Initial checkin of OfflineContentProvider.

components/offline_content/core/offline_content_provider.h

+// Copyright 2017 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.
+
+#ifndef COMPONENTS_OFFLINE_CONTENT_CORE_OFFLINE_CONTENT_PROVIDER_H_
+#define COMPONENTS_OFFLINE_CONTENT_CORE_OFFLINE_CONTENT_PROVIDER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "url/gurl.h"
+
+namespace offline_content {
+
+struct ContentId;
+struct OfflineItem;
+
+// A provider of a set of OfflineItems that are meant to be exposed to the UI.
+// The provider is required to notify all observers of OnItemsAvailable when the
+// underlying data set is initialized.  Without that call it should not expect
+// nor have to support any other calls to this provider.
+class OfflineContentProvider {
+ public:
+  using OfflineItemList = std::vector<OfflineItem>;
+
+  // An observer class that should be notified of relevant changes to the
+  // underlying data source.
+  class Observer {
+   public:
+    // Called when the underlying data source for the provider has been
+    // initialized and the contents are able to be queried and interacted with.
+    // |provider| should be a reference to this OfflineContentProvider that is
+    // initialized.
+    virtual void OnItemsAvailable(OfflineContentProvider* provider) = 0;
+
+    // Called when one or more OfflineItems have been added and should be shown
+    // in the UI.
+    virtual void OnItemsAdded(const OfflineItemList& items) = 0;
+
+    // Called when the OfflineItem represented by |id| should be removed from
+    // the UI.
+    virtual void OnItemRemoved(const ContentId& id) = 0;
+
+    // Called when the contents of |item| have been updated and the UI should be
+    // refreshed for that item.
+    virtual void OnItemUpdated(const OfflineItem& item) = 0;
+
+   protected:
+    virtual ~Observer() = default;
+  };
+
+  // Returns whether or not the underlying data source for this provider has
+  // been initialized and is ready to start returning content.  This provider
+  // should not need to support handling the other data query/manipulation
+  // methods if this returns false.
+  virtual bool AreItemsAvailable() = 0;
+
+  // Called to trigger opening an OfflineItem represented by |id|.
+  virtual void OpenItem(const ContentId& id) = 0;
+
+  // Called to trigger removal of an OfflineItem represented by |id|.
+  virtual void RemoveItem(const ContentId& id) = 0;
+
+  // Called to cancel a download of an OfflineItem represented by |id|.
+  virtual void CancelDownload(const ContentId& id) = 0;
+
+  // Called to pause a download of an OfflineItem represented by |id|.
+  virtual void PauseDownload(const ContentId& id) = 0;
+
+  // Called to resume a paused download of an OfflineItem represented by |id|.
+  virtual void ResumeDownload(const ContentId& id) = 0;
+
+  // Returns an OfflineItem represented by |id| or |nullptr| if none exists.
+  // The caller should not hold ownership of the returned item beyond the scope
+  // of the function call.

[fgorski, 2017/02/14 22:17:55]

should the caller be able to modify it?
once again, perhaps a const OfflineItem*?

[David Trainor- moved to gerrit, 2017/02/22 01:23:12]

Done.  I think this will change as this thing gets built out.  The GetAllItems
call might move to an std::vector<> of pointers to prevent running the copy
constructor on everything.  This is just fleshing out the main interfaces and
kicking things off.

+  virtual OfflineItem* GetItemById(const ContentId& id) = 0;
+
+  // Returns all OfflineItems for this particular provider.
+  virtual OfflineItemList GetAllItems() = 0;
+
+  // Adds an observer that should be notified of OfflineItem list modifications.
+  // If the provider is already initialized OnItemsAvailable should be called
+  // on this observer.

[Dmitry Titov, 2017/02/14 05:41:31]

Maybe makes sense to say that in case of already initialized provider the
OnItemsAvailable should be scheduled via a task rather that directly called.
Less trouble this way :)

[David Trainor- moved to gerrit, 2017/02/22 01:23:12]

Agreed.  I like that you did that in the DownloadUIAdapter and I did the same
thing in the aggregator.  Will comment!

+  virtual void AddObserver(Observer* observer) = 0;
+
+  // Removes an observer.  No further notifications should be sent to it.
+  virtual void RemoveObserver(Observer* observer) = 0;
+
+ protected:
+  virtual ~OfflineContentProvider() = default;
+};
+
+}  // namespace offline_content
+
+#endif  // COMPONENTS_OFFLINE_CONTENT_CORE_OFFLINE_CONTENT_PROVIDER_H_