// Copyright 2018 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_OPTIMIZATION_GUIDE_HINT_CACHE_H_
#define COMPONENTS_OPTIMIZATION_GUIDE_HINT_CACHE_H_

#include <string>

#include "base/callback.h"
#include "base/containers/mru_cache.h"
#include "base/macros.h"
#include "base/optional.h"
#include "base/sequence_checker.h"
#include "base/time/clock.h"
#include "components/optimization_guide/memory_hint.h"
#include "components/optimization_guide/optimization_guide_store.h"
#include "components/optimization_guide/proto/hints.pb.h"

class GURL;

namespace optimization_guide {
class StoreUpdateData;

using HintLoadedCallback = base::OnceCallback<void(const proto::Hint*)>;

// Contains a set of optimization hints received from the Cacao service. This
// may include hints received from the ComponentUpdater and hints fetched from a
// Cacao Optimization Guide Service API. The availability of hints is queryable
// via host name and full URL. The cache itself consists of a backing store,
// which allows for asynchronous loading of any available host-keyed hint, and
// an MRU host-keyed cache and a url-keyed cache, which can be used to
// synchronously retrieve recently loaded hints keyed by URL or host.
class HintCache {
 public:
  // Construct the HintCache with a backing store and an optional max host-keyed
  // cache size. While |optimization_guide_store| is required,
  // |max_memory_cache_hints| is optional and the default max size will be used
  // if it is not provided.
  explicit HintCache(
      std::unique_ptr<OptimizationGuideStore> optimization_guide_store,
      base::Optional<int> max_memory_cache_hints = base::Optional<int>());
  ~HintCache();

  // Initializes the backing store contained within the hint cache and
  // asynchronously runs the callback after initialization is complete.
  // If |purge_existing_data| is set to true, then the cache will purge any
  // pre-existing data and begin in a clean state.
  void Initialize(bool purge_existing_data, base::OnceClosure callback);

  // Returns a StoreUpdateData. During component processing, hints from the
  // component are moved into the StoreUpdateData. After component
  // processing completes, the component update data is provided to the backing
  // store in UpdateComponentHints() and used to update its component hints. In
  // the case the provided component version is not newer than the store's
  // version, nullptr will be returned by the call.
  std::unique_ptr<StoreUpdateData> MaybeCreateUpdateDataForComponentHints(
      const base::Version& version) const;

  // Returns an UpdateData created by the store to hold updates for fetched
  // hints. No version is needed nor applicable for fetched hints. During
  // processing of the GetHintsResponse, hints are moved into the update data.
  // After processing is complete, the update data is provided to the backing
  // store to update hints. |update_time| specifies when the hints within the
  // created update data will be scheduled to be updated.
  std::unique_ptr<StoreUpdateData> CreateUpdateDataForFetchedHints(
      base::Time update_time) const;

  // Updates the store's component data using the provided StoreUpdateData
  // and asynchronously runs the provided callback after the update finishes.
  void UpdateComponentHints(std::unique_ptr<StoreUpdateData> component_data,
                            base::OnceClosure callback);

  // Process |get_hints_response| to be stored in the hint cache store.
  // |callback| is asynchronously run when the hints are successfully stored or
  // if the store is not available. |update_time| specifies when the hints
  // within |get_hints_response| will need to be updated next. |urls_fetched|
  // specifies the URLs for which specific hints were requested to be fetched.
  // It is expected for |this| to keep track of the result, even if a hint was
  // not returned for the URL.
  void UpdateFetchedHints(
      std::unique_ptr<proto::GetHintsResponse> get_hints_response,
      base::Time update_time,
      const base::flat_set<GURL>& urls_fetched,
      base::OnceClosure callback);

  // Purges fetched hints from the owned |optimization_guide_store| that have
  // expired.
  void PurgeExpiredFetchedHints();

  // Purges fetched hints from the owned |optimization_guide_store_| and resets
  // both in-memory hint caches.
  void ClearFetchedHints();

  // Purges fetched hints from the owned |optimization_guide_store_| and resets
  // the host-keyed cache.
  void ClearHostKeyedHints();

  // Returns whether the cache has a hint data for |host| locally (whether
  // in the host-keyed cache or persisted on disk).
  bool HasHint(const std::string& host) const;

  // Requests that hint data for |host| be loaded asynchronously and passed to
  // |callback| if/when loaded.
  void LoadHint(const std::string& host, HintLoadedCallback callback);

  // Returns the update time provided by |hint_store_|, which specifies when the
  // fetched hints within the store are ready to be updated. If |hint_store_| is
  // not initialized, base::Time() is returned.
  base::Time GetFetchedHintsUpdateTime() const;

  // Returns the hint data for |host| if found in the host-keyed cache,
  // otherwise nullptr.
  const proto::Hint* GetHostKeyedHintIfLoaded(const std::string& host);

  // Returns an unepxired hint data for |url| if found in the url-keyed cache,
  // otherwise nullptr. If the hint is expired, it is removed from the URL-keyed
  // cache. Only HTTP/HTTPS URLs without username and password are supported by
  // the URL-keyed cache, if |url| does not meet this criteria, nullptr is
  // returned. The returned hint is not guaranteed to remain valid and will
  // become invalid if any additional URL-keyed hints are added to the cache
  // that evicts the returned hint.
  proto::Hint* GetURLKeyedHint(const GURL& url);

  // Returns true if the url-keyed cache contains an entry for |url|, even if
  // the entry is empty. If a hint exists but is expired, it returns false.
  bool HasURLKeyedEntryForURL(const GURL& url);

  // Verifies and processes |hints| and moves the ones it supports into
  // |update_data| and caches any valid URL keyed hints.
  //
  // Returns true if there was at least one hint is moved into |update_data|.
  bool ProcessAndCacheHints(
      google::protobuf::RepeatedPtrField<proto::Hint>* hints,
      StoreUpdateData* update_data);

  // Returns whether the persistent hint store owned by this is available.
  bool IsHintStoreAvailable() const;

  // Override |clock_| for testing.
  void SetClockForTesting(const base::Clock* clock);

  // Add hint to the URL-keyed cache. For testing only.
  void AddHintForTesting(const GURL& gurl, std::unique_ptr<proto::Hint> hint);

 private:
  using HostKeyedHintCache =
      base::HashingMRUCache<OptimizationGuideStore::EntryKey,
                            std::unique_ptr<MemoryHint>>;

  using URLKeyedHintCache =
      base::HashingMRUCache<std::string, std::unique_ptr<MemoryHint>>;

  // The callback run after the store finishes initialization. This then runs
  // the callback initially provided by the Initialize() call.
  void OnStoreInitialized(base::OnceClosure callback);

  // The callback run after the store finishes loading a hint. This adds the
  // loaded hint to |host_keyed_cache_|, potentially purging the least recently
  // used element, and then runs the callback initially provided by the
  // LoadHint() call.
  void OnLoadStoreHint(
      HintLoadedCallback callback,
      const OptimizationGuideStore::EntryKey& store_hint_entry_key,
      std::unique_ptr<MemoryHint> hint);

  // The backing store used with this hint cache. Set during construction.
  const std::unique_ptr<OptimizationGuideStore> optimization_guide_store_;

  // The cache of host-keyed hints loaded from the store. Maps store
  // EntryKey to Hint proto. This serves two purposes:
  //  1. Allows hints to be requested on navigation and retained in memory until
  //     commit, when they can be synchronously retrieved from the cache.
  //  2. Reduces churn of needing to reload hints from frequently visited sites
  //     multiple times during a session.
  HostKeyedHintCache host_keyed_cache_;

  // The in-memory cache of URL-keyed hints fetched from the remote optimization
  // guide. Maps a full URL to Hint proto. All available URL-keyed hints are
  // maintained within the cache and are not persisted to disk.
  URLKeyedHintCache url_keyed_hint_cache_;

  // The clock used to determine if hints have expired.
  const base::Clock* clock_;

  SEQUENCE_CHECKER(sequence_checker_);

  DISALLOW_COPY_AND_ASSIGN(HintCache);
};

}  // namespace optimization_guide

#endif  // COMPONENTS_OPTIMIZATION_GUIDE_HINT_CACHE_H_