// Copyright 2020 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.

#include "ui/gfx/x/connection.h"

#include <X11/Xlib-xcb.h>
#include <X11/Xlib.h>
#include <xcb/xcb.h>

#include <algorithm>

#include "base/command_line.h"
#include "ui/gfx/x/bigreq.h"
#include "ui/gfx/x/event.h"
#include "ui/gfx/x/randr.h"
#include "ui/gfx/x/x11_switches.h"
#include "ui/gfx/x/xproto_types.h"

namespace x11 {

namespace {

// On the wire, sequence IDs are 16 bits.  In xcb, they're usually extended to
// 32 and sometimes 64 bits.  In Xlib, they're extended to unsigned long, which
// may be 32 or 64 bits depending on the platform.  This function is intended to
// prevent bugs caused by comparing two differently sized sequences.  Also
// handles rollover.  To use, compare the result of this function with 0.  For
// example, to compare seq1 <= seq2, use CompareSequenceIds(seq1, seq2) <= 0.
template <typename T, typename U>
auto CompareSequenceIds(T t, U u) {
  static_assert(std::is_unsigned<T>::value, "");
  static_assert(std::is_unsigned<U>::value, "");
  // Cast to the smaller of the two types so that comparisons will always work.
  // If we casted to the larger type, then the smaller type will be zero-padded
  // and may incorrectly compare less than the other value.
  using SmallerType =
      typename std::conditional<sizeof(T) <= sizeof(U), T, U>::type;
  SmallerType t0 = static_cast<SmallerType>(t);
  SmallerType u0 = static_cast<SmallerType>(u);
  using SignedType = typename std::make_signed<SmallerType>::type;
  return static_cast<SignedType>(t0 - u0);
}

XDisplay* OpenNewXDisplay() {
  if (!XInitThreads())
    return nullptr;
  std::string display_str =
      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
          switches::kX11Display);
  return XOpenDisplay(display_str.empty() ? nullptr : display_str.c_str());
}

}  // namespace

Connection* Connection::Get() {
  static Connection* instance = new Connection;
  return instance;
}

Connection::Connection() : XProto(this), display_(OpenNewXDisplay()) {
  if (display_) {
    XSetEventQueueOwner(display_, XCBOwnsEventQueue);

    setup_ = Read<Setup>(
        reinterpret_cast<const uint8_t*>(xcb_get_setup(XcbConnection())));
    default_screen_ = &setup_.roots[DefaultScreenId()];
    default_root_depth_ = &*std::find_if(
        default_screen_->allowed_depths.begin(),
        default_screen_->allowed_depths.end(), [&](const Depth& depth) {
          return depth.depth == default_screen_->root_depth;
        });
    default_root_visual_ = &*std::find_if(
        default_root_depth_->visuals.begin(),
        default_root_depth_->visuals.end(), [&](const VisualType visual) {
          return visual.visual_id == default_screen_->root_visual;
        });
  } else {
    // Default-initialize the setup data so we always have something to return.
    setup_.roots.emplace_back();
    default_screen_ = &setup_.roots[0];
    default_screen_->allowed_depths.emplace_back();
    default_root_depth_ = &default_screen_->allowed_depths[0];
    default_root_depth_->visuals.emplace_back();
    default_root_visual_ = &default_root_depth_->visuals[0];
  }

  ExtensionManager::Init(this);
  if (auto response = bigreq().Enable({}).Sync())
    extended_max_request_length_ = response->maximum_request_length;
}

Connection::~Connection() {
  if (display_)
    XCloseDisplay(display_);
}

xcb_connection_t* Connection::XcbConnection() {
  if (!display())
    return nullptr;
  return XGetXCBConnection(display());
}

Connection::Request::Request(unsigned int sequence,
                             FutureBase::ResponseCallback callback)
    : sequence(sequence), callback(std::move(callback)) {}

Connection::Request::Request(Request&& other)
    : sequence(other.sequence), callback(std::move(other.callback)) {}

Connection::Request::~Request() = default;

bool Connection::HasNextResponse() const {
  return !requests_.empty() &&
         CompareSequenceIds(XLastKnownRequestProcessed(display_),
                            requests_.front().sequence) >= 0;
}

int Connection::DefaultScreenId() const {
  // This is not part of the setup data as the server has no concept of a
  // default screen. Instead, it's part of the display name. Eg in
  // "localhost:0.0", the screen ID is the second "0".
  return DefaultScreen(display_);
}

bool Connection::Ready() const {
  return display_ && !xcb_connection_has_error(XGetXCBConnection(display_));
}

void Connection::Flush() {
  XFlush(display_);
}

void Connection::Sync() {
  GetInputFocus({}).Sync();
}

void Connection::ReadResponses() {
  while (auto* event = xcb_poll_for_event(XcbConnection())) {
    events_.emplace_back(event, this);
    free(event);
  }
}

bool Connection::HasPendingResponses() const {
  return !events_.empty() || HasNextResponse();
}

void Connection::Dispatch(Delegate* delegate) {
  DCHECK(display_);

  auto process_next_response = [&] {
    xcb_connection_t* connection = XGetXCBConnection(display_);
    auto request = std::move(requests_.front());
    requests_.pop();

    void* raw_reply = nullptr;
    xcb_generic_error_t* raw_error = nullptr;
    xcb_poll_for_reply(connection, request.sequence, &raw_reply, &raw_error);

    std::move(request.callback)
        .Run(FutureBase::RawReply{reinterpret_cast<uint8_t*>(raw_reply)},
             FutureBase::RawError{raw_error});
  };

  auto process_next_event = [&] {
    DCHECK(!events_.empty());

    Event event = std::move(events_.front());
    events_.pop_front();
    PreDispatchEvent(event);
    delegate->DispatchXEvent(&event);
  };

  // Handle all pending events.
  while (delegate->ShouldContinueStream()) {
    Flush();
    ReadResponses();

    if (HasNextResponse() && !events_.empty()) {
      if (!events_.front().sequence_valid()) {
        process_next_event();
        continue;
      }

      auto next_response_sequence = requests_.front().sequence;
      auto next_event_sequence = events_.front().sequence();

      // All events have the sequence number of the last processed request
      // included in them.  So if a reply and an event have the same sequence,
      // the reply must have been received first.
      if (CompareSequenceIds(next_event_sequence, next_response_sequence) <= 0)
        process_next_response();
      else
        process_next_event();
    } else if (HasNextResponse()) {
      process_next_response();
    } else if (!events_.empty()) {
      process_next_event();
    } else {
      break;
    }
  }
}

void Connection::AddRequest(unsigned int sequence,
                            FutureBase::ResponseCallback callback) {
  DCHECK(requests_.empty() ||
         CompareSequenceIds(requests_.back().sequence, sequence) < 0);

  requests_.emplace(sequence, std::move(callback));
}

void Connection::PreDispatchEvent(const Event& event) {
  // This is adapted from XRRUpdateConfiguration.
  if (auto* configure = event.As<x11::ConfigureNotifyEvent>()) {
    int index = ScreenIndexFromRootWindow(configure->window);
    if (index != -1) {
      setup_.roots[index].width_in_pixels = configure->width;
      setup_.roots[index].height_in_pixels = configure->height;
    }
  } else if (auto* screen = event.As<x11::RandR::ScreenChangeNotifyEvent>()) {
    int index = ScreenIndexFromRootWindow(screen->root);
    DCHECK_GE(index, 0);
    bool portrait = static_cast<bool>(
        screen->rotation &
        (x11::RandR::Rotation::Rotate_90 | x11::RandR::Rotation::Rotate_270));
    if (portrait) {
      setup_.roots[index].width_in_pixels = screen->height;
      setup_.roots[index].height_in_pixels = screen->width;
      setup_.roots[index].width_in_millimeters = screen->mheight;
      setup_.roots[index].height_in_millimeters = screen->mwidth;
    } else {
      setup_.roots[index].width_in_pixels = screen->width;
      setup_.roots[index].height_in_pixels = screen->height;
      setup_.roots[index].width_in_millimeters = screen->mwidth;
      setup_.roots[index].height_in_millimeters = screen->mheight;
    }
  }
}

int Connection::ScreenIndexFromRootWindow(x11::Window root) const {
  for (size_t i = 0; i < setup_.roots.size(); i++) {
    if (setup_.roots[i].root == root)
      return i;
  }
  return -1;
}

}  // namespace x11