enum SubscriptionStatus {
        ACTIVE,
        PAUSED,
        CANCELLED,
        EXPIRED
    }
    enum Operation {
        Call,
        DelegateCall,
        Create
    }

  event ExecuteSubscription(
      address from, //the subscriber
      address to, //the target contract or account
      uint256 value, //amount in wei of ether sent from this contract to the to address
      bytes data, //the encoded transaction data (first four bytes of fn plus args, etc)
      Operation operation, //ENUM of operation
      uint256 periodSeconds, //the period in seconds between payments
      address gasToken, //the address of the token to pay relayer (0 for eth)
      uint256 gasPrice, //the amount of tokens or eth to pay relayer (0 for free)
      address gasPayer //the address that will pay the tokens to the relayer
  );

    function updateWhitelist(
        address _account,
        bool _value
    )
        public
        onlyOwner
        returns (bool)

    function isSubscriptionPaid(
        bytes32 subscriptionHash,
        uint256 gracePeriodSeconds
    )
        external
        view
        returns (bool)

    function getSubscriptionStatus(
        bytes32 subscriptionHash
    )
        public
        view
        returns  (uint256)

    function getSubscriptionHash(
        address from, //the subscriber
        address to, //the target contract or account
        uint256 value, //amount in wei of ether sent from this contract to the to address
        bytes data, //the encoded transaction data (first four bytes of fn plus args, etc)
        Operation operation, //ENUM of operation
        uint256 periodSeconds, //the period in seconds between payments
        address gasToken, //the address of the token to pay relayer (0 for eth)
        uint256 gasPrice, //the amount of tokens or eth to pay relayer (0 for free)
        address gasPayer //the address that will pay the tokens to the relayer
    )
        public
        view
        returns (bytes32)

    function getSubscriptionSigner(
        bytes32 subscriptionHash, //hash of subscription
        bytes signature //proof the subscriber signed the meta trasaction
    )
        public
        pure
        returns (address)

    function isSubscriptionReady(
        address from, //the subscriber
        address to, //the publisher
        uint256 value, //amount in wei of ether sent from this contract to the to address
        bytes data, //the encoded transaction data (first four bytes of fn plus args, etc)
        Operation operation, //ENUM of operation
        uint256 periodSeconds, //the period in seconds between payments
        address gasToken, //the address of the token to pay relayer (0 for eth)
        uint256 gasPrice, //the amount of tokens or eth to pay relayer (0 for free)
        address gasPayer, //the address that will pay the tokens to the relayer
        bytes signature //proof the subscriber signed the meta trasaction
    )
        public
        view
        returns (bool)

    function isValidSignerTimestampAndStatus(
        address from,
        address signer,
        bytes32 subscriptionHash
    )
        public
        view
        returns (bool)

    function getModifyStatusHash(
        bytes32 subscriptionHash,
        SubscriptionStatus status
    )
        public
        view
        returns (bytes32)

    function isValidModifyStatusSigner(
        bytes32 subscriptionHash,
        SubscriptionStatus status,
        bytes signature
    )
        public
        view
        returns (bool)

    function modifyStatus(
        bytes32 subscriptionHash,
        SubscriptionStatus status,
        bytes signature
    )
        public
        returns (bool)

    function executeSubscription(
        address from, //the subscriber
        address to, //the target contract or account
        uint256 value, //amount in wei of ether sent from this contract to the to address
        bytes data, //the encoded transaction data (first four bytes of fn plus args, etc)
        Operation operation, //ENUM of operation
        uint256 periodSeconds, //the period in seconds between payments
        address gasToken, //the address of the token to pay relayer (0 for eth)
        uint256 gasPrice, //the amount of tokens or eth to pay relayer (0 for free)
        address gasPayer, //the address that will pay the tokens to the relayer
        bytes signature //proof the subscriber signed the meta trasaction
    )
        public
        returns (bool)