diff --git a/CMakeLists.txt b/CMakeLists.txt
index 12bdcf5..d990e11 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,4 +2,6 @@ cmake_minimum_required(VERSION 3.10)
 
 project(tzdb2nx VERSION 1.0)
 
+set(CMAKE_CXX_STANDARD 20)
+
 add_subdirectory(src)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 0e41555..426fd84 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,4 +1,11 @@
 add_executable(tzdb2nx
-    main.cpp)
+    main.cpp
+    tzif.cpp
+    tzif.h)
+
+add_compile_options(
+    -Werror=all
+    -Werror=extra
+)
 
 include_directories(.)
diff --git a/src/main.cpp b/src/main.cpp
index 3eda31a..fb6c9cc 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,3 +1,48 @@
+#include "tzif.h"
+#include <array>
 #include <cstdio>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
 
-int main() { return 0; }
+constexpr std::size_t ten_megabytes{(1 << 20) * 10};
+
+int main(int argc, char *argv[]) {
+  int f{STDIN_FILENO};
+  char *filename{};
+  std::size_t filesize{ten_megabytes};
+
+  if (argc > 1) {
+    char *filename = argv[1];
+    f = open(filename, O_RDONLY);
+
+    struct stat statbuf;
+    stat(filename, &statbuf);
+
+    filesize = statbuf.st_size;
+  }
+
+  u_int8_t *buf = new u_int8_t[filesize];
+
+  filesize = read(f, buf, filesize);
+  close(f);
+
+  const std::unique_ptr<Tzif::DataImpl> tzif_data =
+      Tzif::ReadData(buf, filesize);
+
+  std::vector<u_int8_t> output_buffer;
+  tzif_data->ReformatNintendo(output_buffer);
+
+  f = STDOUT_FILENO;
+  if (argc > 2) {
+    char *filename = argv[2];
+    f = open(filename, O_WRONLY | O_CREAT | O_TRUNC);
+  }
+
+  write(f, output_buffer.data(), output_buffer.size());
+
+  close(f);
+
+  return 0;
+}
diff --git a/src/tzif.cpp b/src/tzif.cpp
new file mode 100644
index 0000000..e4c1429
--- /dev/null
+++ b/src/tzif.cpp
@@ -0,0 +1,137 @@
+#include "tzif.h"
+#include <cstdint>
+#include <cstring>
+#include <memory>
+#include <sys/types.h>
+
+namespace Tzif {
+
+static std::size_t SkipToVersion2(const u_int8_t *data) {
+  char magic[5];
+  const u_int8_t *p{data};
+
+  std::memcpy(magic, data, 4);
+  magic[4] = '\0';
+
+  if (std::strcmp(magic, "TZif") != 0) {
+    return 0;
+  }
+
+  do {
+    p++;
+  } while (std::strncmp(reinterpret_cast<const char *>(p), "TZif", 4) != 0);
+
+  return p - data;
+}
+
+template <typename Type> constexpr static void SwapEndianess(Type *value) {
+  u_int8_t *data = reinterpret_cast<u_int8_t *>(value);
+
+  union {
+    u_int8_t data[sizeof(Type)];
+    Type value;
+  } temp;
+
+  for (int i = 0; i < sizeof(Type); i++) {
+    int alt_index = sizeof(Type) - i - 1;
+    temp.data[alt_index] = data[i];
+  }
+
+  *value = temp.value;
+}
+
+static void FlipHeader(Header &header) {
+  SwapEndianess(&header.isutcnt);
+  SwapEndianess(&header.isstdcnt);
+  SwapEndianess(&header.leapcnt);
+  SwapEndianess(&header.timecnt);
+  SwapEndianess(&header.typecnt);
+  SwapEndianess(&header.charcnt);
+}
+
+std::unique_ptr<DataImpl> ReadData(const u_int8_t *data, std::size_t size) {
+  const u_int8_t *p = data + SkipToVersion2(data);
+
+  Header header;
+  std::memcpy(&header, p, sizeof(header));
+  p += sizeof(header);
+
+  FlipHeader(header);
+
+  std::unique_ptr<DataImpl> impl = std::make_unique<DataImpl>();
+  impl->header = header;
+
+  impl->transition_times = std::make_unique<int64_t[]>(header.timecnt);
+  impl->transition_types = std::make_unique<u_int8_t[]>(header.timecnt);
+  impl->local_time_type_records =
+      std::make_unique<TimeTypeRecord[]>(header.typecnt);
+  impl->time_zone_designations = std::make_unique<int8_t[]>(header.charcnt);
+  impl->standard_indicators = std::make_unique<u_int8_t[]>(header.isstdcnt);
+  impl->ut_indicators = std::make_unique<u_int8_t[]>(header.isutcnt);
+
+  std::memcpy(impl->transition_times.get(), p,
+              header.timecnt * sizeof(int64_t));
+  p += header.timecnt * sizeof(int64_t);
+
+  std::memcpy(impl->transition_types.get(), p,
+              header.timecnt * sizeof(u_int8_t));
+  p += header.timecnt * sizeof(u_int8_t);
+
+  std::memcpy(impl->local_time_type_records.get(), p,
+              header.typecnt * sizeof(TimeTypeRecord));
+  p += header.typecnt * sizeof(TimeTypeRecord);
+
+  std::memcpy(impl->time_zone_designations.get(), p, header.charcnt);
+  p += header.charcnt * sizeof(int8_t);
+
+  std::memcpy(impl->standard_indicators.get(), p,
+              header.isstdcnt * sizeof(u_int8_t));
+  p += header.isstdcnt * sizeof(u_int8_t);
+
+  std::memcpy(impl->ut_indicators.get(), p, header.isutcnt * sizeof(u_int8_t));
+  p += header.isutcnt * sizeof(u_int8_t);
+
+  const std::size_t footer_string_length = data + size - p - 2;
+  p++;
+
+  impl->footer.tz_string = std::make_unique<char[]>(footer_string_length);
+  std::memcpy(impl->footer.tz_string.get(), p, footer_string_length);
+  impl->footer.footer_string_length = footer_string_length;
+
+  return impl;
+}
+
+static void PushToBuffer(std::vector<u_int8_t> &buffer, const void *data,
+                         std::size_t size) {
+  const u_int8_t *p{reinterpret_cast<const u_int8_t *>(data)};
+  for (std::size_t i = 0; i < size; i++) {
+    buffer.push_back(*p);
+    p++;
+  }
+}
+
+void DataImpl::ReformatNintendo(std::vector<u_int8_t> &buffer) const {
+  buffer.clear();
+
+  Header header_copy{header};
+  header_copy.isstdcnt = 0;
+  header_copy.isutcnt = 0;
+  FlipHeader(header_copy);
+
+  PushToBuffer(buffer, &header_copy, sizeof(Header));
+  PushToBuffer(buffer, transition_times.get(),
+               header.timecnt * sizeof(int64_t));
+  PushToBuffer(buffer, transition_types.get(),
+               header.timecnt * sizeof(u_int8_t));
+  PushToBuffer(buffer, local_time_type_records.get(),
+               header.typecnt * sizeof(TimeTypeRecord));
+  PushToBuffer(buffer, time_zone_designations.get(),
+               header.charcnt * sizeof(int8_t));
+  // omit standard_indicators
+  // omit ut_indicators
+  PushToBuffer(buffer, &footer.nl_a, 1);
+  PushToBuffer(buffer, footer.tz_string.get(), footer.footer_string_length);
+  PushToBuffer(buffer, &footer.nl_b, 1);
+}
+
+} // namespace Tzif
diff --git a/src/tzif.h b/src/tzif.h
new file mode 100644
index 0000000..db56c86
--- /dev/null
+++ b/src/tzif.h
@@ -0,0 +1,72 @@
+#pragma once
+
+#include <array>
+#include <memory>
+#include <sys/types.h>
+#include <vector>
+
+namespace Tzif {
+
+typedef struct {
+  char magic[4];
+  u_int8_t version;
+  u_int8_t reserved[15];
+  u_int32_t isutcnt;
+  u_int32_t isstdcnt;
+  u_int32_t leapcnt;
+  u_int32_t timecnt;
+  u_int32_t typecnt;
+  u_int32_t charcnt;
+} Header;
+static_assert(sizeof(Header) == 0x2c);
+
+class Footer {
+public:
+  explicit Footer() = default;
+  ~Footer() = default;
+
+  const char nl_a{'\n'};
+  std::unique_ptr<char[]> tz_string;
+  const char nl_b{'\n'};
+
+  std::size_t footer_string_length;
+};
+
+#pragma pack(push, 1)
+typedef struct {
+  u_int32_t utoff;
+  u_int8_t dst;
+  u_int8_t idx;
+} TimeTypeRecord;
+#pragma pack(pop)
+static_assert(sizeof(TimeTypeRecord) == 0x6);
+
+class Data {
+public:
+  explicit Data() = default;
+  ~Data() = default;
+
+  virtual void ReformatNintendo(std::vector<u_int8_t> &buffer) const = 0;
+};
+
+class DataImpl : public Data {
+public:
+  explicit DataImpl() = default;
+  ~DataImpl() = default;
+
+  void ReformatNintendo(std::vector<u_int8_t> &buffer) const override;
+
+  Header header;
+  Footer footer;
+
+  std::unique_ptr<int64_t[]> transition_times;
+  std::unique_ptr<u_int8_t[]> transition_types;
+  std::unique_ptr<TimeTypeRecord[]> local_time_type_records;
+  std::unique_ptr<int8_t[]> time_zone_designations;
+  std::unique_ptr<u_int8_t[]> standard_indicators;
+  std::unique_ptr<u_int8_t[]> ut_indicators;
+};
+
+std::unique_ptr<DataImpl> ReadData(const u_int8_t *data, std::size_t size);
+
+} // namespace Tzif