use std::mem::take;

use anyhow::bail;
use itertools::Itertools;
use ordered_float::OrderedFloat;
use roaring::RoaringBitmap;

use crate::facet::FacetType;
use crate::heed_codec::facet::{FacetLevelValueF64Codec, FacetLevelValueI64Codec};
use crate::heed_codec::facet::{FieldDocIdFacetI64Codec, FieldDocIdFacetF64Codec};
use crate::search::facet::FacetIter;
use crate::search::query_tree::Operation;
use crate::{FieldId, Index};
use super::{Candidates, Criterion, CriterionResult};

pub struct AscDesc<'t> {
    index: &'t Index,
    rtxn: &'t heed::RoTxn<'t>,
    field_id: FieldId,
    facet_type: FacetType,
    ascending: bool,
    query_tree: Option<Operation>,
    candidates: Candidates,
    bucket_candidates: Option<RoaringBitmap>,
    faceted_candidates: RoaringBitmap,
    parent: Option<Box<dyn Criterion + 't>>,
}

impl<'t> AscDesc<'t> {
    pub fn initial_asc(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        query_tree: Option<Operation>,
        candidates: Option<RoaringBitmap>,
        field_id: FieldId,
        facet_type: FacetType,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Self::initial(index, rtxn, query_tree, candidates, field_id, facet_type, true)
    }

    pub fn initial_desc(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        query_tree: Option<Operation>,
        candidates: Option<RoaringBitmap>,
        field_id: FieldId,
        facet_type: FacetType,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Self::initial(index, rtxn, query_tree, candidates, field_id, facet_type, false)
    }

    pub fn asc(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        parent: Box<dyn Criterion + 't>,
        field_id: FieldId,
        facet_type: FacetType,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Self::new(index, rtxn, parent, field_id, facet_type, true)
    }

    pub fn desc(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        parent: Box<dyn Criterion + 't>,
        field_id: FieldId,
        facet_type: FacetType,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Self::new(index, rtxn, parent, field_id, facet_type, false)
    }

    fn initial(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        query_tree: Option<Operation>,
        candidates: Option<RoaringBitmap>,
        field_id: FieldId,
        facet_type: FacetType,
        ascending: bool,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Ok(AscDesc {
            index,
            rtxn,
            field_id,
            facet_type,
            ascending,
            query_tree,
            candidates: candidates.map_or_else(Candidates::default, Candidates::Allowed),
            faceted_candidates: index.faceted_documents_ids(rtxn, field_id)?,
            bucket_candidates: None,
            parent: None,
        })
    }

    fn new(
        index: &'t Index,
        rtxn: &'t heed::RoTxn,
        parent: Box<dyn Criterion + 't>,
        field_id: FieldId,
        facet_type: FacetType,
        ascending: bool,
    ) -> anyhow::Result<Self> where Self: Sized
    {
        Ok(AscDesc {
            index,
            rtxn,
            field_id,
            facet_type,
            ascending,
            query_tree: None,
            candidates: Candidates::default(),
            faceted_candidates: index.faceted_documents_ids(rtxn, field_id)?,
            bucket_candidates: None,
            parent: Some(parent),
        })
    }
}

impl<'t> Criterion for AscDesc<'t> {
    fn next(&mut self) -> anyhow::Result<Option<CriterionResult>> {
        use Candidates::{Allowed, Forbidden};

        loop {
            match (&mut self.query_tree, &mut self.candidates) {
                (_, Allowed(candidates)) if candidates.is_empty() => {
                    self.query_tree = None;
                    self.candidates = Candidates::default();
                },
                (Some(qt), Allowed(candidates)) => {
                    let bucket_candidates = match self.parent {
                        Some(_) => self.bucket_candidates.take(),
                        None => Some(candidates.clone()),
                    };

                    let mut found_candidates = facet_ordered(
                        self.index,
                        self.rtxn,
                        self.field_id,
                        self.facet_type,
                        self.ascending,
                        candidates.clone(),
                    )?;

                    found_candidates.intersect_with(&candidates);
                    candidates.difference_with(&found_candidates);

                    return Ok(Some(CriterionResult {
                        query_tree: Some(qt.clone()),
                        candidates: found_candidates,
                        bucket_candidates,
                    }));
                },
                (Some(_qt), Forbidden(_candidates)) => {
                    todo!()
                },
                (None, Allowed(_)) => {
                    let candidates = take(&mut self.candidates).into_inner();
                    return Ok(Some(CriterionResult {
                        query_tree: None,
                        candidates: candidates.clone(),
                        bucket_candidates: Some(candidates),
                    }));
                },
                (None, Forbidden(_)) => {
                    match self.parent.as_mut() {
                        Some(parent) => {
                            match parent.next()? {
                                Some(CriterionResult { query_tree, mut candidates, bucket_candidates }) => {
                                    self.query_tree = query_tree;
                                    candidates.intersect_with(&self.faceted_candidates);
                                    self.candidates = Candidates::Allowed(candidates);
                                    self.bucket_candidates = bucket_candidates;
                                },
                                None => return Ok(None),
                            }
                        },
                        None => return Ok(None),
                    }
                },
            }
        }
    }
}

fn facet_ordered(
    index: &Index,
    rtxn: &heed::RoTxn,
    field_id: FieldId,
    facet_type: FacetType,
    ascending: bool,
    candidates: RoaringBitmap,
) -> anyhow::Result<RoaringBitmap>
{
    match facet_type {
        FacetType::Float => {
            if candidates.len() <= 1000 {
                let db = index.field_id_docid_facet_values.remap_key_type::<FieldDocIdFacetF64Codec>();
                let mut docids_values = Vec::with_capacity(candidates.len() as usize);
                for docid in candidates.iter() {
                    let left = (field_id, docid, f64::MIN);
                    let right = (field_id, docid, f64::MAX);
                    let mut iter = db.range(rtxn, &(left..=right))?;
                    let entry = if ascending { iter.next() } else { iter.last() };
                    if let Some(((_, _, value), ())) = entry.transpose()? {
                        docids_values.push((docid, OrderedFloat(value)));
                    }
                }
                docids_values.sort_unstable_by_key(|(_, value)| *value);
                let iter = docids_values.into_iter();
                let iter = if ascending {
                    Box::new(iter) as Box<dyn Iterator<Item = _>>
                } else {
                    Box::new(iter.rev())
                };
                match iter.group_by(|(_, v)| *v).into_iter().next() {
                    Some((_, ids)) => Ok(ids.map(|(id, _)| id).into_iter().collect()),
                    None => Ok(RoaringBitmap::new())
                }
            } else {
                let facet_fn = if ascending {
                    FacetIter::<f64, FacetLevelValueF64Codec>::new_reducing
                } else {
                    FacetIter::<f64, FacetLevelValueF64Codec>::new_reverse_reducing
                };

                let mut iter = facet_fn(rtxn, index, field_id, candidates)?;
                Ok(iter.next().transpose()?.map(|(_, docids)| docids).unwrap_or_default())
            }
        },
        FacetType::Integer => {
            if candidates.len() <= 1000 {
                let db = index.field_id_docid_facet_values.remap_key_type::<FieldDocIdFacetI64Codec>();
                let mut docids_values = Vec::with_capacity(candidates.len() as usize);
                for docid in candidates.iter() {
                    let left = (field_id, docid, i64::MIN);
                    let right = (field_id, docid, i64::MAX);
                    let mut iter = db.range(rtxn, &(left..=right))?;
                    let entry = if ascending { iter.next() } else { iter.last() };
                    if let Some(((_, _, value), ())) = entry.transpose()? {
                        docids_values.push((docid, value));
                    }
                }
                docids_values.sort_unstable_by_key(|(_, value)| *value);
                let iter = docids_values.into_iter();
                let iter = if ascending {
                    Box::new(iter) as Box<dyn Iterator<Item = _>>
                } else {
                    Box::new(iter.rev())
                };
                match iter.group_by(|(_, v)| *v).into_iter().next() {
                    Some((_, ids)) => Ok(ids.map(|(id, _)| id).into_iter().collect()),
                    None => Ok(RoaringBitmap::new())
                }
            } else {
                let facet_fn = if ascending {
                    FacetIter::<i64, FacetLevelValueI64Codec>::new_reducing
                } else {
                    FacetIter::<i64, FacetLevelValueI64Codec>::new_reverse_reducing
                };

                let mut iter = facet_fn(rtxn, index, field_id, candidates)?;
                Ok(iter.next().transpose()?.map(|(_, docids)| docids).unwrap_or_default())
            }
        },
        FacetType::String => bail!("criteria facet type must be a number"),
    }
}