/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

#include "JSBigString.h"

#include <glog/logging.h>

#include <folly/Memory.h>
#include <folly/ScopeGuard.h>
#include <folly/portability/Fcntl.h>
#include <folly/portability/SysMman.h>
#include <folly/portability/SysStat.h>
#include <folly/portability/Unistd.h>

#include <memory>

namespace facebook {
namespace react {

JSBigFileString::JSBigFileString(int fd, size_t size, off_t offset /*= 0*/)
    : m_fd{-1}, m_data{nullptr} {
  folly::checkUnixError(m_fd = dup(fd), "Could not duplicate file descriptor");

  // Offsets given to mmap must be page aligned. We abstract away that
  // restriction by sending a page aligned offset to mmap, and keeping track
  // of the offset within the page that we must alter the mmap pointer by to
  // get the final desired offset.
  if (offset != 0) {
    const static auto ps = sysconf(_SC_PAGESIZE);
    auto d = lldiv(offset, ps);

    m_mapOff = d.quot;
    m_pageOff = d.rem;
    m_size = size + m_pageOff;
  } else {
    m_mapOff = 0;
    m_pageOff = 0;
    m_size = size;
  }
}

JSBigFileString::~JSBigFileString() {
  if (m_data) {
    munmap((void *)m_data, m_size);
  }
  close(m_fd);
}

const char *JSBigFileString::c_str() const {
  if (m_size == 0) {
    return "";
  }
  if (!m_data) {
    m_data =
        (const char *)mmap(0, m_size, PROT_READ, MAP_PRIVATE, m_fd, m_mapOff);
    CHECK(m_data != MAP_FAILED)
        << " fd: " << m_fd << " size: " << m_size << " offset: " << m_mapOff
        << " error: " << std::strerror(errno);
  }
  static const size_t kMinPageSize = 4096;
  CHECK(!(reinterpret_cast<uintptr_t>(m_data) & (kMinPageSize - 1)))
      << "mmap address misaligned, likely corrupted"
      << " m_data: " << (const void *)m_data;
  CHECK(m_pageOff <= m_size)
      << "offset impossibly large, likely corrupted"
      << " m_pageOff: " << m_pageOff << " m_size: " << m_size;
  return m_data + m_pageOff;
}

size_t JSBigFileString::size() const {
  // Ensure mapping has been initialized.
  c_str();
  return m_size - m_pageOff;
}

int JSBigFileString::fd() const {
  return m_fd;
}

std::unique_ptr<const JSBigFileString> JSBigFileString::fromPath(
    const std::string &sourceURL) {
  int fd = ::open(sourceURL.c_str(), O_RDONLY);
  folly::checkUnixError(fd, "Could not open file", sourceURL);
  SCOPE_EXIT {
    CHECK(::close(fd) == 0);
  };

  struct stat fileInfo;
  folly::checkUnixError(::fstat(fd, &fileInfo), "fstat on bundle failed.");

  return std::make_unique<const JSBigFileString>(fd, fileInfo.st_size);
}

} // namespace react
} // namespace facebook