mago_database/
change.rs

1use std::borrow::Cow;
2use std::sync::Arc;
3use std::sync::Mutex;
4
5use crate::error::DatabaseError;
6use crate::file::File;
7use crate::file::FileId;
8
9/// Represents a single, deferred database operation.
10///
11/// An instruction to be applied to a `Database` as part of a [`ChangeLog`].
12#[derive(Debug)]
13pub enum Change {
14    /// An instruction to add a new file.
15    Add(File),
16    /// An instruction to update an existing file, identified by its `FileId`.
17    Update(FileId, Cow<'static, str>),
18    /// An instruction to delete an existing file, identified by its `FileId`.
19    Delete(FileId),
20}
21
22/// A thread-safe, cloneable transaction log for collecting database operations.
23///
24/// This struct acts as a "Unit of Work," allowing multiple threads to concurrently
25/// record operations without directly mutating the `Database`. The collected changes
26/// can then be applied later in a single batch operation. This pattern avoids lock
27/// contention on the main database during processing.
28#[derive(Clone, Debug)]
29pub struct ChangeLog {
30    pub(crate) changes: Arc<Mutex<Vec<Change>>>,
31}
32
33impl Default for ChangeLog {
34    fn default() -> Self {
35        Self::new()
36    }
37}
38
39impl ChangeLog {
40    /// Creates a new, empty `ChangeLog`.
41    pub fn new() -> Self {
42        Self { changes: Arc::new(Mutex::new(Vec::new())) }
43    }
44
45    /// Records a request to add a new file.
46    ///
47    /// # Errors
48    ///
49    /// Returns a `DatabaseError::PoisonedLogMutex` if another thread panicked
50    /// while holding the lock, leaving the change log in an unusable state.
51    pub fn add(&self, file: File) -> Result<(), DatabaseError> {
52        self.changes.lock().map_err(|_| DatabaseError::PoisonedLogMutex)?.push(Change::Add(file));
53        Ok(())
54    }
55
56    /// Records a request to update an existing file's content by its `FileId`.
57    ///
58    /// # Errors
59    ///
60    /// Returns a `DatabaseError::PoisonedLogMutex` if another thread panicked
61    /// while holding the lock, leaving the change log in an unusable state.
62    pub fn update(&self, id: FileId, new_contents: Cow<'static, str>) -> Result<(), DatabaseError> {
63        self.changes.lock().map_err(|_| DatabaseError::PoisonedLogMutex)?.push(Change::Update(id, new_contents));
64        Ok(())
65    }
66
67    /// Records a request to delete a file by its `FileId`.
68    ///
69    /// # Errors
70    ///
71    /// Returns a `DatabaseError::PoisonedLogMutex` if another thread panicked
72    /// while holding the lock, leaving the change log in an unusable state.
73    pub fn delete(&self, id: FileId) -> Result<(), DatabaseError> {
74        self.changes.lock().map_err(|_| DatabaseError::PoisonedLogMutex)?.push(Change::Delete(id));
75        Ok(())
76    }
77
78    /// Consumes the change log and returns the vector of collected changes.
79    ///
80    /// This operation safely unwraps the underlying list of changes. It will
81    /// only succeed if called on the last remaining reference to the change log,
82    /// which guarantees that no other threads can be modifying the list.
83    ///
84    /// # Errors
85    ///
86    /// - `DatabaseError::ChangeLogInUse`: Returned if other `Arc` references to this change log still exist.
87    /// - `DatabaseError::PoisonedLogMutex`: Returned if the internal lock was poisoned because another thread panicked while holding it.
88    pub fn into_inner(self) -> Result<Vec<Change>, DatabaseError> {
89        match Arc::try_unwrap(self.changes) {
90            Ok(mutex) => mutex.into_inner().map_err(|_| DatabaseError::PoisonedLogMutex),
91            Err(_) => Err(DatabaseError::ChangeLogInUse),
92        }
93    }
94}
mago_database/change.rs

mago_database/
change.rs
