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

//! `wl_data_device_manager` integration — cross-application
//! clipboard.
//!
//! This module bridges ltk's process-local `clipboard: String` to the
//! Wayland selection so that:
//!
//! * **Outbound (Ctrl+C / Cut)** — after the local clipboard is
//!   populated, [`AppData::publish_clipboard_selection`] creates a
//!   [`CopyPasteSource`] offering `text/plain;charset=utf-8` and
//!   installs it as the seat's selection. When a peer pastes,
//!   [`DataSourceHandler::send`] writes the cached string into the
//!   fd the peer hands us.
//!
//! * **Inbound (Ctrl+V from another app)** — when the compositor
//!   advertises a new selection through
//!   [`DataDeviceHandler::selection`], we ask for it as UTF-8 text
//!   via `WlDataOffer::receive`, spawn a tiny thread to drain the
//!   read pipe, and post the result back to the event loop through
//!   the runtime's existing `ChannelSender`-style channel. The
//!   message just updates `self.clipboard`; subsequent local pastes
//!   pick the new value up the next time the user hits Ctrl+V.
//!
//! Drag-and-drop across applications uses the same protocol but
//! involves enter / leave / motion / drop_performed wiring with
//! widget hit-tests, surface coordinates and drop targets that are a
//! separate concern. The handlers in this file accept those events
//! but currently route them to no-ops; an explicit follow-up will
//! cover DnD targets.

use std::io::Read;
use std::sync::mpsc;

use smithay_client_toolkit::data_device_manager::data_device::{ DataDeviceData, DataDeviceHandler };
use smithay_client_toolkit::data_device_manager::data_offer::{ DataOfferHandler, DragOffer };
use smithay_client_toolkit::data_device_manager::data_source::DataSourceHandler;
use smithay_client_toolkit::data_device_manager::{ ReadPipe, WritePipe };
use smithay_client_toolkit::reexports::client::
{
	protocol::
	{
		wl_data_device::WlDataDevice,
		wl_data_device_manager::DndAction,
		wl_data_source::WlDataSource,
		wl_surface::WlSurface,
	},
	Connection, Proxy, QueueHandle,
};

use crate::app::App;
use super::app_data::AppData;

/// MIME type we advertise on outbound copies and request on inbound
/// pastes. `text/plain;charset=utf-8` is the de-facto cross-toolkit
/// baseline (GTK, Qt, electron, Firefox all carry it); `UTF8_STRING`
/// is the X11-era legacy alias still emitted by some compositors.
pub( super ) const CLIPBOARD_MIMES: &[ &str ] = &[ "text/plain;charset=utf-8", "text/plain", "UTF8_STRING" ];

/// Mimes accepted for inter-application drag-and-drop. URI lists
/// (file managers, browsers) come first because they are the most
/// useful payload for typical desktop drops.
pub( super ) const DND_MIMES: &[ &str ] = &[ "text/uri-list", "text/plain;charset=utf-8", "text/plain", "UTF8_STRING" ];

/// Payload delivered from the DnD worker thread back to the run loop.
pub( crate ) struct DropPayload
{
	pub mime: String,
	pub text: String,
	pub x:    f64,
	pub y:    f64,
}

pub( crate ) fn drop_inbox() -> ( std::sync::mpsc::Sender<DropPayload>, std::sync::mpsc::Receiver<DropPayload> )
{
	std::sync::mpsc::channel()
}

impl<A: App> AppData<A>
{
	/// Publish the current `self.clipboard` value as the seat's
	/// selection so other applications can paste it. Called by the
	/// copy / cut handlers after they populate the local buffer.
	/// No-op when the compositor does not advertise
	/// `wl_data_device_manager` or when no seat has appeared yet.
	pub( crate ) fn publish_clipboard_selection( &mut self )
	{
		let ( Some( ref ddm ), Some( ref dd ) ) = ( self.data_device_manager.as_ref(), self.data_device.as_ref() ) else { return };
		let source = ddm.create_copy_paste_source( &self.qh, CLIPBOARD_MIMES.iter().copied() );
		source.set_selection( dd, self.last_input_serial );
		// Hold the source alive: the compositor only keeps the
		// selection while the `WlDataSource` is not dropped. We also
		// need to hang on to it so `DataSourceHandler::send` can find
		// the cached text via `self.clipboard`.
		self.clipboard_source = Some( source );
	}
}

impl<A: App> DataDeviceHandler for AppData<A>
{
	fn enter(
		&mut self,
		_c: &Connection,
		_qh: &QueueHandle<Self>,
		d:   &WlDataDevice,
		x:   f64,
		y:   f64,
		_s:  &WlSurface,
	)
	{
		let Some( data )  = d.data::<DataDeviceData>() else { return };
		let Some( offer ) = data.drag_offer()          else { return };
		let mimes = offer.with_mime_types( |m| m.to_vec() );
		let accepted = DND_MIMES.iter().copied()
			.find( |c| mimes.iter().any( |m| m == *c ) )
			.map( |s| s.to_string() );
		offer.accept_mime_type( self.last_input_serial, accepted.clone() );
		offer.set_actions( smithay_client_toolkit::reexports::client::protocol::wl_data_device_manager::DndAction::Copy,
			smithay_client_toolkit::reexports::client::protocol::wl_data_device_manager::DndAction::Copy );
		self.drop_position = Some( ( x, y ) );
		self.drop_mime     = accepted;
		self.app.on_drop_motion( x as f32, y as f32 );
	}

	fn leave( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _d: &WlDataDevice )
	{
		if self.drop_position.is_some() { self.app.on_drop_leave(); }
		self.drop_position = None;
		self.drop_mime     = None;
	}

	fn motion( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _d: &WlDataDevice, x: f64, y: f64 )
	{
		self.drop_position = Some( ( x, y ) );
		self.app.on_drop_motion( x as f32, y as f32 );
	}

	fn drop_performed( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, d: &WlDataDevice )
	{
		let Some( data )  = d.data::<DataDeviceData>() else { return };
		let Some( offer ) = data.drag_offer()          else { return };
		let Some( mime )  = self.drop_mime.clone()     else { offer.finish(); return };
		let ( x, y )      = self.drop_position.unwrap_or( ( 0.0, 0.0 ) );
		let Ok( pipe )    = offer.receive( mime.clone() ) else { offer.finish(); return };
		offer.finish();
		let tx = self.drop_inbox_tx.clone();
		std::thread::spawn( move ||
		{
			use std::io::Read;
			let mut reader = std::fs::File::from( std::os::fd::OwnedFd::from( pipe ) );
			let mut buf    = String::new();
			let mut bounded = ( &mut reader ).take( 16 * 1024 * 1024 );
			let _ = bounded.read_to_string( &mut buf );
			let _ = tx.send( DropPayload { mime, text: buf, x, y } );
		} );
		self.drop_position = None;
		self.drop_mime     = None;
	}

	/// A new selection arrived from another client. Negotiate
	/// UTF-8 text on a background thread (the receive side of the
	/// data offer is a blocking read pipe) and post the result back
	/// into the event loop through `clipboard_inbox`. The main loop
	/// drains the inbox once per iteration and copies the bytes
	/// into `self.clipboard`.
	fn selection( &mut self, _conn: &Connection, _qh: &QueueHandle<Self>, data_device: &WlDataDevice )
	{
		let Some( data ) = data_device.data::<DataDeviceData>() else { return };
		let Some( offer ) = data.selection_offer() else { return };
		let Some( mime )  = offer.with_mime_types( pick_text_mime ) else { return };
		let Ok( pipe )    = offer.receive( mime ) else { return };
		read_selection( pipe, self.clipboard_inbox_tx.clone() );
	}
}

/// Drain an offered selection on a thread of its own and post the text to `tx`.
pub( super ) fn read_selection( pipe: ReadPipe, tx: mpsc::Sender<String> )
{
	std::thread::spawn( move ||
	{
		let mut reader = std::fs::File::from( std::os::fd::OwnedFd::from( pipe ) );
		let mut buf    = String::new();
		// 16 MiB cap. Compositors are free to keep typing into the
		// pipe forever; a runaway selection should not exhaust
		// memory or stall the worker thread indefinitely.
		let mut bounded = (&mut reader).take( 16 * 1024 * 1024 );
		let _ = bounded.read_to_string( &mut buf );
		let _ = tx.send( buf );
	} );
}

/// Serve `text` to the peer that asked for one of our selections.
pub( super ) fn write_selection( pipe: WritePipe, text: &str )
{
	// SCTK's `WritePipe` derefs to `OwnedFd`; convert to a `File`
	// (no buffering — selection payloads are small). Errors (peer
	// closed early, broken pipe) are ignored: we cannot recover and
	// the compositor will issue a fresh source on the next copy anyway.
	use std::io::Write;
	let mut writer = std::fs::File::from( std::os::fd::OwnedFd::from( pipe ) );
	let _ = writer.write_all( text.as_bytes() );
}

impl<A: App> DataOfferHandler for AppData<A>
{
	fn source_actions( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _offer: &mut DragOffer, _actions: DndAction ) {}
	fn selected_action( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _offer: &mut DragOffer, _actions: DndAction ) {}
}

impl<A: App> DataSourceHandler for AppData<A>
{
	fn accept_mime( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _source: &WlDataSource, _mime: Option<String> ) {}

	fn send_request( &mut self, _conn: &Connection, _qh: &QueueHandle<Self>, source: &WlDataSource, _mime: String, fd: WritePipe )
	{
		// Only honour requests for our own active source — if a stale
		// source is still hanging around (e.g. between a new copy and
		// the compositor dropping the previous selection) the peer
		// might still ask for its data; we just write nothing rather
		// than leak the new clipboard contents through an old source.
		let is_active = self.clipboard_source.as_ref()
			.map( |s| s.inner() == source )
			.unwrap_or( false );
		if !is_active { return; }
		write_selection( fd, &self.clipboard );
	}

	fn cancelled( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, source: &WlDataSource )
	{
		// Compositor dropped our source (another client claimed the
		// selection). Drop the cached handle so a future copy creates
		// a fresh one.
		if self.clipboard_source.as_ref().map( |s| s.inner() == source ).unwrap_or( false )
		{
			self.clipboard_source = None;
		}
	}

	fn dnd_dropped( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _source: &WlDataSource ) {}
	fn dnd_finished( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _source: &WlDataSource ) {}
	fn action( &mut self, _c: &Connection, _qh: &QueueHandle<Self>, _source: &WlDataSource, _action: DndAction ) {}
}

/// Pick the best-supported MIME type from those a selection offers.
/// Order matches `CLIPBOARD_MIMES` — UTF-8 first, then plain text,
/// then the legacy `UTF8_STRING`.
pub( super ) fn pick_text_mime( mimes: &[ String ] ) -> Option<String>
{
	CLIPBOARD_MIMES.iter()
		.find( |c| mimes.iter().any( |m| m == *c ) )
		.map( |s| s.to_string() )
}

/// Buffered channel pair used to ferry inbound-selection bytes from
/// the read-pipe worker thread to the event loop. The receiver is
/// drained once per iteration inside the main run loop.
pub( crate ) fn clipboard_inbox() -> ( mpsc::Sender<String>, mpsc::Receiver<String> )
{
	mpsc::channel()
}