotionOnly(List<Stock> stockList) {
+        return stockList.stream().anyMatch(stock -> stock.getProduct().getPromotionType().isPresent());
+    }
+
+    private boolean hasRegularProduct(List<Stock> stockList) {
+        return stockList.stream().anyMatch(stock -> stock.getProduct().getPromotionType().isEmpty());
+    }
+
+    private Product createRegularProductFromFirstPromotion(List<Stock> stockList) {
+        return stockList.stream()
+                .filter(stock -> stock.getProduct().getPromotionType().isPresent())
+                .findFirst()
+                .map(stock -> new Product(stock.getProduct().getName(), stock.getProduct().getPrice(), null))
+                .orElseThrow(() -> new IllegalStateException(ExceptionMessage.NULL_VALUE_ERROR.getMessage()));
+    }
+}

리뷰: get을 계속 해오면서 Promotion에 직접적인 의존을 하고있지 않은 ProductManager에서 결국 Promotion 관련된 기능을 수행하게 됐습니다. ProductManager와 연관된 객체와만 대화할 수 있도록 하면 좋을 것 같습니다.