// Copyright 2018 The Fuchsia 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 GARNET_LIB_UI_GFX_ENGINE_SESSION_MANAGER_H_
#define GARNET_LIB_UI_GFX_ENGINE_SESSION_MANAGER_H_

#include <set>
#include <unordered_map>

#include "garnet/lib/ui/scenic/command_dispatcher.h"

namespace scenic_impl {
class EventReporter;
class ErrorReporter;
}  // namespace scenic_impl

namespace scenic_impl {
namespace gfx {

using SessionId = ::scenic_impl::SessionId;

class SessionHandler;
class Session;
class Engine;
class UpdateScheduler;

// Manages a collection of SessionHandlers.
// Tracks future updates requested by Sessions, and executes updates for a
// particular presentation time.
class SessionManager {
 public:
  SessionManager() = default;

  virtual ~SessionManager() = default;

  // Finds the session handler corresponding to the given id.
  SessionHandler* FindSession(SessionId id);

  size_t GetSessionCount() { return session_count_; }

  // Returns a SessionHandler, which is casted as a CommandDispatcher. Used by
  // ScenicSystem.
  std::unique_ptr<CommandDispatcher> CreateCommandDispatcher(
      CommandDispatcherContext context, Engine* engine);

  // Tell the UpdateScheduler to schedule a frame, and remember the Session so
  // that we can tell it to apply updates in ApplyScheduledSessionUpdates().
  void ScheduleUpdateForSession(UpdateScheduler* update_scheduler,
                                uint64_t presentation_time,
                                fxl::RefPtr<Session> session);

  // Executes updates that are schedule up to and including a given presentation
  // time. Returns true if rendering is needed.
  bool ApplyScheduledSessionUpdates(uint64_t presentation_time,
                                    uint64_t presentation_interval);

 private:
  friend class Session;
  friend class SessionHandler;

  // Destroys the session with the given id.
  void TearDownSession(SessionId id);

  // Removes the session from the session_manager_ map.  We assume that the
  // SessionHandler has already taken care of itself and its Session.
  void RemoveSession(SessionId id);

  virtual std::unique_ptr<SessionHandler> CreateSessionHandler(
      CommandDispatcherContext context, Engine* engine, SessionId session_id,
      EventReporter* event_reporter, ErrorReporter* error_reporter) const;

  // Map of all the sessions.
  std::unordered_map<SessionId, SessionHandler*> session_manager_;
  size_t session_count_ = 0;
  SessionId next_session_id_ = 1;

  // Lists all Session that have updates to apply, sorted by the earliest
  // requested presentation time of each update.
  std::set<std::pair<uint64_t, fxl::RefPtr<Session>>> updatable_sessions_;
};

}  // namespace gfx
}  // namespace scenic_impl

#endif  // GARNET_LIB_UI_GFX_ENGINE_SESSION_MANAGER_H_