//! This example shows that you can use egui in parallel from multiple threads.

#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release

use std::sync::mpsc;
use std::thread::JoinHandle;

use eframe::egui;

fn main() -> Result<(), eframe::Error> {
    let options = eframe::NativeOptions {
        initial_window_size: Some(egui::vec2(1024.0, 768.0)),
        ..Default::default()
    };
    eframe::run_native(
        "My parallel egui App",
        options,
        Box::new(|_cc| Box::new(MyApp::new())),
    )
}

/// State per thread.
struct ThreadState {
    thread_nr: usize,
    title: String,
    name: String,
    age: u32,
}

impl ThreadState {
    fn new(thread_nr: usize) -> Self {
        let title = format!("Background thread {thread_nr}");
        Self {
            thread_nr,
            title,
            name: "Arthur".into(),
            age: 12 + thread_nr as u32 * 10,
        }
    }

    fn show(&mut self, ctx: &egui::Context) {
        let pos = egui::pos2(16.0, 128.0 * (self.thread_nr as f32 + 1.0));
        egui::Window::new(&self.title)
            .default_pos(pos)
            .show(ctx, |ui| {
                ui.horizontal(|ui| {
                    ui.label("Your name: ");
                    ui.text_edit_singleline(&mut self.name);
                });
                ui.add(egui::Slider::new(&mut self.age, 0..=120).text("age"));
                if ui.button("Click each year").clicked() {
                    self.age += 1;
                }
                ui.label(format!("Hello '{}', age {}", self.name, self.age));
            });
    }
}

fn new_worker(
    thread_nr: usize,
    on_done_tx: mpsc::SyncSender<()>,
) -> (JoinHandle<()>, mpsc::SyncSender<egui::Context>) {
    let (show_tx, show_rc) = mpsc::sync_channel(0);
    let handle = std::thread::Builder::new()
        .name(format!("EguiPanelWorker {}", thread_nr))
        .spawn(move || {
            let mut state = ThreadState::new(thread_nr);
            while let Ok(ctx) = show_rc.recv() {
                state.show(&ctx);
                let _ = on_done_tx.send(());
            }
        })
        .expect("failed to spawn thread");
    (handle, show_tx)
}

struct MyApp {
    threads: Vec<(JoinHandle<()>, mpsc::SyncSender<egui::Context>)>,
    on_done_tx: mpsc::SyncSender<()>,
    on_done_rc: mpsc::Receiver<()>,
}

impl MyApp {
    fn new() -> Self {
        let threads = Vec::with_capacity(3);
        let (on_done_tx, on_done_rc) = mpsc::sync_channel(0);

        let mut slf = Self {
            threads,
            on_done_tx,
            on_done_rc,
        };

        slf.spawn_thread();
        slf.spawn_thread();

        slf
    }

    fn spawn_thread(&mut self) {
        let thread_nr = self.threads.len();
        self.threads
            .push(new_worker(thread_nr, self.on_done_tx.clone()));
    }
}

impl std::ops::Drop for MyApp {
    fn drop(&mut self) {
        for (handle, show_tx) in self.threads.drain(..) {
            std::mem::drop(show_tx);
            handle.join().unwrap();
        }
    }
}

impl eframe::App for MyApp {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::Window::new("Main thread").show(ctx, |ui| {
            if ui.button("Spawn another thread").clicked() {
                self.spawn_thread();
            }
        });

        for (_handle, show_tx) in &self.threads {
            let _ = show_tx.send(ctx.clone());
        }

        for _ in 0..self.threads.len() {
            let _ = self.on_done_rc.recv();
        }
    }
}