use std::collections::HashMap;
use std::borrow::Cow;

use anyhow::bail;
use roaring::RoaringBitmap;

use crate::search::{word_derivations, WordDerivationsCache};
use crate::{Index, DocumentId};

use super::query_tree::{Operation, Query, QueryKind};
use self::typo::Typo;
use self::words::Words;
use self::asc_desc::AscDesc;
use self::proximity::Proximity;
use self::fetcher::Fetcher;

mod typo;
mod words;
mod asc_desc;
mod proximity;
pub mod fetcher;

pub trait Criterion {
    fn next(&mut self, wdcache: &mut WordDerivationsCache) -> anyhow::Result<Option<CriterionResult>>;
}

/// The result of a call to the parent criterion.
#[derive(Debug, Clone, PartialEq)]
pub struct CriterionResult {
    /// The query tree that must be used by the children criterion to fetch candidates.
    query_tree: Option<Operation>,
    /// The candidates that this criterion is allowed to return subsets of,
    /// if None, it is up to the child to compute the candidates itself.
    candidates: Option<RoaringBitmap>,
    /// Candidates that comes from the current bucket of the initial criterion.
    bucket_candidates: RoaringBitmap,
}

/// Either a set of candidates that defines the candidates
/// that are allowed to be returned,
/// or the candidates that must never be returned.
#[derive(Debug)]
enum Candidates {
    Allowed(RoaringBitmap),
    Forbidden(RoaringBitmap)
}

impl Candidates {
    fn into_inner(self) -> RoaringBitmap {
        match self {
            Self::Allowed(inner) => inner,
            Self::Forbidden(inner) => inner,
        }
    }
}

impl Default for Candidates {
    fn default() -> Self {
        Self::Forbidden(RoaringBitmap::new())
    }
}
pub trait Context {
    fn documents_ids(&self) -> heed::Result<RoaringBitmap>;
    fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>>;
    fn word_prefix_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>>;
    fn word_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>>;
    fn word_prefix_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>>;
    fn words_fst<'t>(&self) -> &'t fst::Set<Cow<[u8]>>;
    fn in_prefix_cache(&self, word: &str) -> bool;
    fn docid_words_positions(&self, docid: DocumentId) -> heed::Result<HashMap<String, RoaringBitmap>>;
}
pub struct CriteriaBuilder<'t> {
    rtxn: &'t heed::RoTxn<'t>,
    index: &'t Index,
    words_fst: fst::Set<Cow<'t, [u8]>>,
    words_prefixes_fst: fst::Set<Cow<'t, [u8]>>,
}

impl<'a> Context for CriteriaBuilder<'a> {
    fn documents_ids(&self) -> heed::Result<RoaringBitmap> {
        self.index.documents_ids(self.rtxn)
    }

    fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
        self.index.word_docids.get(self.rtxn, &word)
    }

    fn word_prefix_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
        self.index.word_prefix_docids.get(self.rtxn, &word)
    }

    fn word_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>> {
        let key = (left, right, proximity);
        self.index.word_pair_proximity_docids.get(self.rtxn, &key)
    }

    fn word_prefix_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>> {
        let key = (left, right, proximity);
        self.index.word_prefix_pair_proximity_docids.get(self.rtxn, &key)
    }

    fn words_fst<'t>(&self) -> &'t fst::Set<Cow<[u8]>> {
        &self.words_fst
    }

    fn in_prefix_cache(&self, word: &str) -> bool {
        self.words_prefixes_fst.contains(word)
    }

    fn docid_words_positions(&self, docid: DocumentId) -> heed::Result<HashMap<String, RoaringBitmap>> {
        let mut words_positions = HashMap::new();
        for result in self.index.docid_word_positions.prefix_iter(self.rtxn, &(docid, ""))? {
            let ((_, word), positions) = result?;
            words_positions.insert(word.to_string(), positions);
        }
        Ok(words_positions)
    }
}

impl<'t> CriteriaBuilder<'t> {
    pub fn new(rtxn: &'t heed::RoTxn<'t>, index: &'t Index) -> anyhow::Result<Self> {
        let words_fst = index.words_fst(rtxn)?;
        let words_prefixes_fst = index.words_prefixes_fst(rtxn)?;
        Ok(Self { rtxn, index, words_fst, words_prefixes_fst })
    }

    pub fn build(
        &'t self,
        mut query_tree: Option<Operation>,
        mut facet_candidates: Option<RoaringBitmap>,
    ) -> anyhow::Result<Fetcher<'t>>
    {
        use crate::criterion::Criterion as Name;

        let mut criterion = None as Option<Box<dyn Criterion>>;
        for name in self.index.criteria(&self.rtxn)? {
            criterion = Some(match criterion.take() {
                Some(father) => match name {
                    Name::Typo => Box::new(Typo::new(self, father)),
                    Name::Words => Box::new(Words::new(self, father)),
                    Name::Proximity => Box::new(Proximity::new(self, father)),
                    Name::Asc(field) => Box::new(AscDesc::asc(&self.index, &self.rtxn, father, field)?),
                    Name::Desc(field) => Box::new(AscDesc::desc(&self.index, &self.rtxn, father, field)?),
                    _otherwise => father,
                },
                None => match name {
                    Name::Typo => Box::new(Typo::initial(self, query_tree.take(), facet_candidates.take())),
                    Name::Words => Box::new(Words::initial(self, query_tree.take(), facet_candidates.take())),
                    Name::Proximity => Box::new(Proximity::initial(self, query_tree.take(), facet_candidates.take())),
                    Name::Asc(field) => {
                        Box::new(AscDesc::initial_asc(&self.index, &self.rtxn, query_tree.take(), facet_candidates.take(), field)?)
                    },
                    Name::Desc(field) => {
                        Box::new(AscDesc::initial_desc(&self.index, &self.rtxn, query_tree.take(), facet_candidates.take(), field)?)
                    },
                    _otherwise => continue,
                },
            });
        }

        match criterion {
            Some(criterion) => Ok(Fetcher::new(self, criterion)),
            None => Ok(Fetcher::initial(self, query_tree, facet_candidates)),
        }
    }
}

pub fn resolve_query_tree<'t>(
    ctx: &'t dyn Context,
    query_tree: &Operation,
    cache: &mut HashMap<(Operation, u8), RoaringBitmap>,
    wdcache: &mut WordDerivationsCache,
) -> anyhow::Result<RoaringBitmap>
{
    fn resolve_operation<'t>(
        ctx: &'t dyn Context,
        query_tree: &Operation,
        cache: &mut HashMap<(Operation, u8), RoaringBitmap>,
        wdcache: &mut WordDerivationsCache,
    ) -> anyhow::Result<RoaringBitmap>
    {
        use Operation::{And, Consecutive, Or, Query};

        match query_tree {
            And(ops) => {
                let mut ops = ops.iter().map(|op| {
                    resolve_operation(ctx, op, cache, wdcache)
                }).collect::<anyhow::Result<Vec<_>>>()?;

                ops.sort_unstable_by_key(|cds| cds.len());

                let mut candidates = RoaringBitmap::new();
                let mut first_loop = true;
                for docids in ops {
                    if first_loop {
                        candidates = docids;
                        first_loop = false;
                    } else {
                        candidates.intersect_with(&docids);
                    }
                }
                Ok(candidates)
            },
            Consecutive(ops) => {
                let mut candidates = RoaringBitmap::new();
                let mut first_loop = true;
                for slice in ops.windows(2) {
                    match (&slice[0], &slice[1]) {
                        (Operation::Query(left), Operation::Query(right)) => {
                            match query_pair_proximity_docids(ctx, left, right, 1, wdcache)? {
                                pair_docids if pair_docids.is_empty() => {
                                    return Ok(RoaringBitmap::new())
                                },
                                pair_docids if first_loop => {
                                    candidates = pair_docids;
                                    first_loop = false;
                                },
                                pair_docids => {
                                    candidates.intersect_with(&pair_docids);
                                },
                            }
                        },
                        _ => bail!("invalid consecutive query type"),
                    }
                }
                Ok(candidates)
            },
            Or(_, ops) => {
                let mut candidates = RoaringBitmap::new();
                for op in ops {
                    let docids = resolve_operation(ctx, op, cache, wdcache)?;
                    candidates.union_with(&docids);
                }
                Ok(candidates)
            },
            Query(q) => Ok(query_docids(ctx, q, wdcache)?),
        }
    }

    resolve_operation(ctx, query_tree, cache, wdcache)
}


fn all_word_pair_proximity_docids<T: AsRef<str>, U: AsRef<str>>(
    ctx: &dyn Context,
    left_words: &[(T, u8)],
    right_words: &[(U, u8)],
    proximity: u8
) -> anyhow::Result<RoaringBitmap>
{
    let mut docids = RoaringBitmap::new();
    for (left, _l_typo) in left_words {
        for (right, _r_typo) in right_words {
            let current_docids = ctx.word_pair_proximity_docids(left.as_ref(), right.as_ref(), proximity)?.unwrap_or_default();
            docids.union_with(&current_docids);
        }
    }
    Ok(docids)
}

fn query_docids(
    ctx: &dyn Context,
    query: &Query,
    wdcache: &mut WordDerivationsCache,
) -> anyhow::Result<RoaringBitmap>
{
    match &query.kind {
        QueryKind::Exact { word, .. } => {
            if query.prefix && ctx.in_prefix_cache(&word) {
                Ok(ctx.word_prefix_docids(&word)?.unwrap_or_default())
            } else if query.prefix {
                let words = word_derivations(&word, true, 0, ctx.words_fst(), wdcache)?;
                let mut docids = RoaringBitmap::new();
                for (word, _typo) in words {
                    let current_docids = ctx.word_docids(&word)?.unwrap_or_default();
                    docids.union_with(&current_docids);
                }
                Ok(docids)
            } else {
                Ok(ctx.word_docids(&word)?.unwrap_or_default())
            }
        },
        QueryKind::Tolerant { typo, word } => {
            let words = word_derivations(&word, query.prefix, *typo, ctx.words_fst(), wdcache)?;
            let mut docids = RoaringBitmap::new();
            for (word, _typo) in words {
                let current_docids = ctx.word_docids(&word)?.unwrap_or_default();
                docids.union_with(&current_docids);
            }
            Ok(docids)
        },
    }
}

fn query_pair_proximity_docids(
    ctx: &dyn Context,
    left: &Query,
    right: &Query,
    proximity: u8,
    wdcache: &mut WordDerivationsCache,
) -> anyhow::Result<RoaringBitmap>
{
    if proximity >= 8 {
        let mut candidates = query_docids(ctx, left, wdcache)?;
        let right_candidates = query_docids(ctx, right, wdcache)?;
        candidates.intersect_with(&right_candidates);
        return Ok(candidates);
    }

    let prefix = right.prefix;
    match (&left.kind, &right.kind) {
        (QueryKind::Exact { word: left, .. }, QueryKind::Exact { word: right, .. }) => {
            if prefix && ctx.in_prefix_cache(&right) {
                Ok(ctx.word_prefix_pair_proximity_docids(left.as_str(), right.as_str(), proximity)?.unwrap_or_default())
            } else if prefix {
                let r_words = word_derivations(&right, true, 0, ctx.words_fst(), wdcache)?;
                all_word_pair_proximity_docids(ctx, &[(left, 0)], &r_words, proximity)
            } else {
                Ok(ctx.word_pair_proximity_docids(left.as_str(), right.as_str(), proximity)?.unwrap_or_default())
            }
        },
        (QueryKind::Tolerant { typo, word: left }, QueryKind::Exact { word: right, .. }) => {
            let l_words = word_derivations(&left, false, *typo, ctx.words_fst(), wdcache)?.to_owned();
            if prefix && ctx.in_prefix_cache(&right) {
                let mut docids = RoaringBitmap::new();
                for (left, _) in l_words {
                    let current_docids = ctx.word_prefix_pair_proximity_docids(left.as_ref(), right.as_ref(), proximity)?.unwrap_or_default();
                    docids.union_with(&current_docids);
                }
                Ok(docids)
            } else if prefix {
                let r_words = word_derivations(&right, true, 0, ctx.words_fst(), wdcache)?;
                all_word_pair_proximity_docids(ctx, &l_words, &r_words, proximity)
            } else {
                all_word_pair_proximity_docids(ctx, &l_words, &[(right, 0)], proximity)
            }
        },
        (QueryKind::Exact { word: left, .. }, QueryKind::Tolerant { typo, word: right }) => {
            let r_words = word_derivations(&right, prefix, *typo, ctx.words_fst(), wdcache)?;
            all_word_pair_proximity_docids(ctx, &[(left, 0)], &r_words, proximity)
        },
        (QueryKind::Tolerant { typo: l_typo, word: left }, QueryKind::Tolerant { typo: r_typo, word: right }) => {
            let l_words = word_derivations(&left, false, *l_typo, ctx.words_fst(), wdcache)?.to_owned();
            let r_words = word_derivations(&right, prefix, *r_typo, ctx.words_fst(), wdcache)?;
            all_word_pair_proximity_docids(ctx, &l_words, &r_words, proximity)
        },
    }
}

#[cfg(test)]
pub mod test {
    use maplit::hashmap;
    use rand::{Rng, SeedableRng, rngs::StdRng};

    use super::*;
    use std::collections::HashMap;

    fn s(s: &str) -> String { s.to_string() }
    pub struct TestContext<'t> {
        words_fst: fst::Set<Cow<'t, [u8]>>,
        word_docids: HashMap<String, RoaringBitmap>,
        word_prefix_docids: HashMap<String, RoaringBitmap>,
        word_pair_proximity_docids: HashMap<(String, String, i32), RoaringBitmap>,
        word_prefix_pair_proximity_docids: HashMap<(String, String, i32), RoaringBitmap>,
    }

    impl<'a> Context for TestContext<'a> {
        fn documents_ids(&self) -> heed::Result<RoaringBitmap> {
            Ok(self.word_docids.iter().fold(RoaringBitmap::new(), |acc, (_, docids)| acc | docids))
        }

        fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
            Ok(self.word_docids.get(&word.to_string()).cloned())
        }

        fn word_prefix_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
            Ok(self.word_prefix_docids.get(&word.to_string()).cloned())
        }

        fn word_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>> {
            let key = (left.to_string(), right.to_string(), proximity.into());
            Ok(self.word_pair_proximity_docids.get(&key).cloned())
        }

        fn word_prefix_pair_proximity_docids(&self, left: &str, right: &str, proximity: u8) -> heed::Result<Option<RoaringBitmap>> {
            let key = (left.to_string(), right.to_string(), proximity.into());
            Ok(self.word_prefix_pair_proximity_docids.get(&key).cloned())
        }

        fn words_fst<'t>(&self) -> &'t fst::Set<Cow<[u8]>> {
            &self.words_fst
        }

        fn in_prefix_cache(&self, word: &str) -> bool {
            self.word_prefix_docids.contains_key(&word.to_string())
        }

        fn docid_words_positions(&self, _docid: DocumentId) -> heed::Result<HashMap<String, RoaringBitmap>> {
            todo!()
        }
    }

    impl<'a> Default for TestContext<'a> {
        fn default() -> TestContext<'a> {
            let mut rng = StdRng::seed_from_u64(102);
            let rng = &mut rng;

            fn random_postings<R: Rng>(rng: &mut R, len: usize) -> RoaringBitmap {
                let mut values = Vec::<u32>::with_capacity(len);
                while values.len() != len {
                    values.push(rng.gen());
                }
                values.sort_unstable();

                RoaringBitmap::from_sorted_iter(values.into_iter())
            }

            let word_docids = hashmap!{
                s("hello")      => random_postings(rng,   1500),
                s("hi")         => random_postings(rng,   4000),
                s("word")       => random_postings(rng,   2500),
                s("split")      => random_postings(rng,    400),
                s("ngrams")     => random_postings(rng,   1400),
                s("world")      => random_postings(rng, 15_000),
                s("earth")      => random_postings(rng,   8000),
                s("2021")       => random_postings(rng,    100),
                s("2020")       => random_postings(rng,    500),
                s("is")         => random_postings(rng, 50_000),
                s("this")       => random_postings(rng, 50_000),
                s("good")       => random_postings(rng,   1250),
                s("morning")    => random_postings(rng,    125),
            };

            let word_prefix_docids = hashmap!{
                s("h")   => &word_docids[&s("hello")] | &word_docids[&s("hi")],
                s("wor") => &word_docids[&s("word")]  | &word_docids[&s("world")],
                s("20")  => &word_docids[&s("2020")]  | &word_docids[&s("2021")],
            };

            let hello_world = &word_docids[&s("hello")] & &word_docids[&s("world")];
            let hello_world_split = (hello_world.len() / 2) as usize;
            let hello_world_1 = hello_world.iter().take(hello_world_split).collect();
            let hello_world_2 = hello_world.iter().skip(hello_world_split).collect();

            let hello_word = &word_docids[&s("hello")] & &word_docids[&s("word")];
            let hello_word_split = (hello_word.len() / 2) as usize;
            let hello_word_4 = hello_word.iter().take(hello_word_split).collect();
            let hello_word_6 = hello_word.iter().skip(hello_word_split).take(hello_word_split/2).collect();
            let hello_word_7 = hello_word.iter().skip(hello_word_split + hello_word_split/2).collect();
            let word_pair_proximity_docids = hashmap!{
                (s("good"), s("morning"), 1)   => &word_docids[&s("good")] & &word_docids[&s("morning")],
                (s("hello"), s("world"), 1)   => hello_world_1,
                (s("hello"), s("world"), 4)   => hello_world_2,
                (s("this"), s("is"), 1)   => &word_docids[&s("this")] & &word_docids[&s("is")],
                (s("is"), s("2021"), 1)   => &word_docids[&s("this")] & &word_docids[&s("is")] & &word_docids[&s("2021")],
                (s("is"), s("2020"), 1)   => &word_docids[&s("this")] & &word_docids[&s("is")] & (&word_docids[&s("2020")] - &word_docids[&s("2021")]),
                (s("this"), s("2021"), 2)   => &word_docids[&s("this")] & &word_docids[&s("is")] & &word_docids[&s("2021")],
                (s("this"), s("2020"), 2)   => &word_docids[&s("this")] & &word_docids[&s("is")] & (&word_docids[&s("2020")] - &word_docids[&s("2021")]),
                (s("word"), s("split"), 1)   => &word_docids[&s("word")] & &word_docids[&s("split")],
                (s("world"), s("split"), 1)   => (&word_docids[&s("world")] & &word_docids[&s("split")]) - &word_docids[&s("word")],
                (s("hello"), s("word"), 4) => hello_word_4,
                (s("hello"), s("word"), 6) => hello_word_6,
                (s("hello"), s("word"), 7) => hello_word_7,
                (s("split"), s("ngrams"), 3)   => (&word_docids[&s("split")] & &word_docids[&s("ngrams")]) - &word_docids[&s("word")],
                (s("split"), s("ngrams"), 5)   => &word_docids[&s("split")] & &word_docids[&s("ngrams")] & &word_docids[&s("word")],
                (s("this"), s("ngrams"), 1)   => (&word_docids[&s("split")] & &word_docids[&s("this")] & &word_docids[&s("ngrams")] ) - &word_docids[&s("word")],
                (s("this"), s("ngrams"), 2)   => &word_docids[&s("split")] & &word_docids[&s("this")] & &word_docids[&s("ngrams")] & &word_docids[&s("word")],
            };

            let word_prefix_pair_proximity_docids = hashmap!{
                (s("hello"), s("wor"), 1) => word_pair_proximity_docids.get(&(s("hello"), s("world"), 1)).unwrap().clone(),
                (s("hello"), s("wor"), 4) => word_pair_proximity_docids.get(&(s("hello"), s("world"), 4)).unwrap() | word_pair_proximity_docids.get(&(s("hello"), s("word"), 4)).unwrap(),
                (s("hello"), s("wor"), 6) => word_pair_proximity_docids.get(&(s("hello"), s("word"), 6)).unwrap().clone(),
                (s("hello"), s("wor"), 7) => word_pair_proximity_docids.get(&(s("hello"), s("word"), 7)).unwrap().clone(),
                (s("is"), s("20"), 1) => word_pair_proximity_docids.get(&(s("is"), s("2020"), 1)).unwrap() | word_pair_proximity_docids.get(&(s("is"), s("2021"), 1)).unwrap(),
                (s("this"), s("20"), 2) => word_pair_proximity_docids.get(&(s("this"), s("2020"), 2)).unwrap() | word_pair_proximity_docids.get(&(s("this"), s("2021"), 2)).unwrap(),
            };

            let mut keys = word_docids.keys().collect::<Vec<_>>();
            keys.sort_unstable();
            let words_fst = fst::Set::from_iter(keys).unwrap().map_data(|v| Cow::Owned(v)).unwrap();

            TestContext {
                words_fst,
                word_docids,
                word_prefix_docids,
                word_pair_proximity_docids,
                word_prefix_pair_proximity_docids,
            }
        }
    }
}