use std::collections::{HashMap, HashSet, BTreeSet};

use fst::{SetBuilder, Streamer};
use meilidb_schema::Schema;
use sdset::{SetBuf, SetOperation, duo::DifferenceByKey};

use crate::{DocumentId, RankedMap, MResult, Error};
use crate::serde::extract_document_id;
use crate::update::{Update, next_update_id};
use crate::store;

pub struct DocumentsDeletion {
    updates_store: store::Updates,
    updates_results_store: store::UpdatesResults,
    updates_notifier: crossbeam_channel::Sender<()>,
    documents: Vec<DocumentId>,
}

impl DocumentsDeletion {
    pub fn new(
        updates_store: store::Updates,
        updates_results_store: store::UpdatesResults,
        updates_notifier: crossbeam_channel::Sender<()>,
    ) -> DocumentsDeletion
    {
        DocumentsDeletion {
            updates_store,
            updates_results_store,
            updates_notifier,
            documents: Vec::new(),
        }
    }

    pub fn delete_document_by_id(&mut self, document_id: DocumentId) {
        self.documents.push(document_id);
    }

    pub fn delete_document<D>(&mut self, schema: &Schema, document: D) -> MResult<()>
    where D: serde::Serialize,
    {
        let identifier = schema.identifier_name();
        let document_id = match extract_document_id(identifier, &document)? {
            Some(id) => id,
            None => return Err(Error::MissingDocumentId),
        };

        self.delete_document_by_id(document_id);

        Ok(())
    }

    pub fn finalize(self, writer: &mut rkv::Writer) -> MResult<u64> {
        let _ = self.updates_notifier.send(());
        let update_id = push_documents_deletion(
            writer,
            self.updates_store,
            self.updates_results_store,
            self.documents,
        )?;
        Ok(update_id)
    }
}

impl Extend<DocumentId> for DocumentsDeletion {
    fn extend<T: IntoIterator<Item=DocumentId>>(&mut self, iter: T) {
        self.documents.extend(iter)
    }
}

pub fn push_documents_deletion(
    writer: &mut rkv::Writer,
    updates_store: store::Updates,
    updates_results_store: store::UpdatesResults,
    deletion: Vec<DocumentId>,
) -> MResult<u64>
{
    let last_update_id = next_update_id(writer, updates_store, updates_results_store)?;

    let update = Update::DocumentsDeletion(deletion);
    updates_store.put_update(writer, last_update_id, &update)?;

    Ok(last_update_id)
}

pub fn apply_documents_deletion(
    writer: &mut rkv::Writer,
    main_store: store::Main,
    documents_fields_store: store::DocumentsFields,
    postings_lists_store: store::PostingsLists,
    docs_words_store: store::DocsWords,
    mut ranked_map: RankedMap,
    deletion: Vec<DocumentId>,
) -> MResult<()>
{
    let idset = SetBuf::from_dirty(deletion);

    let schema = match main_store.schema(writer)? {
        Some(schema) => schema,
        None => return Err(Error::SchemaMissing),
    };

    // collect the ranked attributes according to the schema
    let ranked_attrs: Vec<_> = schema.iter()
        .filter_map(|(_, attr, prop)| {
            if prop.is_ranked() { Some(attr) } else { None }
        })
        .collect();

    let mut words_document_ids = HashMap::new();
    for id in idset {
        // remove all the ranked attributes from the ranked_map
        for ranked_attr in &ranked_attrs {
            ranked_map.remove(id, *ranked_attr);
        }

        if let Some(words) = docs_words_store.doc_words(writer, id)? {
            let mut stream = words.stream();
            while let Some(word) = stream.next() {
                let word = word.to_vec();
                words_document_ids.entry(word).or_insert_with(Vec::new).push(id);
            }
        }
    }

    let mut deleted_documents = HashSet::new();
    let mut removed_words = BTreeSet::new();
    for (word, document_ids) in words_document_ids {
        let document_ids = SetBuf::from_dirty(document_ids);

        if let Some(doc_indexes) = postings_lists_store.postings_list(writer, &word)? {
            let op = DifferenceByKey::new(&doc_indexes, &document_ids, |d| d.document_id, |id| *id);
            let doc_indexes = op.into_set_buf();

            if !doc_indexes.is_empty() {
                postings_lists_store.put_postings_list(writer, &word, &doc_indexes)?;
            } else {
                postings_lists_store.del_postings_list(writer, &word)?;
                removed_words.insert(word);
            }
        }

        for id in document_ids {
            if documents_fields_store.del_all_document_fields(writer, id)? != 0 {
                deleted_documents.insert(id);
            }
        }
    }

    let deleted_documents_len = deleted_documents.len() as u64;
    for id in deleted_documents {
        docs_words_store.del_doc_words(writer, id)?;
    }

    let removed_words = fst::Set::from_iter(removed_words).unwrap();
    let words = match main_store.words_fst(writer)? {
        Some(words_set) => {
            let op = fst::set::OpBuilder::new()
                .add(words_set.stream())
                .add(removed_words.stream())
                .difference();

            let mut words_builder = SetBuilder::memory();
            words_builder.extend_stream(op).unwrap();
            words_builder
                .into_inner()
                .and_then(fst::Set::from_bytes)
                .unwrap()
        },
        None => fst::Set::default(),
    };

    main_store.put_words_fst(writer, &words)?;
    main_store.put_ranked_map(writer, &ranked_map)?;

    main_store.put_number_of_documents(writer, |old| old - deleted_documents_len)?;

    Ok(())
}