mogwai 0.7.4

//! # Synchronization primitives
//!
//! This module provides synchronization primitives for managing shared state
//! across different parts of an application. It includes the `Shared` type,
//! which is a thread-safe wrapper around data, allowing for concurrent access
//! and modification.
//!
//! ## Primitives
//!
//! - **[`Global`]**: A utility for managing global state, such as the window and document objects.
//!
//! - **[`Shared`]**: A type that wraps data in a reference-counted pointer, providing
//!   safe concurrent access. On non-wasm32 targets, it uses `Arc<RwLock<T>>` for
//!   thread safety. On wasm32 targets, it uses `Rc<RefCell<T>>` due to the single-threaded
//!   nature of WebAssembly, which simplifies the concurrency model.
//!
//! Mogwai's event setup is geared towards managing UI in short lived steps, which allows for
//! mutability, so for most cases [`Shared`] shouldn't be necessary.
//! Sometimes this is unavoidable though, or prefered even, and so this module exists.

use std::{
    borrow::Cow,
    ops::{Deref, DerefMut},
};

use crate::Str;

/// A global value.
pub struct Global<T> {
    #[cfg(target_arch = "wasm32")]
    data: std::mem::ManuallyDrop<std::cell::LazyCell<T>>,
    #[cfg(not(target_arch = "wasm32"))]
    data: std::sync::LazyLock<T>,
}

impl<T> Global<T> {
    /// Create a new global value.
    pub const fn new(create_fn: fn() -> T) -> Self {
        #[cfg(target_arch = "wasm32")]
        {
            Global {
                data: std::mem::ManuallyDrop::new(std::cell::LazyCell::new(create_fn)),
            }
        }
        #[cfg(not(target_arch = "wasm32"))]
        {
            Global {
                data: std::sync::LazyLock::new(create_fn),
            }
        }
    }
}

unsafe impl<T> Send for Global<T> {}
unsafe impl<T> Sync for Global<T> {}

impl<T> Deref for Global<T> {
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

/// A "shared" value.
///
/// Equivalent to `Arc<RwLock<T>>`.
#[derive(Default)]
pub struct Shared<T> {
    #[cfg(not(target_arch = "wasm32"))]
    inner: std::sync::Arc<std::sync::RwLock<T>>,
    #[cfg(target_arch = "wasm32")]
    inner: std::rc::Rc<std::cell::RefCell<T>>,
}

impl<T: PartialEq> PartialEq for Shared<T> {
    #[cfg(not(target_arch = "wasm32"))]
    fn eq(&self, other: &Self) -> bool {
        self.inner.read().unwrap().eq(&other.inner.read().unwrap())
    }
    #[cfg(target_arch = "wasm32")]
    fn eq(&self, other: &Self) -> bool {
        self.inner.borrow().eq(&other.inner.borrow())
    }
}

impl<T> Clone for Shared<T> {
    fn clone(&self) -> Self {
        Self {
            inner: self.inner.clone(),
        }
    }
}

impl<T: 'static> From<T> for Shared<T> {
    fn from(value: T) -> Self {
        Self::new(value)
    }
}

impl<T> Shared<T> {
    /// Create a new shared `T`.
    pub fn new(value: T) -> Self {
        Self {
            #[cfg(not(target_arch = "wasm32"))]
            inner: std::sync::Arc::new(std::sync::RwLock::new(value)),
            #[cfg(target_arch = "wasm32")]
            inner: std::rc::Rc::new(std::cell::RefCell::new(value)),
        }
    }

    /// Get a reference to the inner `T`.
    pub fn get(&self) -> impl Deref<Target = T> {
        #[cfg(not(target_arch = "wasm32"))]
        {
            self.inner.read().unwrap()
        }
        #[cfg(target_arch = "wasm32")]
        {
            self.inner.borrow()
        }
    }

    /// Get a mutable reference to the inner `T`.
    pub fn get_mut(&self) -> impl DerefMut<Target = T> {
        #[cfg(not(target_arch = "wasm32"))]
        {
            self.inner.write().unwrap()
        }
        #[cfg(target_arch = "wasm32")]
        {
            self.inner.borrow_mut()
        }
    }

    /// Set the inner `T`.
    ///
    /// Returns the previous value.
    pub fn set(&self, value: T) -> T {
        std::mem::replace(self.get_mut().deref_mut(), value)
    }
}

impl Shared<Str> {
    pub fn from_string(s: impl AsRef<str>) -> Self {
        let cow = Cow::from(s.as_ref().to_owned());
        Shared::from(cow)
    }
}