diene-engine-core 0.1.0

//! Application lifecycle and frame coordination.

use std::error::Error as StdError;

use common::{
    logging::macros::{debug, error, info},
    timer::Stopwatch,
};
use engine_renderer_api::{BoxedRenderer, RenderExtent, RendererFactory};
use thiserror::Error;
use winit::{
    application::ApplicationHandler,
    event::WindowEvent,
    event_loop::{ActiveEventLoop, EventLoop},
    window::WindowId,
};

mod windowing;

use self::windowing::Window;
pub use self::windowing::WindowError;

/// Errors returned by application host lifecycle operations.
#[derive(Debug, Error)]
pub enum ApplicationHostError<E>
where
    E: StdError + Send + Sync + 'static,
{
    /// Renderer operation failed.
    #[error("renderer failed: {0}")]
    Renderer(#[source] E),

    /// Window or event loop operation failed.
    #[error("window failed: {0}")]
    Window(#[from] WindowError),

    /// Application host configuration is invalid.
    #[error("application host build failed: {0}")]
    Build(#[from] ApplicationHostBuildError),
}

/// Errors returned while building an [`ApplicationHost`].
#[derive(Debug, Error)]
#[non_exhaustive]
pub enum ApplicationHostBuildError {
    /// Application name cannot be empty or whitespace-only.
    #[error("application name cannot be empty")]
    EmptyName,
}

/// Drives the native window, event loop, and renderer for an application.
#[derive(Debug)]
pub struct ApplicationHost<F>
where
    F: RendererFactory,
{
    name: String,
    renderer_factory: F,
    renderer: Option<BoxedRenderer<F::Error>>,
    window: Option<Window>,
    error: Option<ApplicationHostError<F::Error>>,

    #[allow(dead_code)]
    stopwatch: common::timer::Stopwatch,
}

/// Configures an [`ApplicationHost`].
#[derive(Debug)]
pub struct ApplicationHostBuilder<F>
where
    F: RendererFactory,
{
    name: Option<String>,
    renderer_factory: F,
}

impl<F> ApplicationHostBuilder<F>
where
    F: RendererFactory,
{
    /// Sets the human-readable application name.
    #[must_use]
    pub fn with_name(mut self, name: impl Into<String>) -> Self {
        self.name = Some(name.into());
        self
    }

    /// Builds the application host.
    pub fn build(self) -> Result<ApplicationHost<F>, ApplicationHostError<F::Error>> {
        let name = self.name.unwrap_or_else(|| "Untitled Application".to_owned());

        if name.trim().is_empty() {
            return Err(ApplicationHostBuildError::EmptyName.into());
        }

        debug!("[{}] building application host", name);

        let timer = Stopwatch::new();

        Ok(ApplicationHost {
            name,
            renderer_factory: self.renderer_factory,
            renderer: None,
            window: None,
            error: None,
            stopwatch: timer,
        })
    }
}

impl<F> ApplicationHost<F>
where
    F: RendererFactory,
{
    /// Creates a builder for configuring an [`ApplicationHost`].
    pub fn builder(renderer_factory: F) -> ApplicationHostBuilder<F> {
        ApplicationHostBuilder { name: None, renderer_factory }
    }

    /// Returns the human-readable application name.
    pub fn name(&self) -> &str {
        &self.name
    }

    /// Runs the application until the event loop exits.
    pub fn run(mut self) -> Result<(), ApplicationHostError<F::Error>> {
        info!("[{}] running application", self.name);

        let event_loop = EventLoop::new().map_err(WindowError::from)?;

        event_loop.run_app(&mut self).map_err(WindowError::from)?;

        if let Some(error) = self.error.take() {
            error!("[{}] application event loop exited with error: {}", self.name, error);
            return Err(error);
        }

        info!("[{}] application event loop exited gracefully", self.name);

        Ok(())
    }

    fn fail(&mut self, event_loop: &ActiveEventLoop, error: ApplicationHostError<F::Error>) {
        self.error = Some(error);
        event_loop.exit();
    }

    fn is_main_window(&self, window_id: WindowId) -> bool {
        self.window.as_ref().is_some_and(|window| window.id() == window_id)
    }

    fn render_frame(&mut self, event_loop: &ActiveEventLoop) {
        // WARN: This is only done for debug purposes. Be sure to remove it later!
        if self.stopwatch.is_stopped() {
            self.stopwatch.start();
        }

        let Some(renderer) = self.renderer.as_mut() else {
            return;
        };

        if let Err(error) = renderer.prepare_frame().and_then(|()| renderer.render()) {
            self.fail(event_loop, ApplicationHostError::Renderer(error));
            return;
        }

        if let Some(window) = &self.window {
            window.request_redraw();
        }

        let elapsed = self.stopwatch.elapsed().as_secs_f32();

        if elapsed > 2.0 {
            info!("{:.0} seconds elapsed, exitting gracefully...", elapsed);
            event_loop.exit();
        }
    }

    fn resize_renderer(&mut self, event_loop: &ActiveEventLoop, size: winit::dpi::PhysicalSize<u32>) {
        let Some(renderer) = self.renderer.as_mut() else {
            return;
        };

        let extent = RenderExtent::new(size.width, size.height);

        if let Err(error) = renderer.resize(extent) {
            self.fail(event_loop, ApplicationHostError::Renderer(error));
        }
    }
}

impl<F> ApplicationHandler for ApplicationHost<F>
where
    F: RendererFactory,
{
    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        if self.window.is_some() {
            return;
        }

        let window = match Window::create(event_loop, &self.name) {
            Ok(window) => {
                info!("[{}] created application window (Id: {:?})", self.name, window.id());
                window
            }
            Err(error) => {
                self.fail(event_loop, ApplicationHostError::Window(error));
                return;
            }
        };

        let renderer = match self.renderer_factory.create_renderer(&window) {
            Ok(renderer) => {
                info!("[{}] created renderer", self.name);
                renderer
            }
            Err(error) => {
                self.fail(event_loop, ApplicationHostError::Renderer(error));
                return;
            }
        };

        window.request_redraw();

        self.renderer = Some(renderer);
        self.window = Some(window);
    }

    fn window_event(&mut self, event_loop: &ActiveEventLoop, window_id: WindowId, event: WindowEvent) {
        if !self.is_main_window(window_id) {
            return;
        }

        match event {
            WindowEvent::CloseRequested => {
                info!("[{}] close requested for window {:?}", self.name, window_id);
                event_loop.exit();
            }
            WindowEvent::Resized(size) => {
                self.resize_renderer(event_loop, size);
            }
            WindowEvent::RedrawRequested => {
                self.render_frame(event_loop);
            }
            _ => {}
        }
    }
}