// SPDX-License-Identifier: GPL-3.0-or-later
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity >=0.7.0 <0.9.0;
pragma experimental ABIEncoderV2;

/**
 * @dev Source of truth for all Protocol Fee percentages, that is, how much the protocol charges certain actions. Some
 * of these values may also be retrievable from other places (such as the swap fee percentage), but this is the
 * preferred source nonetheless.
 */
interface IProtocolFeePercentagesProvider {
    // All fee percentages are 18-decimal fixed point numbers, so e.g. 1e18 = 100% and 1e16 = 1%.

    // Emitted when a new fee type is registered.
    event ProtocolFeeTypeRegistered(uint256 indexed feeType, string name, uint256 maximumPercentage);

    // Emitted when the value of a fee type changes.
    // IMPORTANT: it is possible for a third party to modify the SWAP and FLASH_LOAN fee type values directly in the
    // ProtocolFeesCollector, which will result in this event not being emitted despite their value changing. Such usage
    // of the ProtocolFeesCollector is however discouraged: all state-changing interactions with it should originate in
    // this contract.
    event ProtocolFeePercentageChanged(uint256 indexed feeType, uint256 percentage);

    /**
     * @dev Registers a new fee type in the system, making it queryable via `getFeeTypePercentage` and `getFeeTypeName`,
     * as well as configurable via `setFeeTypePercentage`.
     *
     * `feeType` can be any arbitrary value (that is not in use).
     *
     * It is not possible to de-register fee types, nor change their name or maximum value.
     */
    function registerFeeType(
        uint256 feeType,
        string memory name,
        uint256 maximumValue,
        uint256 initialValue
    ) external;

    /**
     * @dev Returns true if `feeType` has been registered and can be queried.
     */
    function isValidFeeType(uint256 feeType) external view returns (bool);

    /**
     * @dev Returns true if `value` is a valid percentage value for `feeType`.
     */
    function isValidFeeTypePercentage(uint256 feeType, uint256 value) external view returns (bool);

    /**
     * @dev Sets the percentage value for `feeType` to `newValue`.
     *
     * IMPORTANT: it is possible for a third party to modify the SWAP and FLASH_LOAN fee type values directly in the
     * ProtocolFeesCollector, without invoking this function. This will result in the `ProtocolFeePercentageChanged`
     * event not being emitted despite their value changing. Such usage of the ProtocolFeesCollector is however
     * discouraged: only this contract should be granted permission to call `setSwapFeePercentage` and
     * `setFlashLoanFeePercentage`.
     */
    function setFeeTypePercentage(uint256 feeType, uint256 newValue) external;

    /**
     * @dev Returns the current percentage value for `feeType`. This is the preferred mechanism for querying these -
     * whenever possible, use this fucntion instead of e.g. querying the ProtocolFeesCollector.
     */
    function getFeeTypePercentage(uint256 feeType) external view returns (uint256);

    /**
     * @dev Returns `feeType`'s maximum value.
     */
    function getFeeTypeMaximumPercentage(uint256 feeType) external view returns (uint256);

    /**
     * @dev Returns `feeType`'s name.
     */
    function getFeeTypeName(uint256 feeType) external view returns (string memory);
}

library ProtocolFeeType {
    // This list is not exhaustive - more fee types can be added to the system. It is expected for this list to be
    // extended with new fee types as they are registered, to keep them all in one place and reduce
    // likelihood of user error.

    // solhint-disable private-vars-leading-underscore
    uint256 internal constant SWAP = 0;
    uint256 internal constant FLASH_LOAN = 1;
    uint256 internal constant YIELD = 2;
    uint256 internal constant AUM = 3;
    // solhint-enable private-vars-leading-underscore
}