// SPDX-License-Identifier: LGPL-2.1-only
// Copyright (C) 2026 Liberux Labs, S. L. <info@liberux.net>

use std::cell::{ Cell, RefCell };
use std::collections::HashMap;
use std::marker::PhantomData;
use std::sync::Arc;

use web_sys::{ Element, HtmlElement, OffscreenCanvas, WebGl2RenderingContext };

use crate::app::{ App, SubsurfaceId };
use crate::event_loop::SurfaceFocus;
use crate::render::Canvas;

use super::desktop::Connection;
use super::run::Listener;
use super::subsurfaces::WebSubsurface;

/// What the runtime's requests go through in a browser: the page's desktop when it has one, the one WebGL context every surface draws through, and what the loop must report back to the runtime.
pub( crate ) struct WebPlatform<A: App>
{
	/// forge/web, when the page has it; the app then has no canvas of its own over the page.
	pub desktop:       Option<Connection>,
	/// Where every surface is painted on the GPU before its frame moves to the surface's own canvas, so the app holds one WebGL context however many surfaces it has. `None` without WebGL2: each surface is then drawn in software.
	pub offscreen:     Option<OffscreenCanvas>,
	pub webgl:         Option<WebGl2RenderingContext>,
	/// `webgl` as the GPU canvas draws through it, wrapped anew when the context is restored.
	pub gl:            Option<Arc<glow::Context>>,
	/// The browser took the WebGL context away; nothing is drawn until it gives it back.
	pub context_lost:  bool,
	/// Where the cursor's shape is set: the element taking the input of the surface the pointer last entered, since CSS gives each element its own.
	pub cursor_target: HtmlElement,
	/// The cursor's shape as CSS names it, for the next surface the pointer enters.
	pub cursor:        &'static str,
	/// A hidden element padded by `env( safe-area-inset-* )`, which tells what a phone's notch and bars cover; only on ltk's own canvas over the page.
	pub inset_probe:   Option<Element>,
	/// The surfaces a frame was presented or asked for; the loop reports them at the next animation frame.
	pub frame_due:     RefCell<Vec<SurfaceFocus>>,
	/// The id the next overlay's or subsurface's surface goes by in forge/web's protocol.
	pub next_surface:  Cell<u32>,
	/// The subsurfaces of [`App::subsurfaces`], each a surface of the desktop.
	pub subsurfaces:   HashMap<SubsurfaceId, WebSubsurface>,
	/// The GPU canvas every subsurface is painted on before its frame moves to its own canvas, which keeps it.
	pub subsurface_canvas: Option<Canvas>,
	/// Text input was asked for and not ended; ltk's own keyboard serves it.
	pub text_input:    bool,
	/// The input of every surface, the window's `resize` and the context's loss, removed when the app exits.
	pub listeners:     Vec<Listener>,
	_app:              PhantomData<fn() -> A>,
}

impl<A: App> WebPlatform<A>
{
	pub( crate ) fn new( desktop: Option<Connection>, offscreen: Option<( OffscreenCanvas, WebGl2RenderingContext )>, cursor_target: HtmlElement, listeners: Vec<Listener>, inset_probe: Option<Element> ) -> Self
	{
		let ( offscreen, webgl ) = offscreen.unzip();
		let gl = webgl.clone().map( |context| Arc::new( glow::Context::from_webgl2_context( context ) ) );
		Self
		{
			desktop,
			offscreen,
			webgl,
			gl,
			context_lost:  false,
			cursor_target,
			cursor:        "default",
			inset_probe,
			frame_due:     RefCell::new( Vec::new() ),
			next_surface:  Cell::new( super::desktop::MAIN + 1 ),
			subsurfaces:   HashMap::new(),
			subsurface_canvas: None,
			text_input:    false,
			listeners,
			_app:          PhantomData,
		}
	}

	/// Report a frame of `focus` at the next animation frame.
	pub( super ) fn owe_frame( &self, focus: SurfaceFocus )
	{
		let mut due = self.frame_due.borrow_mut();
		if !due.contains( &focus ) { due.push( focus ); }
	}

	pub( super ) fn surface_id( &self ) -> u32
	{
		let id = self.next_surface.get();
		self.next_surface.set( id + 1 );
		id
	}
}