Add pattern strategy. OverbookingPolicy example.

Author: ilopX

patterns/strategy/reservation_cargo_spaces/application/application.dart

@@ -0,0 +1,20 @@
+import '../partners/cargo.dart';
+import '../partners/voyage.dart';
+import '../policy/overbooking_policy.dart';
+import 'order_confirmation_sequence.dart';
+
+class Application {
+  final OverbookingPolicy overbookingPolicy;
+  final orderConfirmationSequence = OrderConfirmationSequence();
+
+  Application(this.overbookingPolicy);
+
+  void makeBooking(Cargo cargo, Voyage voyage) {
+    if (overbookingPolicy.isAllowed(cargo, voyage)) {
+      final confirmation = orderConfirmationSequence.next();
+      voyage.addCargo(cargo, confirmation);
+    } else {
+      throw 'The weight of the cargo exceeds the permissible norm.';
+    }
+  }
+}

patterns/strategy/reservation_cargo_spaces/application/order_confirmation_sequence.dart

@@ -0,0 +1,5 @@
+class OrderConfirmationSequence {
+  var _index = 0;
+
+  int next() => _index++;
+}

patterns/strategy/reservation_cargo_spaces/main.dart

@@ -0,0 +1,18 @@
+import 'application/application.dart';
+import 'partners/cargo.dart';
+import 'partners/voyage.dart';
+import 'policy/overbooking_policy.dart';
+
+void main() {
+  final overbookingPolicy = OverbookingPolicy();
+  final app = Application(overbookingPolicy);
+  final voyage = Voyage();
+
+  try {
+    app.makeBooking(Cargo(1000), voyage);
+    app.makeBooking(Cargo(500), voyage);
+    app.makeBooking(Cargo(800), voyage); // error
+  } catch (e) {
+    print(e);
+  }
+}

patterns/strategy/reservation_cargo_spaces/partners/cargo.dart

@@ -0,0 +1,5 @@
+class Cargo {
+  final double size;
+
+  Cargo(this.size);
+}

patterns/strategy/reservation_cargo_spaces/partners/voyage.dart

@@ -0,0 +1,16 @@
+import 'cargo.dart';
+
+class Voyage {
+  final _cargo = <int, Cargo>{};
+
+  double get capacity => 2000.0;
+
+  double bookedCargoSize() {
+    return _cargo.values.fold(0, (prev, cargo) => prev + cargo.size);
+  }
+
+  void addCargo(Cargo cargo, int confirmation) {
+    _cargo.putIfAbsent(confirmation, () => cargo);
+    print('Add Cargo(${cargo.size}) to voyage.');
+  }
+}

patterns/strategy/reservation_cargo_spaces/policy/overbooking_policy.dart

@@ -0,0 +1,13 @@
+import '../partners/cargo.dart';
+import '../partners/voyage.dart';
+
+class OverbookingPolicy {
+  static const allowableRedundancy = 1.1;
+
+  bool isAllowed(Cargo cargo, Voyage voyage) {
+    final maxBooking = voyage.capacity * allowableRedundancy;
+    final futureWeight = voyage.bookedCargoSize() + cargo.size;
+
+    return futureWeight < maxBooking;
+  }
+}