use std::sync::Arc;

use conduwuit::Result;
use futures::{FutureExt, Stream, StreamExt, TryFutureExt, TryStreamExt};
use rocksdb::Direction;
use serde::Deserialize;
use tokio::task;

use super::rev_stream::is_cached;
use crate::{keyval, keyval::Key, stream};

impl super::Map {
	pub fn rev_keys<'a, K>(self: &'a Arc<Self>) -> impl Stream<Item = Result<Key<'a, K>>> + Send
	where
		K: Deserialize<'a> + Send,
	{
		self.rev_raw_keys().map(keyval::result_deserialize_key::<K>)
	}

	#[tracing::instrument(skip(self), fields(%self), level = "trace")]
	pub fn rev_raw_keys(self: &Arc<Self>) -> impl Stream<Item = Result<Key<'_>>> + Send {
		use crate::pool::Seek;

		let opts = super::iter_options_default(&self.db);
		let state = stream::State::new(self, opts);
		if is_cached(self) {
			let state = state.init_rev(None);
			return task::consume_budget()
				.map(move |()| stream::KeysRev::<'_>::from(state))
				.into_stream()
				.flatten()
				.boxed();
		}

		let seek = Seek {
			map: self.clone(),
			dir: Direction::Reverse,
			state: crate::pool::into_send_seek(state),
			key: None,
			res: None,
		};

		self.db
			.pool
			.execute_iter(seek)
			.ok_into::<stream::KeysRev<'_>>()
			.into_stream()
			.try_flatten()
			.boxed()
	}
}
