Exercise 3: Budget plan

src/main/java/com/odde/tdd/BudgetPlan.java

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+package com.odde.tdd;
+
+import java.time.YearMonth;
+import java.util.Calendar;
+import java.util.Date;
+
+public class BudgetPlan {
+  private final BudgetRepo budgetRepo;
+
+  public BudgetPlan(BudgetRepo budgetRepo) {
+
+    this.budgetRepo = budgetRepo;
+  }
+
+  public double getBudget(Date from, Date to) {
+    if (from.compareTo(to) > 0) {
+      return 0;
+    }
+    YearMonth fromYearMonth = getYearMonth(from);
+    YearMonth toYearMonth = getYearMonth(to);
+    int fromYear = fromYearMonth.getYear();
+    int fromMonth = fromYearMonth.getMonthValue();
+    int toYear = toYearMonth.getYear();
+    int toMonth = toYearMonth.getMonthValue();
+    double amount = 0.0;
+    for (int year = fromYear; year <= toYear; year++) {
+      for (int i = 1; i <= 12; i++) {
+        amount += getMonthlyBudget(YearMonth.of(year, i));
+      }
+    }
+    for (int i = 1; i < fromMonth; i++) {
+      amount -= getMonthlyBudget(YearMonth.of(fromYear, i));
+    }
+    for (int i = toMonth + 1; i <= 12; i++) {
+      amount -= getMonthlyBudget(YearMonth.of(toYear, i));
+    }
+    amount -= getMonthlyBudget(fromYearMonth) / fromYearMonth.lengthOfMonth() * (getDayOfMonth(from) - 1);
+    amount -= getMonthlyBudget(toYearMonth) / toYearMonth.lengthOfMonth() * (toYearMonth.lengthOfMonth() - getDayOfMonth(to));
+    return amount;
+  }
+
+  private double getMonthlyBudget(YearMonth yearMonth) {
+    return (double) this.budgetRepo.findAll().stream().filter(budget ->
+        budget.getMonth().equals(yearMonth)).findFirst().map(Budget::getAmount).orElse(0L);
+  }
+
+  private YearMonth getYearMonth(Date date) {
+    Calendar calendar = Calendar.getInstance();
+    calendar.setTime(date);
+    return YearMonth.of(calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH) + 1);
+  }
+
+  private int getDayOfMonth(Date date) {
+    Calendar calendar = Calendar.getInstance();
+    calendar.setTime(date);
+    return calendar.get(Calendar.DAY_OF_MONTH);
+  }
+}

src/test/java/com/odde/tdd/BudgetPlanTest.java

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+package com.odde.tdd;
+
+import org.junit.Test;
+
+import java.time.YearMonth;
+import java.util.*;
+
+import static org.junit.Assert.assertEquals;
+
+public class BudgetPlanTest {
+  MockBudgetRepo budgetRepo = new MockBudgetRepo();
+  BudgetPlan target = new BudgetPlan(budgetRepo);
+  Calendar calendar = new GregorianCalendar();
+
+  @Test
+  public void budge_of_22_01_01() {
+    calendar.set(2022, Calendar.JANUARY, 1);
+    Date from = calendar.getTime();
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(1.0, amount, 0.0);
+  }
+
+  @Test
+  public void budge_from_22_01_01_to_22_01_02() {
+    calendar.set(2022, Calendar.JANUARY, 1);
+    Date from = calendar.getTime();
+    calendar.set(2022, Calendar.JANUARY, 3);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(3.0, amount, 0.0);
+  }
+
+  @Test
+  public void budge_from_22_01_31_to_22_02_01() {
+    calendar.set(2022, Calendar.JANUARY, 31);
+    Date from = calendar.getTime();
+    calendar.set(2022, Calendar.FEBRUARY, 1);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(3.0, amount, 0.0);
+  }
+
+  @Test
+  public void budget_from_22_01_31_to_22_03_01() {
+    calendar.set(2022, Calendar.JANUARY, 31);
+    Date from = calendar.getTime();
+    calendar.set(2022, Calendar.MARCH, 1);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(60.0, amount, 0.0);
+  }
+
+  @Test
+  public void budget_from_21_12_31_to_22_02_01() {
+    calendar.set(2021, Calendar.DECEMBER, 31);
+    Date from = calendar.getTime();
+    calendar.set(2022, Calendar.FEBRUARY, 1);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(34.0, amount, 0.0);
+  }
+
+  @Test
+  public void budge_from_21_12_31_to_23_01_01() {
+    calendar.set(2021, Calendar.DECEMBER, 31);
+    Date from = calendar.getTime();
+    calendar.set(2023, Calendar.JANUARY, 1);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(2384.0, amount, 0);
+  }
+
+  @Test
+  public void budget_from_20_01_01_to_20_12_31() {
+    calendar.set(2020, Calendar.JANUARY, 1);
+    Date from = calendar.getTime();
+    calendar.set(2020, Calendar.DECEMBER, 31);
+    Date to = calendar.getTime();
+    double amount = target.getBudget(from, to);
+    assertEquals(0, amount, 0);
+  }
+
+}
+
+class MockBudgetRepo implements BudgetRepo {
+
+  @Override
+  public List<Budget> findAll() {
+    return Arrays.asList(
+        new Budget(YearMonth.of(2021, 12), 31),
+        new Budget(YearMonth.of(2022, 1), 31),
+        new Budget(YearMonth.of(2022, 2), 56),
+        new Budget(YearMonth.of(2022, 3), 93),
+        new Budget(YearMonth.of(2022, 4), 120),
+        new Budget(YearMonth.of(2022, 5), 155),
+        new Budget(YearMonth.of(2022, 6), 180),
+        new Budget(YearMonth.of(2022, 7), 217),
+        new Budget(YearMonth.of(2022, 8), 248),
+        new Budget(YearMonth.of(2022, 9), 270),
+        new Budget(YearMonth.of(2022, 10), 310),
+        new Budget(YearMonth.of(2022, 11), 330),
+        new Budget(YearMonth.of(2022, 12), 372),
+        new Budget(YearMonth.of(2023, 1), 31)
+    );
+  }
+
+}