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use serde::Deserialize;
use serde::Serialize;
use tokio::io::AsyncRead;
use tokio::io::AsyncSeek;

use super::LogId;

// Everytime a snapshot is created, it is assigned with a globally unique id.
pub type SnapshotId = String;

/// The identity of a segment of a snapshot.
#[derive(Debug, Default, Clone, PartialOrd, PartialEq, Eq, Serialize, Deserialize)]
pub struct SnapshotSegmentId {
    pub id: SnapshotId,
    pub offset: u64,
}

#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
pub struct SnapshotMeta {
    // Log entries upto which this snapshot includes, inclusive.
    pub last_log_id: Option<LogId>,

    /// To identify a snapshot when transferring.
    /// Caveat: even when two snapshot is built with the same `last_log_id`, they still could be different in bytes.
    pub snapshot_id: SnapshotId,
}

/// The data associated with the current snapshot.
#[derive(Debug)]
pub struct Snapshot<S>
where S: AsyncRead + AsyncSeek + Send + Unpin + 'static
{
    /// metadata of a snapshot
    pub meta: SnapshotMeta,

    /// A read handle to the associated snapshot.
    pub snapshot: Box<S>,
}