use std::borrow::Cow;
use std::collections::hash_map::Entry;
use std::hash::Hash;

use fxhash::FxHashMap;
use heed::types::ByteSlice;
use heed::{BytesEncode, Database, RoTxn};
use roaring::RoaringBitmap;

use super::interner::Interned;
use super::Word;
use crate::heed_codec::{BytesDecodeOwned, StrBEU16Codec};
use crate::update::{merge_cbo_roaring_bitmaps, MergeFn};
use crate::{
    CboRoaringBitmapCodec, CboRoaringBitmapLenCodec, Result, RoaringBitmapCodec, SearchContext,
};

/// A cache storing pointers to values in the LMDB databases.
///
/// Used for performance reasons only. By using this cache, we avoid performing a
/// database lookup and instead get a direct reference to the value using a fast
/// local HashMap lookup.
#[derive(Default)]
pub struct DatabaseCache<'ctx> {
    pub word_pair_proximity_docids:
        FxHashMap<(u8, Interned<String>, Interned<String>), Option<Cow<'ctx, [u8]>>>,
    pub word_prefix_pair_proximity_docids:
        FxHashMap<(u8, Interned<String>, Interned<String>), Option<Cow<'ctx, [u8]>>>,
    pub prefix_word_pair_proximity_docids:
        FxHashMap<(u8, Interned<String>, Interned<String>), Option<Cow<'ctx, [u8]>>>,
    pub word_docids: FxHashMap<Interned<String>, Option<Cow<'ctx, [u8]>>>,
    pub exact_word_docids: FxHashMap<Interned<String>, Option<Cow<'ctx, [u8]>>>,
    pub word_prefix_docids: FxHashMap<Interned<String>, Option<Cow<'ctx, [u8]>>>,
    pub exact_word_prefix_docids: FxHashMap<Interned<String>, Option<Cow<'ctx, [u8]>>>,

    pub words_fst: Option<fst::Set<Cow<'ctx, [u8]>>>,
    pub word_position_docids: FxHashMap<(Interned<String>, u16), Option<Cow<'ctx, [u8]>>>,
    pub word_prefix_position_docids: FxHashMap<(Interned<String>, u16), Option<Cow<'ctx, [u8]>>>,
    pub word_positions: FxHashMap<Interned<String>, Vec<u16>>,
    pub word_prefix_positions: FxHashMap<Interned<String>, Vec<u16>>,

    pub word_fid_docids: FxHashMap<(Interned<String>, u16), Option<Cow<'ctx, [u8]>>>,
    pub word_prefix_fid_docids: FxHashMap<(Interned<String>, u16), Option<Cow<'ctx, [u8]>>>,
    pub word_fids: FxHashMap<Interned<String>, Vec<u16>>,
    pub word_prefix_fids: FxHashMap<Interned<String>, Vec<u16>>,
}
impl<'ctx> DatabaseCache<'ctx> {
    fn get_value<'v, K1, KC, DC>(
        txn: &'ctx RoTxn,
        cache_key: K1,
        db_key: &'v KC::EItem,
        cache: &mut FxHashMap<K1, Option<Cow<'ctx, [u8]>>>,
        db: Database<KC, ByteSlice>,
    ) -> Result<Option<DC::DItem>>
    where
        K1: Copy + Eq + Hash,
        KC: BytesEncode<'v>,
        DC: BytesDecodeOwned,
    {
        if let Entry::Vacant(entry) = cache.entry(cache_key) {
            let bitmap_ptr = db.get(txn, db_key)?.map(Cow::Borrowed);
            entry.insert(bitmap_ptr);
        }

        match cache.get(&cache_key).unwrap() {
            Some(Cow::Borrowed(bytes)) => {
                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
            }
            Some(Cow::Owned(bytes)) => {
                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
            }
            None => Ok(None),
        }
    }

    fn get_value_from_keys<'v, K1, KC, DC>(
        txn: &'ctx RoTxn,
        cache_key: K1,
        db_keys: &'v [KC::EItem],
        cache: &mut FxHashMap<K1, Option<Cow<'ctx, [u8]>>>,
        db: Database<KC, ByteSlice>,
        merger: MergeFn,
    ) -> Result<Option<DC::DItem>>
    where
        K1: Copy + Eq + Hash,
        KC: BytesEncode<'v>,
        DC: BytesDecodeOwned,
        KC::EItem: Sized,
    {
        if let Entry::Vacant(entry) = cache.entry(cache_key) {
            let bitmap_ptr: Option<Cow<'ctx, [u8]>> = match db_keys {
                [] => None,
                [key] => db.get(txn, key)?.map(Cow::Borrowed),
                keys => {
                    let bitmaps = keys
                        .iter()
                        .filter_map(|key| db.get(txn, key).transpose())
                        .map(|v| v.map(Cow::Borrowed))
                        .collect::<std::result::Result<Vec<Cow<[u8]>>, _>>()?;

                    if bitmaps.is_empty() {
                        None
                    } else {
                        Some(merger(&[], &bitmaps[..])?)
                    }
                }
            };

            entry.insert(bitmap_ptr);
        }

        match cache.get(&cache_key).unwrap() {
            Some(Cow::Borrowed(bytes)) => {
                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
            }
            Some(Cow::Owned(bytes)) => {
                DC::bytes_decode_owned(bytes).ok_or(heed::Error::Decoding.into()).map(Some)
            }
            None => Ok(None),
        }
    }
}

impl<'ctx> SearchContext<'ctx> {
    pub fn get_words_fst(&mut self) -> Result<fst::Set<Cow<'ctx, [u8]>>> {
        if let Some(fst) = self.db_cache.words_fst.clone() {
            Ok(fst)
        } else {
            let fst = self.index.words_fst(self.txn)?;
            self.db_cache.words_fst = Some(fst.clone());
            Ok(fst)
        }
    }

    pub fn word_docids(&mut self, word: Word) -> Result<Option<RoaringBitmap>> {
        match word {
            Word::Original(word) => {
                let exact = self.get_db_exact_word_docids(word)?;
                let tolerant = self.get_db_word_docids(word)?;
                Ok(match (exact, tolerant) {
                    (None, None) => None,
                    (None, Some(tolerant)) => Some(tolerant),
                    (Some(exact), None) => Some(exact),
                    (Some(exact), Some(tolerant)) => {
                        let mut both = exact;
                        both |= tolerant;
                        Some(both)
                    }
                })
            }
            Word::Derived(word) => self.get_db_word_docids(word),
        }
    }

    /// Retrieve or insert the given value in the `word_docids` database.
    fn get_db_word_docids(&mut self, word: Interned<String>) -> Result<Option<RoaringBitmap>> {
        match &self.restricted_fids {
            Some(restricted_fids) => {
                let interned = self.word_interner.get(word).as_str();
                let keys: Vec<_> = restricted_fids.iter().map(|fid| (interned, *fid)).collect();

                DatabaseCache::get_value_from_keys::<_, _, CboRoaringBitmapCodec>(
                    self.txn,
                    word,
                    &keys[..],
                    &mut self.db_cache.word_docids,
                    self.index.word_fid_docids.remap_data_type::<ByteSlice>(),
                    merge_cbo_roaring_bitmaps,
                )
            }
            None => DatabaseCache::get_value::<_, _, RoaringBitmapCodec>(
                self.txn,
                word,
                self.word_interner.get(word).as_str(),
                &mut self.db_cache.word_docids,
                self.index.word_docids.remap_data_type::<ByteSlice>(),
            ),
        }
    }

    fn get_db_exact_word_docids(
        &mut self,
        word: Interned<String>,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, RoaringBitmapCodec>(
            self.txn,
            word,
            self.word_interner.get(word).as_str(),
            &mut self.db_cache.exact_word_docids,
            self.index.exact_word_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn word_prefix_docids(&mut self, prefix: Word) -> Result<Option<RoaringBitmap>> {
        match prefix {
            Word::Original(prefix) => {
                let exact = self.get_db_exact_word_prefix_docids(prefix)?;
                let tolerant = self.get_db_word_prefix_docids(prefix)?;
                Ok(match (exact, tolerant) {
                    (None, None) => None,
                    (None, Some(tolerant)) => Some(tolerant),
                    (Some(exact), None) => Some(exact),
                    (Some(exact), Some(tolerant)) => {
                        let mut both = exact;
                        both |= tolerant;
                        Some(both)
                    }
                })
            }
            Word::Derived(prefix) => self.get_db_word_prefix_docids(prefix),
        }
    }

    /// Retrieve or insert the given value in the `word_prefix_docids` database.
    fn get_db_word_prefix_docids(
        &mut self,
        prefix: Interned<String>,
    ) -> Result<Option<RoaringBitmap>> {
        match &self.restricted_fids {
            Some(restricted_fids) => {
                let interned = self.word_interner.get(prefix).as_str();
                let keys: Vec<_> = restricted_fids.iter().map(|fid| (interned, *fid)).collect();

                DatabaseCache::get_value_from_keys::<_, _, CboRoaringBitmapCodec>(
                    self.txn,
                    prefix,
                    &keys[..],
                    &mut self.db_cache.word_prefix_docids,
                    self.index.word_prefix_fid_docids.remap_data_type::<ByteSlice>(),
                    merge_cbo_roaring_bitmaps,
                )
            }
            None => DatabaseCache::get_value::<_, _, RoaringBitmapCodec>(
                self.txn,
                prefix,
                self.word_interner.get(prefix).as_str(),
                &mut self.db_cache.word_prefix_docids,
                self.index.word_prefix_docids.remap_data_type::<ByteSlice>(),
            ),
        }
    }

    fn get_db_exact_word_prefix_docids(
        &mut self,
        prefix: Interned<String>,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, RoaringBitmapCodec>(
            self.txn,
            prefix,
            self.word_interner.get(prefix).as_str(),
            &mut self.db_cache.exact_word_prefix_docids,
            self.index.exact_word_prefix_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_pair_proximity_docids(
        &mut self,
        word1: Interned<String>,
        word2: Interned<String>,
        proximity: u8,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (proximity, word1, word2),
            &(
                proximity,
                self.word_interner.get(word1).as_str(),
                self.word_interner.get(word2).as_str(),
            ),
            &mut self.db_cache.word_pair_proximity_docids,
            self.index.word_pair_proximity_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_pair_proximity_docids_len(
        &mut self,
        word1: Interned<String>,
        word2: Interned<String>,
        proximity: u8,
    ) -> Result<Option<u64>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapLenCodec>(
            self.txn,
            (proximity, word1, word2),
            &(
                proximity,
                self.word_interner.get(word1).as_str(),
                self.word_interner.get(word2).as_str(),
            ),
            &mut self.db_cache.word_pair_proximity_docids,
            self.index.word_pair_proximity_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_prefix_pair_proximity_docids(
        &mut self,
        word1: Interned<String>,
        prefix2: Interned<String>,
        proximity: u8,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (proximity, word1, prefix2),
            &(
                proximity,
                self.word_interner.get(word1).as_str(),
                self.word_interner.get(prefix2).as_str(),
            ),
            &mut self.db_cache.word_prefix_pair_proximity_docids,
            self.index.word_prefix_pair_proximity_docids.remap_data_type::<ByteSlice>(),
        )
    }
    pub fn get_db_prefix_word_pair_proximity_docids(
        &mut self,
        left_prefix: Interned<String>,
        right: Interned<String>,
        proximity: u8,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (proximity, left_prefix, right),
            &(
                proximity,
                self.word_interner.get(left_prefix).as_str(),
                self.word_interner.get(right).as_str(),
            ),
            &mut self.db_cache.prefix_word_pair_proximity_docids,
            self.index.prefix_word_pair_proximity_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_fid_docids(
        &mut self,
        word: Interned<String>,
        fid: u16,
    ) -> Result<Option<RoaringBitmap>> {
        // if the requested fid isn't in the restricted list, return None.
        if self.restricted_fids.as_ref().map_or(false, |fids| !fids.contains(&fid)) {
            return Ok(None);
        }

        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (word, fid),
            &(self.word_interner.get(word).as_str(), fid),
            &mut self.db_cache.word_fid_docids,
            self.index.word_fid_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_prefix_fid_docids(
        &mut self,
        word_prefix: Interned<String>,
        fid: u16,
    ) -> Result<Option<RoaringBitmap>> {
        // if the requested fid isn't in the restricted list, return None.
        if self.restricted_fids.as_ref().map_or(false, |fids| !fids.contains(&fid)) {
            return Ok(None);
        }

        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (word_prefix, fid),
            &(self.word_interner.get(word_prefix).as_str(), fid),
            &mut self.db_cache.word_prefix_fid_docids,
            self.index.word_prefix_fid_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_fids(&mut self, word: Interned<String>) -> Result<Vec<u16>> {
        let fids = match self.db_cache.word_fids.entry(word) {
            Entry::Occupied(fids) => fids.get().clone(),
            Entry::Vacant(entry) => {
                let mut key = self.word_interner.get(word).as_bytes().to_owned();
                key.push(0);
                let mut fids = vec![];
                let remap_key_type = self
                    .index
                    .word_fid_docids
                    .remap_types::<ByteSlice, ByteSlice>()
                    .prefix_iter(self.txn, &key)?
                    .remap_key_type::<StrBEU16Codec>();
                for result in remap_key_type {
                    let ((_, fid), value) = result?;
                    // filling other caches to avoid searching for them again
                    self.db_cache.word_fid_docids.insert((word, fid), Some(Cow::Borrowed(value)));
                    fids.push(fid);
                }
                entry.insert(fids.clone());
                fids
            }
        };
        Ok(fids)
    }

    pub fn get_db_word_prefix_fids(&mut self, word_prefix: Interned<String>) -> Result<Vec<u16>> {
        let fids = match self.db_cache.word_prefix_fids.entry(word_prefix) {
            Entry::Occupied(fids) => fids.get().clone(),
            Entry::Vacant(entry) => {
                let mut key = self.word_interner.get(word_prefix).as_bytes().to_owned();
                key.push(0);
                let mut fids = vec![];
                let remap_key_type = self
                    .index
                    .word_prefix_fid_docids
                    .remap_types::<ByteSlice, ByteSlice>()
                    .prefix_iter(self.txn, &key)?
                    .remap_key_type::<StrBEU16Codec>();
                for result in remap_key_type {
                    let ((_, fid), value) = result?;
                    // filling other caches to avoid searching for them again
                    self.db_cache
                        .word_prefix_fid_docids
                        .insert((word_prefix, fid), Some(Cow::Borrowed(value)));
                    fids.push(fid);
                }
                entry.insert(fids.clone());
                fids
            }
        };
        Ok(fids)
    }

    pub fn get_db_word_position_docids(
        &mut self,
        word: Interned<String>,
        position: u16,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (word, position),
            &(self.word_interner.get(word).as_str(), position),
            &mut self.db_cache.word_position_docids,
            self.index.word_position_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_prefix_position_docids(
        &mut self,
        word_prefix: Interned<String>,
        position: u16,
    ) -> Result<Option<RoaringBitmap>> {
        DatabaseCache::get_value::<_, _, CboRoaringBitmapCodec>(
            self.txn,
            (word_prefix, position),
            &(self.word_interner.get(word_prefix).as_str(), position),
            &mut self.db_cache.word_prefix_position_docids,
            self.index.word_prefix_position_docids.remap_data_type::<ByteSlice>(),
        )
    }

    pub fn get_db_word_positions(&mut self, word: Interned<String>) -> Result<Vec<u16>> {
        let positions = match self.db_cache.word_positions.entry(word) {
            Entry::Occupied(positions) => positions.get().clone(),
            Entry::Vacant(entry) => {
                let mut key = self.word_interner.get(word).as_bytes().to_owned();
                key.push(0);
                let mut positions = vec![];
                let remap_key_type = self
                    .index
                    .word_position_docids
                    .remap_types::<ByteSlice, ByteSlice>()
                    .prefix_iter(self.txn, &key)?
                    .remap_key_type::<StrBEU16Codec>();
                for result in remap_key_type {
                    let ((_, position), value) = result?;
                    // filling other caches to avoid searching for them again
                    self.db_cache
                        .word_position_docids
                        .insert((word, position), Some(Cow::Borrowed(value)));
                    positions.push(position);
                }
                entry.insert(positions.clone());
                positions
            }
        };
        Ok(positions)
    }

    pub fn get_db_word_prefix_positions(
        &mut self,
        word_prefix: Interned<String>,
    ) -> Result<Vec<u16>> {
        let positions = match self.db_cache.word_prefix_positions.entry(word_prefix) {
            Entry::Occupied(positions) => positions.get().clone(),
            Entry::Vacant(entry) => {
                let mut key = self.word_interner.get(word_prefix).as_bytes().to_owned();
                key.push(0);
                let mut positions = vec![];
                let remap_key_type = self
                    .index
                    .word_prefix_position_docids
                    .remap_types::<ByteSlice, ByteSlice>()
                    .prefix_iter(self.txn, &key)?
                    .remap_key_type::<StrBEU16Codec>();
                for result in remap_key_type {
                    let ((_, position), value) = result?;
                    // filling other caches to avoid searching for them again
                    self.db_cache
                        .word_prefix_position_docids
                        .insert((word_prefix, position), Some(Cow::Borrowed(value)));
                    positions.push(position);
                }
                entry.insert(positions.clone());
                positions
            }
        };
        Ok(positions)
    }
}