//! This module defines backends for WebAssembly execution.
//!
//! Canary is designed to support multiple WebAssembly runtimes for different
//! purposes. Currently, [wasmtime](https://wasmtime.dev) is the only one
//! implemented, but in the future, [wasm3](https://github.com/wasm3/wasm3)
//! will also be provided.

use super::*;

pub mod wasmtime;

/// Creates the default WebAssembly backend.
///
/// Currently, only ever creates [wasmtime::WasmtimeBackend].
pub fn make_default_backend() -> anyhow::Result<Box<dyn Backend>> {
    let backend = wasmtime::WasmtimeBackend::new()?;
    Ok(Box::new(backend))
}

/// A WebAssembly runtime backend.
pub trait Backend {
    fn load_module(&self, module: &[u8]) -> anyhow::Result<Arc<dyn Instance>>;
}

/// An instance of a WebAssembly module.
///
/// All self parameters to this trait's functions are immutable, so the
/// implementation must provide interior mutability. This allows instances
/// to intelligently optimize the execution of their scripts, for example, by
/// allowing the execution of multiple ABI calls from multiple threads when
/// a script supports the WebAssembly multithreading extension.
pub trait Instance {
    /// Binds script data to a Canary panel.
    ///
    /// To "bind" a Canary panel to a Canary script, this function must be
    /// called. It passes the ID of a panel to the script, plus an
    /// initialization message, and the script returns an integer as
    /// userdata. All panel events will be identified to the script with this
    /// userdata as the first argument.
    ///
    /// The intended usecase for this userdata is to contain a pointer. A
    /// Canary script can allocate some high-level object in memory, and when
    /// a panel is bound, the script will return a pointer to that object as the
    /// userdata. Then, when the runtime calls back into the script, the
    /// userdata will be reinterpreted as a pointer and a method can be called
    /// on that object in memory.
    fn bind_panel(&self, panel: PanelId, msg: Vec<u8>) -> u32;

    fn update(&self, panel_ud: u32, dt: f32);

    fn draw(&self, panel_ud: u32) -> Vec<DrawCommand>;

    fn on_resize(&self, panel_ud: u32, new_size: Vec2);

    fn on_cursor_event(&self, panel_ud: u32, kind: CursorEventKind, at: Vec2);

    fn on_message(&self, panel_ud: u32, msg: Vec<u8>);
}