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use std::fmt::Debug;
use std::num::NonZeroUsize;
use std::time::Duration;

use tokio::{sync::mpsc::UnboundedReceiver, time::interval};

use crate::{client::NoopClient, dispatch::LogEvent, CloudWatchClient};

#[derive(Debug, Clone)]
pub struct ExportConfig {
    batch_size: NonZeroUsize,
    interval: Duration,
    destination: LogDestination,
}

#[derive(Debug, Clone, Default)]
pub struct LogDestination {
    pub log_group_name: String,
    pub log_stream_name: String,
}

impl Default for ExportConfig {
    fn default() -> Self {
        Self {
            batch_size: NonZeroUsize::new(5).unwrap(),
            interval: Duration::from_secs(5),
            destination: LogDestination::default(),
        }
    }
}

impl ExportConfig {
    pub fn with_batch_size<T>(self, batch_size: T) -> Self
    where
        T: TryInto<NonZeroUsize>,
        <T as TryInto<NonZeroUsize>>::Error: Debug,
    {
        Self {
            batch_size: batch_size
                .try_into()
                .expect("batch size must be greater than or equal to 1"),
            ..self
        }
    }

    pub fn with_interval(self, interval: Duration) -> Self {
        Self { interval, ..self }
    }

    pub fn with_log_group_name(self, log_group_name: impl Into<String>) -> Self {
        Self {
            destination: LogDestination {
                log_group_name: log_group_name.into(),
                log_stream_name: self.destination.log_stream_name,
            },
            ..self
        }
    }

    pub fn with_log_stream_name(self, log_stream_name: impl Into<String>) -> Self {
        Self {
            destination: LogDestination {
                log_stream_name: log_stream_name.into(),
                log_group_name: self.destination.log_group_name,
            },
            ..self
        }
    }
}

pub(crate) struct BatchExporter<C> {
    client: C,
    queue: Vec<LogEvent>,
    config: ExportConfig,
}

impl Default for BatchExporter<NoopClient> {
    fn default() -> Self {
        Self::new(NoopClient::new(), ExportConfig::default())
    }
}

impl<C> BatchExporter<C> {
    pub(crate) fn new(client: C, config: ExportConfig) -> Self {
        Self {
            client,
            config,
            queue: Vec::new(),
        }
    }
}

impl<C> BatchExporter<C>
where
    C: CloudWatchClient + Send + Sync + 'static,
{
    pub(crate) async fn run(self, mut rx: UnboundedReceiver<LogEvent>) {
        let BatchExporter {
            client,
            mut queue,
            config,
        } = self;

        let mut interval = interval(config.interval);

        loop {
            tokio::select! {
                 _ = interval.tick() => {
                    if queue.is_empty() {
                        continue;
                    }
                }
                event = rx.recv() => {
                    let Some(event) = event else {
                        break;
                    };

                    queue.push(event);
                    if queue.len() < config.batch_size.into() {
                        continue
                    }
                }
            }

            let logs = queue.drain(..).collect();

            if let Err(err) = client.put_logs(config.destination.clone(), logs).await {
                eprintln!(
                    "[tracing-cloudwatch] Unable to put logs to cloudwatch. Error: {err} {:?}",
                    config.destination
                );
            }
        }
    }
}