// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "services/device/hid/hid_report_descriptor_item.h"

#include <stdlib.h>
#include <string.h>

#include "base/check.h"
#include "base/check_op.h"
#include "base/compiler_specific.h"
#include "base/logging.h"

namespace device {

namespace {

struct Header {
  uint8_t size : 2;
  uint8_t type : 2;
  uint8_t tag : 4;
};

}  // namespace

HidReportDescriptorItem::HidReportDescriptorItem(
    base::span<const uint8_t> bytes)
    : shortData_(0), payload_size_(0) {
  const auto* header = reinterpret_cast<const Header*>(bytes.data());
  tag_ = static_cast<Tag>(header->tag << 2 | header->type);

  if (IsLong()) {
    // In a long item, payload size is the second byte.
    if (bytes.size() >= 2) {
      payload_size_ = bytes[1];
    }
  } else {
    // As per HID spec, a bSize value of 3 means 4 bytes.
    payload_size_ = header->size == 0x3 ? 4 : header->size;
    DCHECK_LE(payload_size_, sizeof(shortData_));
    if (GetHeaderSize() + payload_size() <= bytes.size()) {
      UNSAFE_TODO(
          memcpy(&shortData_, bytes.data() + GetHeaderSize(), payload_size()));
    }
  }
}

bool HidReportDescriptorItem::IsLong() const {
  return tag() == kTagLong;
}

size_t HidReportDescriptorItem::GetHeaderSize() const {
  return IsLong() ? 3 : 1;
}

size_t HidReportDescriptorItem::GetSize() const {
  return GetHeaderSize() + payload_size();
}

uint32_t HidReportDescriptorItem::GetShortData() const {
  DCHECK(!IsLong());
  return shortData_;
}

}  // namespace device