#![forbid(unsafe_code)]

use crate::app::{flatten_handle, flatten_handles, Web3ProxyApp};
use crate::config::TopConfig;
use crate::{frontend, prometheus};
use argh::FromArgs;
use futures::StreamExt;
use num::Zero;
use std::path::PathBuf;
use std::sync::atomic::AtomicU16;
use std::sync::Arc;
use std::time::Duration;
use std::{fs, thread};
use tokio::select;
use tokio::sync::{broadcast, oneshot};
use tokio::time::{sleep_until, Instant};
use tracing::{error, info, trace, warn};

/// start the main proxy daemon
#[derive(FromArgs, PartialEq, Debug, Eq)]
#[argh(subcommand, name = "proxyd")]
pub struct ProxydSubCommand {
    /// path to a toml of rpc servers
    /// what port the proxy should listen on
    #[argh(option, default = "8544")]
    pub port: u16,

    /// what port the proxy should expose prometheus stats on
    #[argh(option, default = "8543")]
    pub prometheus_port: u16,
}

impl ProxydSubCommand {
    pub async fn main(
        self,
        top_config: TopConfig,
        top_config_path: PathBuf,
        num_workers: usize,
    ) -> anyhow::Result<()> {
        let (frontend_shutdown_sender, _) = broadcast::channel(1);
        // TODO: i think there is a small race. if config_path changes

        let frontend_port = Arc::new(self.port.into());
        let prometheus_port = Arc::new(self.prometheus_port.into());
        let (_flush_stat_buffer_sender, flush_stat_buffer_receiver) = flume::bounded(1);

        Self::_main(
            top_config,
            Some(top_config_path),
            frontend_port,
            prometheus_port,
            num_workers,
            frontend_shutdown_sender,
            flush_stat_buffer_receiver,
        )
        .await
    }

    /// this shouldn't really be pub except it makes test fixtures easier
    pub async fn _main(
        top_config: TopConfig,
        top_config_path: Option<PathBuf>,
        frontend_port: Arc<AtomicU16>,
        prometheus_port: Arc<AtomicU16>,
        num_workers: usize,
        frontend_shutdown_sender: broadcast::Sender<()>,
        flush_stat_buffer_receiver: flume::Receiver<oneshot::Sender<(usize, usize)>>,
    ) -> anyhow::Result<()> {
        // tokio has code for catching ctrl+c so we use that to shut down in most cases
        // frontend_shutdown_sender is currently only used in tests, but we might make a /shutdown endpoint or something
        // we do not need this receiver. new receivers are made by `shutdown_sender.subscribe()`
        let (app_shutdown_sender, _app_shutdown_receiver) = broadcast::channel(1);

        let frontend_shutdown_receiver = frontend_shutdown_sender.subscribe();
        let prometheus_shutdown_receiver = app_shutdown_sender.subscribe();

        // TODO: should we use a watch or broadcast for these?
        let (frontend_shutdown_complete_sender, mut frontend_shutdown_complete_receiver) =
            broadcast::channel(1);

        // start the main app
        let mut spawned_app = Web3ProxyApp::spawn(
            frontend_port,
            prometheus_port,
            top_config.clone(),
            num_workers,
            app_shutdown_sender.clone(),
            flush_stat_buffer_receiver,
        )
        .await?;

        let mut head_block_receiver = spawned_app.app.head_block_receiver();

        // start thread for watching config
        if let Some(top_config_path) = top_config_path {
            let config_sender = spawned_app.new_top_config;
            {
                let mut current_config = config_sender.borrow().clone();

                thread::spawn(move || loop {
                    match fs::read_to_string(&top_config_path) {
                        Ok(new_top_config) => match toml::from_str::<TopConfig>(&new_top_config) {
                            Ok(new_top_config) => {
                                if new_top_config != current_config {
                                    // TODO: print the differences
                                    // TODO: first run seems to always see differences. why?
                                    info!("config @ {:?} changed", top_config_path);
                                    config_sender.send(new_top_config.clone()).unwrap();
                                    current_config = new_top_config;
                                }
                            }
                            Err(err) => {
                                // TODO: panic?
                                error!("Unable to parse config! {:#?}", err);
                            }
                        },
                        Err(err) => {
                            // TODO: panic?
                            error!("Unable to read config! {:#?}", err);
                        }
                    }

                    thread::sleep(Duration::from_secs(10));
                });
            }
        }

        // start the prometheus metrics port
        let prometheus_handle = tokio::spawn(prometheus::serve(
            spawned_app.app.clone(),
            prometheus_shutdown_receiver,
        ));

        info!("waiting for head block");
        let max_wait_until = Instant::now() + Duration::from_secs(35);
        loop {
            select! {
                _ = sleep_until(max_wait_until) => {
                    return Err(anyhow::anyhow!("oh no! we never got a head block!"))
                }
                _ = head_block_receiver.changed() => {
                    if let Some(head_block) = spawned_app
                        .app
                        .head_block_receiver()
                        .borrow_and_update()
                        .as_ref()
                    {
                        info!(head_hash=?head_block.hash(), head_num=%head_block.number());
                        break;
                    } else {
                        info!("no head block yet!");
                        continue;
                    }
                }
            }
        }

        // start the frontend port
        let frontend_handle = tokio::spawn(frontend::serve(
            spawned_app.app,
            frontend_shutdown_receiver,
            frontend_shutdown_complete_sender,
        ));

        let frontend_handle = flatten_handle(frontend_handle);

        // if everything is working, these should all run forever
        let mut exited_with_err = false;
        let mut frontend_exited = false;
        tokio::select! {
            x = flatten_handles(spawned_app.app_handles) => {
                match x {
                    Ok(_) => info!("app_handle exited"),
                    Err(e) => {
                        error!("app_handle exited: {:#?}", e);
                        exited_with_err = true;
                    }
                }
            }
            x = frontend_handle => {
                frontend_exited = true;
                match x {
                    Ok(_) => info!("frontend exited"),
                    Err(e) => {
                        error!("frontend exited: {:#?}", e);
                        exited_with_err = true;
                    }
                }
            }
            x = flatten_handle(prometheus_handle) => {
                match x {
                    Ok(_) => info!("prometheus exited"),
                    Err(e) => {
                        error!("prometheus exited: {:#?}", e);
                        exited_with_err = true;
                    }
                }
            }
            x = tokio::signal::ctrl_c() => {
                // TODO: unix terminate signal, too
                match x {
                    Ok(_) => info!("quiting from ctrl-c"),
                    Err(e) => {
                        // TODO: i don't think this is possible
                        error!("error quiting from ctrl-c: {:#?}", e);
                        exited_with_err = true;
                    }
                }
            }
            // TODO: This seems to have been removed on the main branch
            // TODO: how can we properly watch background handles here? this returns None immediatly and the app exits. i think the bug is somewhere else though
            x = spawned_app.background_handles.next() => {
                match x {
                    Some(Ok(_)) => info!("quiting from background handles"),
                    Some(Err(e)) => {
                        error!("quiting from background handle error: {:#?}", e);
                        exited_with_err = true;
                    }
                    None => {
                        // TODO: is this an error?
                        warn!("background handles exited");
                    }
                }
            }
        };

        // TODO: This is also not there on the main branch
        // if a future above completed, make sure the frontend knows to start turning off
        if !frontend_exited {
            if let Err(err) = frontend_shutdown_sender.send(()) {
                // TODO: this is actually expected if the frontend is already shut down
                warn!(?err, "shutdown sender");
            };
        }

        // TODO: Also not there on main branch
        // TODO: wait until the frontend completes
        if let Err(err) = frontend_shutdown_complete_receiver.recv().await {
            warn!(?err, "shutdown completition");
        } else {
            info!("frontend exited gracefully");
        }

        // now that the frontend is complete, tell all the other futures to finish
        if let Err(err) = app_shutdown_sender.send(()) {
            warn!(?err, "backend sender");
        };

        info!(
            "waiting on {} important background tasks",
            spawned_app.background_handles.len()
        );
        let mut background_errors = 0;
        while let Some(x) = spawned_app.background_handles.next().await {
            match x {
                Err(e) => {
                    error!("{:?}", e);
                    background_errors += 1;
                }
                Ok(Err(e)) => {
                    error!("{:?}", e);
                    background_errors += 1;
                }
                Ok(Ok(_)) => {
                    // TODO: how can we know which handle exited?
                    trace!("a background handle exited");
                    continue;
                }
            }
        }

        if background_errors.is_zero() && !exited_with_err {
            info!("finished");
            Ok(())
        } else {
            // TODO: collect all the errors here instead?
            Err(anyhow::anyhow!("finished with errors!"))
        }
    }
}