use heed::RoTxn;
use roaring::RoaringBitmap;

use super::{
    db_cache::DatabaseCache, RankingRule, RankingRuleOutput, RankingRuleOutputIter,
    RankingRuleOutputIterWrapper, RankingRuleQueryTrait,
};
use crate::{
    // facet::FacetType,
    heed_codec::{facet::FacetGroupKeyCodec, ByteSliceRefCodec},
    search::facet::{ascending_facet_sort, descending_facet_sort},
    FieldId,
    Index,
    Result,
};

// TODO: The implementation of Sort is not correct:
// (1) it should not return documents it has already returned (does the current implementation have the same bug?)
// (2) at the end, it should return all the remaining documents (this could be ensured at the trait level?)

pub struct Sort<'transaction, Query> {
    field_id: Option<FieldId>,
    is_ascending: bool,
    iter: Option<RankingRuleOutputIterWrapper<'transaction, Query>>,
}
impl<'transaction, Query> Sort<'transaction, Query> {
    pub fn new(
        index: &'transaction Index,
        rtxn: &'transaction heed::RoTxn,
        field_name: String,
        is_ascending: bool,
    ) -> Result<Self> {
        let fields_ids_map = index.fields_ids_map(rtxn)?;
        let field_id = fields_ids_map.id(&field_name);

        // TODO: What is this, why?
        // let faceted_candidates = match field_id {
        //     Some(field_id) => {
        //         let number_faceted =
        //             index.faceted_documents_ids(rtxn, field_id, FacetType::Number)?;
        //         let string_faceted =
        //             index.faceted_documents_ids(rtxn, field_id, FacetType::String)?;
        //         number_faceted | string_faceted
        //     }
        //     None => RoaringBitmap::default(),
        // };

        Ok(Self { field_id, is_ascending, iter: None })
    }
}

impl<'transaction, Query: RankingRuleQueryTrait> RankingRule<'transaction, Query>
    for Sort<'transaction, Query>
{
    fn start_iteration(
        &mut self,
        index: &Index,
        txn: &'transaction RoTxn,
        _db_cache: &mut DatabaseCache<'transaction>,
        parent_candidates: &RoaringBitmap,
        parent_query_graph: &Query,
    ) -> Result<()> {
        let iter: RankingRuleOutputIterWrapper<Query> = match self.field_id {
            Some(field_id) => {
                let make_iter =
                    if self.is_ascending { ascending_facet_sort } else { descending_facet_sort };

                let number_iter = make_iter(
                    txn,
                    index
                        .facet_id_f64_docids
                        .remap_key_type::<FacetGroupKeyCodec<ByteSliceRefCodec>>(),
                    field_id,
                    parent_candidates.clone(),
                )?;

                let string_iter = make_iter(
                    txn,
                    index
                        .facet_id_string_docids
                        .remap_key_type::<FacetGroupKeyCodec<ByteSliceRefCodec>>(),
                    field_id,
                    parent_candidates.clone(),
                )?;
                let query_graph = parent_query_graph.clone();
                RankingRuleOutputIterWrapper::new(Box::new(number_iter.chain(string_iter).map(
                    move |docids| {
                        Ok(RankingRuleOutput { query: query_graph.clone(), candidates: docids? })
                    },
                )))
            }
            None => RankingRuleOutputIterWrapper::new(Box::new(std::iter::empty())),
        };
        self.iter = Some(iter);
        Ok(())
    }

    fn next_bucket(
        &mut self,
        _index: &Index,
        _txn: &'transaction RoTxn,
        _db_cache: &mut DatabaseCache<'transaction>,
        _universe: &RoaringBitmap,
    ) -> Result<Option<RankingRuleOutput<Query>>> {
        let iter = self.iter.as_mut().unwrap();
        // TODO: we should make use of the universe in the function below
        iter.next_bucket()
    }

    fn end_iteration(
        &mut self,
        _index: &Index,
        _txn: &'transaction RoTxn,
        _db_cache: &mut DatabaseCache<'transaction>,
    ) {
        self.iter = None;
    }
}