use chrono::Utc;
use roaring::RoaringBitmap;
use crate::{ExternalDocumentsIds, Index, FieldsDistribution};

pub struct ClearDocuments<'t, 'u, 'i> {
    wtxn: &'t mut heed::RwTxn<'i, 'u>,
    index: &'i Index,
    _update_id: u64,
}

impl<'t, 'u, 'i> ClearDocuments<'t, 'u, 'i> {
    pub fn new(
        wtxn: &'t mut heed::RwTxn<'i, 'u>,
        index: &'i Index,
        update_id: u64
    ) -> ClearDocuments<'t, 'u, 'i> {

        ClearDocuments { wtxn, index, _update_id: update_id }
    }

    pub fn execute(self) -> anyhow::Result<u64> {
        self.index.set_updated_at(self.wtxn, &Utc::now())?;
        let Index {
            env: _env,
            main: _main,
            word_docids,
            word_prefix_docids,
            docid_word_positions,
            word_pair_proximity_docids,
            word_prefix_pair_proximity_docids,
            facet_field_id_value_docids,
            field_id_docid_facet_values,
            documents,
        } = self.index;

        // We retrieve the number of documents ids that we are deleting.
        let number_of_documents = self.index.number_of_documents(self.wtxn)?;
        let faceted_fields = self.index.faceted_fields_ids(self.wtxn)?;

        // We clean some of the main engine datastructures.
        self.index.put_words_fst(self.wtxn, &fst::Set::default())?;
        self.index.put_words_prefixes_fst(self.wtxn, &fst::Set::default())?;
        self.index.put_external_documents_ids(self.wtxn, &ExternalDocumentsIds::default())?;
        self.index.put_documents_ids(self.wtxn, &RoaringBitmap::default())?;
        self.index.put_fields_distribution(self.wtxn, &FieldsDistribution::default())?;

        // We clean all the faceted documents ids.
        for (field_id, _) in faceted_fields {
            self.index.put_faceted_documents_ids(self.wtxn, field_id, &RoaringBitmap::default())?;
        }

        // Clear the other databases.
        word_docids.clear(self.wtxn)?;
        word_prefix_docids.clear(self.wtxn)?;
        docid_word_positions.clear(self.wtxn)?;
        word_pair_proximity_docids.clear(self.wtxn)?;
        word_prefix_pair_proximity_docids.clear(self.wtxn)?;
        facet_field_id_value_docids.clear(self.wtxn)?;
        field_id_docid_facet_values.clear(self.wtxn)?;
        documents.clear(self.wtxn)?;

        Ok(number_of_documents)
    }
}

#[cfg(test)]
mod tests {
    use heed::EnvOpenOptions;

    use crate::update::{IndexDocuments, UpdateFormat};
    use super::*;

    #[test]
    fn clear_documents() {
        let path = tempfile::tempdir().unwrap();
        let mut options = EnvOpenOptions::new();
        options.map_size(10 * 1024 * 1024); // 10 MB
        let index = Index::new(options, &path).unwrap();

        let mut wtxn = index.write_txn().unwrap();
        let content = &br#"[
            { "id": 0, "name": "kevin", "age": 20 },
            { "id": 1, "name": "kevina" },
            { "id": 2, "name": "benoit", "country": "France" }
        ]"#[..];
        let mut builder = IndexDocuments::new(&mut wtxn, &index, 0);
        builder.update_format(UpdateFormat::Json);
        builder.execute(content, |_, _| ()).unwrap();

        // Clear all documents from the database.
        let builder = ClearDocuments::new(&mut wtxn, &index, 1);
        assert_eq!(builder.execute().unwrap(), 3);

        wtxn.commit().unwrap();

        let rtxn = index.read_txn().unwrap();

        assert_eq!(index.fields_ids_map(&rtxn).unwrap().len(), 4);

        assert!(index.words_fst(&rtxn).unwrap().is_empty());
        assert!(index.words_prefixes_fst(&rtxn).unwrap().is_empty());
        assert!(index.external_documents_ids(&rtxn).unwrap().is_empty());
        assert!(index.documents_ids(&rtxn).unwrap().is_empty());
        assert!(index.fields_distribution(&rtxn).unwrap().is_empty());

        assert!(index.word_docids.is_empty(&rtxn).unwrap());
        assert!(index.word_prefix_docids.is_empty(&rtxn).unwrap());
        assert!(index.docid_word_positions.is_empty(&rtxn).unwrap());
        assert!(index.word_pair_proximity_docids.is_empty(&rtxn).unwrap());
        assert!(index.word_prefix_pair_proximity_docids.is_empty(&rtxn).unwrap());
        assert!(index.facet_field_id_value_docids.is_empty(&rtxn).unwrap());
        assert!(index.field_id_docid_facet_values.is_empty(&rtxn).unwrap());
        assert!(index.documents.is_empty(&rtxn).unwrap());
    }
}