// Copyright 2019 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 LIB_SYS_CPP_OUTGOING_DIRECTORY_H_
#define LIB_SYS_CPP_OUTGOING_DIRECTORY_H_

#include <lib/async/dispatcher.h>
#include <lib/fit/function.h>
#include <lib/vfs/cpp/pseudo_dir.h>
#include <lib/vfs/cpp/service.h>

#include <memory>
#include <utility>

namespace sys {

// The directory provided by this component to the component manager.
//
// A component's outgoing directory contains services, data, and other objects
// that can be consumed by either the component manager itself or by other
// components in the system.
//
// The outgoing directory contains several subdirectories with well-known
// names:
//
//  * public. This directory contains the services offered by this component to
//    other components.
//  * debug. This directory contains arbitrary debugging output offered by this
//    component.
//
// The outgoing directory may optionally contain other directories constructed
// using |GetOrCreateDirectory|. Common optional directories include:
//
//  * objects. This directory contains Inspect API files and interfaces for use
//    in component inspection.
//
// This class is thread-hostile.
//
//  # Simple usage
//
// Instances of this class should be owned and managed on the same thread
// that services their connections.
//
// # Advanced usage
//
// You can use a background thread to service connections provided:
// async_dispatcher_t for the background thread is stopped or suspended
// prior to destroying the class object.
class OutgoingDirectory final {
 public:
  OutgoingDirectory();
  ~OutgoingDirectory();

  // Outgoing objects cannot be copied.
  OutgoingDirectory(const OutgoingDirectory&) = delete;
  OutgoingDirectory& operator=(const OutgoingDirectory&) = delete;

  // Starts serving the outgoing directory on the given channel.
  //
  // This object will implement the |fuchsia.io.Directory| interface using this
  // channel.
  //
  // If |dispatcher| is NULL, this object will serve the outgoing directory
  // using the |async_dispatcher_t| from |async_get_default_dispatcher()|.
  //
  // # Errors
  //
  // ZX_ERR_BAD_HANDLE: |directory_request| is not a valid handle.
  //
  // ZX_ERR_ACCESS_DENIED: |directory_request| has insufficient rights.
  //
  // TODO: Document more errors.
  zx_status_t Serve(zx::channel directory_request,
                    async_dispatcher_t* dispatcher = nullptr);

  // Starts serving the outgoing directory on the channel provided to this
  // process at startup as |PA_DIRECTORY_REQUEST|.
  //
  // This object will implement the |fuchsia.io.Directory| interface using this
  // channel.
  //
  // If |dispatcher| is NULL, this object will serve the outgoing directory
  // using the |async_dispatcher_t| from |async_get_default_dispatcher()|.
  //
  // # Errors
  //
  // ZX_ERR_BAD_HANDLE: the process did not receive a |PA_DIRECTORY_REQUEST|
  // startup handle or it was already taken.
  //
  // ZX_ERR_ACCESS_DENIED: |directory_request| has insufficient rights.
  //
  // TODO: Document more errors.
  zx_status_t ServeFromStartupInfo(async_dispatcher_t* dispatcher = nullptr);

  // Adds the specified interface to the set of public interfaces.
  //
  // Adds a supported service with the given |service_name|, using the given
  // |interface_request_handler|. |interface_request_handler| should
  // remain valid for the lifetime of this object.
  //
  // # Errors
  //
  // ZX_ERR_ALREADY_EXISTS: The public directory already contains an entry for
  // this service.
  //
  // # Example
  //
  // ```
  // fidl::BindingSet<fuchsia::foo::Controller> bindings;
  // outgoing.AddPublicService(bindings.GetHandler(this));
  // ```
  template <typename Interface>
  zx_status_t AddPublicService(
      fidl::InterfaceRequestHandler<Interface> handler,
      std::string service_name = Interface::Name_) const {
    return AddPublicService(std::make_unique<vfs::Service>(std::move(handler)),
                            std::move(service_name));
  }

  // Adds the specified service to the set of public services.
  //
  // Adds a supported service with the given |service_name|, using the given
  // |service|.
  //
  // # Errors
  //
  // ZX_ERR_ALREADY_EXISTS: The public directory already contains an entry for
  // this service.
  zx_status_t AddPublicService(std::unique_ptr<vfs::Service> service,
                               std::string service_name) const;

  // Removes the specified interface from the set of public interfaces.
  //
  // # Errors
  //
  // ZX_ERR_NOT_FOUND: The public directory does not contain an entry for this
  // service.
  //
  // # Example
  //
  // ```
  // outgoing.RemovePublicService<fuchsia::foo::Controller>();
  // ```
  template <typename Interface>
  zx_status_t RemovePublicService(
      const std::string& name = Interface::Name_) const {
    return public_->RemoveEntry(name);
  }

  // Gets the directory to publish debug data.
  // The returned directory is owned by this class.
  vfs::PseudoDir* debug_dir() { return debug_; }

  // Gets a subdirectory with the given |name|, creates it if it does not
  // already exist.
  // The returned directory is owned by this class.
  vfs::PseudoDir* GetOrCreateDirectory(const std::string& name);

 private:
  // Adds a new empty directory to |root_| and returns pointer to new directory.
  // Will fail silently if directory with that name already exists.
  vfs::PseudoDir* AddNewEmptyDirectory(std::string name);

  // The root of the outgoing directory itself.
  std::unique_ptr<vfs::PseudoDir> root_;

  // The public subdirectory of the root directory.
  //
  // The underlying |vfs::PseudoDir| object is owned by |root_|.
  vfs::PseudoDir* public_;

  // The debug subdirectory of the root directory.
  //
  // The underlying |vfs::PseudoDir| object is owned by |root_|.
  vfs::PseudoDir* debug_;
};

}  // namespace sys

#endif  // LIB_SYS_CPP_OUTGOING_DIRECTORY_H_