// SPDX-License-Identifier: MIT

pragma solidity ^0.8.13;

interface IExchangeRatePolicy {
    function setParam(uint param) external;

    /**
     * Conversion from Operator's internal token to DATA when undelegating
     * We calculate using valueWithoutEarnings() because smart contract's can't check the outstanding earnings of arbitrary number of Sponsorships
     * @dev specifically, dataWei should be the *highest* amount of DATA that can be received from undelegating operatorTokenWei
     * @param operatorTokenWei Amount of Operator's internal token to undelegate
     * @return dataWei Amount of DATA token that would be received from the undelegation
     */
    function operatorTokenToData(uint operatorTokenWei) external view returns (uint dataWei);

    /**
     * (Inverse) conversion from DATA to Operator's internal token when undelegating
     * We calculate using valueWithoutEarnings() because smart contract's can't check the outstanding earnings of arbitrary number of Sponsorships
     * @dev specifically, operatorTokenWei should be the *least* amount that must be undelegated to receive dataWei
     * @dev for bijective conversion functions, this MUST be the inverse of operatorTokenToData()
     * @param dataWei Amount of DATA we want from undelegating
     * @return operatorTokenWei Amount of Operator's internal token to undelegate to receive the given amount of DATA
     */
    function operatorTokenToDataInverse(uint dataWei) external view returns (uint operatorTokenWei);

    /**
     * Conversion from DATA to Operator's internal token when delegating
     * We calculate using valueWithoutEarnings() because smart contract's can't check the outstanding earnings of arbitrary number of Sponsorships
     * First delegation should be the operator's self-delegation. For that, use 1:1 exchange rate.
     * NOTE: this function can be called after the DATA tokens have actually been transferred (which is typically the case),
     *       the exchange rate is just adjusted accordingly by subtracting alreadyTransferredWei from the Operator value
     * @dev specifically, operatorTokenWei should be the *highest* amount of DATA that can be received from delegating dataWei
     * @param dataWei Amount of DATA token to delegate
     * @param alreadyTransferredWei Amount of DATA to subtract from Operator value for calculations (because DATA balance already was incremented but calculation needs the pre-increment value)
     * @return operatorTokenWei Amount of Operator's internal token that would be received from the delegation
     **/
    function dataToOperatorToken(uint dataWei, uint alreadyTransferredWei) external view returns (uint operatorTokenWei);
}