Upstream Chrome on iOS source code [1/11].

ios/chrome/browser/browser_coordinator.mm

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// ======                        New Architecture                         =====
+// =         This code is only used in the new iOS Chrome architecture.       =
+// ============================================================================
+
+#import "base/logging.h"
+#import "ios/chrome/browser/browser_coordinator+internal.h"
+#import "ios/chrome/browser/browser_coordinator.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@interface BrowserCoordinator ()
+// Child coordinators owned by this object.
+@property(nonatomic, strong)
+    NSMutableSet<BrowserCoordinator*>* childCoordinators;
+// Parent coordinator of this object, if any.
+@property(nonatomic, readwrite, weak) BrowserCoordinator* parentCoordinator;
+@property(nonatomic, readwrite) BOOL overlaying;
+@end
+
+@implementation BrowserCoordinator
+
+@synthesize browserState = _browserState;
+@synthesize rootViewController = _rootViewController;
+@synthesize childCoordinators = _childCoordinators;
+@synthesize parentCoordinator = _parentCoordinator;
+@synthesize overlaying = _overlaying;
+
+- (instancetype)init {
+  if (self = [super init]) {
+    _childCoordinators = [NSMutableSet set];
+  }
+  return self;
+}
+
+- (void)dealloc {
+  [self stop];
+}
+
+#pragma mark - Public API
+
+- (void)start {
+  // Default implementation is a no-op.
+}
+
+- (void)stop {
+  // Default implementation is a no-op.
+}
+
+@end
+
+@implementation BrowserCoordinator (Internal)
+// Concrete implementations must implement a |viewController| property.
+@dynamic viewController;
+
+- (NSSet*)children {
+  return [self.childCoordinators copy];
+}
+
+- (void)addChildCoordinator:(BrowserCoordinator*)coordinator {
+  [self.childCoordinators addObject:coordinator];
+  coordinator.browserState = self.browserState;
+  coordinator.parentCoordinator = self;
+  coordinator.rootViewController = self.viewController;
+}
+
+- (BrowserCoordinator*)overlayCoordinator {
+  if (self.overlaying)
+    return self;
+  for (BrowserCoordinator* child in self.children) {
+    BrowserCoordinator* overlay = child.overlayCoordinator;
+    if (overlay)
+      return overlay;
+  }
+  return nil;
+}
+
+- (void)addOverlayCoordinator:(BrowserCoordinator*)overlayCoordinator {
+  // If this object has no children, then add |overlayCoordinator| as a child
+  // and mark it as such.
+  if ([self canAddOverlayCoordinator:overlayCoordinator]) {
+    [self addChildCoordinator:overlayCoordinator];
+    overlayCoordinator.overlaying = YES;
+  } else if (self.childCoordinators.count == 1) {
+    [[self.childCoordinators anyObject]
+        addOverlayCoordinator:overlayCoordinator];
+  } else {
+    CHECK(NO) << "Coordinators with multiple children must explicitly "
+              << "handle -addOverlayCoordinator: or return NO to "
+              << "-canAddOverlayCoordinator:";
+  }
+}
+
+- (void)removeOverlayCoordinator {
+  BrowserCoordinator* overlay = self.overlayCoordinator;
+  [overlay.parentCoordinator removeChildCoordinator:overlay];
+}
+
+- (BOOL)canAddOverlayCoordinator:(BrowserCoordinator*)overlayCoordinator {
+  // By default, coordinators with no other children can add an overlay.
+  return self.childCoordinators.count == 0;
+}
+
+- (void)removeChildCoordinator:(BrowserCoordinator*)coordinator {
+  [self.childCoordinators removeObject:coordinator];
+}
+
+@end