pragma solidity >=0.4.24;

import "../math/SafeMath.sol";

/**
 * @dev 资产列表共通，除资产负债之外提供一个账目清单数组，便于统计和查找.
 */
library BalanceList {
  using SafeMath for uint256;

  struct element {
    address addr;
    uint256 idx;
    uint256 balance;
  }
  struct balanceMap {
    mapping(address => uint256) mapList;
    element[] list;
  }

  function exist(balanceMap storage self, address _addr)
    internal
    view
    returns (bool)
  {
    if (self.list.length == 0) return false;
    return (self.list[self.mapList[_addr]].addr == _addr);
  }

  function insert(
    balanceMap storage self,
    address _addr,
    uint256 _amount
  ) internal returns (bool) {
    element memory e =
      element({addr: _addr, idx: self.list.length, balance: _amount});
    self.list.push(e);
    self.mapList[_addr] = e.idx;
    return true;
  }

  function remove(balanceMap storage self, address _addr)
    internal
    returns (bool)
  {
    if (!exist(self, _addr)) {
      return false;
    }
    if (self.list[self.mapList[_addr]].balance > 0) {
      return false;
    }

    uint256 row2Del = self.mapList[_addr];
    element storage keyToMove = self.list[self.list.length.sub(1)];
    self.list[row2Del] = keyToMove;
    self.mapList[keyToMove.addr] = row2Del;
    self.list.length = self.list.length.sub(1);

    return true;
  }

  function add(
    balanceMap storage self,
    address _addr,
    uint256 _amount
  ) internal returns (uint256) {
    // 对于已经存在的数据更新状态即可
    if (exist(self, _addr)) {
      self.list[self.mapList[_addr]].balance = self.list[self.mapList[_addr]]
        .balance
        .add(_amount);
    } else {
      // 新建数据
      require(insert(self, _addr, _amount), "insert data fail");
    }

    return self.list[self.mapList[_addr]].balance;
  }

  function sub(
    balanceMap storage self,
    address _addr,
    uint256 _amount
  ) internal returns (uint256) {
    require(exist(self, _addr), "can not sub no exist element");

    self.list[self.mapList[_addr]].balance = self.list[self.mapList[_addr]]
      .balance
      .sub(_amount);

    if (self.list[self.mapList[_addr]].balance == 0) {
      require(remove(self, _addr), "remove data fail");
      return 0;
    }

    return self.list[self.mapList[_addr]].balance;
  }

  function count(balanceMap storage self) internal view returns (uint256) {
    return self.list.length;
  }

  function balance(balanceMap storage self, address _addr)
    internal
    view
    returns (uint256)
  {
    return exist(self, _addr) ? self.list[self.mapList[_addr]].balance : 0;
  }

  function get(balanceMap storage self, uint256 index)
    internal
    view
    returns (element memory)
  {
    require(index < self.list.length, "index must small than current count");

    return self.list[index];
  }

  // 获取指定下标范围的数据，本函数可以用于分页查询
  function getList(
    balanceMap storage self,
    uint256 from,
    uint256 _count
  ) internal view returns (element[] memory) {
    require(_count > 0, "count number must bigger than 0");

    uint256 _idx = 0;
    element[] memory res = new element[](_count);

    for (uint256 i = from; i < self.list.length; i++) {
      if (_idx == _count) {
        break;
      }

      res[_idx] = self.list[i];
      _idx = _idx.add(1);
    }

    return res;
  }
}