use std::time::Instant;
use glium::Display;
use glium::glutin::surface::WindowSurface;
use imgui::{Context as ImguiContext};
use imgui_winit_support::{HiDpiMode, WinitPlatform};
use imgui_glium_renderer::Renderer as ImguiGliumRenderer;
use winit::window::Window;
use winit::event::Event;
use glium::Frame;
use crate::RenderingSystem;
use crate::system::RenderingContext;

pub struct ImguiBridge {
    imgui: ImguiContext,
    platform: WinitPlatform,
    renderer: ImguiGliumRenderer,
    last_frame: Instant,
    rendered_this_frame: bool,
}

impl RenderingSystem for ImguiBridge {
    fn handle_event(&mut self, window: &mut Window, event: Event<()>) {
        self.platform.handle_event(self.imgui.io_mut(), window, &event);
    }

    fn prepare_frame(&mut self, window: &mut Window) {
        self.rendered_this_frame = false;
        let now = Instant::now();
        self.imgui.io_mut().update_delta_time(now - self.last_frame);
        self.last_frame = now;
        self.platform
            .prepare_frame(self.imgui.io_mut(), window)
            .expect("Failed to prepare frame");
    }

    fn render(&mut self, ctx: &mut RenderingContext) {
        if self.rendered_this_frame { return; }
        self.rendered_this_frame = true;

        let ui = self.imgui.frame();
        ctx.debug_ui_buffer.borrow().write_buffer(&ui);

        self.platform.prepare_render(&ui, ctx.window);
        let draw_data = self.imgui.render();
        if draw_data.total_vtx_count == 0 && draw_data.total_idx_count == 0 {
            return;
        }

        self.renderer.render(ctx.target, draw_data).expect("imgui rendering failed");
    }

    fn initialize(display: &Display<WindowSurface>, window: &Window) -> Self {
        let mut imgui = ImguiContext::create();
        imgui.set_ini_filename(None);
        let mut platform = WinitPlatform::new(&mut imgui);
        platform.attach_window(imgui.io_mut(), window, HiDpiMode::Default);
        imgui.fonts().add_font(&[imgui::FontSource::DefaultFontData { config: None }]);
        let renderer = ImguiGliumRenderer::new(&mut imgui, display).unwrap();

        Self {
            imgui,
            platform,
            renderer,
            last_frame: Instant::now(),
            rendered_this_frame: false,
        }
    }
}