// Copyright 2014 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 EXTENSIONS_BROWSER_USER_SCRIPT_LOADER_H_
#define EXTENSIONS_BROWSER_USER_SCRIPT_LOADER_H_

#include <map>
#include <memory>
#include <set>

#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/memory/shared_memory.h"
#include "base/memory/weak_ptr.h"
#include "base/observer_list.h"
#include "base/scoped_observer.h"
#include "content/public/browser/notification_observer.h"
#include "content/public/browser/notification_registrar.h"
#include "extensions/common/host_id.h"
#include "extensions/common/user_script.h"

namespace base {
class SharedMemory;
}

namespace content {
class BrowserContext;
class RenderProcessHost;
}

namespace extensions {

// Manages one "logical unit" of user scripts in shared memory by constructing a
// new shared memory region when the set of scripts changes. Also notifies
// renderers of new shared memory region when new renderers appear, or when
// script reloading completes. Script loading lives on the UI thread. Instances
// of this class are embedded within classes with names ending in
// UserScriptMaster. These "master" classes implement the strategy for which
// scripts to load/unload on this logical unit of scripts.
class UserScriptLoader : public content::NotificationObserver {
 public:
  using LoadScriptsCallback =
      base::Callback<void(std::unique_ptr<UserScriptList>,
                          std::unique_ptr<base::SharedMemory>)>;
  class Observer {
   public:
    virtual void OnScriptsLoaded(UserScriptLoader* loader) = 0;
    virtual void OnUserScriptLoaderDestroyed(UserScriptLoader* loader) = 0;
  };

  // Parses the includes out of |script| and returns them in |includes|.
  static bool ParseMetadataHeader(const base::StringPiece& script_text,
                                  UserScript* script);

  UserScriptLoader(content::BrowserContext* browser_context,
                   const HostID& host_id);
  ~UserScriptLoader() override;

  // Add |scripts| to the set of scripts managed by this loader.
  void AddScripts(const std::set<UserScript>& scripts);

  // Add |scripts| to the set of scripts managed by this loader.
  // The fetch of the content of the script starts URL request
  // to the associated render specified by
  // |render_process_id, render_view_id|.
  // TODO(hanxi): The renderer information doesn't really belong in this base
  // class, but it's not an easy fix.
  virtual void AddScripts(const std::set<UserScript>& scripts,
                          int render_process_id,
                          int render_view_id);

  // Remove |scripts| from the set of scripts managed by this loader.
  void RemoveScripts(const std::set<UserScript>& scripts);

  // Clears the set of scripts managed by this loader.
  void ClearScripts();

  // Initiates procedure to start loading scripts on the file thread.
  void StartLoad();

  // Returns true if we have any scripts ready.
  bool scripts_ready() const { return shared_memory_.get() != NULL; }

  // Pickle user scripts and return pointer to the shared memory.
  static std::unique_ptr<base::SharedMemory> Serialize(
      const extensions::UserScriptList& scripts);

  // Adds or removes observers.
  void AddObserver(Observer* observer);
  void RemoveObserver(Observer* observer);

 protected:
  // Allows the derived classes have different ways to load user scripts.
  virtual void LoadScripts(std::unique_ptr<UserScriptList> user_scripts,
                           const std::set<HostID>& changed_hosts,
                           const std::set<int>& added_script_ids,
                           LoadScriptsCallback callback) = 0;

  // Sets the flag if the initial set of hosts has finished loading; if it's
  // set to be true, calls AttempLoad() to bootstrap.
  void SetReady(bool ready);

  content::BrowserContext* browser_context() const { return browser_context_; }
  const HostID& host_id() const { return host_id_; }

 private:
  // content::NotificationObserver implementation.
  void Observe(int type,
               const content::NotificationSource& source,
               const content::NotificationDetails& details) override;

  // Returns whether or not it is possible that calls to AddScripts(),
  // RemoveScripts(), and/or ClearScripts() have caused any real change in the
  // set of scripts to be loaded.
  bool ScriptsMayHaveChanged() const;

  // Attempts to initiate a load.
  void AttemptLoad();

  // Called once we have finished loading the scripts on the file thread.
  void OnScriptsLoaded(std::unique_ptr<UserScriptList> user_scripts,
                       std::unique_ptr<base::SharedMemory> shared_memory);

  // Sends the renderer process a new set of user scripts. If
  // |changed_hosts| is not empty, this signals that only the scripts from
  // those hosts should be updated. Otherwise, all hosts will be
  // updated.
  void SendUpdate(content::RenderProcessHost* process,
                  base::SharedMemory* shared_memory,
                  const std::set<HostID>& changed_hosts);

  bool is_loading() const {
    // Ownership of |user_scripts_| is passed to the file thread when loading.
    return user_scripts_.get() == NULL;
  }

  // Manages our notification registrations.
  content::NotificationRegistrar registrar_;

  // Contains the scripts that were found the last time scripts were updated.
  std::unique_ptr<base::SharedMemory> shared_memory_;

  // List of scripts from currently-installed extensions we should load.
  std::unique_ptr<UserScriptList> user_scripts_;

  // The mutually-exclusive sets of scripts that were added or removed since the
  // last script load.
  std::set<UserScript> added_scripts_;
  std::set<UserScript> removed_scripts_;

  // Indicates whether the the collection of scripts should be cleared before
  // additions and removals on the next script load.
  bool clear_scripts_;

  // The IDs of the extensions which changed in the last update sent to the
  // renderer.
  std::set<HostID> changed_hosts_;

  // If the initial set of hosts has finished loading.
  bool ready_;

  // If list of user scripts is modified while we're loading it, we note
  // that we're currently mid-load and then start over again once the load
  // finishes.  This boolean tracks whether another load is pending.
  bool pending_load_;

  // The browser_context for which the scripts managed here are installed.
  content::BrowserContext* browser_context_;

  // ID of the host that owns these scripts, if any. This is only set to a
  // non-empty value for declarative user script shared memory regions.
  HostID host_id_;

  // The associated observers.
  base::ObserverList<Observer> observers_;

  base::WeakPtrFactory<UserScriptLoader> weak_factory_;

  DISALLOW_COPY_AND_ASSIGN(UserScriptLoader);
};

}  // namespace extensions

#endif  // EXTENSIONS_BROWSER_USER_SCRIPT_LOADER_H_