agg_gui/
persistence.rs

1//! Small persistence helpers shared across platform harnesses.
2//!
3//! Both the native (disk) and wasm (localStorage) harnesses follow the
4//! same auto-save policy: each frame, serialize the current session
5//! state, compare to the last-persisted blob, and write only when they
6//! differ AND no mouse button is currently held.  The "no mouse held"
7//! guard keeps us from hammering the backend while the user is
8//! mid-drag / mid-resize.
9//!
10//! This module owns the diff-and-save policy so hosts don't reimplement
11//! it.  Callers plug in their own serializer and persist backend via
12//! closures — [`AutoSave::tick`] takes care of the rest.
13
14/// Tracks the last-persisted serialized blob so the platform harness
15/// can avoid writing unchanged state every frame.
16///
17/// # Example (pseudo-Rust)
18/// ```ignore
19/// let mut auto_save = AutoSave::new();
20/// loop {
21///     paint_frame();
22///     auto_save.tick(
23///         mouse_buttons_held == 0,
24///         || state.serialize(),
25///         |blob| std::fs::write("state.json", blob).ok(),
26///     );
27/// }
28/// ```
29#[derive(Default)]
30pub struct AutoSave {
31    last_saved: String,
32}
33
34impl AutoSave {
35    /// Create an empty auto-save tracker.  First `tick` call will always
36    /// persist (because the last-saved blob is empty).
37    pub const fn new() -> Self {
38        Self { last_saved: String::new() }
39    }
40
41    /// Consider persisting the current state.
42    ///
43    /// `idle` — guard that must be `true` for the save to happen.
44    /// Typically `mouse_buttons_held == 0`; callers can layer other
45    /// conditions (e.g. "no in-flight drag").
46    ///
47    /// `serialize_now` — closure that produces the current serialized
48    /// blob.  Only invoked when `idle` is `true`.
49    ///
50    /// `persist` — closure that writes the blob to the platform backend
51    /// (file / localStorage / network).  Only invoked when the blob
52    /// differs from the last persisted version.
53    ///
54    /// Returns `true` iff the persist closure was called.
55    pub fn tick<S, P>(
56        &mut self,
57        idle:          bool,
58        serialize_now: S,
59        persist:       P,
60    ) -> bool
61    where
62        S: FnOnce() -> String,
63        P: FnOnce(&str),
64    {
65        if !idle { return false; }
66        let blob = serialize_now();
67        if blob == self.last_saved { return false; }
68        persist(&blob);
69        self.last_saved = blob;
70        true
71    }
72
73    /// Seed the tracker with a blob that's already on disk (on startup).
74    /// Prevents the first `tick` from writing the same content back to
75    /// the backend unnecessarily.
76    pub fn seed(&mut self, last_saved: String) {
77        self.last_saved = last_saved;
78    }
79}
agg_gui/persistence.rs

agg_gui/
persistence.rs
