diff --git a/coding/coding_tests/file_data_test.cpp b/coding/coding_tests/file_data_test.cpp
index 661f27a0e2..3a4684ad34 100644
--- a/coding/coding_tests/file_data_test.cpp
+++ b/coding/coding_tests/file_data_test.cpp
@@ -5,6 +5,7 @@
 
 #include "base/logging.hpp"
 
+#include <cstring>  // strlen
 #include <fstream>
 #include <string>
 #include <vector>
@@ -16,13 +17,13 @@ namespace file_data_test
 
   void MakeFile(std::string const & name)
   {
-    base::FileData f(name, base::FileData::OP_WRITE_TRUNCATE);
+    base::FileData f(name, base::FileData::Op::WRITE_TRUNCATE);
     f.Write(name.c_str(), name.size());
   }
 
   void MakeFile(std::string const & name, size_t const size, const char c)
   {
-    base::FileData f(name, base::FileData::OP_WRITE_TRUNCATE);
+    base::FileData f(name, base::FileData::Op::WRITE_TRUNCATE);
     f.Write(std::string(size, c).c_str(), size);
   }
 
@@ -195,7 +196,7 @@ UNIT_TEST(EmptyFile)
 
   {
     // Create empty file with zero size.
-    FileData f(name, base::FileData::OP_WRITE_TRUNCATE);
+    FileData f(name, base::FileData::Op::WRITE_TRUNCATE);
   }
 
   // Check that empty file is on disk.
@@ -225,11 +226,11 @@ UNIT_TEST(File_StdGetLine)
 {
   std::string const fName = "test.txt";
 
-  for (std::string buffer : { "x\nxy\nxyz\nxyzk", "x\nxy\nxyz\nxyzk\n" })
+  for (char const * buffer : { "x\nxy\nxyz\nxyzk", "x\nxy\nxyz\nxyzk\n" })
   {
     {
-      base::FileData f(fName, base::FileData::OP_WRITE_TRUNCATE);
-      f.Write(buffer.c_str(), buffer.size());
+      base::FileData f(fName, base::FileData::Op::WRITE_TRUNCATE);
+      f.Write(buffer, std::strlen(buffer));
     }
 
     {
diff --git a/coding/file_reader.cpp b/coding/file_reader.cpp
index 6092da171f..28d57c45c5 100644
--- a/coding/file_reader.cpp
+++ b/coding/file_reader.cpp
@@ -55,7 +55,7 @@ private:
   {
   public:
     explicit FileDataWithCachedSize(std::string const & fileName)
-      : base::FileData(fileName, FileData::OP_READ), m_Size(FileData::Size())
+      : base::FileData(fileName, Op::READ), m_Size(FileData::Size())
     {
     }
 
diff --git a/coding/internal/file64_api.hpp b/coding/internal/file64_api.hpp
index 9ed9acb3b2..febb3da3c0 100644
--- a/coding/internal/file64_api.hpp
+++ b/coding/internal/file64_api.hpp
@@ -1,7 +1,5 @@
 #pragma once
 
-#include "base/base.hpp"
-
 #include "std/target_os.hpp"
 
 #if defined(OMIM_OS_WINDOWS_NATIVE)
@@ -21,7 +19,7 @@
   #if defined(OMIM_OS_ANDROID) && (defined(__arm__) || defined(__i386__))
     static_assert(sizeof(off_t) == 4, "32-bit Android NDK < API 24 has only 32-bit file operations support");
   #else
-    static_assert(sizeof(off_t) == 8, "Our FileReader/Writer require 64-bit file operations");
+    static_assert(sizeof(off_t) == 8, "FileReader and FileWriter require 64-bit file operations");
   #endif
   #define fseek64 fseeko
   #define ftell64 ftello
diff --git a/coding/internal/file_data.cpp b/coding/internal/file_data.cpp
index 4b39db1acb..d0e3e3b3a9 100644
--- a/coding/internal/file_data.cpp
+++ b/coding/internal/file_data.cpp
@@ -1,6 +1,7 @@
 #include "coding/internal/file_data.hpp"
 
 #include "coding/constants.hpp"
+#include "coding/internal/file64_api.hpp"
 #include "coding/reader.hpp" // For Reader exceptions.
 #include "coding/writer.hpp" // For Writer exceptions.
 
@@ -15,7 +16,6 @@
 #include <cstring>
 #include <exception>
 #include <fstream>
-#include <thread>
 #include <vector>
 
 #ifdef OMIM_OS_WINDOWS
@@ -28,23 +28,35 @@ namespace base
 {
 using namespace std;
 
+std::ostream & operator<<(std::ostream & stream, FileData::Op op)
+{
+  switch (op)
+  {
+  case FileData::Op::READ: stream << "READ"; break;
+  case FileData::Op::WRITE_TRUNCATE: stream << "WRITE_TRUNCATE"; break;
+  case FileData::Op::WRITE_EXISTING: stream << "WRITE_EXISTING"; break;
+  case FileData::Op::APPEND: stream << "APPEND"; break;
+  }
+  return stream;
+}
+
 FileData::FileData(string const & fileName, Op op)
   : m_FileName(fileName), m_Op(op)
 {
   char const * const modes [] = {"rb", "wb", "r+b", "ab"};
 
-  m_File = fopen(fileName.c_str(), modes[op]);
+  m_File = fopen(fileName.c_str(), modes[static_cast<int>(op)]);
   if (m_File)
   {
 #if defined(_MSC_VER)
     // Move file pointer to the end of the file to make it consistent with other platforms
-    if (op == OP_APPEND)
+    if (op == Op::OP_APPEND)
       fseek64(m_File, 0, SEEK_END);
 #endif
     return;
   }
 
-  if (op == OP_WRITE_EXISTING)
+  if (op == Op::WRITE_EXISTING)
   {
     // Special case, since "r+b" fails if file doesn't exist.
     m_File = fopen(fileName.c_str(), "wb");
@@ -53,7 +65,7 @@ FileData::FileData(string const & fileName, Op op)
   }
 
   // if we're here - something bad is happened
-  if (m_Op != OP_READ)
+  if (m_Op != Op::READ)
     MYTHROW(Writer::OpenException, (GetErrorProlog()));
   else
     MYTHROW(Reader::OpenException, (GetErrorProlog()));
@@ -70,19 +82,12 @@ FileData::~FileData()
 
 string FileData::GetErrorProlog() const
 {
-  char const * s;
-  switch (m_Op)
-  {
-  case OP_READ: s = "Read"; break;
-  case OP_WRITE_TRUNCATE: s = "Write truncate"; break;
-  case OP_WRITE_EXISTING: s = "Write existing"; break;
-  case OP_APPEND: s = "Append"; break;
-  }
-
-  return m_FileName + "; " + s + "; " + strerror(errno);
+  std::ostringstream stream;
+  stream << m_FileName << "; " << m_Op << "; " << strerror(errno);
+  return stream.str();
 }
 
-static int64_t const INVALID_POS = -1;
+static int64_t constexpr INVALID_POS = -1;
 
 uint64_t FileData::Size() const
 {
@@ -126,7 +131,7 @@ uint64_t FileData::Pos() const
 
 void FileData::Seek(uint64_t pos)
 {
-  ASSERT_NOT_EQUAL(m_Op, OP_APPEND, (m_FileName, m_Op, pos));
+  ASSERT_NOT_EQUAL(m_Op, Op::APPEND, (m_FileName, m_Op, pos));
   if (fseek64(m_File, static_cast<off_t>(pos), SEEK_SET))
     MYTHROW(Writer::SeekException, (GetErrorProlog(), pos));
 }
@@ -160,8 +165,8 @@ bool GetFileSize(string const & fName, uint64_t & sz)
 {
   try
   {
-    typedef base::FileData fdata_t;
-    fdata_t f(fName, fdata_t::OP_READ);
+    typedef FileData fdata_t;
+    fdata_t f(fName, fdata_t::Op::READ);
     sz = f.Size();
     return true;
   }
@@ -299,12 +304,12 @@ bool CopyFileX(string const & fOld, string const & fNew)
 
 bool IsEqualFiles(string const & firstFile, string const & secondFile)
 {
-  base::FileData first(firstFile, base::FileData::OP_READ);
-  base::FileData second(secondFile, base::FileData::OP_READ);
+  FileData first(firstFile, FileData::Op::READ);
+  FileData second(secondFile, FileData::Op::READ);
   if (first.Size() != second.Size())
     return false;
 
-  size_t const bufSize = READ_FILE_BUFFER_SIZE;
+  size_t constexpr bufSize = READ_FILE_BUFFER_SIZE;
   vector<char> buf1, buf2;
   buf1.resize(bufSize);
   buf2.resize(bufSize);
@@ -329,7 +334,7 @@ bool IsEqualFiles(string const & firstFile, string const & secondFile)
 
 std::vector<uint8_t> ReadFile(std::string const & filePath)
 {
-  base::FileData file(filePath, base::FileData::OP_READ);
+  FileData file(filePath, FileData::Op::READ);
   uint64_t const sz = file.Size();
   std::vector<uint8_t> contents(sz);
   file.Read(0, contents.data(), sz);
diff --git a/coding/internal/file_data.hpp b/coding/internal/file_data.hpp
index 3437d5d626..a2c04fbbc9 100644
--- a/coding/internal/file_data.hpp
+++ b/coding/internal/file_data.hpp
@@ -1,12 +1,7 @@
 #pragma once
 
-#include "coding/internal/file64_api.hpp"
-
-#include "base/base.hpp"
 #include "base/macros.hpp"
 
-#include "std/target_os.hpp"
-
 #include <cstddef>
 #include <cstdint>
 #include <functional>
@@ -18,7 +13,7 @@ class FileData
 {
 public:
   /// @note Do not change order (@see FileData::FileData).
-  enum Op { OP_READ = 0, OP_WRITE_TRUNCATE, OP_WRITE_EXISTING, OP_APPEND };
+  enum class Op { READ = 0, WRITE_TRUNCATE, WRITE_EXISTING, APPEND };
 
   FileData(std::string const & fileName, Op op);
   ~FileData();
@@ -38,8 +33,8 @@ public:
 
 private:
   FILE * m_File;
-  std::string m_FileName;
-  Op m_Op;
+  const std::string m_FileName;
+  const Op m_Op;
 
   std::string GetErrorProlog() const;
 
diff --git a/coding/sha1.cpp b/coding/sha1.cpp
index 1825d68a3f..384ba43cb7 100644
--- a/coding/sha1.cpp
+++ b/coding/sha1.cpp
@@ -18,14 +18,14 @@ namespace coding
 // static
 SHA1::Hash SHA1::Calculate(std::string const & filePath)
 {
-  uint32_t constexpr kFileBufferSize = 8192;
   try
   {
-    base::FileData file(filePath, base::FileData::OP_READ);
+    base::FileData file(filePath, base::FileData::Op::READ);
     uint64_t const fileSize = file.Size();
 
     CSHA1 sha1;
     uint64_t currSize = 0;
+    uint32_t constexpr kFileBufferSize = 8192;
     unsigned char buffer[kFileBufferSize];
     while (currSize < fileSize)
     {
diff --git a/coding/zip_creator.cpp b/coding/zip_creator.cpp
index 11f576832b..e6b8912c26 100644
--- a/coding/zip_creator.cpp
+++ b/coding/zip_creator.cpp
@@ -94,7 +94,7 @@ bool CreateZipFromFiles(std::vector<std::string> const & files, std::vector<std:
       if (zip::Code::Ok != zip::OpenNewFileInZip(zip.Handle(), fileInArchive, fileInfo, "", Z_DEFLATED, compressionLevel))
         return false;
 
-      base::FileData file(filePath, base::FileData::OP_READ);
+      base::FileData file(filePath, base::FileData::Op::READ);
       uint64_t const fileSize = file.Size();
       uint64_t writtenSize = 0;
       std::array<char, zip::kFileBufferSize> buffer;
diff --git a/generator/generator_tests/speed_cameras_test.cpp b/generator/generator_tests/speed_cameras_test.cpp
index 6f42e94617..2b915605f1 100644
--- a/generator/generator_tests/speed_cameras_test.cpp
+++ b/generator/generator_tests/speed_cameras_test.cpp
@@ -125,13 +125,13 @@ void TestSpeedCameraSectionBuilding(string const & osmContent, CameraMap const &
   if (!answer.empty())
   {
     // Check that intermediate file is non-empty.
-    TEST_NOT_EQUAL(base::FileData(camerasFilename, base::FileData::OP_READ).Size(), 0,
+    TEST_NOT_EQUAL(base::FileData(camerasFilename, base::FileData::Op::READ).Size(), 0,
                    ("SpeedCam intermediate file is empty"));
   }
   else
   {
     // Check that intermediate file is empty.
-    TEST_EQUAL(base::FileData(camerasFilename, base::FileData::OP_READ).Size(), 0,
+    TEST_EQUAL(base::FileData(camerasFilename, base::FileData::Op::READ).Size(), 0,
                ("SpeedCam intermediate file is non empty"));
   }
 
diff --git a/platform/platform_tests/platform_test.cpp b/platform/platform_tests/platform_test.cpp
index a94fa019ca..8ec9f8e711 100644
--- a/platform/platform_tests/platform_test.cpp
+++ b/platform/platform_tests/platform_test.cpp
@@ -45,7 +45,7 @@ UNIT_TEST(WritableDir)
 
   try
   {
-    base::FileData f(path, base::FileData::OP_WRITE_TRUNCATE);
+    base::FileData f(path, base::FileData::Op::WRITE_TRUNCATE);
   }
   catch (Writer::OpenException const &)
   {