// Copyright 2023 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.

use futures::stream::{FusedStream, Stream, StreamExt};
use std::sync::Arc;
use std::task::Poll;

use bt_bass::types::BroadcastId;
use bt_common::packet_encoding::Decodable;
use bt_common::packet_encoding::Error as PacketError;
use bt_common::PeerId;
use bt_gatt::central::{AdvertisingDatum, ScanResult};
use core::pin::Pin;

use crate::assistant::{
    DiscoveredBroadcastSources, Error, BASIC_AUDIO_ANNOUNCEMENT_SERVICE,
    BROADCAST_AUDIO_ANNOUNCEMENT_SERVICE,
};
use crate::types::{BroadcastAudioSourceEndpoint, BroadcastSource};

#[derive(Debug)]
pub enum Event {
    FoundBroadcastSource { peer: PeerId, source: BroadcastSource },
    CouldNotParseAdvertisingData { peer: PeerId, error: PacketError },
}

/// A stream of discovered broadcast sources.
/// This stream polls the scan results from GATT client to discover
/// available broadcast sources.
pub struct EventStream {
    // Central scan result stream for finding broadcast sources.
    scan_result_stream: Pin<Box<dyn Stream<Item = Result<ScanResult, bt_gatt::types::Error>>>>,
    terminated: bool,

    broadcast_sources: Arc<DiscoveredBroadcastSources>,
}

impl EventStream {
    pub(crate) fn new(
        scan_result_stream: impl Stream<Item = Result<ScanResult, bt_gatt::types::Error>> + 'static,
        broadcast_sources: Arc<DiscoveredBroadcastSources>,
    ) -> Self {
        Self {
            scan_result_stream: Box::pin(scan_result_stream),
            terminated: false,
            broadcast_sources,
        }
    }

    /// Returns the broadcast source if the scanned peer is a broadcast source.
    /// Returns an error if parsing of the scan result data fails and None if
    /// the scanned peer is not a broadcast source.
    fn try_into_broadcast_source(
        scan_result: &ScanResult,
    ) -> Result<Option<BroadcastSource>, PacketError> {
        let mut source = None;
        for datum in &scan_result.advertised {
            let AdvertisingDatum::ServiceData(uuid, data) = datum else {
                continue;
            };
            if *uuid == BROADCAST_AUDIO_ANNOUNCEMENT_SERVICE {
                let (bid, _) = BroadcastId::decode(data.as_slice())?;
                source.get_or_insert(BroadcastSource::default()).with_broadcast_id(bid);
            } else if *uuid == BASIC_AUDIO_ANNOUNCEMENT_SERVICE {
                // TODO(dayeonglee): revisit when we implement periodic advertisement.
                let (base, _) = BroadcastAudioSourceEndpoint::decode(data.as_slice())?;
                source.get_or_insert(BroadcastSource::default()).with_endpoint(base);
            }
        }
        Ok(source)
    }
}

impl FusedStream for EventStream {
    fn is_terminated(&self) -> bool {
        self.terminated
    }
}

impl Stream for EventStream {
    type Item = Result<Event, Error>;

    fn poll_next(
        mut self: std::pin::Pin<&mut Self>,
        cx: &mut std::task::Context<'_>,
    ) -> Poll<Option<Self::Item>> {
        if self.terminated {
            return Poll::Ready(None);
        }

        // Poll scan result stream to check if there were any newly discovered peers
        // that we're interested in.
        match futures::ready!(self.scan_result_stream.poll_next_unpin(cx)) {
            Some(Ok(scanned)) => {
                match Self::try_into_broadcast_source(&scanned) {
                    Err(e) => {
                        return Poll::Ready(Some(Ok(Event::CouldNotParseAdvertisingData {
                            peer: scanned.id,
                            error: e,
                        })));
                    }
                    Ok(Some(found_source)) => {
                        // If we found a broadcast source, we add its information in the
                        // internal records.
                        let (broadcast_source, changed) = self
                            .broadcast_sources
                            .merge_broadcast_source_data(&scanned.id, &found_source);

                        // Broadcast found event is relayed to the client iff complete
                        // information has been gathered.
                        if broadcast_source.into_add_source() && changed {
                            return Poll::Ready(Some(Ok(Event::FoundBroadcastSource {
                                peer: scanned.id,
                                source: broadcast_source,
                            })));
                        }

                        Poll::Pending
                    }
                    Ok(None) => Poll::Pending,
                }
            }
            None | Some(Err(_)) => {
                self.terminated = true;
                Poll::Ready(Some(Err(Error::CentralScanTerminated)))
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use assert_matches::assert_matches;

    use bt_common::core::{AddressType, AdvertisingSetId};
    use bt_gatt::central::{AdvertisingDatum, PeerName};
    use bt_gatt::test_utils::ScannedResultStream;
    use bt_gatt::types::Error as BtGattError;
    use bt_gatt::types::GattError;

    fn setup_stream() -> (EventStream, ScannedResultStream) {
        let fake_scan_result_stream = ScannedResultStream::new();
        let broadcast_sources = DiscoveredBroadcastSources::new();

        (
            EventStream::new(fake_scan_result_stream.clone(), broadcast_sources),
            fake_scan_result_stream,
        )
    }

    #[test]
    fn poll_found_broadcast_source_events() {
        let (mut stream, mut scan_result_stream) = setup_stream();

        // Scanned a broadcast source and its broadcast id.
        let broadcast_source_pid = PeerId(1005);

        scan_result_stream.set_scanned_result(Ok(ScanResult {
            id: broadcast_source_pid,
            connectable: true,
            name: PeerName::Unknown,
            advertised: vec![AdvertisingDatum::ServiceData(
                BROADCAST_AUDIO_ANNOUNCEMENT_SERVICE,
                vec![0x01, 0x02, 0x03],
            )],
        }));

        // Found broadcast source event shouldn't have been sent since braodcast source
        // information isn't complete.
        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        assert!(stream.poll_next_unpin(&mut noop_cx).is_pending());

        // Pretend somehow address, address type, and advertising sid were
        // filled out. This completes the broadcast source information.
        // TODO(b/308481381): replace this block with sending a central scan result that
        // contains the data.
        let _ = stream.broadcast_sources.merge_broadcast_source_data(
            &broadcast_source_pid,
            &BroadcastSource::default()
                .with_address([1, 2, 3, 4, 5, 6])
                .with_address_type(AddressType::Public)
                .with_advertising_sid(AdvertisingSetId(1)),
        );

        // Scanned broadcast source's BASE data.
        // TODO(b/308481381): replace this block sending data through PA train instead.
        #[rustfmt::skip]
        let base_data = vec![
            0x10, 0x20, 0x30, 0x02, // presentation delay, num of subgroups
            0x01, 0x03, 0x00, 0x00, 0x00, 0x00, // num of bis, codec id (big #1)
            0x00, // codec specific config len
            0x00, // metadata len,
            0x01, 0x00, // bis index, codec specific config len (big #1 / bis #1)
            0x01, 0x02, 0x00, 0x00, 0x00, 0x00, // num of bis, codec id (big #2)
            0x00, // codec specific config len
            0x00, // metadata len,
            0x01, 0x03, 0x02, 0x05,
            0x08, /* bis index, codec specific config len, codec frame blocks LTV
                    * (big #2 / bis #2) */
        ];

        scan_result_stream.set_scanned_result(Ok(ScanResult {
            id: broadcast_source_pid,
            connectable: true,
            name: PeerName::Unknown,
            advertised: vec![AdvertisingDatum::ServiceData(
                BASIC_AUDIO_ANNOUNCEMENT_SERVICE,
                base_data.clone(),
            )],
        }));

        // Expect the stream to send out broadcast source found event since information
        // is complete.
        let Poll::Ready(Some(Ok(event))) = stream.poll_next_unpin(&mut noop_cx) else {
            panic!("should have received event");
        };
        assert_matches!(event, Event::FoundBroadcastSource{peer, ..} => {
            assert_eq!(peer, broadcast_source_pid)
        });

        assert!(stream.poll_next_unpin(&mut noop_cx).is_pending());

        // Scanned the same broadcast source's BASE data.
        scan_result_stream.set_scanned_result(Ok(ScanResult {
            id: broadcast_source_pid,
            connectable: true,
            name: PeerName::Unknown,
            advertised: vec![AdvertisingDatum::ServiceData(
                BASIC_AUDIO_ANNOUNCEMENT_SERVICE,
                base_data.clone(),
            )],
        }));

        // Shouldn't have gotten the event again since the information remained the
        // same.
        assert!(stream.poll_next_unpin(&mut noop_cx).is_pending());
    }

    #[test]
    fn central_scan_stream_terminates() {
        let (mut stream, mut scan_result_stream) = setup_stream();

        // Mimick scan error.
        scan_result_stream.set_scanned_result(Err(BtGattError::Gatt(GattError::InvalidPdu)));

        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        match stream.poll_next_unpin(&mut noop_cx) {
            Poll::Ready(Some(Err(e))) => assert_matches!(e, Error::CentralScanTerminated),
            _ => panic!("should have received central scan terminated error"),
        }

        // Entire stream should have terminated.
        assert_matches!(stream.poll_next_unpin(&mut noop_cx), Poll::Ready(None));
        assert_matches!(stream.is_terminated(), true);
    }
}