/**
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                           Trust math, not hardware.
*/

pragma solidity 0.5.17;

/// @title Keep Random Beacon
///
/// @notice Keep Random Beacon generates verifiable randomness that is resistant
/// to bad actors both in the relay network and on the anchoring blockchain.
interface IRandomBeacon {
    /// @notice Event emitted for each new relay entry generated. It contains
    /// request ID allowing to associate the generated relay entry with relay
    /// request created previously with `requestRelayEntry` function. Event is
    /// emitted no matter if callback was executed or not.
    ///
    /// @param requestId Relay request ID for which entry was generated.
    /// @param entry Generated relay entry.
    event RelayEntryGenerated(uint256 requestId, uint256 entry);

    /// @notice Provides the customer with an estimated entry fee in wei to use
    /// in the request. The fee estimate is only valid for the transaction it is
    /// called in, so the customer must make the request immediately after
    /// obtaining the estimate. Insufficient payment will lead to the request
    /// being rejected and the transaction reverted.
    ///
    /// The customer may decide to provide more ether for an entry fee than
    /// estimated by this function. This is especially helpful when callback gas
    /// cost fluctuates. Any surplus between the passed fee and the actual cost
    /// of producing an entry and executing a callback is returned back to the
    /// customer.
    /// @param callbackGas Gas required for the callback.
    function entryFeeEstimate(uint256 callbackGas)
        external
        view
        returns (uint256);

    /// @notice Submits a request to generate a new relay entry. Executes
    /// callback on the provided callback contract with the generated entry and
    /// emits `RelayEntryGenerated(uint256 requestId, uint256 entry)` event.
    /// Callback contract has to declare public `__beaconCallback(uint256)`
    /// function that is going to be executed with the result, once ready.
    /// It is recommended to implement `IRandomBeaconConsumer` interface to
    /// ensure the correct callback function signature.
    ///
    /// @dev Beacon does not support concurrent relay requests. No new requests
    /// should be made while the beacon is already processing another request.
    /// Requests made while the beacon is busy will be rejected and the
    /// transaction reverted.
    ///
    /// @param callbackContract Callback contract address. Callback is called
    /// once a new relay entry has been generated. Must declare public
    /// `__beaconCallback(uint256)` function. It is recommended to implement
    /// `IRandomBeaconConsumer` interface to ensure the correct callback function
    /// signature.
    /// @param callbackGas Gas required for the callback.
    /// The customer needs to ensure they provide a sufficient callback gas
    /// to cover the gas fee of executing the callback. Any surplus is returned
    /// to the customer. If the callback gas amount turns to be not enough to
    /// execute the callback, callback execution is skipped.
    /// @return An uint256 representing uniquely generated relay request ID
    function requestRelayEntry(address callbackContract, uint256 callbackGas)
        external
        payable
        returns (uint256);

    /// @notice Submits a request to generate a new relay entry. Emits
    /// `RelayEntryGenerated(uint256 requestId, uint256 entry)` event for the
    /// generated entry.
    ///
    /// @dev Beacon does not support concurrent relay requests. No new requests
    /// should be made while the beacon is already processing another request.
    /// Requests made while the beacon is busy will be rejected and the
    /// transaction reverted.
    ///
    /// @return An uint256 representing uniquely generated relay request ID
    function requestRelayEntry() external payable returns (uint256);
}

/// @title Keep Random Beacon Consumer
///
/// @notice Receives Keep Random Beacon relay entries with `__beaconCallback`
/// function. Contract implementing this interface does not have to be the one
/// requesting relay entry but it is the one receiving the requested relay entry
/// once it is produced.
///
/// @dev Use this interface to indicate the contract receives relay entries from
/// the beacon and to ensure the correctness of callback function signature.
interface IRandomBeaconConsumer {
    /// @notice Receives relay entry produced by Keep Random Beacon. This function
    /// should be called only by Keep Random Beacon.
    ///
    /// @param relayEntry Relay entry (random number) produced by Keep Random
    /// Beacon.
    function __beaconCallback(uint256 relayEntry) external;
}