// Copyright 2019 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use base::{AsRawDescriptor, RawDescriptor};
use data_model::DataInit;
use linux_input_sys::{
    virtio_input_event, InputEventDecoder, ABS_MT_POSITION_X, ABS_MT_POSITION_Y, ABS_MT_SLOT,
    ABS_MT_TRACKING_ID,
};
use std::cmp::max;
use std::collections::VecDeque;
use std::io::{self, Error, ErrorKind, Read, Write};
use std::iter::ExactSizeIterator;
use std::os::unix::net::UnixStream;

const EVENT_SIZE: usize = virtio_input_event::SIZE;
const EVENT_BUFFER_LEN_MAX: usize = 16 * EVENT_SIZE;

// /// Half-way build `EventDevice` with only the `event_socket` defined. Finish building the
// /// `EventDevice` by using `status_socket`.
// pub struct PartialEventDevice(UnixStream);

// impl PartialEventDevice {
//     /// Finish build `EventDevice` by providing the `status_socket`.
//     pub fn status_socket(self, status_socket: UnixStream) -> EventDevice {
//         EventDevice {
//             event_socket: self.0,
//             status_socket,
//         }
//     }
// }

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum EventDeviceKind {
    /// Produces relative mouse motions, wheel, and button clicks while the real mouse is captured.
    Mouse,
    /// Produces absolute motion and touch events from the display window's events.
    Touchscreen,
    /// Produces key events while the display window has focus.
    Keyboard,
}

/// Encapsulates a virtual event device, such as a mouse or keyboard
pub struct EventDevice {
    kind: EventDeviceKind,
    event_buffer: VecDeque<u8>,
    event_socket: UnixStream,
}

// Captures information for emulating MT events. Once more than slot 0 is supported will need to
// store slot information as well.
#[derive(Default, Copy, Clone)]
struct MTEvent {
    id: i32,
    x: i32,
    y: i32,
}

impl EventDevice {
    pub fn new(kind: EventDeviceKind, event_socket: UnixStream) -> EventDevice {
        let _ = event_socket.set_nonblocking(true);
        EventDevice {
            kind,
            event_buffer: Default::default(),
            event_socket,
        }
    }

    #[inline]
    pub fn mouse(event_socket: UnixStream) -> EventDevice {
        Self::new(EventDeviceKind::Mouse, event_socket)
    }

    #[inline]
    pub fn touchscreen(event_socket: UnixStream) -> EventDevice {
        Self::new(EventDeviceKind::Touchscreen, event_socket)
    }

    #[inline]
    pub fn keyboard(event_socket: UnixStream) -> EventDevice {
        Self::new(EventDeviceKind::Keyboard, event_socket)
    }

    #[inline]
    pub fn kind(&self) -> EventDeviceKind {
        self.kind
    }

    /// Flushes the buffered events that did not fit into the underlying transport, if any.
    ///
    /// Returns `Ok(true)` if, after this function returns, there all the buffer of events is
    /// empty.
    pub fn flush_buffered_events(&mut self) -> io::Result<bool> {
        while !self.event_buffer.is_empty() {
            let written = self.event_socket.write(self.event_buffer.as_slices().0)?;
            if written == 0 {
                return Ok(false);
            }
            self.event_buffer.drain(..written);
        }
        Ok(true)
    }

    pub fn is_buffered_events_empty(&self) -> bool {
        self.event_buffer.is_empty()
    }

    /// Compares (potential) events and calculates the oldest one
    fn capture_oldest_event(
        current_mt_event: &Option<MTEvent>,
        oldest_mt_event: &mut Option<MTEvent>,
    ) {
        if let Some(current) = current_mt_event {
            if current.id != -1 {
                if let Some(oldest) = oldest_mt_event {
                    if current.id < oldest.id {
                        *oldest_mt_event = Some(*current);
                    }
                } else {
                    *oldest_mt_event = Some(*current);
                }
            }
        }
    }

    pub fn send_report<E: IntoIterator<Item = virtio_input_event>>(
        &mut self,
        events: E,
    ) -> io::Result<bool>
    where
        E::IntoIter: ExactSizeIterator,
    {
        let it = events.into_iter();
        let mut emulated_events: Vec<virtio_input_event> = vec![];
        let mut evdev_st_events_present = false;
        let mut oldest_mt_event: Option<MTEvent> = None;
        let mut current_mt_event: Option<MTEvent> = None;

        if self.event_buffer.len() > (EVENT_BUFFER_LEN_MAX - EVENT_SIZE * (it.len() + 1)) {
            return Ok(false);
        }

        // Assumptions made for MT emulation:
        // * There may exist real ABS_* events coming from e.g. evdev. cancel emulation in this case
        // * For current gpu_display_{x, wl} implementations, there is only one slot and all
        //   available tracking id information is sent. If this assumption is broken in the future,
        //   `EventDevice` will need to maintain state of the oldest contact for each slot, so that
        //   this can be compared to any incoming 'sparse' event set.
        for event in it {
            let bytes = event.as_slice();
            self.event_buffer.extend(bytes.iter());

            if event.is_valid_st_event() {
                // Real evdev event, we shouldnt emulate anything
                evdev_st_events_present = true;
            }

            // For MT events, we want to also emulate their corresponding ST events
            if !evdev_st_events_present {
                match event.code.to_native() {
                    ABS_MT_SLOT => {
                        // MT packets begin with a SLOT event, begin a new current event and potentially
                        // store the current as oldest.
                        EventDevice::capture_oldest_event(&current_mt_event, &mut oldest_mt_event);
                        // Only care about slot 0 in current implementation, if more slots are added
                        // we will need to keep track of events / ids per slot, as well as maintain
                        // which slot is currently active.
                        current_mt_event = Some(MTEvent {
                            ..Default::default()
                        })
                    }
                    ABS_MT_TRACKING_ID => {
                        if let Some(mut current) = current_mt_event {
                            current.id = event.value.to_native();
                        }
                    }
                    ABS_MT_POSITION_X => {
                        if let Some(mut current) = current_mt_event {
                            current.x = event.value.to_native();
                        }
                    }
                    ABS_MT_POSITION_Y => {
                        if let Some(mut current) = current_mt_event {
                            current.y = event.value.to_native();
                        }
                    }
                    _ => {}
                }
            }
        }

        // Finalize the current event - MT packets have a 'begin' signal but not an 'end' signal, so the
        // last collected 'current' event has no chance to be compared in the event loop.
        EventDevice::capture_oldest_event(&current_mt_event, &mut oldest_mt_event);

        if !evdev_st_events_present {
            if let Some(oldest_event) = oldest_mt_event {
                emulated_events.push(virtio_input_event::touch(true));
                emulated_events.push(virtio_input_event::absolute_x(max(0, oldest_event.x)));
                emulated_events.push(virtio_input_event::absolute_y(max(0, oldest_event.y)));
            } else {
                // No contacts remain, emit lift
                emulated_events.push(virtio_input_event::touch(false));
            }
        }

        for event in emulated_events.into_iter() {
            let bytes = event.as_slice();
            self.event_buffer.extend(bytes.iter());
        }

        self.event_buffer
            .extend(virtio_input_event::syn().as_slice().iter());

        self.flush_buffered_events()
    }

    /// Sends the given `event`, returning `Ok(true)` if, after this function returns, there are no
    /// buffered events remaining.
    pub fn send_event_encoded(&mut self, event: virtio_input_event) -> io::Result<bool> {
        if !self.flush_buffered_events()? {
            return Ok(false);
        }

        let bytes = event.as_slice();
        let written = self.event_socket.write(bytes)?;

        if written == bytes.len() {
            return Ok(true);
        }

        if self.event_buffer.len() <= (EVENT_BUFFER_LEN_MAX - EVENT_SIZE) {
            self.event_buffer.extend(bytes[written..].iter());
        }

        Ok(false)
    }

    pub fn recv_event_encoded(&self) -> io::Result<virtio_input_event> {
        let mut event_bytes = [0u8; 24];
        (&self.event_socket).read_exact(&mut event_bytes)?;
        match virtio_input_event::from_slice(&event_bytes) {
            Some(event) => Ok(*event),
            None => Err(Error::new(
                ErrorKind::InvalidInput,
                "failed to read virtio_input_event",
            )),
        }
    }
}

impl AsRawDescriptor for EventDevice {
    fn as_raw_descriptor(&self) -> RawDescriptor {
        self.event_socket.as_raw_descriptor()
    }
}