// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! This crate contains the rust OpenThread platform implementation for Fuchsia.

#![warn(rust_2018_idioms)]

mod backing;
mod binding;
pub mod logging;
pub(crate) mod to_escaped_string;

use futures::prelude::*;
use openthread::prelude::*;

use backing::*;
use binding::*;

use anyhow::Error;
use fuchsia_async as fasync;
use futures::channel::mpsc as fmpsc;
use lowpan_driver_common::spinel::*;
use std::cell::RefCell;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::mpsc;
use std::task::{Context, Poll};

#[allow(unused_imports)]
use tracing::{debug, error, info, trace, warn};

// Number of entries in the frame-ready channel.
// This length doesn't need to be very large, as it
// is effectively just a wakeup flag.
const FRAME_READY_BUFFER_LEN: usize = 2;

const UDP_PACKET_MAX_LENGTH: usize = 1280usize;

/// Builder type for the OpenThread platform. Create using [`Platform::builder()`].
pub struct PlatformBuilder {
    pub(crate) thread_netif_index: Option<u32>,
    pub(crate) backbone_netif_index: Option<u32>,
}

impl PlatformBuilder {
    #[must_use]
    pub fn thread_netif_index(mut self, index: u32) -> Self {
        self.thread_netif_index = Some(index);
        self
    }

    #[must_use]
    pub fn backbone_netif_index(mut self, index: u32) -> Self {
        self.backbone_netif_index = Some(index);
        self
    }

    /// Initializes the OpenThread platform.
    ///
    /// The instance returned by this method must be passed to
    /// [`ot::Instance::new()`](openthread_rust::ot::Instance::new).
    ///
    /// The returned object is a singleton. Attempting to have more than one instance
    /// around at a time will cause a panic.
    pub fn init<SpinelSink, SpinelStream>(
        self,
        spinel_sink: SpinelSink,
        spinel_stream: SpinelStream,
    ) -> Platform
    where
        SpinelSink: SpinelDeviceClient + 'static,
        SpinelStream: Stream<Item = Result<Vec<u8>, anyhow::Error>> + 'static + Unpin + Send,
    {
        Platform::init(self, spinel_sink, spinel_stream)
    }
}

/// OpenThread Singleton Platform Implementation.
///
/// An instance of this type must be passed to
/// [`ot::Instance::new()`](openthread_rust::ot::Instance::new).
///
/// This type is a singleton. Attempting to init more than a
/// single instance of `Platform` at a time will cause a panic.
pub struct Platform {
    timer_receiver: fmpsc::Receiver<usize>,
    rcp_to_ot_frame_ready_receiver: fmpsc::Receiver<()>,
    nat64_platform_instance: Nat64PlatformInstance,
    ot_to_rcp_task: fasync::Task<()>,
    rcp_to_ot_task: fasync::Task<()>,
}

impl Platform {
    #[must_use]
    pub fn build() -> PlatformBuilder {
        PlatformBuilder { thread_netif_index: None, backbone_netif_index: None }
    }

    /// This method is called by `PlatformBuilder::init`.
    fn init<SpinelSink, SpinelStream>(
        builder: PlatformBuilder,
        mut spinel_sink: SpinelSink,
        mut spinel_stream: SpinelStream,
    ) -> Self
    where
        SpinelSink: SpinelDeviceClient + 'static,
        SpinelStream: Stream<Item = Result<Vec<u8>, anyhow::Error>> + 'static + Unpin + Send,
    {
        // OpenThread to RCP data-pump and related machinery.
        let (alarm, timer_receiver) = backing::AlarmInstance::new();
        let (ot_to_rcp_sender, ot_to_rcp_receiver) = mpsc::channel::<Vec<u8>>();
        let ot_to_rcp_task = fasync::Task::spawn(async move {
            spinel_sink.open().await.expect("Unable to open spinel stream");
            loop {
                trace!(tag = "ot_to_rcp_task", "waiting on frame from OpenThread");

                let frame = match ot_to_rcp_receiver.recv() {
                    Ok(frame) => frame,
                    Err(e) => {
                        warn!(
                            tag = "ot_to_rcp_task",
                            "ot_to_rcp_receiver.recv() failed with {:?}", e
                        );
                        break;
                    }
                };

                trace!(tag = "ot_to_rcp_task", "sending frame from OpenThread to RCP");
                if let Err(e) = spinel_sink.send(frame.as_slice()).await {
                    warn!(tag = "ot_to_rcp_task", "spinel_sink.send() failed with {:?}", e);
                    break;
                }
            }
        });

        // RCP to OpenThread data-pump and related machinery.
        let (mut rcp_to_ot_frame_ready_sender, rcp_to_ot_frame_ready_receiver) =
            fmpsc::channel(FRAME_READY_BUFFER_LEN);
        let (rcp_to_ot_sender, rcp_to_ot_receiver) = mpsc::channel::<Vec<u8>>();
        let rcp_to_ot_task = fasync::Task::spawn(async move {
            while let Some(frame_result) = spinel_stream.next().await {
                match frame_result {
                    Ok(frame) => {
                        trace!(tag = "rcp_to_ot_task", "sending frame from RCP to OpenThread");

                        if let Err(e) = rcp_to_ot_sender.send(frame) {
                            warn!(
                                tag = "rcp_to_ot_task",
                                "rcp_to_ot_sender.send() failed with {:?}", e
                            );
                            break;
                        }

                        // Notify our `process_poll` that it needs to call `platformRadioProcess`.
                        match rcp_to_ot_frame_ready_sender.try_send(()) {
                            Ok(()) => {}
                            Err(e) if e.is_full() => {}
                            Err(e) => {
                                warn!(
                                    tag = "rcp_to_ot_task",
                                    "rcp_to_ot_frame_ready_sender.send() failed with {:?}", e
                                );
                                break;
                            }
                        }
                    }
                    Err(e) => {
                        warn!(tag = "rcp_to_ot_task", "spinel_stream.next() failed with {:?}", e);
                        break;
                    }
                }
            }
            trace!(tag = "rcp_to_ot_task", "Stream ended.");
        });

        let (nat64_prefix_req_sender, nat64_prefix_req_receiver) = fmpsc::unbounded();

        unsafe {
            // Initialize our singleton
            PlatformBacking::set_singleton(PlatformBacking {
                ot_to_rcp_sender: RefCell::new(ot_to_rcp_sender),
                rcp_to_ot_receiver: RefCell::new(rcp_to_ot_receiver),
                alarm,
                netif_index_thread: builder.thread_netif_index,
                netif_index_backbone: builder.backbone_netif_index,
                trel: RefCell::new(None),
                infra_if: InfraIfInstance::new(builder.backbone_netif_index.unwrap_or(0)),
                is_platform_reset_requested: AtomicBool::new(false),
                nat64: Nat64Instance::new(nat64_prefix_req_sender),
                resolver: Resolver::new(),
            });

            // Initialize the lower-level platform implementation
            otSysInit(&mut otPlatformConfig { reset_rcp: false } as *mut otPlatformConfig);
        };

        Platform {
            timer_receiver,
            rcp_to_ot_frame_ready_receiver,
            ot_to_rcp_task,
            rcp_to_ot_task,
            nat64_platform_instance: Nat64PlatformInstance::new(nat64_prefix_req_receiver),
        }
    }
}

impl Drop for Platform {
    fn drop(&mut self) {
        debug!(tag = "openthread_fuchsia", "Dropping Platform");
        unsafe {
            // SAFETY: Both calls below must only be called from Drop.
            otSysDeinit();
            PlatformBacking::drop_singleton()
        }
    }
}

impl ot::Platform for Platform {
    unsafe fn process_poll(
        &mut self,
        instance: &ot::Instance,
        cx: &mut Context<'_>,
    ) -> Result<(), Error> {
        self.process_poll_alarm(instance, cx);
        self.process_poll_radio(instance, cx);
        self.process_poll_udp(instance, cx);
        self.process_poll_trel(instance, cx);
        self.process_poll_infra_if(instance, cx);
        self.process_poll_nat64(instance, cx);
        self.process_poll_tasks(cx);
        PlatformBacking::as_ref().resolver.process_poll_resolver(instance, cx);
        if PlatformBacking::as_ref().is_platform_reset_requested.load(Ordering::SeqCst) {
            return Err(PlatformResetRequested {}.into());
        }
        Ok(())
    }
}

impl Platform {
    fn process_poll_radio(&mut self, instance: &ot::Instance, cx: &mut Context<'_>) {
        let instance_ptr = instance.as_ot_ptr();

        while let Poll::Ready(Some(())) = self.rcp_to_ot_frame_ready_receiver.poll_next_unpin(cx) {
            trace!(tag = "rcp", "Firing platformRadioProcess");

            // SAFETY: Must be called with a valid pointer to otInstance,
            //         must also only be called from the main OpenThread thread,
            //         which is a guarantee of this method.
            unsafe {
                platformRadioProcess(instance_ptr, std::ptr::null());
            }
        }
    }

    fn process_poll_udp(&mut self, instance: &ot::Instance, cx: &mut Context<'_>) {
        for udp_socket in instance.udp_get_sockets() {
            // This `poll` call comes from the trait `UdpSocketHelpers` in `backing/udp.rs`
            if let Poll::Ready(Err(err)) = poll_ot_udp_socket(udp_socket, instance, cx) {
                error!(tag = "udp", "Error in {:?}: {:?}", udp_socket, err);
            }
        }
    }

    fn process_poll_trel(&mut self, instance: &ot::Instance, cx: &mut Context<'_>) {
        // Poll for discovery. This must be `mut` because it calls poll methods internally,
        // and is not reentrant.
        {
            // SAFETY: Guaranteed to only be called from the OpenThread thread.
            let mut trel = unsafe { PlatformBacking::as_ref() }.trel.borrow_mut();
            if let Some(trel) = trel.as_mut() {
                trel.poll(instance, cx);
            }
        }

        // Poll for I/O. This is separate from the above poll because it must not be
        // `mut` so that it can be reentrant.
        {
            // SAFETY: Guaranteed to only be called from the OpenThread thread.
            let trel = unsafe { PlatformBacking::as_ref() }.trel.borrow();
            if let Some(trel) = trel.as_ref() {
                trel.poll_io(instance, cx);
            }
        }
    }

    fn process_poll_infra_if(&mut self, instance: &ot::Instance, cx: &mut Context<'_>) {
        // SAFETY: Guaranteed to only be called from the OpenThread thread.
        let infra_if = unsafe { PlatformBacking::as_ref() }.infra_if.as_ref();
        if let Some(infra_if) = infra_if {
            infra_if.poll(instance, cx);
        }
    }

    fn process_poll_tasks(&mut self, cx: &mut Context<'_>) {
        if Poll::Ready(()) == self.rcp_to_ot_task.poll_unpin(cx) {
            panic!("Platform: rcp_to_ot_task finished unexpectedly");
        }

        if Poll::Ready(()) == self.ot_to_rcp_task.poll_unpin(cx) {
            panic!("Platform: ot_to_rcp_task finished unexpectedly");
        }
    }
}