// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CHROME_BROWSER_PERFORMANCE_MANAGER_POLICIES_BACKGROUND_TAB_LOADING_POLICY_H_
#define CHROME_BROWSER_PERFORMANCE_MANAGER_POLICIES_BACKGROUND_TAB_LOADING_POLICY_H_

#include <map>
#include <optional>
#include <vector>

#include "base/gtest_prod_util.h"
#include "base/memory/memory_pressure_listener.h"
#include "base/memory/raw_ptr.h"
#include "components/performance_manager/public/graph/graph.h"
#include "components/performance_manager/public/graph/node_data_describer.h"
#include "components/performance_manager/public/graph/page_node.h"
#include "components/performance_manager/public/graph/system_node.h"
#include "url/gurl.h"

namespace performance_manager {

namespace mechanism {
class PageLoader;
}  // namespace mechanism

FORWARD_DECLARE_TEST(BackgroundTabLoadingBrowserTest,
                     RestoredTabsAreLoadedGradually);
class BackgroundTabLoadingBrowserTest;
class SiteDataReader;

namespace policies {

// This policy manages loading of background tabs created by session restore. It
// is responsible for assigning priorities and controlling the load of
// background tab loading at all times.
class BackgroundTabLoadingPolicy : public GraphOwned,
                                   public NodeDataDescriberDefaultImpl,
                                   public PageNodeObserver,
                                   public SystemNodeObserver {
 public:
  // `all_restored_tabs_loaded_callback` is invoked when all tabs passed to
  // ScheduleLoadForRestoredTabs() are loaded.
  explicit BackgroundTabLoadingPolicy(
      base::RepeatingClosure all_restored_tabs_loaded_callback);
  ~BackgroundTabLoadingPolicy() override;
  BackgroundTabLoadingPolicy(const BackgroundTabLoadingPolicy& other) = delete;
  BackgroundTabLoadingPolicy& operator=(const BackgroundTabLoadingPolicy&) =
      delete;

  // GraphOwned implementation:
  void OnPassedToGraph(Graph* graph) override;
  void OnTakenFromGraph(Graph* graph) override;

  // PageNodeObserver implementation:
  void OnLoadingStateChanged(const PageNode* page_node,
                             PageNode::LoadingState previous_state) override;
  void OnBeforePageNodeRemoved(const PageNode* page_node) override;

  // Holds data about a PageNode being added to this policy.
  struct PageNodeData {
    explicit PageNodeData(
        base::WeakPtr<PageNode> page_node,
        GURL main_frame_url = GURL(),
        blink::mojom::PermissionStatus notification_permission_status =
            blink::mojom::PermissionStatus::ASK);
    PageNodeData(PageNodeData&& other);
    PageNodeData& operator=(PageNodeData&& other);
    PageNodeData(const PageNodeData& other);
    PageNodeData& operator=(const PageNodeData& other);
    ~PageNodeData();

    base::WeakPtr<PageNode> page_node;
    GURL main_frame_url;
    blink::mojom::PermissionStatus notification_permission_status;
    std::optional<size_t> site_engagement;
  };

  // Schedules the PageNodes in |page_node_and_permission_vector| to be loaded
  // when appropriate.
  void ScheduleLoadForRestoredTabs(
      std::vector<PageNodeData> page_node_and_permission_vector);

  void SetMockLoaderForTesting(std::unique_ptr<mechanism::PageLoader> loader);
  void SetMaxSimultaneousLoadsForTesting(size_t loading_slots);
  void SetFreeMemoryForTesting(size_t free_memory_mb);
  void ResetPolicyForTesting();

  // Returns the instance of BackgroundTabLoadingPolicy within the graph.
  static BackgroundTabLoadingPolicy* GetInstance();

 private:
  friend class ::performance_manager::BackgroundTabLoadingBrowserTest;
  friend class BackgroundTabLoadingPolicyTest;

  // Holds data about a PageNode waiting to be loaded by this policy.
  struct PageNodeToLoadData {
    PageNodeToLoadData(const PageNode* page_node,
                       std::optional<size_t> site_engagement);
    ~PageNodeToLoadData();

    // Move-only.
    PageNodeToLoadData(const PageNodeToLoadData&) = delete;
    PageNodeToLoadData& operator=(const PageNodeToLoadData&) = delete;
    PageNodeToLoadData(PageNodeToLoadData&&) = default;
    PageNodeToLoadData& operator=(PageNodeToLoadData&&) = default;

    // Returns true if the data about this PageNode indicates it uses background
    // communication.
    bool UsesBackgroundCommunication() const;

    // Keeps a pointer to the corresponding PageNode.
    raw_ptr<const PageNode> page_node;

    // A higher value here means the tab has higher priority for restoring.
    std::optional<float> score;

    // Whether the tab updates its title or favicon when backgrounded.
    // Initialized to nullopt and set asynchronously with the proper value from
    // the sites database.
    std::optional<bool> updates_title_or_favicon_in_bg;

    std::optional<size_t> site_engagement;
  };

  // Comparator used to sort PageNodeToLoadData.
  struct ScoredTabComparator;

  // NodeDataDescriber implementation:
  base::Value::Dict DescribePageNodeData(const PageNode* node) const override;
  base::Value::Dict DescribeSystemNodeData(
      const SystemNode* node) const override;

  // SystemNodeObserver:
  void OnMemoryPressure(
      base::MemoryPressureListener::MemoryPressureLevel new_level) override;

  // Returns the SiteDataReader instance for |page_node|, if any. Virtual for
  // testing.
  virtual SiteDataReader* GetSiteDataReader(const PageNode* page_node) const;

  // Determines whether or not the given PageNode should be loaded. If this
  // returns false, then the policy no longer attempts to load |page_node| and
  // removes it from the policy's internal state. This is called immediately
  // prior to trying to load the PageNode.
  bool ShouldLoad(const PageNodeToLoadData& page_node_data);

  // This will initialize |page_node_to_load_data->used_in_bg| to the proper
  // value, score the tab and call DispatchNotifyAllTabsScoredIfNeeded().
  void OnUsedInBackgroundAvailable(base::WeakPtr<PageNode> page_node);

  // Stops loading tabs by clearing |page_nodes_to_load_|.
  void StopLoadingTabs();

  // Calculates a |score| for the given tab.
  void ScoreTab(PageNodeToLoadData* page_node_to_load_data);

  // Schedule the task that will initialize |PageNodeToLoadData::used_in_bg|
  // from the local site characteristics database.
  void SetUsedInBackgroundAsync(PageNodeToLoadData* page_node_to_load_data);

  // Invoke "NotifyAllTabsScored" if all tabs are scored.
  void DispatchNotifyAllTabsScoredIfNeeded();

  // Notifying that all tabs have final scores and starts loading.
  void NotifyAllTabsScored();

  // Move the PageNode from |page_nodes_to_load_| to
  // |page_nodes_load_initiated_| and make the call to load the PageNode.
  void InitiateLoad(const PageNode* page_node);

  // Removes the PageNode from all the sets of PageNodes that the policy is
  // tracking.
  void RemovePageNode(const PageNode* page_node);

  // Initiates the load of enough tabs to fill all loading slots. No-ops if all
  // loading slots are occupied.
  void MaybeLoadSomeTabs();

  // Determines the number of tab loads that can be started at the moment to
  // avoid exceeding the number of loading slots.
  size_t GetMaxNewTabLoads() const;

  // Loads the next tab. This should only be called if there is a next tab to
  // load. This will always start loading a next tab even if the number of
  // simultaneously loading tabs is exceeded.
  void LoadNextTab();

  // Compute the amount of free memory on the system.
  size_t GetFreePhysicalMemoryMib() const;

  // If `page_node` is in the set of page nodes to load, removes it and returns
  // true.
  bool ErasePageNodeToLoadData(const PageNode* page_node);

  // Returns the `PageNodeToLoadData` for `page_node` if it exists, nullptr
  // otherwise.
  PageNodeToLoadData* FindPageNodeToLoadData(const PageNode* page_node);

  // Returns true if there are restored tabs that must be loaded by this policy
  // and aren't fully loaded yet.
  bool HasRestoredTabsToLoad() const;

  // Updates `has_restored_tabs_to_load_` to match `HasRestoredTabsToLoad()` and
  // invokes `all_restored_tabs_loaded_callback_` if needed.
  void UpdateHasRestoredTabsToLoad();

  // The callback to invoke when all restored tabs are loaded.
  const base::RepeatingClosure all_restored_tabs_loaded_callback_;

  // Whether there are restored tabs that that must be loaded by this policy and
  // aren't fully loaded yet.
  //
  // Set to true when ScheduleLoadForRestoredTabs() is invoked. Set to false
  // when HasRestoredTabsToLoad() becomes false.
  bool has_restored_tabs_to_load_ = false;

  // The mechanism used to load the pages.
  std::unique_ptr<performance_manager::mechanism::PageLoader> page_loader_;

  // The set of PageNodes that have been restored for which we need to schedule
  // loads.
  std::vector<std::unique_ptr<PageNodeToLoadData>> page_nodes_to_load_;

  // The set of PageNodes that BackgroundTabLoadingPolicy has initiated loading,
  // and for which we are waiting for the loading to actually start. This signal
  // will be received from |OnIsLoadingChanged|.
  std::vector<raw_ptr<const PageNode, VectorExperimental>>
      page_nodes_load_initiated_;

  // PageNodes that are currently loading, mapped to a boolean indicating
  // whether this policy was responsible for scheduling the load.
  std::map<const PageNode*, bool> page_nodes_loading_;

  // The number of simultaneous tab loads that are permitted by policy. This
  // is computed based on the number of cores on the machine.
  size_t max_simultaneous_tab_loads_;

  // The number of tab loads that have started. Every call to InitiateLoad
  // increments this value.
  size_t tab_loads_started_ = 0;

  // The number of tabs for which an accurate initial score has been assigned.
  // This is incremented only after all tab data is available, which
  // may happen asynchronously.
  size_t tabs_scored_ = 0;

  // Used to overwrite the amount of free memory available on the system.
  size_t free_memory_mb_for_testing_ = 0;

  // The minimum total number of restored tabs to load.
  static constexpr uint32_t kMinTabsToLoad = 4;

  // The maximum total number of restored tabs to load.
  static constexpr uint32_t kMaxTabsToLoad = 20;

  // The minimum amount of memory to keep free.
  static constexpr uint32_t kDesiredAmountOfFreeMemoryMb = 150;

  // The maximum time since last use of a tab in order for it to be loaded.
  static constexpr base::TimeDelta kMaxTimeSinceLastUseToLoad = base::Days(30);

  // Lower bound for the maximum number of tabs to load simultaneously.
  static constexpr uint32_t kMinSimultaneousTabLoads = 1;

  // Upper bound for the maximum number of tabs to load simultaneously.
  static constexpr uint32_t kMaxSimultaneousTabLoads = 4;

  // The number of CPU cores required per permitted simultaneous tab
  // load.
  static constexpr uint32_t kCoresPerSimultaneousTabLoad = 2;

  // It's possible for this policy object to be destroyed while it has posted
  // tasks. The tasks are bound to a weak pointer so that they are not executed
  // after the policy object is destroyed.
  base::WeakPtrFactory<BackgroundTabLoadingPolicy> weak_factory_{this};

  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicyTest,
                           ShouldLoad_MaxTabsToRestore);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicyTest,
                           ShouldLoad_MinTabsToRestore);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicyTest,
                           ShouldLoad_FreeMemory);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicyTest, ShouldLoad_OldTab);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicyTest,
                           ShouldLoad_SiteEngagement);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicySiteEngagementTest,
                           ShouldLoad_NoBackgroundCommunication);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicySiteEngagementTest,
                           ShouldLoad_NotificationPermission);
  FRIEND_TEST_ALL_PREFIXES(BackgroundTabLoadingPolicySiteEngagementTest,
                           ShouldLoad_UpdatesTitleOrFaviconInBackground);
  FRIEND_TEST_ALL_PREFIXES(
      BackgroundTabLoadingPolicyScheduleLoadTest,
      ScheduleLoadForRestoredTabs_WithoutNotificationPermission);
  FRIEND_TEST_ALL_PREFIXES(
      BackgroundTabLoadingPolicyScheduleLoadTest,
      ScheduleLoadForRestoredTabs_WithNotificationPermission);
  FRIEND_TEST_ALL_PREFIXES(
      ::performance_manager::BackgroundTabLoadingBrowserTest,
      RestoredTabsAreLoadedGradually);
};

}  // namespace policies

}  // namespace performance_manager

#endif  // CHROME_BROWSER_PERFORMANCE_MANAGER_POLICIES_BACKGROUND_TAB_LOADING_POLICY_H_