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

//! Platform backends: what ties the runtime to a windowing system.
//!
//! The runtime (`event_loop/`, `input/`, `draw/`) holds the app, the widget tree, focus, gestures, text editing and every `App` callback, and is the same on every platform. A backend feeds it input through the entry points of [`crate::input::event`], keeps its own half of every surface in `SurfaceState::platform`, and carries out the requests of [`Platform`].
//!
//! A backend also owns the run loop: it connects to the system, builds `AppData` with `AppData::new`, installs the shared event sources with `AppData::install_sources`, and on every wake-up calls `AppData::before_draw`, `AppData::draw_due` and `AppData::after_draw` around its own work.
//!
//! The backends are `wayland`, `android` and `web`, each behind the feature of its name; `build.rs` refuses more than one. Each backend sets the two aliases below and `run` / `try_run` under its own `cfg`, and `build.rs` sets `cfg( backend )`, which builds the runtime, when one is enabled.

#[ cfg( feature = "android" ) ]
pub( crate ) mod android;
#[ cfg( feature = "wayland" ) ]
pub( crate ) mod wayland;
#[ cfg( feature = "web" ) ]
pub( crate ) mod web;
#[ cfg( test ) ]
pub( crate ) mod mock;

#[ cfg( feature = "android" ) ]
pub( crate ) use android::run::{ run, try_run };
#[ cfg( feature = "wayland" ) ]
pub( crate ) use wayland::run::{ run, try_run };
#[ cfg( feature = "web" ) ]
pub( crate ) use web::run::{ run, try_run };

use crate::event_loop::SurfaceFocus;
use crate::event_loop::cursor_shape::ResizeEdge;
use crate::osk::Purpose;
use crate::render::Canvas;
use crate::types::{ Color, CursorShape, Rect };

/// The backend the runtime runs on, held by `AppData::platform`.
#[ cfg( feature = "wayland" ) ]
pub( crate ) type NativePlatform<A> = wayland::WaylandPlatform<A>;
#[ cfg( feature = "android" ) ]
pub( crate ) type NativePlatform<A> = android::AndroidPlatform<A>;
#[ cfg( feature = "web" ) ]
pub( crate ) type NativePlatform<A> = web::WebPlatform<A>;

/// The backend's half of every surface, held by `SurfaceState::platform`.
#[ cfg( feature = "wayland" ) ]
pub( crate ) type NativeSurface = wayland::WaylandSurfaceState;
#[ cfg( feature = "android" ) ]
pub( crate ) type NativeSurface = android::AndroidSurfaceState;
#[ cfg( feature = "web" ) ]
pub( crate ) type NativeSurface = web::WebSurfaceState;

/// The user's language as `LANG` gives it (`es_ES.UTF-8`), or in a browser as the page does (`es-ES`).
#[ cfg( not( feature = "web" ) ) ]
pub( crate ) fn language() -> String
{
	std::env::var( "LANG" ).unwrap_or_default()
}

#[ cfg( feature = "web" ) ]
pub( crate ) fn language() -> String
{
	web_sys::window().and_then( |w| w.navigator().language() ).unwrap_or_default()
}

/// What [`Platform::present`] needs to know about a painted frame. Rects are in physical pixels, top-left origin.
pub( crate ) struct Presentation<'a>
{
	/// What changed since the last frame; empty for the whole surface.
	pub damage:        &'a [Rect],
	/// The surface is opaque where `bg` is, and elsewhere over `opaque_region`.
	pub bg:            Color,
	pub opaque_region: Option<&'a [Rect]>,
	/// Where the surface takes input; `None` everywhere, empty nowhere.
	pub input_region:  Option<&'a [Rect]>,
	/// Logical size and the physical pixels per logical one.
	pub width:         u32,
	pub height:        u32,
	pub scale:         f32,
	/// Report the next frame to the runtime as one of this surface; `None` for a surface that is not paced by frames.
	pub frame:         Option<SurfaceFocus>,
}

/// What the runtime asks of the windowing system. `AppData::platform` implements it.
///
/// Drawing a surface takes three calls: [`Self::prepare_canvas`], then the runtime paints the widget tree on the canvas, then [`Self::present`]. The canvas is the surface's own and keeps its pixels between frames, so a partial repaint only touches the damaged rects, and presenting adds no copy beyond the one into the system's buffer that a software canvas always needs.
pub( crate ) trait Platform: 'static
{
	/// The backend's half of a surface, held by `SurfaceState::platform`.
	type Surface;

	/// A display that one of `AppData::secondaries` covers.
	type Output;

	/// Whether a full repaint of `surface` should report the rects that changed rather than the whole surface.
	fn precise_damage( &self, surface: &Self::Surface ) -> bool;

	/// Make `canvas` ready to paint `surface` at `pw × ph` physical pixels, creating it on the first frame; `false` when the surface cannot be drawn now.
	fn prepare_canvas( &self, surface: &mut Self::Surface, canvas: &mut Option<Canvas>, pw: u32, ph: u32, scale: f32 ) -> bool;

	/// Show what was painted on `canvas` since [`Self::prepare_canvas`]; `false` when nothing reached the screen.
	fn present( &self, surface: &mut Self::Surface, canvas: &mut Canvas, frame: &Presentation<'_> ) -> bool;

	/// Offer `text`, which the runtime also keeps in `AppData::clipboard`, to other applications as the clipboard.
	fn publish_clipboard( &mut self, text: &str );

	/// Offer `text`, which the runtime also keeps in `AppData::primary_selection`, to other applications as the selection the middle button pastes; no-op where there is none.
	fn publish_primary_selection( &mut self, text: &str );

	/// Whether `main` is an application window the user can move, resize and minimise, rather than a shell or lock surface.
	fn is_toplevel( &self, main: &Self::Surface ) -> bool;

	/// Whether back with nothing left to go back to may minimise or close `main`, as [`crate::app::BackAtRoot`] says: an application's window or activity, not a shell or lock surface.
	fn back_leaves( &self, main: &Self::Surface ) -> bool;

	/// Let the system move the window with the pointer whose left button was just pressed.
	fn begin_window_move( &self, main: &Self::Surface );

	/// Let the system resize the window from `edge` with the pointer whose left button was just pressed.
	fn begin_window_resize( &self, main: &Self::Surface, edge: ResizeEdge );

	fn minimize_window( &self, main: &Self::Surface );

	/// `false` when `main` is not a window, so the runtime asks again later.
	fn set_fullscreen( &self, main: &Self::Surface, fullscreen: bool ) -> bool;

	/// Ask for a frame of `surface`, reported as one of `focus`, without presenting a new buffer; `false` while the surface does not exist yet.
	fn request_frame( &self, surface: &Self::Surface, focus: SurfaceFocus ) -> bool;

	/// `false` when the system lets the app set no cursor shape.
	fn set_cursor_shape( &mut self, shape: CursorShape ) -> bool;

	/// Whether the input method is serving a text field or the app.
	fn text_input_active( &self ) -> bool;

	/// Ask the input method for text, or renew the request so a keyboard the system folded comes back.
	fn activate_text_input( &mut self, secure: bool, purpose: Purpose );

	fn deactivate_text_input( &mut self );

	/// Send an active request again with a new purpose; no-op when none is active.
	fn reenable_text_input( &self, secure: bool, purpose: Purpose );
}