use std::borrow::Cow;
use std::collections::{BTreeMap, HashMap};
use std::convert::TryFrom;

use deunicode::deunicode_with_tofu;
use meilisearch_schema::IndexedPos;
use meilisearch_tokenizer::{is_cjk, SeqTokenizer, Token, Tokenizer};
use sdset::SetBuf;

use crate::{DocIndex, DocumentId};
use crate::FstSetCow;

const WORD_LENGTH_LIMIT: usize = 80;

type Word = Vec<u8>; // TODO make it be a SmallVec

pub struct RawIndexer<A> {
    word_limit: usize, // the maximum number of indexed words
    stop_words: fst::Set<A>,
    words_doc_indexes: BTreeMap<Word, Vec<DocIndex>>,
    docs_words: HashMap<DocumentId, Vec<Word>>,
}

pub struct Indexed<'a> {
    pub words_doc_indexes: BTreeMap<Word, SetBuf<DocIndex>>,
    pub docs_words: HashMap<DocumentId, FstSetCow<'a>>,
}

impl<A> RawIndexer<A> {
    pub fn new(stop_words: fst::Set<A>) -> RawIndexer<A> {
        RawIndexer::with_word_limit(stop_words, 1000)
    }

    pub fn with_word_limit(stop_words: fst::Set<A>, limit: usize) -> RawIndexer<A> {
        RawIndexer {
            word_limit: limit,
            stop_words,
            words_doc_indexes: BTreeMap::new(),
            docs_words: HashMap::new(),
        }
    }
}

impl<A: AsRef<[u8]>> RawIndexer<A> {
    pub fn index_text(&mut self, id: DocumentId, indexed_pos: IndexedPos, text: &str) -> usize {
        let mut number_of_words = 0;

        for token in Tokenizer::new(text) {
            let must_continue = index_token(
                token,
                id,
                indexed_pos,
                self.word_limit,
                &self.stop_words,
                &mut self.words_doc_indexes,
                &mut self.docs_words,
            );

            number_of_words += 1;

            if !must_continue {
                break;
            }
        }

        number_of_words
    }

    pub fn index_text_seq<'s, I>(&mut self, id: DocumentId, indexed_pos: IndexedPos, iter: I)
    where
        I: IntoIterator<Item = &'s str>,
    {
        let iter = iter.into_iter();
        for token in SeqTokenizer::new(iter) {
            let must_continue = index_token(
                token,
                id,
                indexed_pos,
                self.word_limit,
                &self.stop_words,
                &mut self.words_doc_indexes,
                &mut self.docs_words,
            );

            if !must_continue {
                break;
            }
        }
    }

    pub fn build(self) -> Indexed<'static> {
        let words_doc_indexes = self
            .words_doc_indexes
            .into_iter()
            .map(|(word, indexes)| (word, SetBuf::from_dirty(indexes)))
            .collect();

        let docs_words = self
            .docs_words
            .into_iter()
            .map(|(id, mut words)| {
                words.sort_unstable();
                words.dedup();
                let fst = fst::Set::from_iter(words).unwrap().map_data(Cow::Owned).unwrap();
                (id, fst)
            })
            .collect();

        Indexed {
            words_doc_indexes,
            docs_words,
        }
    }
}

fn index_token<A>(
    token: Token,
    id: DocumentId,
    indexed_pos: IndexedPos,
    word_limit: usize,
    stop_words: &fst::Set<A>,
    words_doc_indexes: &mut BTreeMap<Word, Vec<DocIndex>>,
    docs_words: &mut HashMap<DocumentId, Vec<Word>>,
) -> bool
where A: AsRef<[u8]>,
{
    if token.word_index >= word_limit {
        return false;
    }

    let lower = token.word.to_lowercase();
    let token = Token {
        word: &lower,
        ..token
    };

    if !stop_words.contains(&token.word) {
        match token_to_docindex(id, indexed_pos, token) {
            Some(docindex) => {
                let word = Vec::from(token.word);

                if word.len() <= WORD_LENGTH_LIMIT {
                    words_doc_indexes
                        .entry(word.clone())
                        .or_insert_with(Vec::new)
                        .push(docindex);
                    docs_words.entry(id).or_insert_with(Vec::new).push(word);

                    if !lower.contains(is_cjk) {
                        let unidecoded = deunicode_with_tofu(&lower, "");
                        if unidecoded != lower && !unidecoded.is_empty() {
                            let word = Vec::from(unidecoded);
                            if word.len() <= WORD_LENGTH_LIMIT {
                                words_doc_indexes
                                    .entry(word.clone())
                                    .or_insert_with(Vec::new)
                                    .push(docindex);
                                docs_words.entry(id).or_insert_with(Vec::new).push(word);
                            }
                        }
                    }
                }
            }
            None => return false,
        }
    }

    true
}

fn token_to_docindex(id: DocumentId, indexed_pos: IndexedPos, token: Token) -> Option<DocIndex> {
    let word_index = u16::try_from(token.word_index).ok()?;
    let char_index = u16::try_from(token.char_index).ok()?;
    let char_length = u16::try_from(token.word.chars().count()).ok()?;

    let docindex = DocIndex {
        document_id: id,
        attribute: indexed_pos.0,
        word_index,
        char_index,
        char_length,
    };

    Some(docindex)
}

#[cfg(test)]
mod tests {
    use super::*;
    use meilisearch_schema::IndexedPos;

    #[test]
    fn strange_apostrophe() {
        let mut indexer = RawIndexer::new(fst::Set::default());

        let docid = DocumentId(0);
        let indexed_pos = IndexedPos(0);
        let text = "Zut, l’aspirateur, j’ai oublié de l’éteindre !";
        indexer.index_text(docid, indexed_pos, text);

        let Indexed {
            words_doc_indexes, ..
        } = indexer.build();

        assert!(words_doc_indexes.get(&b"l"[..]).is_some());
        assert!(words_doc_indexes.get(&b"aspirateur"[..]).is_some());
        assert!(words_doc_indexes.get(&b"ai"[..]).is_some());
        assert!(words_doc_indexes.get(&b"eteindre"[..]).is_some());
        assert!(words_doc_indexes
            .get(&"éteindre".to_owned().into_bytes())
            .is_some());
    }

    #[test]
    fn strange_apostrophe_in_sequence() {
        let mut indexer = RawIndexer::new(fst::Set::default());

        let docid = DocumentId(0);
        let indexed_pos = IndexedPos(0);
        let text = vec!["Zut, l’aspirateur, j’ai oublié de l’éteindre !"];
        indexer.index_text_seq(docid, indexed_pos, text);

        let Indexed {
            words_doc_indexes, ..
        } = indexer.build();

        assert!(words_doc_indexes.get(&b"l"[..]).is_some());
        assert!(words_doc_indexes.get(&b"aspirateur"[..]).is_some());
        assert!(words_doc_indexes.get(&b"ai"[..]).is_some());
        assert!(words_doc_indexes.get(&b"eteindre"[..]).is_some());
        assert!(words_doc_indexes
            .get(&"éteindre".to_owned().into_bytes())
            .is_some());
    }

    #[test]
    fn basic_stop_words() {
        let stop_words = sdset::SetBuf::from_dirty(vec!["l", "j", "ai", "de"]);
        let stop_words = fst::Set::from_iter(stop_words).unwrap();

        let mut indexer = RawIndexer::new(stop_words);

        let docid = DocumentId(0);
        let indexed_pos = IndexedPos(0);
        let text = "Zut, l’aspirateur, j’ai oublié de l’éteindre !";
        indexer.index_text(docid, indexed_pos, text);

        let Indexed {
            words_doc_indexes, ..
        } = indexer.build();

        assert!(words_doc_indexes.get(&b"l"[..]).is_none());
        assert!(words_doc_indexes.get(&b"aspirateur"[..]).is_some());
        assert!(words_doc_indexes.get(&b"j"[..]).is_none());
        assert!(words_doc_indexes.get(&b"ai"[..]).is_none());
        assert!(words_doc_indexes.get(&b"de"[..]).is_none());
        assert!(words_doc_indexes.get(&b"eteindre"[..]).is_some());
        assert!(words_doc_indexes
            .get(&"éteindre".to_owned().into_bytes())
            .is_some());
    }

    #[test]
    fn no_empty_unidecode() {
        let mut indexer = RawIndexer::new(fst::Set::default());

        let docid = DocumentId(0);
        let indexed_pos = IndexedPos(0);
        let text = "🇯🇵";
        indexer.index_text(docid, indexed_pos, text);

        let Indexed {
            words_doc_indexes, ..
        } = indexer.build();

        assert!(words_doc_indexes
            .get(&"🇯🇵".to_owned().into_bytes())
            .is_some());
    }
}