refactoring : mutable data - separate query from modifier

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/Billing.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+public class Billing {
+
+    private Customer customer;
+
+    private EmailGateway emailGateway;
+
+    public Billing(Customer customer, EmailGateway emailGateway) {
+        this.customer = customer;
+        this.emailGateway = emailGateway;
+    }
+
+    // 어떤 값을 조회하는 메소드에서는 사이드이펙트가 생기지 않도록 조회와 명령을 분리한다.
+    public double getTotalOutstanding() {
+        return customer.getInvoices().stream()
+                .map(Invoice::getAmount)
+                .reduce((double) 0, Double::sum);
+    }
+
+    public void sendBill() {
+        emailGateway.send(formatBill(customer));
+    }
+
+    private String formatBill(Customer customer) {
+        return "sending bill for " + customer.getName();
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/Criminal.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+import java.util.List;
+
+public class Criminal {
+
+    public void alertForMiscreant(List<Person> people) {
+        if (!findMiscreant(people).isBlank()) {
+            setOffAlarms();
+        }
+    }
+
+    public String findMiscreant(List<Person> people) {
+        for (Person p : people) {
+            if (p.getName().equals("Don")) {
+                return "Don";
+            }
+
+            if (p.getName().equals("John")) {
+                return "John";
+            }
+        }
+
+        return "";
+    }
+
+    private void setOffAlarms() {
+        System.out.println("set off alarm");
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/Customer.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+import java.util.List;
+
+public class Customer {
+
+    private String name;
+
+    private List<Invoice> invoices;
+
+    public Customer(String name, List<Invoice> invoices) {
+        this.name = name;
+        this.invoices = invoices;
+    }
+
+    public List<Invoice> getInvoices() {
+        return invoices;
+    }
+
+    public String getName() {
+        return name;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/EmailGateway.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+public class EmailGateway {
+    public void send(String bill) {
+        System.out.println(bill);
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/Invoice.java

@@ -0,0 +1,14 @@
+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+public class Invoice {
+
+    private double amount;
+
+    public Invoice(double amount) {
+        this.amount = amount;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/Person.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+public class Person {
+
+    private String name;
+
+    public Person(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/Billing.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+public class Billing {
+
+    private Customer customer;
+
+    private EmailGateway emailGateway;
+
+    public Billing(Customer customer, EmailGateway emailGateway) {
+        this.customer = customer;
+        this.emailGateway = emailGateway;
+    }
+
+    public double getTotalOutstandingAndSendBill() {
+        double result = customer.getInvoices().stream()
+                .map(Invoice::getAmount)
+                .reduce((double) 0, Double::sum);
+        sendBill();
+        return result;
+    }
+
+    private void sendBill() {
+        emailGateway.send(formatBill(customer));
+    }
+
+    private String formatBill(Customer customer) {
+        return "sending bill for " + customer.getName();
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/Criminal.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+import java.util.List;
+
+public class Criminal {
+
+    public String alertForMiscreant(List<Person> people) {
+        for (Person p : people) {
+            if (p.getName().equals("Don")) {
+                setOffAlarms();
+                return "Don";
+            }
+
+            if (p.getName().equals("John")) {
+                setOffAlarms();
+                return "John";
+            }
+        }
+
+        return "";
+    }
+
+    private void setOffAlarms() {
+        System.out.println("set off alarm");
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/Customer.java

@@ -0,0 +1,23 @@
+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+import java.util.List;
+
+public class Customer {
+
+    private String name;
+
+    private List<Invoice> invoices;
+
+    public Customer(String name, List<Invoice> invoices) {
+        this.name = name;
+        this.invoices = invoices;
+    }
+
+    public List<Invoice> getInvoices() {
+        return invoices;
+    }
+
+    public String getName() {
+        return name;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/EmailGateway.java

@@ -0,0 +1,7 @@
+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+public class EmailGateway {
+    public void send(String bill) {
+        System.out.println(bill);
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/Invoice.java

@@ -0,0 +1,14 @@
+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+public class Invoice {
+
+    private double amount;
+
+    public Invoice(double amount) {
+        this.amount = amount;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/before/Person.java

@@ -0,0 +1,14 @@
+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier.before;
+
+public class Person {
+
+    private String name;
+
+    public Person(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return this.name;
+    }
+}

refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/BillingTest.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BillingTest {
+
+    @Test
+    void totalOutstanding() {
+        Billing billing = new Billing(new Customer("kim", List.of(new Invoice(20), new Invoice(30))),
+                new EmailGateway());
+        assertEquals(50d, billing.getTotalOutstanding());
+
+        billing.sendBill();
+    }
+
+}

refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_19_separate_query_from_modifier/CriminalTest.java

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+package com.example.refactoring._06_mutable_data._19_separate_query_from_modifier;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CriminalTest {
+
+    @Test
+    void alertForMiscreant() {
+        Criminal criminal = new Criminal();
+        String found = criminal.findMiscreant(List.of(new Person("kim"), new Person("Don")));
+        assertEquals("Don", found);
+
+        found = criminal.findMiscreant(List.of(new Person("John"), new Person("Don")));
+        assertEquals("John", found);
+
+        found = criminal.findMiscreant(List.of(new Person("kim"), new Person("Jane")));
+        assertEquals("", found);
+    }
+
+}