// Copyright 2024 Google LLC
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Safe to be first, does not include POSIX headers.
#include "hwy/detect_compiler_arch.h"
// Only compile this file on non-Windows; it replaces io_win.cc. It is easier to
// check this in source code because we support multiple build systems.
#if !HWY_OS_WIN

// Request POSIX 2008, including `pread()` and `posix_fadvise()`.
#if !defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 700
#undef _XOPEN_SOURCE
#define _XOPEN_SOURCE 700
#endif
#if !defined(_POSIX_C_SOURCE) || _POSIX_C_SOURCE < 200809
#define _POSIX_C_SOURCE 200809
#endif

// Make `off_t` 64-bit even on 32-bit systems. Works for Android >= r15c.
#undef _FILE_OFFSET_BITS
#define _FILE_OFFSET_BITS 64

#include <fcntl.h>  // open
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>     // SEEK_END - unistd isn't enough for IDE.
#include <sys/stat.h>  // O_RDONLY
#include <unistd.h>    // read, write, close

#include <memory>

#include "compression/io.h"
#include "hwy/base.h"  // HWY_ASSERT

namespace gcpp {

class FilePosix : public File {
  int fd_ = 0;

 public:
  explicit FilePosix(int fd) : fd_(fd) { HWY_ASSERT(fd > 0); }
  ~FilePosix() override {
    if (fd_ != 0) {
      HWY_ASSERT(close(fd_) != -1);
    }
  }

  uint64_t FileSize() const override {
    static_assert(sizeof(off_t) == 8, "64-bit off_t required");
    const off_t size = lseek(fd_, 0, SEEK_END);
    if (size < 0) {
      return 0;
    }
    return static_cast<uint64_t>(size);
  }

  bool Read(uint64_t offset, uint64_t size, void* to) const override {
    uint8_t* bytes = reinterpret_cast<uint8_t*>(to);
    uint64_t pos = 0;
    for (;;) {
      // pread seems to be faster than lseek + read when parallelized.
      const auto bytes_read = pread(fd_, bytes + pos, size - pos, offset + pos);
      if (bytes_read <= 0) break;
      pos += bytes_read;
      HWY_ASSERT(pos <= size);
      if (pos == size) break;
    }
    return pos == size;  // success if managed to read desired size
  }

  bool Write(const void* from, uint64_t size, uint64_t offset) override {
    const uint8_t* bytes = reinterpret_cast<const uint8_t*>(from);
    uint64_t pos = 0;
    for (;;) {
      const auto bytes_written =
          pwrite(fd_, bytes + pos, size - pos, offset + pos);
      if (bytes_written <= 0) break;
      pos += bytes_written;
      HWY_ASSERT(pos <= size);
      if (pos == size) break;
    }
    return pos == size;  // success if managed to write desired size
  }
};  // FilePosix

HWY_MAYBE_UNUSED extern std::unique_ptr<File> OpenFileGoogle(
    const Path& filename, const char* mode);

std::unique_ptr<File> OpenFileOrNull(const Path& filename, const char* mode) {
  std::unique_ptr<File> file;  // OpenFileGoogle omitted
  if (file) return file;

  const bool is_read = mode[0] != 'w';
  const int flags = is_read ? O_RDONLY : O_CREAT | O_RDWR | O_TRUNC;
  const int fd = open(filename.path.c_str(), flags, 0644);
  if (fd < 0) return file;

#if HWY_OS_LINUX && (!defined(__ANDROID_API__) || __ANDROID_API__ >= 21)
  if (is_read) {
    // Doubles the readahead window, which seems slightly faster when cached.
    (void)posix_fadvise(fd, 0, 0, POSIX_FADV_SEQUENTIAL);
  }
#endif

  return std::make_unique<FilePosix>(fd);
}

}  // namespace gcpp
#endif  // !HWY_OS_WIN