//! Connects to the Bluetooth GATT echo service and tests it.

use bluer::{gatt::remote::Characteristic, AdapterEvent, Device, Result};
use futures::{pin_mut, StreamExt};
use rand::Rng;
use std::time::Duration;
use tokio::{
    io::{AsyncReadExt, AsyncWriteExt},
    time::{sleep, timeout},
};

include!("gatt_echo.inc");

async fn find_our_characteristic(device: &Device) -> Result<Option<Characteristic>> {
    let addr = device.address();
    let uuids = device.uuids().await?.unwrap_or_default();
    println!("Discovered device {} with service UUIDs {:?}", addr, &uuids);
    let md = device.manufacturer_data().await?;
    println!("    Manufacturer data: {:x?}", &md);

    if uuids.contains(&SERVICE_UUID) {
        println!("    Device provides our service!");
        if !device.is_connected().await? {
            println!("    Connecting...");
            let mut retries = 2;
            loop {
                match device.connect().await {
                    Ok(()) => break,
                    Err(err) if retries > 0 => {
                        println!("    Connect error: {}", &err);
                        retries -= 1;
                    }
                    Err(err) => return Err(err),
                }
            }
            println!("    Connected");
        } else {
            println!("    Already connected");
        }

        println!("    Enumerating services...");
        for service in device.services().await? {
            let uuid = service.uuid().await?;
            println!("    Service UUID: {}", &uuid);
            if uuid == SERVICE_UUID {
                println!("    Found our service!");
                for char in service.characteristics().await? {
                    let uuid = char.uuid().await?;
                    println!("    Characteristic UUID: {}", &uuid);
                    if uuid == CHARACTERISTIC_UUID {
                        println!("    Found our characteristic!");
                        return Ok(Some(char));
                    }
                }
            }
        }

        println!("    Not found!");
    }

    Ok(None)
}

async fn exercise_characteristic(char: &Characteristic) -> Result<()> {
    let mut write_io = char.write_io().await?;
    println!("    Obtained write IO with MTU {} bytes", write_io.mtu());
    let mut notify_io = char.notify_io().await?;
    println!("    Obtained notification IO with MTU {} bytes", notify_io.mtu());

    // Flush notify buffer.
    let mut buf = [0; 1024];
    while let Ok(Ok(_)) = timeout(Duration::from_secs(1), notify_io.read(&mut buf)).await {}

    let mut rng = rand::thread_rng();
    for i in 0..1024 {
        let mut len = rng.gen_range(0..20000);

        // Try to trigger packet reordering over EATT.
        if i % 10 == 0 {
            // Big packet is split into multiple small packets.
            // (by L2CAP layer, because GATT MTU is bigger than L2CAP MTU)
            len = write_io.mtu(); // 512
        }
        if i % 10 == 1 {
            // Small packet can use different L2CAP channel when EATT is enabled.
            len = 20;
        }
        // Thus small packet can arrive before big packet.
        // The solution is to disable EATT in /etc/bluetooth/main.conf.

        println!("    Test iteration {i} with data size {len}");
        let data: Vec<u8> = (0..len).map(|_| rng.gen()).collect();

        // We must read back the data while sending, otherwise the connection
        // buffer will overrun and we will lose data.
        let read_task = tokio::spawn(async move {
            let mut echo_buf = vec![0u8; len];
            let res = match notify_io.read_exact(&mut echo_buf).await {
                Ok(_) => Ok(echo_buf),
                Err(err) => Err(err),
            };
            (notify_io, res)
        });

        // Note that write_all will automatically split the buffer into
        // multiple writes of MTU size.
        write_io.write_all(&data).await.expect("write failed");

        println!("    Waiting for echo");
        let (notify_io_back, res) = read_task.await.unwrap();
        notify_io = notify_io_back;
        let echo_buf = res.expect("read failed");

        if echo_buf != data {
            println!();
            println!("Echo data mismatch!");
            println!("Send data:     {:x?}", &data);
            println!("Received data: {:x?}", &echo_buf);
            println!();
            println!("By 512 blocks:");
            for (sent, recv) in data.chunks(512).zip(echo_buf.chunks(512)) {
                println!();
                println!(
                    "Send: {:x?} ... {:x?}",
                    &sent[0..4.min(sent.len())],
                    &sent[sent.len().saturating_sub(4)..]
                );
                println!(
                    "Recv: {:x?} ... {:x?}",
                    &recv[0..4.min(recv.len())],
                    &recv[recv.len().saturating_sub(4)..]
                );
            }
            println!();

            panic!("echoed data does not match sent data");
        }
        println!("    Data matches");
    }

    println!("    Test okay");
    Ok(())
}

#[tokio::main]
async fn main() -> bluer::Result<()> {
    env_logger::init();
    let session = bluer::Session::new().await?;
    let adapter = session.default_adapter().await?;
    adapter.set_powered(true).await?;

    {
        println!(
            "Discovering on Bluetooth adapter {} with address {}\n",
            adapter.name(),
            adapter.address().await?
        );
        let discover = adapter.discover_devices().await?;
        pin_mut!(discover);
        let mut done = false;
        while let Some(evt) = discover.next().await {
            match evt {
                AdapterEvent::DeviceAdded(addr) => {
                    let device = adapter.device(addr)?;
                    match find_our_characteristic(&device).await {
                        Ok(Some(char)) => match exercise_characteristic(&char).await {
                            Ok(()) => {
                                println!("    Characteristic exercise completed");
                                done = true;
                            }
                            Err(err) => {
                                println!("    Characteristic exercise failed: {}", &err);
                            }
                        },
                        Ok(None) => (),
                        Err(err) => {
                            println!("    Device failed: {}", &err);
                            let _ = adapter.remove_device(device.address()).await;
                        }
                    }
                    match device.disconnect().await {
                        Ok(()) => println!("    Device disconnected"),
                        Err(err) => println!("    Device disconnection failed: {}", &err),
                    }
                    println!();
                }
                AdapterEvent::DeviceRemoved(addr) => {
                    println!("Device removed {addr}");
                }
                _ => (),
            }
            if done {
                break;
            }
        }
        println!("Stopping discovery");
    }

    sleep(Duration::from_secs(1)).await;
    Ok(())
}