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// Copyright (c) 2024-present, fjall-rs
// This source code is licensed under both the Apache 2.0 and MIT License
// (found in the LICENSE-* files in the repository)
use crate::{Guard, Iter, Keyspace};
use lsm_tree::UserValue;
use std::ops::RangeBounds;
/// Readable snapshot
///
/// Can be used to pass a write transaction into a function that expects a snapshot.
pub trait Readable {
/// Retrieves an item from the snapshot.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "my_value")?;
///
/// let snapshot = db.snapshot();
/// let item = snapshot.get(&tree, "a")?;
/// assert_eq!(Some("my_value".as_bytes().into()), item);
///
/// tree.insert("b", "my_updated_value")?;
///
/// // Repeatable read
/// let item = snapshot.get(&tree, "a")?;
/// assert_eq!(Some("my_value".as_bytes().into()), item);
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
///
/// # Errors
///
/// Will return `Err` if an IO error occurs.
fn get<K: AsRef<[u8]>>(
&self,
keyspace: impl AsRef<Keyspace>,
key: K,
) -> crate::Result<Option<UserValue>>;
/// Returns `true` if the snapshot contains the specified key.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "my_value")?;
///
/// let snapshot = db.snapshot();
/// assert!(snapshot.contains_key(&tree, "a")?);
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
///
/// # Errors
///
/// Will return `Err` if an IO error occurs.
fn contains_key<K: AsRef<[u8]>>(
&self,
keyspace: impl AsRef<Keyspace>,
key: K,
) -> crate::Result<bool>;
/// Returns the first key-value pair in the snapshot.
/// The key in this pair is the minimum key in the snapshot.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("1", "abc")?;
/// tree.insert("3", "abc")?;
/// tree.insert("5", "abc")?;
///
/// let key = db.snapshot().first_key_value(&tree).expect("item should exist").key()?;
/// assert_eq!(&*key, "1".as_bytes());
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
fn first_key_value(&self, keyspace: impl AsRef<Keyspace>) -> Option<Guard>;
/// Returns the last key-value pair in the snapshot.
/// The key in this pair is the maximum key in the snapshot.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("1", "abc")?;
/// tree.insert("3", "abc")?;
/// tree.insert("5", "abc")?;
///
/// let key = db.snapshot().last_key_value(&tree).expect("item should exist").key()?;
/// assert_eq!(&*key, "5".as_bytes());
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
fn last_key_value(&self, keyspace: impl AsRef<Keyspace>) -> Option<Guard>;
/// Retrieves the size of an item from the snapshot.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "my_value")?;
///
/// let snapshot = db.snapshot();
/// let item = snapshot.size_of(&tree, "a")?.unwrap_or_default();
/// assert_eq!("my_value".len() as u32, item);
///
/// tree.insert("b", "my_updated_value")?;
///
/// // Repeatable read
/// let item = snapshot.size_of(&tree, "a")?.unwrap_or_default();
/// assert_eq!("my_value".len() as u32, item);
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
///
/// # Errors
///
/// Will return `Err` if an IO error occurs.
fn size_of<K: AsRef<[u8]>>(
&self,
keyspace: impl AsRef<Keyspace>,
key: K,
) -> crate::Result<Option<u32>>;
/// Returns `true` if the parkeyspacetition is empty.
///
/// This operation has O(log N) complexity.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// assert!(db.snapshot().is_empty(&tree)?);
///
/// tree.insert("a", "abc")?;
/// assert!(!db.snapshot().is_empty(&tree)?);
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
///
/// # Errors
///
/// Will return `Err` if an IO error occurs.
fn is_empty(&self, keyspace: impl AsRef<Keyspace>) -> crate::Result<bool> {
Ok(self
.first_key_value(keyspace)
.map(Guard::key)
.transpose()?
.is_none())
}
/// Iterates over the snapshot.
///
/// Avoid using this function, or limit it as otherwise it may scan a lot of items.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "abc")?;
/// tree.insert("f", "abc")?;
/// tree.insert("g", "abc")?;
///
/// assert_eq!(3, db.snapshot().iter(&tree).count());
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
fn iter(&self, keyspace: impl AsRef<Keyspace>) -> Iter;
/// Scans the entire keyspace, returning the number of items.
///
/// # Caution
///
/// This operation scans the entire keyspace: O(n) complexity!
///
/// Never, under any circumstances, use .`len()` == 0 to check
/// if the keyspace is empty, use [`Readable::is_empty`] instead.
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "my_value")?;
/// tree.insert("b", "my_value2")?;
///
/// let snapshot = db.snapshot();
/// assert_eq!(2, snapshot.len(&tree)?);
///
/// tree.insert("c", "my_value3")?;
///
/// // Repeatable read
/// assert_eq!(2, snapshot.len(&tree)?);
///
/// // Start new snapshot
/// let snapshot = db.snapshot();
/// assert_eq!(3, snapshot.len(&tree)?);
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
///
/// # Errors
///
/// Will return `Err` if an IO error occurs.
fn len(&self, keyspace: impl AsRef<Keyspace>) -> crate::Result<usize> {
let mut count = 0;
for guard in self.iter(keyspace) {
let _ = guard.key()?;
count += 1;
}
Ok(count)
}
/// Iterates over a range of the snapshot.
///
/// Avoid using full or unbounded ranges as they may scan a lot of items (unless limited).
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "abc")?;
/// tree.insert("f", "abc")?;
/// tree.insert("g", "abc")?;
///
/// assert_eq!(2, db.snapshot().range(&tree, "a"..="f").count());
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
fn range<K: AsRef<[u8]>, R: RangeBounds<K>>(
&self,
keyspace: impl AsRef<Keyspace>,
range: R,
) -> Iter;
/// Iterates over a prefixed set of the snapshot.
///
/// Avoid using an empty prefix as it may scan a lot of items (unless limited).
///
/// # Examples
///
/// ```
/// # use fjall::{Database, KeyspaceCreateOptions, Readable};
/// #
/// # let folder = tempfile::tempdir()?;
/// # let db = Database::builder(folder).open()?;
/// # let tree = db.keyspace("default", KeyspaceCreateOptions::default)?;
/// tree.insert("a", "abc")?;
/// tree.insert("ab", "abc")?;
/// tree.insert("abc", "abc")?;
///
/// assert_eq!(2, db.snapshot().prefix(&tree, "ab").count());
/// #
/// # Ok::<(), fjall::Error>(())
/// ```
fn prefix<K: AsRef<[u8]>>(&self, keyspace: impl AsRef<Keyspace>, prefix: K) -> Iter;
}