//! The viewer on the GPU compositor (egui_kittest with wgpu): frames composited on the GPU match
//! the CPU viewer. Skips without a GPU adapter (CI). Set `EC_SNAPSHOT_DIR` to keep PNGs.

use effectcraft_engine::Session;
use effectcraft_ui_egui::EffectcraftApp;
use egui_kittest::Harness;
use serde_json::json;

fn settle(h: &mut Harness<'_, EffectcraftApp>) {
    for _ in 0..600 {
        h.step();
        if h.state().frames.inflight() == 0 && h.state().frames.last_ms.lock().map(|v| *v > 0.0).unwrap_or(false) {
            break;
        }
        std::thread::sleep(std::time::Duration::from_millis(20));
    }
    for _ in 0..4 {
        h.step();
    }
}

/// egui_kittest's wgpu setup on the adapter the headless compositor picked (`name (Backend)`),
/// like the desktop app's window. Left alone, egui_kittest prefers a CPU adapter, which on
/// Windows is WARP on DirectX 12, where FXC fails to compile the compositor's kernels: the
/// viewer would stay on the CPU and the comparison would never run.
fn same_adapter(name: String) -> eframe::egui_wgpu::WgpuSetup {
    let mut setup = egui_kittest::wgpu::default_wgpu_setup();
    if let eframe::egui_wgpu::WgpuSetup::CreateNew(c) = &mut setup {
        let fallback = c.native_adapter_selector.take();
        c.native_adapter_selector = Some(std::sync::Arc::new(move |adapters, surface| {
            let named = |a: &&eframe::wgpu::Adapter| format!("{} ({:?})", a.get_info().name, a.get_info().backend) == name;
            match (adapters.iter().find(named), &fallback) {
                (Some(a), _) => Ok(a.clone()),
                (None, Some(f)) => f(adapters, surface),
                (None, None) => adapters.first().cloned().ok_or_else(|| "No adapter found".to_owned()),
            }
        }));
    }
    setup
}

#[test]
fn viewer_draws_gpu_frames_that_match_the_cpu() {
    let Some(probe) = effectcraft_gpu::Gpu::headless() else {
        eprintln!("no GPU adapter: skipping");
        return;
    };
    let adapter = effectcraft_engine::render::Accelerator::name(&probe);
    eprintln!("headless compositor adapter: {adapter}");
    // egui-wgpu creates its GL device with WebGL2's limits, which the compositor declines.
    let gl = adapter.ends_with("(Gl)");
    drop(probe);
    let mut s = Session::default();
    s.execute("file.openDemoProject", json!({})).unwrap();
    s.execute("time.set", json!({"time": 2.0})).unwrap();
    let mut h = Harness::builder()
        .with_size(egui::vec2(1400.0, 900.0))
        .with_pixels_per_point(1.0)
        .wgpu_setup(same_adapter(adapter))
        .build_eframe(|_| EffectcraftApp::new(s));
    settle(&mut h);
    if gl && h.state().gpu_adapter().is_none() {
        eprintln!("egui-wgpu's GL device has WebGL2 limits: the viewer stays on the CPU, skipping");
        return;
    }
    assert!(h.state().gpu_adapter().is_some(), "GPU compositor on egui-wgpu's device");
    eprintln!("viewer compositor adapter: {:?}", h.state().gpu_adapter());
    let gpu_px = h.state_mut().viewer_pixels().expect("read back the GPU frame");
    let gpu_shot = h.render().expect("render");
    // Mercury Software Only: the same frame from the CPU.
    h.state_mut().session.execute("render.backend", json!({"backend": "cpu"})).unwrap();
    settle(&mut h);
    let cpu_px = h.state_mut().viewer_pixels().expect("CPU frame");
    let cpu_shot = h.render().expect("render");
    assert_eq!(gpu_px.size, cpu_px.size);
    let mut worst = 0i32;
    let mut over = 0usize;
    for (a, b) in gpu_px.pixels.iter().zip(&cpu_px.pixels) {
        let d = a.to_array().iter().zip(b.to_array()).map(|(x, y)| (*x as i32 - y as i32).abs()).max().unwrap_or(0);
        worst = worst.max(d);
        over += usize::from(d > 1);
    }
    assert!(over * 1000 <= gpu_px.pixels.len() * 3 && worst <= 4, "viewer GPU vs CPU: {over} pixels > 1/255, worst {worst}/255");
    if let Ok(d) = std::env::var("EC_SNAPSHOT_DIR") {
        gpu_shot.save(format!("{d}/ui_gpu_viewer.png")).unwrap();
        cpu_shot.save(format!("{d}/ui_cpu_viewer.png")).unwrap();
    }
}