You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: channel.rs
    path of file: ./repos/hash/apps/hash-graph/libs/graph/src/snapshot/owner
    
    the code of the file until where you have to start completion: use std::{
    pin::Pin,
    result::Result as StdResult,
    task::{ready, Context, Poll},
};

use authorization::schema::AccountGroupRelationAndSubject;
use error_stack::{Report, ResultExt};
use futures::{
    channel::mpsc::{self, Sender},
    stream::{select_all, BoxStream, SelectAll},
    Sink, SinkExt, Stream, StreamExt,
};
use graph_types::account::AccountGroupId;

use crate::snapshot::{
    owner::{AccountGroupRow, AccountRow, AccountRowBatch, Owner},
    SnapshotRestoreError,
};

/// A sink to insert [`AccountId`]s and [`AccountGroupId`]s.
///
/// An `AccountSender` with the corresponding [`OwnerReceiver`] are created using the [`channel`]
/// function.
///
/// [`AccountId`]: graph_types::account::AccountId
/// [`AccountGroupId`]: graph_types::account::Accoun
    
    fn start_send(mut self: Pin<&mut Self>, item: Owner) -> StdResult<(), Self::Error> {
        match item {
            Owner::Account(account) => self
                .account_id
                .start_send_unpin(AccountRow {
                    account_id: account.id,
                })
                .change_context(SnapshotRestoreError::Read)
                .attach_printable("could not send account"),
            Owner::AccountGroup(account_group) => {
                self.account_group_id
                    .start_send_unpin(AccountGroupRow {
                        account_group_id: account_group.id,
                    })
                    .change_context(SnapshotRestoreError::Read)
                    .attach_printable("could not send account group")?;
                for relation in account_group.relations {
                    self.account_group_relations
                        .start_send_unpin((account_group.id, relation))
                        .change_context(SnapshotRestoreError::Read)
                        .attach_printable("could not send account group relation")?;
                }
                Ok(())
            }
        }
    }