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use std::{
    collections::VecDeque,
    marker::PhantomData,
    sync::{Arc, Mutex},
};

use derivative::Derivative;
use enclose::enclose;
use futures::{
    future::{self, Either},
    Future, FutureExt,
};
use serde::Serialize;

use crate::{
    models::{ctx::Ctx, streaming_server::StreamingServer},
    runtime::{Env, EnvError, TryEnvFuture},
    types::{
        api::{fetch_api, APIRequest, APIResult, SuccessResponse},
        profile::AuthKey,
    },
};

#[cfg(debug_assertions)]
use crate::{runtime::EnvFutureExt, types::True};

#[derive(Clone, PartialEq, Serialize, Debug)]
struct Event {
    #[serde(flatten)]
    data: serde_json::Value,
    #[serde(rename = "eventName")]
    name: String,
    #[serde(rename = "eventTime")]
    time: i64,
    #[serde(rename = "eventNumber")]
    number: u64,
    #[serde(rename = "app")]
    context: serde_json::Value,
}

#[derive(Clone, PartialEq, Debug)]
struct EventsBatch {
    auth_key: AuthKey,
    events: Vec<Event>,
}

#[derive(Default)]
struct State {
    number: u64,
    queue: VecDeque<EventsBatch>,
    pending: Option<EventsBatch>,
}

impl State {
    fn next_number(&mut self) -> u64 {
        self.number = self.number.wrapping_add(1);
        self.number
    }
    fn pop_batch(&mut self) -> Option<EventsBatch> {
        self.queue.pop_front()
    }
    fn push_event(&mut self, event: Event, auth_key: AuthKey) {
        match self.queue.back_mut() {
            Some(batch) if batch.auth_key == auth_key => {
                batch.events.push(event);
            }
            _ => self.queue.push_back(EventsBatch {
                auth_key,
                events: vec![event],
            }),
        };
    }
    fn revert_pending(&mut self) {
        if let Some(batch) = self.pending.take() {
            self.queue.push_front(batch);
        };
    }
}

#[derive(Derivative)]
#[derivative(Default)]
pub struct Analytics<E: Env> {
    state: Arc<Mutex<State>>,
    env: PhantomData<E>,
}

impl<E: Env + 'static> Analytics<E> {
    pub fn emit(
        &self,
        name: String,
        data: serde_json::Value,
        ctx: &Ctx,
        streaming_server: &StreamingServer,
        path: &str,
    ) {
        let mut state = self.state.lock().expect("analytics state lock failed");
        let auth_key = match ctx.profile.auth_key() {
            Some(auth_key) => auth_key.to_owned(),
            _ => return,
        };
        let event = Event {
            name,
            data,
            number: state.next_number(),
            time: E::now().timestamp_millis(),
            context: E::analytics_context(ctx, streaming_server, path),
        };
        state.push_event(event, auth_key);
    }
    pub fn send_next_batch(&self) -> impl Future<Output = ()> {
        let mut state = self.state.lock().expect("analytics state lock failed");
        if state.pending.is_none() {
            let batch = state.pop_batch();
            if let Some(batch) = batch {
                state.pending = Some(batch.to_owned());
                return Either::Left(
                    send_events_batch_to_api::<E>(&batch)
                        .map(|result| match result {
                            Ok(APIResult::Err(error)) if error.code != 1 => Err(()),
                            Err(EnvError::Fetch(_)) | Err(EnvError::Serde(_)) => Err(()),
                            _ => Ok(()),
                        })
                        .then(enclose!((self.state => state) move |result| async move {
                            let mut state = state.lock().expect("analytics state lock failed");
                            if state.pending == Some(batch) {
                                match result {
                                    Ok(_) => {
                                        state.pending = None;
                                    }
                                    Err(_) => {
                                        state.revert_pending();
                                    }
                                };
                            };
                        })),
                );
            };
        };
        Either::Right(future::ready(()))
    }
    pub fn flush(&self) -> impl Future<Output = ()> {
        let mut state = self.state.lock().expect("analytics state lock failed");
        state.pending = None;
        future::join_all(
            state
                .queue
                .drain(..)
                .map(|batch| send_events_batch_to_api::<E>(&batch)),
        )
        .map(|_| ())
    }
}

fn send_events_batch_to_api<E: Env>(
    batch: &EventsBatch,
) -> TryEnvFuture<APIResult<SuccessResponse>> {
    #[cfg(debug_assertions)]
    if cfg!(debug_assertions) {
        E::log(format!("send_events_batch_to_api: {:#?}", &batch));
        return future::ok(APIResult::Ok(SuccessResponse { success: True })).boxed_env();
    };

    fetch_api::<E, _, _, _>(&APIRequest::Events {
        auth_key: batch.auth_key.to_owned(),
        events: batch
            .events
            .iter()
            .map(|value| serde_json::to_value(value).unwrap())
            .collect(),
    })
}