//
// Created by 马也驰 on 2024/12/9.
//

#ifndef LEVELDB_SLOTPAGE_H
#define LEVELDB_SLOTPAGE_H

#include <cassert>
#include <cstdint>
#include <cstdlib>
#include <vector>
#include <iostream>
#include <fstream>
#include <mutex>

#define BITMAP_SIZE 8192
#define BITS_PER_BYTE 8

#define POSMASK(off) (0x01 << (BITS_PER_BYTE-(off)-1))
#define SETBIT(byte, off) (*(byte) |= POSMASK(off))
#define RESETBIT(byte, off) (*(byte) &= (0xff ^ POSMASK(off)))
#define HASFREESLOT(byte) ((byte) != ~0x0)

struct slot_content {
  uint32_t vlog_num;
  uint32_t value_offset;
  slot_content(uint32_t vn, uint32_t vo) {
    vlog_num = vn;
    value_offset = vo;
  }
};

class SlotCache {
// slot number -> slot content
#define BLOCK_NUM 16
#define BLOCK_SIZE 4096
#define SLOT_PER_BLOCK (BLOCK_SIZE/sizeof(slot_content))
#define SLOT_OFFSET_IN_BLOCK(slot_num) ((slot_num)%SLOT_PER_BLOCK)
public:
  SlotCache() {
    for (auto i = 0; i < BLOCK_NUM; i++) {
      block_cache[i] = static_cast<struct slot_content*>(malloc(BLOCK_SIZE));
      access_time[i] = 0;
      info[i] = block_info();
    }
  }

  void get_slot(std::string &slotpage_fname, size_t slot_num, struct slot_content *sc) {
    auto block_num = slotnum_hash2_blocknum(slot_num);
    auto blockcache_num = block_num % BLOCK_NUM;
    mtx.lock();
    if (info[blockcache_num].slotpage_fname != slotpage_fname) {  // cache miss
      write_back_block(blockcache_num);
      read_in_block(blockcache_num, slotpage_fname, block_num);
    }
    read_slot(sc, blockcache_num, SLOT_OFFSET_IN_BLOCK(slot_num));
    access_time[blockcache_num]++;
    mtx.unlock();
  }

  void set_slot(std::string &slotpage_fname, size_t slot_num, struct slot_content *sc) {
    auto block_num = slotnum_hash2_blocknum(slot_num);
    auto blockcache_num = block_num % BLOCK_NUM;
    mtx.lock();
    if (info[blockcache_num].slotpage_fname != slotpage_fname) {
      write_back_block(blockcache_num);
      read_in_block(blockcache_num, slotpage_fname, block_num);
    }
    set_slot(sc, blockcache_num, SLOT_OFFSET_IN_BLOCK(slot_num));
    access_time[blockcache_num]++;
    info[blockcache_num].is_dirty = true;
    mtx.unlock();
  }

private:
 struct block_info {
  std::string slotpage_fname;
  size_t block_num;
  bool is_dirty;
  block_info() {}
  block_info(std::string &slotpage_fname, size_t block_num, bool is_dirty=false) {
    this->slotpage_fname = slotpage_fname;
    this->block_num = block_num;
    this->is_dirty = is_dirty;
  }
};

private:
  inline static size_t slotnum_hash2_blocknum(size_t slot_num) {
    return slot_num * sizeof(slot_content) / BLOCK_SIZE;
  }
  void write_back_block(size_t blockcache_num) {
    auto &fname = info[blockcache_num].slotpage_fname;
    auto write_pos = info[blockcache_num].block_num * BLOCK_SIZE;
    auto slotpage_handler = std::fstream(fname, std::ios::in | std::ios::out);
    slotpage_handler.seekp(write_pos);
    slotpage_handler.write(
        reinterpret_cast<const char*>(block_cache[blockcache_num]), BLOCK_SIZE);
  }
  void read_in_block(size_t blockcache_num, std::string &slotpage_fname, size_t block_num) {
    auto slotpage_handler = std::fstream(slotpage_fname, std::ios::in | std::ios::out);
    slotpage_handler.seekp(block_num*BLOCK_SIZE);
    slotpage_handler.read(reinterpret_cast<char*>(block_cache[blockcache_num]), BLOCK_SIZE);
    access_time[blockcache_num] = 0;
    info[blockcache_num] = block_info(slotpage_fname, block_num);
  }
  inline void read_slot(struct slot_content *sc, size_t blockcache_num, size_t slot_num_offset) {
    auto src = &block_cache[blockcache_num][slot_num_offset];
    memcpy(sc, src, sizeof(slot_content));
  }
  inline void set_slot(struct slot_content *sc, size_t blockcache_num, size_t slot_num_offset) {
    auto src = &block_cache[blockcache_num][slot_num_offset];
    memcpy(src, sc, sizeof(slot_content));
  }

private:
  std::mutex mtx;
  struct slot_content *block_cache[BLOCK_NUM];
  size_t access_time[BLOCK_NUM];
  struct block_info info[BLOCK_NUM];
};


class BitMap {
  // in memory bitmap
public:
  BitMap() {
    char *bitmap = static_cast<char*>(malloc(BITMAP_SIZE*sizeof(char)));
    bitmaps_.push_back(bitmap);
    size = BITMAP_SIZE;
    first_empty_slot = 0;
  }

  void dealloc_slot(size_t slot_num) {
    mtx.lock();
    const size_t byte = slot2byte(slot_num);
    const size_t off  = slot2offset(slot_num);
    char *target_byte = get_bitmap_byte(byte);
    assert(*target_byte & POSMASK(off));
    RESETBIT(target_byte, off);
//    set_bitmap_byte(byte, target_byte);
    first_empty_slot = first_empty_slot < slot_num ? first_empty_slot:slot_num;
    mtx.unlock();
  }

  size_t alloc_slot() {
    mtx.lock();
    size_t target_slot = first_empty_slot;
    char *start_byte = get_bitmap_byte(slot2byte(first_empty_slot));
    const size_t off = slot2offset(first_empty_slot);
    SETBIT(start_byte, off);
    if (HASFREESLOT(*start_byte)) {
      auto bit_off = find_first_free_slot_inbyte(*start_byte);
      first_empty_slot += bit_off - off;
    } else {
      size_t i;
      for (i = slot2byte(first_empty_slot)+1; i < size; i++) {
        char *byte  = get_bitmap_byte(i);
        if (HASFREESLOT(*byte)) {
          auto bit_off = find_first_free_slot_inbyte(*byte);
          first_empty_slot = byte2slot(i) + bit_off;
        }
      }
      // scale the bitmap
      if (i >= size) {
        alloc_new_bitmap();
        char *byte = get_bitmap_byte(i);
        SETBIT(byte, 0);
        first_empty_slot = byte2slot(i) + 1;
      }
    }
    mtx.unlock();
    return target_slot;
  }

private:
  static inline size_t slot2byte(size_t slot_num) { return slot_num / BITS_PER_BYTE; }
  static inline size_t byte2slot(uint8_t byte_num) { return byte_num * BITS_PER_BYTE; }
  static inline size_t slot2offset(size_t slot_num) { return slot_num % BITS_PER_BYTE; }
  inline char *get_bitmap_byte(size_t byte_num) {
    char *bitmap = bitmaps_.at(byte_num / BITMAP_SIZE);
    return &bitmap[byte_num % BITMAP_SIZE];
  }
//  inline void set_bitmap_byte(size_t byte_num, char byte) {
//    char *bitmap = bitmaps_.at(byte_num / BITMAP_SIZE);
//    bitmap[byte_num % BITMAP_SIZE] = byte;
//  }
  static inline size_t find_first_free_slot_inbyte(uint8_t byte) {
    uint32_t rbyte = __builtin_bswap32((uint32_t)byte) >> 24;  // 使用 32 位变量
    return BITS_PER_BYTE - __builtin_ctz(~rbyte) - 1;  // 使用 GCC 内建函数找到最低位 1 的位置
  }
  void alloc_new_bitmap() {
    char *bitmap = static_cast<char*>(malloc(BITMAP_SIZE*sizeof(char)));
    bitmaps_.push_back(bitmap);
    size += BITMAP_SIZE;
  }

private:
  std::vector<char *> bitmaps_;
  size_t size;
  size_t first_empty_slot;
  std::mutex mtx;
};


// read and write slot in disk
// first version with no cache
class SlotPage {
public:
  SlotPage(std::string &dbname) {
    slotpage_fname = slotpage_handler_name(dbname);
    bitmap = new BitMap();
  }

public:
  void get_slot(size_t slot_num, struct slot_content *sc) {
    slotcache->get_slot(slotpage_fname, slot_num, sc);
  }
  void set_slot(size_t slot_num, struct slot_content *sc) {
    slotcache->set_slot(slotpage_fname, slot_num, sc);
  }
  size_t alloc_slot() { return bitmap->alloc_slot(); }
  void dealloc_slot(size_t slot_num) { bitmap->dealloc_slot(slot_num); }

private:
  static std::string slotpage_handler_name(std::string &dbname) {
    return "./" + dbname + "_slotpage";
  }
  inline static size_t slotpage_pos(size_t slot_num) {
    return slot_num * sizeof(slot_content);
  }

private:
  std::string slotpage_fname;
  BitMap *bitmap;
  static SlotCache *slotcache;
};

SlotCache *SlotPage::slotcache = new SlotCache();

#endif  // LEVELDB_SLOTPAGE_H