use std::{convert::AsRef, fmt::Debug, sync::Arc};

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

use crate::{
	keyval::{KeyVal, result_deserialize, serialize_key},
	stream,
	util::is_incomplete,
};

/// Iterate key-value entries in the map starting from upper-bound.
///
/// - Query is serialized
/// - Result is deserialized
#[implement(super::Map)]
pub fn rev_stream_from<'a, K, V, P>(
	self: &'a Arc<Self>,
	from: &P,
) -> impl Stream<Item = Result<KeyVal<'_, K, V>>> + Send + use<'a, K, V, P>
where
	P: Serialize + ?Sized + Debug,
	K: Deserialize<'a> + Send,
	V: Deserialize<'a> + Send,
{
	self.rev_stream_from_raw(from)
		.map(result_deserialize::<K, V>)
}

/// Iterate key-value entries in the map starting from upper-bound.
///
/// - Query is serialized
/// - Result is raw
#[implement(super::Map)]
#[tracing::instrument(skip(self), level = "trace")]
pub fn rev_stream_from_raw<P>(
	self: &Arc<Self>,
	from: &P,
) -> impl Stream<Item = Result<KeyVal<'_>>> + Send + use<'_, P>
where
	P: Serialize + ?Sized + Debug,
{
	let key = serialize_key(from).expect("failed to serialize query key");
	self.rev_raw_stream_from(&key)
}

/// Iterate key-value entries in the map starting from upper-bound.
///
/// - Query is raw
/// - Result is deserialized
#[implement(super::Map)]
pub fn rev_stream_raw_from<'a, K, V, P>(
	self: &'a Arc<Self>,
	from: &P,
) -> impl Stream<Item = Result<KeyVal<'_, K, V>>> + Send + use<'a, K, V, P>
where
	P: AsRef<[u8]> + ?Sized + Debug + Sync,
	K: Deserialize<'a> + Send,
	V: Deserialize<'a> + Send,
{
	self.rev_raw_stream_from(from)
		.map(result_deserialize::<K, V>)
}

/// Iterate key-value entries in the map starting from upper-bound.
///
/// - Query is raw
/// - Result is raw
#[implement(super::Map)]
#[tracing::instrument(skip(self, from), fields(%self), level = "trace")]
pub fn rev_raw_stream_from<P>(
	self: &Arc<Self>,
	from: &P,
) -> impl Stream<Item = Result<KeyVal<'_>>> + Send + use<'_, P>
where
	P: AsRef<[u8]> + ?Sized + Debug,
{
	use crate::pool::Seek;

	let opts = super::iter_options_default(&self.db);
	let state = stream::State::new(self, opts);
	if is_cached(self, from) {
		let state = state.init_rev(from.as_ref().into());
		return task::consume_budget()
			.map(move |()| stream::ItemsRev::<'_>::from(state))
			.into_stream()
			.flatten()
			.boxed();
	};

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

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

#[tracing::instrument(
    name = "cached",
    level = "trace",
    skip(map, from),
    fields(%map),
)]
pub(super) fn is_cached<P>(map: &Arc<super::Map>, from: &P) -> bool
where
	P: AsRef<[u8]> + ?Sized,
{
	let cache_opts = super::cache_iter_options_default(&map.db);
	let cache_status = stream::State::new(map, cache_opts)
		.init_rev(from.as_ref().into())
		.status();

	!matches!(cache_status, Some(e) if is_incomplete(&e))
}