help

streams/src/streams/Main.java

@@ -2,10 +2,10 @@ package streams;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import javax.swing.text.html.Option;
 import tester.Tester;
 
 class Customer {
@@ -95,6 +95,78 @@ interface PurchaseDB {
     getPurchasesForSince(List<Integer> customerIds, int numberOfDaysAgo);
 }
 
+class Accounting {
+    CustomerDB customers;
+    InventoryDB inventory;
+    PurchaseDB purchases;
+
+    Accounting(
+        CustomerDB customers, InventoryDB inventory, PurchaseDB purchases
+    ) {
+        this.customers = customers;
+        this.inventory = inventory;
+        this.purchases = purchases;
+    }
+
+    int revenueSince(int days) {
+        return this.purchases.getPurchasesSince(days)
+            .stream()
+            .flatMap(purchase -> purchase.getLineItems().stream())
+            .map(item -> {
+                Inventory inv =
+                    this.inventory.getInventoryById(item.getInventoryId())
+                        .orElseThrow(() -> new Error("Not there."));
+                return inv.getCostPerUnit() * item.getNumberOfItemsPurchased();
+            })
+            .reduce(0, (a, b) -> a + b);
+    }
+
+    int unitsSoldInPastMonth(int inventoryId) {
+        return purchases.getPurchasesSince(30)
+            .stream()
+            .flatMap(p -> p.getLineItems().stream())
+            .filter(item -> item.getInventoryId() == inventoryId)
+            .mapToInt(LineItem::getNumberOfItemsPurchased)
+            .sum();
+    }
+
+    String bestCustomer() {
+        return this.customers.getAllCustomers()
+            .stream()
+            .reduce((best, current) -> {
+                int bestSpent = howStupidIs(best.getId());
+                int currentSpent = howStupidIs(current.getId());
+                return currentSpent > bestSpent ? current : best;
+            })
+            .map(Customer::getName)
+            .orElseThrow(
+                ()
+                    -> new RuntimeException(
+                        "You didn't have a best customer, fool."
+                    )
+            );
+    }
+
+    private int howStupidIs(int customerId) {
+        return this.purchases.getPurchasesFor(customerId)
+            .stream()
+            .flatMap(p -> p.getLineItems().stream())
+            .map(
+                item
+                -> this.inventory.getInventoryById(item.getInventoryId())
+                       .map(
+                           inv
+                           -> inv.getCostPerUnit() *
+                                  item.getNumberOfItemsPurchased()
+                       )
+                       .orElseThrow(
+                           () -> new Error("That's not an inventory fool.")
+                       )
+            )
+            .reduce(0, Integer::sum);
+    }
+}
+
 class Examples {
     Customer borace, germany, vietnam;
     Inventory cabbages, cinderBlocks, traps;
@@ -105,6 +177,8 @@ class Examples {
     InventoryDB loot;
     PurchaseDB crimes;
 
+    Accounting dave;
+
     void init() {
         borace = new Customer(0, "Borace");
         germany = new Customer(1, "Germany");
@@ -209,6 +283,8 @@ class Examples {
                     .toList();
             }
         };
+
+        dave = new Accounting(victims, loot, crimes);
     }
 
     void test(Tester t) {
@@ -243,4 +319,16 @@ class Examples {
             List.of(profit, ireland, biden, cob)
         );
     }
+
+    void testDave(Tester t) {
+        init();
+
+        t.checkExpect(dave.revenueSince(-1), 0);
+        t.checkExpect(dave.revenueSince(0), 54 * 28 + 1 * 1 + 3 * 10);
+        t.checkExpect(
+            dave.revenueSince(1), 2 * (54 * 28) + 2 * (1 * 1) + 3 * 10
+        );
+        t.checkExpect(dave.unitsSoldInPastMonth(0), 54 * 2);
+        t.checkExpect(dave.bestCustomer(), "Vietnam");
+    }
 }