@@ -0,0 +1,371 @@
+package store;
+
+import camp.nextstep.edu.missionutils.DateTimes;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+import store.io.ProductFile;
+import store.io.PromotionFile;
+import store.product.Product;
+import store.product.PurchaseRequest;
+import store.product.Receipt;
+import store.product.promotion.Promotion;
+import store.product.promotion.PromotionResult;
+import store.product.promotion.PromotionState;
+import store.utils.ExceptionFactory;
+import store.utils.ExceptionType;
+import store.utils.Transformer;
+
+public class StoreModel {
+    static private final  Product NOT_FOUND = null;
+    private final List<Product> productRepository;
+    private final HashMap<String,Promotion> promotionHashMap;
+    final static String NAME_REGULAR_EXPRESSION = "^[a-zA-Z가-힣0-9]+$";
+    final static Pattern NAME_PATTERN = Pattern.compile(StoreModel.NAME_REGULAR_EXPRESSION);
+
+    StoreModel(){
+        this.productRepository = new ArrayList<>();
+        this.promotionHashMap = new HashMap<>();
+    }
+
+    public void initStore(List<Product> products, List<Promotion> promotions){
+        addProducts(products);
+        putPromotion(promotions);
+        applyPromotions();
+    }
+
+    private void addProducts(List<Product> products){
+        for(Product origin : products){
+            this.productRepository.add(origin.clone());
+        }
+        checkInitProduct(this.productRepository);
+    }
+
+    public void checkInitProduct(List<Product> products){
+        for(Product product : products){
+            validateSameProductsHaveSamePrice(product);
+        }
+    }
+
+    public void validateSameProductsHaveSamePrice(Product product){
+        List<Product> finds = findProduct(product.getName());
+        int price = 0;
+        for(Product find : finds){
+            price += find.getPrice();
+        }
+        int averagePrice = price / finds.size();
+        if(finds.getFirst().getPrice() != averagePrice){
+            System.out.println("[Error] 동일 이름의 상품은 가격이 같아야 합니다. 잘못된 상품 :" + product.getName());
+            ExceptionFactory.throwIllegalStateException(ExceptionType.INVALID_FILE_FORMAT);
+        }
+    }
+
+    private void putPromotion(List<Promotion> promotions){
+        /*TODO
+           - 프로모션 이름 중복이 없도록 해야함.
+               - 날짜가 다르더라도, 이름 중복이 없도록 해야함.
+               - 프로모션 중복이 있는 경우, promotions.md 파일이 문제이므로 해당 파일에서 확인 필요.
+        * */
+        for(Promotion promotion : promotions){
+            this.promotionHashMap.put(promotion.getName(),promotion.clone());
+        }
+    }
+
+    private void applyPromotions(){
+        for(Product product : this.productRepository){
+            product.setPromotion(this.promotionHashMap.get(product.getPromotionName()));
+        }
+    }
+
+    public List<Product> getProducts(){
+        List<Product> copied = new ArrayList<>();
+        for(Product origin : this.productRepository){
+            copied.add(origin.clone());
+        }
+
+        return copied;
+    }
+
+    /*TODO
+       - 접근지시자, static 키워드 기준으로 메소드 정렬하기
+    * */
+    public Product findOneProduct(String name, boolean isPromoted){
+        return this.findOneOriginProduct(name,isPromoted).clone();
+    }
+
+    public List<Product> findProduct(String name){
+        return this.findProductOrigin(name).stream()
+                .map(Product::clone)
+                .toList();
+    }
+
+    public Product findOneOriginProduct(String name, boolean isPromoted){
+        if(isPromoted){
+            return findProductPromoted(name);
+        }
+        return findProductNonPromoted(name);
+    }
+
+    public List<Product> findProductOrigin(String name){
+        return this.productRepository.stream()
+                .filter((product)->product.getName().equals(name))
+                .collect(Collectors.toList());
+    }
+
+    private Product findProductPromoted(String name){
+        List<Product> finds = findProductOrigin(name).stream()
+                .filter((product -> product.getPromotionName()!=null))
+                .toList();
+        validateFindList(finds);
+        if(finds.isEmpty()){
+            return NOT_FOUND;
+        }
+        return finds.getFirst();
+    }
+
+    private Product findProductNonPromoted(String name){
+        List<Product> finds = findProductOrigin(name).stream()
+                .filter(product -> product.getPromotionName() == Product.NO_PROMOTION)
+                .toList();
+        validateFindList(finds);
+        if(finds.isEmpty()){
+            return NOT_FOUND;
+        }
+        return finds.getFirst();
+    }
+
+    private void validateFindList(List<?> finds){
+        int limit = 1;
+        if(finds.size() > limit){
+            ExceptionFactory.throwIllegalStateException(ExceptionType.INTERNAL_ERROR);
+        }
+    }
+
+    /*TODO
+    *   - promotion과 product 생성 관련 static 함수를 다른 클래스에 책임 맡길 것으 고려하기
+    *   - promotion과 product 생성시 예외처리 고려
+    *       - 잘못된 타입 입력
+    *       - 잘못된 형식 입력
+    * */
+
+    static public List<String> parseString(String string){
+        if (string == null || string.isBlank()) {
+            throw new IllegalArgumentException("List is empty");
+        }
+        final String delimiter = ",";
+        String[] parsed = string.split(delimiter);
+
+        return List.of(parsed);
+    }
+
+    static public Product createProduct(String rawProduct){
+        List<String> parsedRawProduct = StoreModel.parseString(rawProduct);
+        String name = parsedRawProduct.get(ProductFile.NAME.getColumnIdx());
+        String price = parsedRawProduct.get(ProductFile.PRICE.getColumnIdx());
+        String quantity = parsedRawProduct.get(ProductFile.QUANTITY.getColumnIdx());
+        String promotion = parsedRawProduct.get(ProductFile.PROMOTION.getColumnIdx());
+        validateNameFormat(name);
+        if(promotion.equals("null")){
+            promotion = null;
+        }
+        return new Product(name, Transformer.parsePositiveInt(price),Transformer.parseNonNegativeNumber(quantity),promotion);
+    }
+
+    static public List<Product> createProducts(String rawProductList){
+        List<Product> products = new ArrayList<>();
+        String[] rawProducts  = rawProductList.split("\n");
+
+        int idx = 1;
+
+        for( ; idx < rawProducts.length; idx++){
+            String rawProduct = rawProducts[idx];
+            products.add(StoreModel.createProduct(rawProduct));
+        }
+        return products;
+    }
+    static public void validateNameFormat(String name){
+        Matcher matcher = NAME_PATTERN.matcher(name);
+        if(!matcher.matches()){
+            ExceptionFactory.throwIllegalArgumentException(ExceptionType.INVALID_NAME_FORMAT);
+        }
+    }
+
+    static public Promotion createPromotion(String rawPromotion){
+        List<String> parsedRawPromotion = StoreModel.parseString(rawPromotion);
+        String name = parsedRawPromotion.get(PromotionFile.NAME.getColumnIdx());
+        String buyCount = parsedRawPromotion.get(PromotionFile.BUY.getColumnIdx());
+        String returnCount = parsedRawPromotion.get(PromotionFile.GET.getColumnIdx());
+        String startDate = parsedRawPromotion.get(PromotionFile.START_DATE.getColumnIdx());
+        String endDate = parsedRawPromotion.get(PromotionFile.END_DATE.getColumnIdx());
+        Promotion.validateReturnCount(returnCount);
+        return new Promotion(name, Transformer.parseStartDate(startDate,PromotionFile.DATE_TIME_FORMATTER),Transformer.parseEndDate(endDate,PromotionFile.DATE_TIME_FORMATTER),Transformer.parsePositiveInt(buyCount));
+    }
+
+    static public List<Promotion> createPromotions(String rawPromotionList){
+        List<Promotion> promotions = new ArrayList<>();
+        String[] rawPromotions  = rawPromotionList.split("\n");
+
+        int idx = 1;
+
+        for( ; idx < rawPromotions.length; idx++){
+            String rawPromotion = rawPromotions[idx];
+            promotions.add(StoreModel.createPromotion(rawPromotion));
+        }
+        return promotions;
+    }
+
+    public List<StoreViewMessage> checkPurchaseRequests(List<PurchaseRequest> requests) {
+        List<StoreViewMessage> messageBox = new ArrayList<>();
+
+        for(PurchaseRequest request : requests){
+            checkPurchaseRequest(request,messageBox);
+        }
+
+        return messageBox;
+    }
+
+    public void checkPurchaseRequest(PurchaseRequest request, List<StoreViewMessage> messageBox){
+        checkPurchaseProductExist(request,messageBox);
+        checkPurchaseProductCount(request,messageBox);
+
+    }
+
+    public void checkPurchaseProductExist(PurchaseRequest request, List<StoreViewMessage> messageBox){
+        List<Product> finds = findProduct(request.getProductName());
+        if(finds.isEmpty()){
+            messageBox.add(StoreViewMessage.ERROR_NOT_EXIST_PRODUCT);
+        }
+    }
+
+    public void checkPurchaseProductCount(PurchaseRequest request, List<StoreViewMessage> messageBox){
+        List<Product> finds = findProduct(request.getProductName());
+        int zero = 0;
+        int totalCount = finds.stream().map(Product::getCount).reduce(zero,Integer::sum);
+        if(totalCount == zero){
+            messageBox.add(StoreViewMessage.ERROR_NO_COUNT_PRODUCT);
+        }
+        if(totalCount != zero && totalCount < request.getCountPurchased()){
+            messageBox.add(StoreViewMessage.ERROR_OVERFLOW_PURCHASE);
+        }
+    }
+
+    public List<PromotionResult> checkPromotionAvailable(List<PurchaseRequest> purchaseRequests){
+        List<PromotionResult> promotionResults = new ArrayList<>();
+        for(PurchaseRequest request : purchaseRequests){
+            promotionResults.addAll(checkPromotionBoth(request.getProductName(),request.getCountPurchased()));
+        }
+
+        return promotionResults;
+    }
+
+    public List<PromotionResult> checkPromotionBoth(String productName , int buyCount){
+        PromotionResult resultPromotion = checkProductPromotionAvailable(productName,buyCount);
+        PromotionResult resultNonPromotion = null;
+
+        Product product = findProductNonPromoted(productName);
+        if(findProductPromoted(productName) == NOT_FOUND){
+            resultNonPromotion = PromotionResult.createNoPromotion(productName,buyCount);
+            return List.of(resultNonPromotion);
+        }
+
+        if(resultPromotion.getState()==PromotionState.INSUFFICIENT
+        && resultPromotion.getTotalItemCount() < buyCount){
+            int remainCountToBuy = buyCount - resultPromotion.getTotalItemCount();
+            resultNonPromotion = PromotionResult.createNoPromotion(productName,remainCountToBuy);
+            return List.of(resultPromotion, resultNonPromotion);
+        }
+
+        return List.of(resultPromotion);
+    }
+
+    public PromotionResult checkProductPromotionAvailable(String productName, int buyCount){
+        Product product = findProductPromoted(productName);
+        if(findProductPromoted(productName) == NOT_FOUND){
+            return PromotionResult.createNoPromotion(productName,buyCount);
+        }
+        if(product.isEnoughToBuy(buyCount)){
+            return product.estimatePromotionResult(buyCount, DateTimes.now());
+        }
+
+        int maxCountToBuyPromotion = product.calculateMaxCountToBuy(buyCount);
+        PromotionResult promotionResult = product.estimatePromotionResult(maxCountToBuyPromotion,DateTimes.now());
+        return promotionResult.transitState(PromotionState.INSUFFICIENT);
+
+    }
+
+    public List<Receipt> buyProducts(List<PurchaseRequest> purchaseRequests){
+        List<Receipt> receipts = new ArrayList<>();
+        for(PurchaseRequest request : purchaseRequests){
+            receipts.add(buyProduct(request));
+        }
+        return receipts;
+    }
+
+    public Receipt buyProduct(PurchaseRequest request){
+
+        if(request.getPromotionState() == PromotionState.NO_PROMOTION){
+            return tryBuyProductNonPromoted(request);
+        }
+
+        Receipt resultPromoted = tryBuyProductPromoted(request);
+        Receipt resultNonPromoted = tryBuyProductNonPromoted(request);
+
+        return combineReceipt(resultPromoted,resultNonPromoted);
+    }
+
+    public int calculateDiscount(List<Receipt> receipts){
+        /*TODO
+        *   - 합계산 도중 오버플로우 점검 필요*/
+        final int maxDisCount = 8000;
+        final double disCountRate = 0.3;
+        int totalNonPromotedPrice = 0;
+        for(Receipt receipt : receipts){
+            totalNonPromotedPrice += receipt.getNonPromotedPrice();
+        }
+        int disCountPrice = (int)Math.round(disCountRate * totalNonPromotedPrice);
+        return Math.min(maxDisCount, disCountPrice);
+    }
+
+    private Receipt combineReceipt(Receipt promoted, Receipt nonPromoted) {
+        if(!promoted.getProductName().equals(nonPromoted.getProductName())){
+            ExceptionFactory.throwIllegalStateException(ExceptionType.INTERNAL_ERROR);
+        }
+        return promoted.combine(nonPromoted);
+    }
+
+    private Receipt tryBuyProductPromoted(PurchaseRequest request){
+        boolean isPromoted = true;
+        Product product = this.findOneOriginProduct(request.getProductName(),isPromoted);
+        if(product == NOT_FOUND){
+            return Receipt.createEmptyReceipt(request.getProductName());
+        }
+        if(product.getCount() < request.getCountPurchased()){
+            int buyCount = product.getCount();
+            return buyProduct(product,buyCount,request);
+        }
+        return buyProduct(product,request.getCountPurchased(),request);
+    }
+
+
+    private Receipt tryBuyProductNonPromoted(PurchaseRequest request){
+        boolean isPromoted = false;
+        Product product = this.findOneOriginProduct(request.getProductName(),isPromoted);
+        if(product == NOT_FOUND){
+            return Receipt.createEmptyReceipt(request.getProductName());
+        }
+        if(product.getCount() < request.getCountPurchased()){
+            ExceptionFactory.throwIllegalStateException(ExceptionType.INTERNAL_ERROR);
+        }
+        return buyProduct(product,request.getCountPurchased(),request);
+    }
+
+    private Receipt buyProduct(Product product, int buyCount, PurchaseRequest request){
+        request.decreaseCount(buyCount);
+        return product.buy(buyCount);
+    }
+
+}

리뷰: `null`도 상수로 처리하신 것이 인상깊네요! 저는 `null` 자체만으로도 충분히 의미를 드러낸다고 생각하여 상수화하지 않았는데, @armcortex3445 님의 상수화 기준이 궁금합니다!