/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <memory>
#include <string>
#include <unordered_map>
#include <vector>

#include <folly/Conv.h>
#include <folly/CppAttributes.h>
#include <folly/Range.h>
#include <folly/ScopeGuard.h>
#include <folly/Synchronized.h>
#include <folly/detail/StaticSingletonManager.h>
#include <folly/logging/LogName.h>

namespace folly {

class LogCategory;
class LogConfig;
class LogHandler;
class LogHandlerFactory;
enum class LogLevel : uint32_t;

/**
 * LoggerDB stores the set of LogCategory objects.
 */
class LoggerDB {
  using ContextCallback = folly::Function<std::string() const>;

 public:
  /**
   * Get the main LoggerDB singleton.
   */
  static LoggerDB& get();

  ~LoggerDB();

  /**
   * Get the LogCategory for the specified name.
   *
   * This creates the LogCategory for the specified name if it does not exist
   * already.
   */
  LogCategory* getCategory(folly::StringPiece name);

  /**
   * Get the LogCategory for the specified name, if it already exists.
   *
   * This returns nullptr if no LogCategory has been created yet for the
   * specified name.
   */
  LogCategory* FOLLY_NULLABLE getCategoryOrNull(folly::StringPiece name);

  /**
   * Set the log level for the specified category.
   *
   * Messages logged to a specific log category will be ignored unless the
   * message log level is greater than the LogCategory's effective log level.
   *
   * If inherit is true, LogCategory's effective log level is the minimum of
   * its level and it's parent category's effective log level.  If inherit is
   * false, the LogCategory's effective log level is simply its log level.
   * (Setting inherit to false is necessary if you want a child LogCategory to
   * use a less verbose level than its parent categories.)
   */
  void setLevel(folly::StringPiece name, LogLevel level, bool inherit = true);
  void setLevel(LogCategory* category, LogLevel level, bool inherit = true);

  /**
   * Get a LogConfig object describing the current state of the LoggerDB.
   */
  LogConfig getConfig() const;

  /**
   * Get a LogConfig object fully describing the state of the LoggerDB.
   *
   * This is similar to getConfig(), but it returns LogCategoryConfig objects
   * for all defined log categories, including ones that are using the default
   * configuration settings.
   */
  LogConfig getFullConfig() const;

  /**
   * Update the current LoggerDB state with the specified LogConfig settings.
   *
   * Log categories and handlers listed in the LogConfig object will be updated
   * to the new state listed in the LogConfig.  Settings on categories and
   * handlers not listed in the config will be left as-is.
   */
  void updateConfig(const LogConfig& config);

  /**
   * Reset the current LoggerDB state to the specified LogConfig settings.
   *
   * All LogCategories not mentioned in the new LogConfig will have all
   * currently configured log handlers removed and their log level set to its
   * default state.  For the root category the default log level is
   * kDefaultLogLevel (see LogLevel.h); for all other categories the default
   * level is MAX_LEVEL with log level inheritance enabled.
   *
   * LogCategories listed in the new config but without LogHandler information
   * defined will have all existing handlers removed.
   */
  void resetConfig(const LogConfig& config);

  /**
   * Remove all registered LogHandlers on all LogCategory objects.
   *
   * This is called on the main LoggerDB object during shutdown.
   */
  void cleanupHandlers();

  /**
   * Call flush() on all LogHandler objects registered on any LogCategory in
   * this LoggerDB.
   *
   * Returns the number of registered LogHandlers.
   */
  size_t flushAllHandlers();

  /**
   * Register a LogHandlerFactory.
   *
   * The LogHandlerFactory will be used to create LogHandler objects from a
   * LogConfig object during updateConfig() and resetConfig() calls.
   *
   * Only one factory can be registered for a given handler type name.
   * LogHandlerFactory::getType() returns the handler type supported by this
   * LogHandlerFactory.
   *
   * If an existing LogHandlerFactory is already registered with this type name
   * and replaceExisting is false a std::range_error will be thrown.
   * Otherwise, if replaceExisting is true, the new factory will replace the
   * existing factory.
   */
  void registerHandlerFactory(
      std::unique_ptr<LogHandlerFactory> factory, bool replaceExisting = false);

  /**
   * Remove a registered LogHandlerFactory.
   *
   * The type parameter should be the name of the handler type, as returned by
   * LogHandlerFactory::getType().
   *
   * Throws std::range_error if no handler factory with this type name exists.
   */
  void unregisterHandlerFactory(folly::StringPiece type);

  /**
   * Initialize the LogCategory* and std::atomic<LogLevel> used by an XLOG()
   * statement.
   *
   * Returns the current effective LogLevel of the category.
   */
  LogLevel xlogInit(
      folly::StringPiece categoryName,
      std::atomic<LogLevel>* xlogCategoryLevel,
      LogCategory** xlogCategory);
  LogCategory* xlogInitCategory(
      folly::StringPiece categoryName,
      LogCategory** xlogCategory,
      std::atomic<bool>* isInitialized);

  enum TestConstructorArg { TESTING };

  /**
   * Construct a LoggerDB for testing purposes.
   *
   * Most callers should not need this function, and should use
   * LoggerDB::get() to obtain the main LoggerDB singleton.  This function
   * exists mainly to allow testing LoggerDB objects in unit tests.
   * It requires an explicit argument just to prevent callers from calling it
   * unintentionally.
   */
  explicit LoggerDB(TestConstructorArg);

  /**
   * Add a new context string callback to the list.
   *
   * The callbacks will be invoked during the construction of log messages,
   * and returned strings will be appended in order to the tail of log
   * log entry prefixes with space prepended to each item.
   */
  void addContextCallback(ContextCallback);

  /**
   * Return a context string to be appended after default log prefixes.
   *
   * The context string is cutomized through adding context callbacks to
   * LoggerDB objects.
   */
  std::string getContextString() const;

  /**
   * internalWarning() is used to report a problem when something goes wrong
   * internally in the logging library.
   *
   * We can't log these messages through the normal logging flow since logging
   * itself has failed.
   *
   * Example scenarios where this is used:
   * - We fail to write to a log file (for instance, when the disk is full)
   * - A LogHandler throws an unexpected exception
   */
  template <typename... Args>
  static void internalWarning(
      folly::StringPiece file, int lineNumber, Args&&... args) noexcept {
    internalWarningImpl(
        file, lineNumber, folly::to<std::string>(std::forward<Args>(args)...));
  }

  using InternalWarningHandler =
      void (*)(folly::StringPiece file, int lineNumber, std::string&&);

  /**
   * Set a function to be called when the logging library generates an internal
   * warning.
   *
   * The supplied handler should never throw exceptions.
   *
   * If a null handler is supplied, the default built-in handler will be used.
   *
   * The default handler reports the message with _CrtDbgReport(_CRT_WARN) on
   * Windows, and prints the message to stderr on other platforms.  It also
   * rate limits messages if they are arriving too quickly.
   */
  static void setInternalWarningHandler(InternalWarningHandler handler);

 private:
  using LoggerNameMap = std::unordered_map<
      folly::StringPiece,
      std::unique_ptr<LogCategory>,
      LogName::Hash,
      LogName::Equals>;

  using HandlerFactoryMap =
      std::unordered_map<std::string, std::unique_ptr<LogHandlerFactory>>;
  using HandlerMap = std::unordered_map<std::string, std::weak_ptr<LogHandler>>;
  struct HandlerInfo {
    HandlerFactoryMap factories;
    HandlerMap handlers;
  };

  class ContextCallbackList {
   public:
    void addCallback(ContextCallback);
    std::string getContextString() const;
    ~ContextCallbackList();

   private:
    class CallbacksObj;
    std::atomic<CallbacksObj*> callbacks_{nullptr};
    std::mutex writeMutex_;
  };

  // Forbidden copy constructor and assignment operator
  LoggerDB(LoggerDB const&) = delete;
  LoggerDB& operator=(LoggerDB const&) = delete;

  LoggerDB();
  LogCategory* getOrCreateCategoryLocked(
      LoggerNameMap& loggersByName, folly::StringPiece name);
  LogCategory* createCategoryLocked(
      LoggerNameMap& loggersByName,
      folly::StringPiece name,
      LogCategory* parent);

  using NewHandlerMap =
      std::unordered_map<std::string, std::shared_ptr<LogHandler>>;
  using OldToNewHandlerMap = std::
      unordered_map<std::shared_ptr<LogHandler>, std::shared_ptr<LogHandler>>;
  LogConfig getConfigImpl(bool includeAllCategories) const;
  void startConfigUpdate(
      const Synchronized<HandlerInfo>::LockedPtr& handlerInfo,
      const LogConfig& config,
      NewHandlerMap* handlers,
      OldToNewHandlerMap* oldToNewHandlerMap);
  void finishConfigUpdate(
      const Synchronized<HandlerInfo>::LockedPtr& handlerInfo,
      NewHandlerMap* handlers,
      OldToNewHandlerMap* oldToNewHandlerMap);
  std::vector<std::shared_ptr<LogHandler>> buildCategoryHandlerList(
      const NewHandlerMap& handlerMap,
      StringPiece categoryName,
      const std::vector<std::string>& categoryHandlerNames);

  static void internalWarningImpl(
      folly::StringPiece filename, int lineNumber, std::string&& msg) noexcept;
  static void defaultInternalWarningImpl(
      folly::StringPiece filename, int lineNumber, std::string&& msg) noexcept;

  /**
   * A map of LogCategory objects by name.
   *
   * Lookups can be performed using arbitrary StringPiece values that do not
   * have to be in canonical form.
   */
  folly::Synchronized<LoggerNameMap> loggersByName_;

  /**
   * The LogHandlers and LogHandlerFactories.
   *
   * For lock ordering purposes, if you need to acquire both the loggersByName_
   * and handlerInfo_ locks, the handlerInfo_ lock must be acquired first.
   */
  folly::Synchronized<HandlerInfo> handlerInfo_;

  /**
   * Callbacks returning context strings.
   *
   * Exceptions from the callbacks are catched and reflected in corresponding
   * position in log entries.
   */
  ContextCallbackList contextCallbacks_;
  static std::atomic<InternalWarningHandler> warningHandler_;
};

/**
 * initializeLoggerDB() will be called to configure the main LoggerDB singleton
 * the first time that LoggerDB::get() is called.
 *
 * This function can be used apply basic default settings to the LoggerDB,
 * including default log level and log handler settings.
 *
 * A default implementation is provided as a weak symbol, so it can be
 * overridden on a per-program basis if you want to customize the initial
 * LoggerDB settings for your program.
 *
 * However, note that this function may be invoked before main() starts (if
 * other code that runs before main uses the logging library).  Therefore you
 * should be careful about what code runs here.  For instance, you probably
 * should not create LogHandler objects that spawn new threads.  It is
 * generally a good idea to defer more complicated setup until after main()
 * starts.
 *
 * In most situations it is normally better to override getBaseLoggingConfig()
 * from logging/Init.h rather than overriding initializeLoggerDB().  You only
 * need to override initializeLoggerDB() if you want to change the settings
 * that are used for messages that get logged before initLogging() is called.
 *
 * The default implementation configures the root log category to write all
 * warning and higher-level log messages to stderr, using a format similar to
 * that used by GLOG.
 */
void initializeLoggerDB(LoggerDB& db);

FOLLY_ALWAYS_INLINE LoggerDB& LoggerDB::get() {
  struct Singleton : LoggerDB {
    Singleton() {
      initializeLoggerDB(*this);
      // This allows log handlers to flush any buffered messages before
      // the program exits.
      /* library-local */ static auto guard =
          makeGuard([this] { cleanupHandlers(); });
    }
  };

  // We intentionally leak the LoggerDB singleton and all of the LogCategory
  // objects it contains.
  //
  // We want Logger objects to remain valid for the entire lifetime of the
  // program, without having to worry about destruction ordering issues, or
  // making the Logger perform reference counting on the LoggerDB.
  return detail::createGlobal<Singleton, void>();
}

} // namespace folly
