pragma solidity ^0.4.21;

import "zeppelin-solidity/contracts/token/ERC20/ERC20.sol";
import "zeppelin-solidity/contracts/math/SafeMath.sol";
import "zeppelin-solidity/contracts/ownership/Ownable.sol";


contract Subscription is Ownable {
  using SafeMath for uint256;

  /// @dev The token being use
  ERC20 public token;

  /// @dev Address where fee are collected
  address public wallet;

  /// @dev Cost per day of membership
  uint256 public subscriptionRate;

  mapping(uint256 => uint256) subscriptionExpiration;

  /**
   * Event for subscription purchase logging
   * @param purchaser who paid for the subscription
   * @param userId user id who will benefit from purchase
   * @param day day of subscription purchased
   * @param amount amount of subscription purchased in wei
   * @param expiration expiration of user subscription.
   */
  event SubscriptionPurchase(
    address indexed purchaser,
    uint256 indexed userId,
    uint256 day,
    uint256 amount,
    uint256 expiration
  );

  function Subscription(
    uint256 _rate,
    address _fundWallet,
    ERC20 _token) public
  {
    require(_token != address(0));
    require(_fundWallet != address(0));
    require(_rate > 0);
    token = _token;
    wallet = _fundWallet;
    subscriptionRate = _rate;
  }

  function renewSubscription(uint256 _userId, uint _day) external {
    require(_day > 0);
    // Calculate amount token amount to purchase by number of day.
    uint256 amount = subscriptionRate.mul(_day);
    uint256 currentExpiration = subscriptionExpiration[_userId];

    // If their membership already expired...
    if (currentExpiration < now) {
      // ...use `now` as the starting point of their new subscription
      currentExpiration = now;
    }
    uint256 newExpiration = currentExpiration.add(_day.mul(1 days));
    subscriptionExpiration[_userId] = newExpiration;

    // Transfer token to our wallet. Always do this last to prevent race conditions.
    require(token.transferFrom(msg.sender, wallet, amount));
    emit SubscriptionPurchase(
      msg.sender,
      _userId,
      _day,
      amount,
      newExpiration);
  }
}