Service to apply discounts and price a grocerys basket.

.gitignore

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+target/
+bin/
+
+## Intellij IDEA ##
+.idea
+.iml
+
+*.log

Assumptions

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+Notes:
+1. Each offer is applied independently, offer applied previously have no bearing on next offer.
+2. May be rules be externalized, may be a rules engine like Drools.
+3. Possibly could have implemented visitor pattern.
+4. Could have added more options at command line i.e show available products, offers or discount applied. but kept it to minimal to calculate the final price after applying discounts.
+5.

lombok.config

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+lombok.anyConstructor.addConstructorProperties=true
+lombok.log.fieldName=LOGGER
+lombok.log.log4j2.flagUsage=error
+lombok.log.log4j.flagUsage=error
+lombok.log.javaUtilLogging.flagUsage=error
+lombok.log.apacheCommons.flagUsage=error

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.industriallogic.henrysgroceries</groupId>
+    <artifactId>PriceGroceryBasket</artifactId>
+    <version>1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.2.1.RELEASE</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-devtools</artifactId>
+            <optional>true</optional>
+        </dependency>
+
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.0</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <scope>provided</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>repackage</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

src/main/java/com/industriallogic/henrysgroceries/PriceShoppingBasketApplication.java

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+package com.industriallogic.henrysgroceries;
+
+import com.industriallogic.henrysgroceries.exception.ProductNotFoundException;
+import com.industriallogic.henrysgroceries.service.ShoppingBasketServiceImpl;
+import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.lang3.StringUtils;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+import java.math.BigDecimal;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Scanner;
+
+@SpringBootApplication
+@Slf4j
+public class PriceShoppingBasketApplication implements CommandLineRunner {
+
+    @Autowired
+    private ShoppingBasketServiceImpl shoppingBasketService;
+
+    public static void main(String[] args) {
+        SpringApplication.run(PriceShoppingBasketApplication.class, args);
+    }
+
+    @Override
+    public void run(String... args)  {
+        startShopping();
+    }
+
+    public void startShopping() {
+        try (Scanner scanner = new Scanner(System.in)) {
+            while (true) {
+                LOGGER.info("Enter 1. To add products to basket | Enter 2. To checkout | Enter X. To EXIT");
+                String option = scanner.next();
+                switch (option) {
+                    case "1":
+                        addProductsToBasket(  scanner);
+                        break;
+                    case "2":
+                        checkout( );
+                        break;
+                    case "X":
+                        return;
+                    default:
+                        LOGGER.info("Invalid entry, please re-enter '1' OR '2' OR 'X'");
+                }
+            }
+        }
+    }
+
+    private void addProductsToBasket(  Scanner scanner) {
+        LOGGER.info("Enter products separated with space to add to basket: ");
+        scanner.nextLine();
+        List<String> productsNameList = Arrays.asList(StringUtils.split(scanner.nextLine()));
+        productsNameList.forEach(productName -> {
+            try {
+                BigDecimal curntTotalAmount = shoppingBasketService.addProductToBasket(productName);
+                LOGGER.info(String.format("Added %s to basket. Current total amount %.2f  " ,productName, curntTotalAmount));
+            } catch (ProductNotFoundException e) {
+                LOGGER.error("Product not found for .. " + productName);
+            }
+        });
+    }
+
+    private void checkout( ) {
+        BigDecimal toPay = shoppingBasketService.totalPriceToPay();
+        LOGGER.info("Total to Pay after discount " + toPay);
+    }
+
+}

src/main/java/com/industriallogic/henrysgroceries/exception/ProductNotFoundException.java

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+package com.industriallogic.henrysgroceries.exception;
+
+public class ProductNotFoundException extends  Exception {
+
+    private static final long serialVersionUID = 1L;
+
+    public ProductNotFoundException(String message) {
+        super(message);
+    }
+
+    public ProductNotFoundException(String message, Throwable cause) {
+        super(message, cause);
+    }
+
+}

src/main/java/com/industriallogic/henrysgroceries/model/MeasurementUnit.java

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+package com.industriallogic.henrysgroceries.model;
+
+public enum MeasurementUnit {
+    TIN, LOAF, BOTTLE, SINGLE
+}

src/main/java/com/industriallogic/henrysgroceries/model/Product.java

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+package com.industriallogic.henrysgroceries.model;
+
+import lombok.Data;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+
+import java.math.BigDecimal;
+
+@RequiredArgsConstructor
+@Data
+public class Product {
+    @NonNull private String productCode;
+    @NonNull private String name;
+    @NonNull private BigDecimal price;
+    @NonNull private MeasurementUnit unit;
+}

src/main/java/com/industriallogic/henrysgroceries/model/ShoppingBasket.java

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+package com.industriallogic.henrysgroceries.model;
+
+
+import lombok.NoArgsConstructor;
+import org.springframework.stereotype.Component;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+@NoArgsConstructor
+@Component
+public class ShoppingBasket {
+
+    private final Map<Product, Integer> basket = new HashMap<>();
+    private LocalDate shoppingDate = LocalDate.now();
+    private BigDecimal curTotalAmount = BigDecimal.ZERO;
+
+    public BigDecimal addProductToBasket(Product product) {
+        basket.compute(product,
+                (k, v) -> {
+                    return v == null ? 1 : v + 1;
+                });
+        curTotalAmount = curTotalAmount.add(product.getPrice());
+        return curTotalAmount;
+    }
+
+    public LocalDate getShoppingDate() {
+        return this.shoppingDate;
+    }
+
+    public Map<Product, Integer> getProductsInBasket() {
+        return Collections.unmodifiableMap(basket);
+    }
+
+    public BigDecimal getCurTotalAmount() {
+        return curTotalAmount;
+    }
+
+    public void setShoppingDate(LocalDate shoppingDate) {
+        this.shoppingDate = shoppingDate;
+    }
+}
+
+
+

src/main/java/com/industriallogic/henrysgroceries/offers/ComboDiscountOffer.java

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+package com.industriallogic.henrysgroceries.offers;
+
+import com.industriallogic.henrysgroceries.model.Product;
+import com.industriallogic.henrysgroceries.model.ShoppingBasket;
+import lombok.Data;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+@RequiredArgsConstructor
+@Data
+public class ComboDiscountOffer implements Offer {
+
+    @NonNull
+    private String offerName;
+    @NonNull
+    private Product qualifyingProduct;
+    @NonNull
+    private Integer qualifyingProdMinQnty;
+    @NonNull
+    private Product offerOnProduct;
+    @NonNull
+    private BigDecimal discountFactor;
+    @NonNull
+    private LocalDate offerStartDate;
+    @NonNull
+    private LocalDate offerEndDate;
+
+    /**
+     * Applies Combo discount offer if basket qualifies for the offer
+     * @param basket - basket with products
+     * @return - discount amount to be applied on the basket
+     */
+    @Override
+    public BigDecimal getDiscount(ShoppingBasket basket) {
+        if (isOfferStillValid(basket.getShoppingDate(), offerStartDate, offerEndDate)) {
+            Integer qualifyingProdCountInBasket = basket.getProductsInBasket().getOrDefault(qualifyingProduct, 0);
+            if (qualifyingProdCountInBasket >= qualifyingProdMinQnty) {
+                int purchaseQnty = basket.getProductsInBasket().getOrDefault(offerOnProduct, 0);
+                int eligibleOfferCount = Math.min(qualifyingProdCountInBasket/qualifyingProdMinQnty, purchaseQnty);
+                return offerOnProduct.getPrice().multiply(discountFactor).divide(ONE_HUNDRED ).multiply( new BigDecimal(eligibleOfferCount)).setScale(2);
+            }
+        }
+        return BigDecimal.ZERO;
+    }
+}
+

src/main/java/com/industriallogic/henrysgroceries/offers/Offer.java

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+package com.industriallogic.henrysgroceries.offers;
+
+import com.industriallogic.henrysgroceries.model.ShoppingBasket;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+public interface Offer {
+
+    BigDecimal ONE_HUNDRED = new BigDecimal(100);
+
+    default boolean isOfferStillValid(LocalDate shoppingDate, LocalDate offerStartDate, LocalDate offerEndDate) {
+        return ( shoppingDate.compareTo(offerStartDate) >= 0  &&  shoppingDate.compareTo(offerEndDate) <= 0) ;
+    }
+
+    public BigDecimal getDiscount(ShoppingBasket basket);
+}

src/main/java/com/industriallogic/henrysgroceries/offers/PercentageDiscountOffer.java

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+package com.industriallogic.henrysgroceries.offers;
+
+import com.industriallogic.henrysgroceries.model.Product;
+import com.industriallogic.henrysgroceries.model.ShoppingBasket;
+import lombok.Data;
+import lombok.NonNull;
+import lombok.RequiredArgsConstructor;
+
+import java.math.BigDecimal;
+import java.time.LocalDate;
+
+@RequiredArgsConstructor
+@Data
+public class PercentageDiscountOffer implements Offer {
+    @NonNull
+    private String offerName;
+    @NonNull
+    private Product product;
+    @NonNull
+    private BigDecimal discountPercentage;
+    @NonNull
+    private LocalDate offerStartDate;
+    @NonNull
+    private LocalDate offerEndDate;
+
+    /**
+     * Apples percentage discount offer if basket qualifies for the offer
+     * @param basket - basket with products
+     * @return - discount amount to be applied on the basket
+     */
+    public BigDecimal getDiscount(ShoppingBasket basket) {
+        if (isOfferStillValid(basket.getShoppingDate(), offerStartDate, offerEndDate)) {
+            Integer productQuantity = basket.getProductsInBasket().getOrDefault(product, 0);
+            return product.getPrice().multiply(discountPercentage).divide(ONE_HUNDRED ).multiply(new BigDecimal(productQuantity));
+        }
+        return BigDecimal.ZERO;
+    }
+}