/*

  Copyright 2020 ZeroEx Intl.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

*/

pragma solidity ^0.6.5;
pragma experimental ABIEncoderV2;


/// @dev Common storage helpers
library LibStorage {

    /// @dev What to bit-shift a storage ID by to get its slot.
    ///      This gives us a maximum of 2**128 inline fields in each bucket.
    uint256 private constant STORAGE_SLOT_EXP = 128;

    /// @dev Storage IDs for feature storage buckets.
    ///      WARNING: APPEND-ONLY.
    enum StorageId {
        Proxy,
        SimpleFunctionRegistry,
        Ownable,
        TokenSpender,
        TransformERC20,
        MetaTransactions,
        ReentrancyGuard,
        LiquidityProvider
    }

    /// @dev Get the storage slot given a storage ID. We assign unique, well-spaced
    ///     slots to storage bucket variables to ensure they do not overlap.
    ///     See: https://solidity.readthedocs.io/en/v0.6.6/assembly.html#access-to-external-variables-functions-and-libraries
    /// @param storageId An entry in `StorageId`
    /// @return slot The storage slot.
    function getStorageSlot(StorageId storageId)
        internal
        pure
        returns (uint256 slot)
    {
        // This should never overflow with a reasonable `STORAGE_SLOT_EXP`
        // because Solidity will do a range check on `storageId` during the cast.
        return (uint256(storageId) + 1) << STORAGE_SLOT_EXP;
    }
}
