/*
  Copyright (c) 2023, Antonio SJ Musumeci <trapexit@spawn.link>

  Permission to use, copy, modify, and/or distribute this software for any
  purpose with or without fee is hereby granted, provided that the above
  copyright notice and this permission notice appear in all copies.

  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#include "fuse_readdir_cor.hpp"

#include "config.hpp"
#include "dirinfo.hpp"
#include "errno.hpp"
#include "fs_close.hpp"
#include "fs_closedir.hpp"
#include "fs_getdents64.hpp"
#include "fs_inode.hpp"
#include "fs_opendir.hpp"
#include "fs_path.hpp"
#include "fs_readdir.hpp"
#include "hashset.hpp"
#include "scope_guard.hpp"
#include "ugid.hpp"

#include "fuse_dirents.h"
#include "linux_dirent64.h"

#include "int_types.h"

#define MAX_ENTRIES_PER_LOOP 64


FUSE::ReadDirCOR::ReadDirCOR(unsigned concurrency_,
                             unsigned max_queue_depth_)
  : _tp(concurrency_,max_queue_depth_,"readdir.cor")
{

}

FUSE::ReadDirCOR::~ReadDirCOR()
{

}

static
u64
_dirent_exact_namelen(const struct dirent *d_)
{
#ifdef _D_EXACT_NAMLEN
  return _D_EXACT_NAMLEN(d_);
#elif defined _DIRENT_HAVE_D_NAMLEN
  return d_->d_namlen;
#else
  return strlen(d_->d_name);
#endif
}

namespace l
{
  struct Error
  {
  private:
    int _err;

  public:
    Error()
      : _err(ENOENT)
    {
    }

    operator int()
    {
      return _err;
    }

    Error&
    operator=(int v_)
    {
      if(_err != 0)
        _err = v_;

      return *this;
    }
  };

  static
  inline
  int
  readdir(const std::string &branch_path_,
          const std::string &rel_dirpath_,
          HashSet           &names_,
          fuse_dirents_t    *buf_,
          std::mutex        &mutex_)
  {
    int rv;
    DIR *dir;
    std::string rel_filepath;
    std::string abs_dirpath;

    abs_dirpath = fs::path::make(branch_path_,rel_dirpath_);

    errno = 0;
    dir = fs::opendir(abs_dirpath);
    if(dir == NULL)
      return errno;

    DEFER{ fs::closedir(dir); };

    // The default buffer size in glibc is 32KB. 64 is based on a
    // guess of an average size of 512B per entry. This is to limit
    // contention on the lock when needing to request more data from
    // the kernel. This could be handled better by using getdents but
    // due to the differences between Linux and FreeBSD a more
    // complicated abstraction needs to be created to handle them to
    // make it easier to use across the codebase.
    // * https://man7.org/linux/man-pages/man2/getdents.2.html
    // * https://man.freebsd.org/cgi/man.cgi?query=getdents
    while(true)
      {
        std::lock_guard<std::mutex> lk(mutex_);
        for(int i = 0; i < MAX_ENTRIES_PER_LOOP; i++)
          {
            dirent *de;
            u64 namelen;

            de = fs::readdir(dir);
            if(de == NULL)
              return 0;

            namelen = ::_dirent_exact_namelen(de);

            rv = names_.put(de->d_name,namelen);
            if(rv == 0)
              continue;

            rel_filepath = fs::path::make(rel_dirpath_,de->d_name);
            de->d_ino = fs::inode::calc(branch_path_,
                                        rel_filepath,
                                        DTTOIF(de->d_type),
                                        de->d_ino);

            rv = fuse_dirents_add(buf_,de,namelen);
            if(rv >= 0)
              continue;

            return ENOMEM;
          }
      }

    return 0;
  }

  static
  inline
  int
  concurrent_readdir(ThreadPool          &tp_,
                     const Branches::Ptr &branches_,
                     const std::string   &rel_dirpath_,
                     fuse_dirents_t      *buf_,
                     const uid_t          uid_,
                     const gid_t          gid_)
  {
    HashSet names;
    std::mutex mutex;
    std::vector<std::future<int>> futures;

    fuse_dirents_reset(buf_);
    futures.reserve(branches_->size());

    for(const auto &branch : *branches_)
      {
        auto func =
          [&,buf_,uid_,gid_]()
          {
            const ugid::Set ugid(uid_,gid_);

            return l::readdir(branch.path,
                              rel_dirpath_,
                              names,
                              buf_,
                              mutex);
          };

        auto rv = tp_.enqueue_task(std::move(func));

        futures.emplace_back(std::move(rv));
      }

    Error error;
    for(auto &future : futures)
      error = future.get();

    return -error;
  }
}

int
FUSE::ReadDirCOR::operator()(const fuse_file_info_t *ffi_,
                             fuse_dirents_t         *buf_)
{
  Config::Read        cfg;
  DirInfo            *di = reinterpret_cast<DirInfo*>(ffi_->fh);
  const fuse_context *fc = fuse_get_context();

  return l::concurrent_readdir(_tp,
                               cfg->branches,
                               di->fusepath,
                               buf_,
                               fc->uid,
                               fc->gid);
}