module Block {

  resource T {
    // Height of the current block
    height: u64,
  }

  // This can only be invoked by the Association address, and only a single time.
  // Currently, it is invoked in the genesis transaction
  public initialize() {
    // Only callable by the Association address
    assert(get_txn_sender() == 0xA550C18, 1);

    move_to_sender<T>(T { height: 0 });
    return;
  }

  // Set the metadata for the current block.
  // The runtime always runs this before executing the transactions in a block.
  // TODO: make this private, support other metadata
  public prologue(height: u64) acquires T {
    let height_ref: &mut u64;
    let old_height: u64;

    height_ref = &mut borrow_global_mut<T>(0xA550C18).height;
    old_height = *copy(height_ref);
    // ensure that height increases by 1
    if (move(height) == copy(old_height) + 1) {
        *move(height_ref) = move(old_height) + 1;
        return;
    } else {
        // TODO: standardize this error code
        abort(99);
    }
  }

  // Get the current block height
  public get_current_height(): u64 acquires T {
    return *&(borrow_global<T>(0xA550C18)).height;
  }

}