/// @dev Reads a block hash up to 8 191 blocks ago after the Pectra fork.
///      Falls back to the BLOCKHASH opcode for <256 blocks.
library BlockhashHistory {
    address constant _HISTORY_ADDR = 0x0000F90827F1C53a10Cb7A02335B175320002935;
    uint256 constant _WINDOW = 8191;

    /// @notice Returns the hash of block `n` or reverts if too old / future.
    function hashOf(uint256 n) internal view returns (bytes32 h) {
        uint256 current = block.number;
        if (n >= current) revert("future block");
        unchecked {
            if (current - n <= 256) {
                return blockhash(n); // cheap path
            }
            if (current - n > _WINDOW) revert("too old");
        }
        bytes memory input = abi.encodePacked(bytes32(n));
        // solhint-disable-next-line no-inline-assembly
        assembly {
            let success := staticcall(gas(), _HISTORY_ADDR, add(input, 32), 32, 0, 32)
            if iszero(success) { revert(0, 0) }
            h := mload(0)
        }
    }
}