Add ContentSuggestionsService

components/ntp_snippets/content_suggestions_provider.h

Index: components/ntp_snippets/content_suggestions_provider.h
diff --git a/components/ntp_snippets/content_suggestions_provider.h b/components/ntp_snippets/content_suggestions_provider.h
new file mode 100644
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+++ b/components/ntp_snippets/content_suggestions_provider.h
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+// 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.
+
+#ifndef COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
+#define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/callback.h"
+#include "components/ntp_snippets/content_suggestion.h"
+#include "components/ntp_snippets/content_suggestions_provider_type.h"
+
+namespace gfx {
+class Image;
+}
+
+namespace ntp_snippets {
+
+// Provides content suggestions from one particular source. The provided
+// suggestions can belong to different ContentSuggestionCategories. A provider
+// can be a keyed service, in which case it should notify the
+// ContentSuggestionsService through the delegate before it shuts down.
+class ContentSuggestionsProvider {
+ public:
+  using ImageFetchedCallback =
+      base::Callback<void(const std::string& suggestion_id, const gfx::Image&)>;
+
+  // The delegate of a provider is notified when new data is available.
+  class Delegate {
+   public:
+    // Called when the available content changed.
+    // If a provider provides suggestions of multiple categories, it must call
+    // this callback for every category individually. The |suggestions|
+    // parameter should always contain the full list of currently available
+    // suggestions of that category, i.e., passing an empty list will remove
+    // all suggestions of the given category for the provider. Note that to
+    // clear them from the UI immediately, the provider needs to shut down. The
+    // list must not contain ContentSuggestions assigned to a category other
+    // than the passed |changed_category|.
+    virtual void OnSuggestionsChanged(
+        const ContentSuggestionsProvider& source,
+        ContentSuggestionCategory changed_category,
+        std::vector<ContentSuggestion> suggestions) = 0;
+    virtual void OnProviderShutdown(
+        const ContentSuggestionsProvider& source) = 0;
+  };
+
+  // Returns the type of the provider.
+  virtual ContentSuggestionsProviderType GetProviderType() const = 0;
+
+  // Accessor for delegate, which is notified about new available suggestions.
+  virtual void SetDelegate(Delegate* delegate) = 0;
+
+  // Used only for debugging purposes. Clears all caches so that the next
+  // fetch starts from scratch.
+  virtual void ClearCachedSuggestions() {}
+
+  // Used only for debugging purposes. Clears the cache of discarded
+  // suggestions, if present, so that no suggestions are suppressed. This does
+  // not necessarily make previously discarded suggestions reappear, as they may
+  // have been permanently deleted, depending on the provider implementation.
+  virtual void ClearDiscardedSuggestions() {}
+
+  // Discards the suggestion with the given ID. A provider needs to ensure that
+  // a once-discarded suggestion is never delivered again (through the
+  // Delegate).
+  virtual void Discard(const std::string& suggestion_id) = 0;
+
+  // Fetches the image for the suggestion with the given ID and returns it
+  // through the callback. This fetch may occur locally or from the internet.
+  virtual void FetchImage(const std::string& suggestion_id,
+                          const ImageFetchedCallback& callback) = 0;
+
+ protected:
+  virtual ~ContentSuggestionsProvider() {}
+};
+
+}  // namespace ntp_snippets
+
+#endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTIONS_PROVIDER_H_