/*
 * 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 "JSIndexedRAMBundle.h"

#include <glog/logging.h>
#include <fstream>
#include <memory>
#include <sstream>

namespace facebook::react {

std::function<std::unique_ptr<JSModulesUnbundle>(std::string)>
JSIndexedRAMBundle::buildFactory() {
  return [](const std::string& bundlePath) {
    return std::make_unique<JSIndexedRAMBundle>(bundlePath.c_str());
  };
}

JSIndexedRAMBundle::JSIndexedRAMBundle(const char* sourcePath) {
  m_bundle = std::make_unique<std::ifstream>(sourcePath, std::ifstream::binary);
  if (!m_bundle) {
    throw std::ios_base::failure(folly::to<std::string>(
        "Bundle ", sourcePath, "cannot be opened: ", m_bundle->rdstate()));
  }
  init();
}

JSIndexedRAMBundle::JSIndexedRAMBundle(
    std::unique_ptr<const JSBigString> script) {
  // tmpStream is needed because m_bundle is std::istream type
  // which has no member 'write'
  std::unique_ptr<std::stringstream> tmpStream =
      std::make_unique<std::stringstream>();
  tmpStream->write(script->c_str(), script->size());
  m_bundle = std::move(tmpStream);
  if (!m_bundle) {
    throw std::ios_base::failure(folly::to<std::string>(
        "Bundle from string cannot be opened: ", m_bundle->rdstate()));
  }
  init();
}

void JSIndexedRAMBundle::init() {
  // read in magic header, number of entries, and length of the startup section
  uint32_t header[3];
  static_assert(
      sizeof(header) == 12,
      "header size must exactly match the input file format");

  readBundle(reinterpret_cast<char*>(header), sizeof(header));
  const size_t numTableEntries = folly::Endian::little(header[1]);
  const size_t startupCodeSize = folly::Endian::little(header[2]);

  // allocate memory for meta data and lookup table.
  m_table = ModuleTable(numTableEntries);
  m_baseOffset = sizeof(header) + m_table.byteLength();

  // read the lookup table from the file
  readBundle(reinterpret_cast<char*>(m_table.data.get()), m_table.byteLength());

  // read the startup code
  m_startupCode = std::unique_ptr<JSBigBufferString>(
      new JSBigBufferString{startupCodeSize - 1});

  readBundle(m_startupCode->data(), startupCodeSize - 1);
}

JSIndexedRAMBundle::Module JSIndexedRAMBundle::getModule(
    uint32_t moduleId) const {
  Module ret;
  ret.name = folly::to<std::string>(moduleId, ".js");
  ret.code = getModuleCode(moduleId);
  return ret;
}

std::unique_ptr<const JSBigString> JSIndexedRAMBundle::getStartupCode() {
  CHECK(m_startupCode)
      << "startup code for a RAM Bundle can only be retrieved once";
  return std::move(m_startupCode);
}

std::string JSIndexedRAMBundle::getModuleCode(const uint32_t id) const {
  const auto moduleData = id < m_table.numEntries ? &m_table.data[id] : nullptr;

  // entries without associated code have offset = 0 and length = 0
  const uint32_t length =
      moduleData ? folly::Endian::little(moduleData->length) : 0;
  if (length == 0) {
    throw std::ios_base::failure(
        folly::to<std::string>("Error loading module", id, "from RAM Bundle"));
  }

  std::string ret(length - 1, '\0');
  readBundle(
      &ret.front(),
      length - 1,
      m_baseOffset + folly::Endian::little(moduleData->offset));
  return ret;
}

void JSIndexedRAMBundle::readBundle(char* buffer, const std::streamsize bytes)
    const {
  if (!m_bundle->read(buffer, bytes)) {
    if (m_bundle->rdstate() & std::ios::eofbit) {
      throw std::ios_base::failure("Unexpected end of RAM Bundle file");
    }
    throw std::ios_base::failure(folly::to<std::string>(
        "Error reading RAM Bundle: ", m_bundle->rdstate()));
  }
}

void JSIndexedRAMBundle::readBundle(
    char* buffer,
    const std::streamsize bytes,
    const std::ifstream::pos_type position) const {
  if (!m_bundle->seekg(position)) {
    throw std::ios_base::failure(folly::to<std::string>(
        "Error reading RAM Bundle: ", m_bundle->rdstate()));
  }
  readBundle(buffer, bytes);
}

} // namespace facebook::react