IYieldSource.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.6.0;

/// @title Defines the functions used to interact with a yield source.  The Prize Pool inherits this contract.
/// @notice Prize Pools subclasses need to implement this interface so that yield can be generated.
interface IYieldSource {
    /// @notice Returns the ERC20 asset token used for deposits.
    /// @return The ERC20 asset token address.
    function depositToken() external view returns (address);

    /// @notice Returns the total balance (in asset tokens).  This includes the deposits and interest.
    /// @return The underlying balance of asset tokens.
    function balanceOfToken(address addr) external returns (uint256);

    /// @notice Supplies tokens to the yield source.  Allows assets to be supplied on other user's behalf using the `to` param.
    /// @param amount The amount of asset tokens to be supplied.  Denominated in `depositToken()` as above.
    /// @param to The user whose balance will receive the tokens
    function supplyTokenTo(uint256 amount, address to) external;

    /// @notice Redeems tokens from the yield source.
    /// @param amount The amount of asset tokens to withdraw.  Denominated in `depositToken()` as above.
    /// @return The actual amount of interst bearing tokens that were redeemed.
    function redeemToken(uint256 amount) external returns (uint256);
}