//
// Created by 马也驰 on 2024/12/29.
//

#include "vlog_gc.h"
#include "../db/vlog_set.h"


void VlogGC::do_gc(size_t old_vlog_num, size_t new_vlog_num) {
  thread_pool_->enqueue([this, old_vlog_num, new_vlog_num]()
                        { this->exec_gc(old_vlog_num, new_vlog_num); });
}

void VlogGC::exec_gc(size_t old_vlog_num, size_t new_vlog_num) {
  auto old_vlog_name = vlog_set->get_vlog_name(old_vlog_num);
  auto new_vlog_name = vlog_set->get_vlog_name(new_vlog_num);
  auto old_vlog_info = vlog_set->get_vlog_info(old_vlog_num);
  auto new_vlog_info = vlog_set->get_vlog_info(new_vlog_num);
  auto old_vlog_handler = vlog_set->get_vlog_handler(old_vlog_num);
  auto new_vlog_handler = vlog_set->get_vlog_handler(new_vlog_num);

  old_vlog_handler->vlog_latch_.soft_lock();
  new_vlog_info->vlog_info_latch_.lock();
  new_vlog_handler->vlog_latch_.hard_lock();

  auto old_vlog = std::fstream(old_vlog_name, std::ios::in | std::ios::out);
  auto new_vlog = std::fstream(new_vlog_name, std::ios::in | std::ios::out);

  char old_vlog_buff[VLOG_SIZE];
  char new_vlog_buff[VLOG_SIZE];
  old_vlog.seekp(0);
  old_vlog.read(old_vlog_buff, VLOG_SIZE);
//  memcpy(new_vlog_buff, &value_nums, sizeof(size_t));

  size_t value_nums = old_vlog_info->value_nums;
  size_t ovb_off = 2 * sizeof(size_t);
  size_t nvb_off = 2 * sizeof(size_t);
  size_t new_vlog_value_nums = 0;
  for (auto i = 0; i < value_nums; i++) {
    char *value = &old_vlog_buff[ovb_off];
    uint16_t value_len = get_value_len(value);
    size_t slot_num = get_value_slotnum(value);
    if (!value_deleted(value_len)) {
      memcpy(&new_vlog_buff[nvb_off], &old_vlog_buff[ovb_off], value_len);
      struct slot_content scn(new_vlog_info->vlog_num, nvb_off);
      slot_page_->set_slot(slot_num, &scn);
      nvb_off += value_len;
      new_vlog_value_nums ++;
    }
    ovb_off += value_len;
  }
  new_vlog_info->value_nums = value_nums;
  new_vlog_info->curr_size = nvb_off;
  memcpy(new_vlog_buff, &nvb_off, sizeof(size_t));
  memcpy(&new_vlog_buff[sizeof(size_t)], &new_vlog_value_nums, sizeof(size_t));
  new_vlog.write(new_vlog_buff, VLOG_SIZE);
  new_vlog.flush();

  old_vlog.close();
  new_vlog.close();

  old_vlog_handler->vlog_latch_.soft_unlock();
  new_vlog_info->vlog_info_latch_.unlock();
  new_vlog_handler->vlog_latch_.hard_unlock();

  vlog_set->remove_old_vlog(old_vlog_num);
}