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

//! Per-frame drawing pipeline.
//!
//! The run loop hands each configured surface to [`draw_frame`] once per
//! vblank; this module walks it through a decision tree:
//!
//! * **Skip** — no content changed and no interaction state moved, so the
//!   previously committed buffer is still correct.
//! * **Partial** — only focus / hover / pressed changed. Install a clip
//!   mask covering the paint rects of the affected widgets, repaint only
//!   under the clip, damage Wayland with exactly those rects.
//! * **Full** — something substantive changed (app message, animation
//!   tick, configure, text edit, scroll, slider drag). Clear + redraw
//!   the entire view, let damage tracking tighten the commit.
//!
//! Each of those paths has a software variant (CPU + SHM pool) and a
//! GLES variant (FBO + EGL swap). The four resulting functions live in
//! [`software`] and [`gles`]; this file is just the router plus the
//! small shared setup ([`DrawCtx`], [`pick_shm_format`]).
//!
//! # Submodule layout
//!
//! * [`software`] — `draw_surface_full` / `draw_surface_partial`
//! * [`gles`] — `draw_surface_full_gpu` / `draw_surface_partial_gpu`
//! * [`damage`] — `compute_interaction_dirty_rects`, `compute_damage`,
//!   `clamp_rect_to`
//! * [`chrome`] — `draw_titlebar`, `apply_input_region`
//! * [`layout`] — `layout_and_draw` (the recursive element walker)

use std::collections::HashMap;
use std::sync::Arc;
use smithay_client_toolkit::reexports::client::protocol::{ wl_shm, wl_surface::WlSurface };
use smithay_client_toolkit::shm::Shm;

use crate::app::App;
use crate::event_loop::{ AppData, SurfaceFocus, SurfaceState };
use crate::render::Canvas;
use crate::types::{ Color, Rect };
use crate::widget::{ Element, LaidOutWidget };

pub( crate ) mod software;
pub( crate ) mod gles;
pub( crate ) mod damage;
pub( crate ) mod chrome;
pub( crate ) mod layout;

pub( crate ) use damage::{ compute_damage, compute_interaction_dirty_rects };
pub( crate ) use layout::layout_and_draw;

/// Pick the best wl_shm format for our RGBA-premultiplied pixmap.
///
/// Abgr8888 matches tiny-skia's byteorder on little-endian systems, so we can
/// copy with a plain memcpy. If the compositor doesn't advertise it, fall back
/// to Argb8888 (mandatory per wl_shm) which requires a per-channel swap.
///
/// Returns `(format, swap_rb)`.
pub( crate ) fn pick_shm_format( shm: &Shm ) -> ( wl_shm::Format, bool )
{
	if shm.formats().contains( &wl_shm::Format::Abgr8888 )
	{
		( wl_shm::Format::Abgr8888, false )
	} else {
		( wl_shm::Format::Argb8888, true )
	}
}

/// Per-frame draw state threaded through [`layout_and_draw`]. Captures
/// the interaction snapshot (focus / hover / pressed), scratch space
/// for the widget-rect list the frame will produce, and the scroll
/// offsets / sub-canvases carried across frames.
///
/// `scroll_canvases` arrives populated (the previous frame's
/// sub-canvases) so `layout_and_draw` can re-use them for Scroll
/// viewports whose size did not change. `scroll_rects` and
/// `widget_rects` start empty and get filled as the element tree is
/// walked.
pub( crate ) struct DrawCtx<Msg: Clone>
{
	pub focused_idx:   Option<usize>,
	pub hovered_idx:   Option<usize>,
	pub pressed_idx:   Option<usize>,
	pub cursor_state:  HashMap<usize, usize>,
	pub selection_anchor: HashMap<usize, usize>,
	pub widget_rects:  Vec<LaidOutWidget<Msg>>,
	pub debug_layout:  bool,
	pub scroll_offsets:  HashMap<usize, f32>,
	pub scroll_rects:    Vec<(Rect, usize)>,
	pub scroll_canvases: HashMap<usize, Canvas>,
	/// Per-scroll navigation map: list of `(flat_idx, content_y, height)`
	/// for every interactive item the scroll's child laid out, in
	/// document order, **including items currently scrolled off-screen**.
	/// Keyboard arrow handlers read this to step the runtime's
	/// `hovered_idx` item-by-item without needing to know how the popup
	/// content was composed. The Y is in pre-translation, pre-offset
	/// coordinates (i.e. relative to the start of the scroll's child
	/// content) so the keyboard auto-scroll can compute the offset
	/// needed to bring an item into view without depending on the
	/// current scroll position.
	pub scroll_navigable_items: HashMap<usize, Vec<( usize, f32, f32 )>>,
	/// Snapshot of the previous frame's `widget_rects`. Read by
	/// [`crate::widget::anchored_overlay::AnchoredOverlay`] at draw time
	/// to look up the rect of an anchor widget by [`crate::WidgetId`] and
	/// re-position itself relative to that rect. Drivers populate this
	/// before invoking the recursive layout / draw walk.
	pub previous_widget_rects: Vec<LaidOutWidget<Msg>>,
}

/// Paint the built-in Copy / Cut / Paste context menu on top of the
/// finished surface content. Called from the software and GLES draw
/// paths right before `present()` so the menu sits above everything
/// the widget tree painted, matching the convention every other
/// toolkit follows for runtime-internal popups.
pub( crate ) fn draw_context_menu(
	canvas: &mut crate::render::Canvas,
	menu:   &crate::event_loop::context_menu::ContextMenu,
)
{
	let palette = crate::theme::palette();
	let bg      = palette.surface;
	let border  = palette.divider;
	let text    = palette.text_primary;
	let muted   = palette.text_secondary;
	let hi      = palette.surface_alt;

	let r = menu.rect;
	canvas.fill_rect( r, bg, 8.0 );
	canvas.stroke_rect( r, border, 1.0, 8.0 );

	let ( ys, row_h ) = menu.row_ys();
	// Row order: Copy / Cut / Paste / Delete. Labels go through
	// `rust_i18n::t!()` so the menu picks up the active locale; the
	// `enabled` flag mirrors the gating in `handle_context_menu_press`.
	let labels: [ ( String, bool ); 4 ] =
	[
		( rust_i18n::t!( "context_menu.copy"   ).to_string(), menu.has_selection ),
		( rust_i18n::t!( "context_menu.cut"    ).to_string(), menu.has_selection ),
		( rust_i18n::t!( "context_menu.paste"  ).to_string(), menu.can_paste     ),
		( rust_i18n::t!( "context_menu.delete" ).to_string(), menu.has_selection ),
	];

	// Subtle accent band on the row matching the *primary* action so
	// the menu reads as "Paste is the default" when there is no
	// selection (the common case for a paste-into-empty-field click)
	// and "Copy is the default" when a selection is active. Just a
	// hint, not a binding — every row still works on its own click.
	let primary_idx = if menu.has_selection { 0 } else { 2 };
	let primary_band = crate::types::Rect
	{
		x: r.x + 4.0, y: ys[ primary_idx ] + 2.0,
		width: r.width - 8.0, height: row_h - 4.0,
	};
	canvas.fill_rect( primary_band, hi, 6.0 );

	for ( i, ( label, enabled ) ) in labels.iter().enumerate()
	{
		let color = if *enabled { text } else { muted };
		canvas.draw_text(
			label,
			r.x + 16.0,
			ys[ i ] + row_h * 0.5 + 5.0,
			14.0,
			color,
		);
	}

	// Thin separator between every pair of rows.
	let sep_color = palette.divider;
	for y in ys.iter().skip( 1 )
	{
		canvas.draw_line( r.x + 8.0, *y, r.x + r.width - 8.0, *y, sep_color, 1.0 );
	}
}

pub( crate ) fn draw_frame<A: App>( data: &mut AppData<A> )
{
	// Caches were refreshed by the run loop just before calling us; pull them
	// by reference instead of re-invoking `App::view` / `App::overlays` each
	// frame. The two `expect`s document the run loop's contract.
	let main_view = data.cached_view.as_ref().expect( "view cache populated" );
	let overlays  = data.cached_overlays.as_ref().expect( "overlays cache populated" );

	let main_bg      = data.app.background_color();
	let main_region  = data.app.input_region();
	let debug_layout = data.debug_layout;
	let ( format, swap_rb ) = pick_shm_format( &data.shm );
	let egl_ctx = data.egl_context.as_ref();
	let qh      = &data.qh;

	if data.main.configured && data.main.needs_redraw && !data.main.frame_pending
	{
		let req_frame = | wl: &WlSurface | { let _ = wl.frame( qh, SurfaceFocus::Main ); };
		draw_surface::<A::Message>(
			&mut data.main,
			&data.compositor_state,
			egl_ctx,
			main_view,
			main_bg,
			main_region.as_deref(),
			debug_layout,
			format,
			swap_rb,
			&req_frame,
		);
		data.main.needs_redraw = false;
		data.main.last_draw    = std::time::Instant::now();
	}

	for spec in overlays
	{
		if let Some( ss ) = data.overlays.get_mut( &spec.id )
		{
			if !ss.configured || !ss.needs_redraw || ss.frame_pending { continue; }
			let focus     = SurfaceFocus::Overlay( spec.id );
			let req_frame = | wl: &WlSurface | { let _ = wl.frame( qh, focus ); };
			let bg        = Color::rgba( 0.0, 0.0, 0.0, 0.0 );
			draw_surface::<A::Message>(
				ss,
				&data.compositor_state,
				egl_ctx,
				&spec.view,
				bg,
				spec.input_region.as_deref(),
				debug_layout,
				format,
				swap_rb,
				&req_frame,
			);
			ss.needs_redraw = false;
			ss.last_draw    = std::time::Instant::now();
		}
	}
}

/// Render one surface's current view. Picks between software and GLES,
/// and within each picks between full and partial redraw based on what
/// changed since the last committed frame.
///
/// The decision:
/// * **Skip** — `content_dirty` is false and no interaction state
///   changed. Previously committed buffer stays on screen.
/// * **Partial** — `content_dirty` is false but focus / hover / pressed
///   transitioned. Canvas is preserved across frames, so clip to the
///   dirty widgets and repaint only under the clip.
/// * **Full** — `content_dirty` is true. Clear + redraw + damage.
///
/// Partial eligibility also bails out when the total dirty area >50%
/// of the surface: at that ratio per-region clipping is no faster than
/// a plain full redraw, so the code prefers one big damage rect over
/// several small ones.
fn draw_surface<Msg: Clone>(
	ss:            &mut SurfaceState<Msg>,
	compositor:    &smithay_client_toolkit::compositor::CompositorState,
	egl_ctx:       Option<&Arc<crate::egl_context::EglContext>>,
	view:          &Element<Msg>,
	bg:            Color,
	input_region:  Option<&[Rect]>,
	debug_layout:  bool,
	shm_format:    wl_shm::Format,
	swap_rb:       bool,
	request_frame: &dyn Fn( &WlSurface ),
)
{
	let scale = ss.scale_factor.max( 1 ) as u32;
	let w = ss.width;
	let h = ss.height;
	if w == 0 || h == 0 { return; }
	let pw     = w * scale;
	let ph     = h * scale;

	// Decide partial-redraw eligibility BEFORE allocating a buffer. If we end
	// up skipping the frame, we want to avoid touching the SHM pool at all.
	let canvas_ready = ss.canvas.as_ref()
		.map( |c| c.size() == ( pw, ph ) )
		.unwrap_or( false );
	let partial_eligible = !ss.content_dirty
		&& canvas_ready
		&& !ss.widget_rects.is_empty();

	if partial_eligible
	{
		let dirty_rects = compute_interaction_dirty_rects(
			&ss.widget_rects,
			ss.prev_focused, ss.prev_hovered, ss.prev_pressed,
			ss.focused_idx,  ss.hovered_idx,  ss.gesture.pressed_idx,
			pw, ph,
		);
		if dirty_rects.is_empty()
		{
			// Nothing visible changed — keep the previously committed buffer.
			return;
		}
		// Total dirty area > 50% of screen: a full redraw is no slower than
		// per-region clipping but emits a single damage rect.
		let total: f32 = dirty_rects.iter().map( |r| r.width * r.height ).sum();
		if total < pw as f32 * ph as f32 * 0.5
		{
			if let ( Some( ctx ), true ) = ( egl_ctx, ss.egl_surface.is_some() )
			{
				gles::draw_surface_partial_gpu(
					ss, compositor, ctx, view, bg, input_region,
					dirty_rects, pw, ph, scale, request_frame,
				);
			} else {
				software::draw_surface_partial(
					ss, compositor, view, bg, input_region,
					shm_format, swap_rb, dirty_rects, pw, ph, scale, request_frame,
				);
			}
			return;
		}
	}

	if let ( Some( ctx ), true ) = ( egl_ctx, ss.egl_surface.is_some() )
	{
		gles::draw_surface_full_gpu(
			ss, compositor, ctx, view, bg, input_region, debug_layout,
			pw, ph, scale, request_frame,
		);
	} else {
		software::draw_surface_full(
			ss, compositor, view, bg, input_region, debug_layout,
			shm_format, swap_rb, pw, ph, scale, request_frame,
		);
	}
}