/*
    This file is part of jellything (https://codeberg.org/metamuffin/jellything)
    which is licensed under the GNU Affero General Public License (version 3); see /COPYING.
    Copyright (C) 2026 metamuffin <metamuffin.org>
*/

pub mod binning;
pub mod helpers;
pub mod index;
pub mod index_key;
pub mod merge_iterator;
pub mod prefix_iterator;
pub mod sort;

use std::borrow::Cow;

use crate::{
    Database, Query, RowNum, Transaction,
    kv::{
        helpers::{read_counter, write_counter},
        index::{iter_index, read_count_index, update_index},
        index_key::{IndexKey, SortKey},
        merge_iterator::MergeIterator,
        prefix_iterator::PrefixIterator,
    },
};
use anyhow::{Result, anyhow};
use jellyobject::ObjectBuffer;

pub type SubtreeNum = u32;

const T_ROW_COUNTER: SubtreeNum = 0;
const T_ROWS: SubtreeNum = 1;
const T_INDEX_COUNTER: SubtreeNum = 2;
const T_INDICES: SubtreeNum = 3;

const INDEX_TNUM_OFFSET: SubtreeNum = 64;

impl<T: jellykv::Store> Database for T {
    fn transaction(&self, f: &mut dyn FnMut(&mut dyn Transaction) -> Result<()>) -> Result<()> {
        jellykv::Store::transaction(self, &mut |mut txn| f(&mut txn))
    }
}

impl Transaction for &mut dyn jellykv::Transaction {
    fn insert(&mut self, entry: ObjectBuffer) -> Result<RowNum> {
        let mut id_counter = read_counter(*self, &T_ROW_COUNTER.to_be_bytes(), 0)?;
        let row = id_counter;
        id_counter += 1;
        write_counter(*self, &T_ROW_COUNTER.to_be_bytes(), id_counter)?;

        jellykv::Transaction::set(
            *self,
            &row_key(row),
            bytemuck::cast_slice(entry.0.as_slice()),
        )?;

        let ob = entry.as_object();
        for (is, ik) in list_indices(*self)? {
            update_index(*self, is, &ik, row, ob, false)?;
        }

        Ok(row)
    }
    fn remove(&mut self, row: RowNum) -> Result<()> {
        let entry = self.get(row)?.ok_or(anyhow!("row did not exist"))?;
        let ob = entry.as_object();
        for (is, ik) in list_indices(*self)? {
            update_index(*self, is, &ik, row, ob, true)?;
        }
        jellykv::Transaction::del(*self, &row_key(row))
    }
    fn update(&mut self, row: RowNum, entry: ObjectBuffer) -> Result<()> {
        let before = self.get(row)?.ok_or(anyhow!("row to update missing"))?;
        let before = before.as_object();
        let after = entry.as_object();

        jellykv::Transaction::set(
            *self,
            &row_key(row),
            bytemuck::cast_slice(entry.0.as_slice()),
        )?;

        for (is, ik) in list_indices(*self)? {
            update_index(*self, is, &ik, row, before, true)?;
            update_index(*self, is, &ik, row, after, false)?;
        }

        Ok(())
    }

    fn get(&self, row: RowNum) -> Result<Option<ObjectBuffer>> {
        Ok(jellykv::Transaction::get(*self, &row_key(row))?.map(ObjectBuffer::from))
    }

    fn query<'a>(
        &'a mut self,
        query: Query,
    ) -> Result<Box<dyn Iterator<Item = Result<(RowNum, Vec<u8>)>> + 'a>> {
        let mut prefixes = Vec::new();
        for (binning, mut prefix) in query.filter.get_bins() {
            let ik = IndexKey(binning, query.sort.key());
            let is = get_or_create_index(*self, &ik)?;
            prefix.splice(0..0, is.to_be_bytes());
            prefixes.push(prefix);
        }
        let mut iters = Vec::new();
        for prefix in prefixes {
            iters.push(iter_index(*self, prefix, &query.sort)?)
        }
        if iters.len() == 1 {
            return Ok(iters.pop().unwrap());
        }
        Ok(Box::new(MergeIterator::new(iters)))
    }
    fn query_single(&mut self, query: Query) -> Result<Option<RowNum>> {
        Ok(self.query(query)?.next().transpose()?.map(|(e, _)| e))
    }
    fn count(&mut self, query: Query) -> Result<u64> {
        let mut total = 0;
        for (binning, mut prefix) in query.filter.get_bins() {
            let ik = IndexKey(binning, SortKey::Count);
            let is = get_or_create_index(*self, &ik)?;
            prefix.splice(0..0, is.to_be_bytes());
            total += read_count_index(*self, prefix)?;
        }
        Ok(total)
    }
}

fn get_or_create_index(txn: &mut dyn jellykv::Transaction, ik: &IndexKey) -> Result<SubtreeNum> {
    match jellykv::Transaction::get(txn, &ik.to_bytes())? {
        Some(is) => Ok(SubtreeNum::from_be_bytes(is.try_into().unwrap())),
        None => {
            let is = alloc_subtree(txn)?;
            create_index(txn, is, ik)?;
            jellykv::Transaction::set(txn, &ik.to_bytes(), &is.to_be_bytes())?;
            Ok(is)
        }
    }
}

fn alloc_subtree(txn: &mut dyn jellykv::Transaction) -> Result<SubtreeNum> {
    let is = read_counter(
        txn,
        &T_INDEX_COUNTER.to_be_bytes(),
        INDEX_TNUM_OFFSET as u64,
    )?;
    write_counter(txn, &T_INDEX_COUNTER.to_be_bytes(), is + 1)?;
    Ok(is as SubtreeNum)
}

fn create_index(txn: &mut dyn jellykv::Transaction, is: SubtreeNum, ik: &IndexKey) -> Result<()> {
    let rowkeys = PrefixIterator {
        inner: txn.iter(&T_ROWS.to_be_bytes(), false)?,
        prefix: Cow::Borrowed(&T_ROWS.to_be_bytes()),
    }
    .collect::<Result<Vec<_>, _>>()?; // TODO dont collect this

    for rowkey in rowkeys {
        let row = inv_row_key(&rowkey);
        let buf = ObjectBuffer::from(jellykv::Transaction::get(txn, &rowkey)?.unwrap());
        update_index(txn, is, ik, row, buf.as_object(), false)?;
    }

    Ok(())
}

fn list_indices(txn: &dyn jellykv::Transaction) -> Result<Vec<(SubtreeNum, IndexKey)>> {
    let indices = PrefixIterator {
        inner: jellykv::Transaction::iter(txn, &T_INDICES.to_be_bytes(), false)?,
        prefix: Cow::Borrowed(&T_INDICES.to_be_bytes()),
    };
    let mut out = Vec::new();
    for i in indices {
        let i = i?;
        let ik = IndexKey::from_bytes(&i);
        let is = read_counter(txn, &i, 0)? as SubtreeNum;
        out.push((is, ik));
    }
    Ok(out)
}

fn row_key(row: RowNum) -> Vec<u8> {
    let mut key = Vec::new();
    key.extend(T_ROWS.to_be_bytes());
    key.extend(row.to_be_bytes());
    key
}
fn inv_row_key(k: &[u8]) -> RowNum {
    RowNum::from_be_bytes(k[4..12].try_into().unwrap())
}

#[cfg(test)]
mod test {
    use crate::{
        Database, Filter, Query, Sort,
        test_shared::{AGE, NAME, new_alice, new_bob, new_charlie},
    };
    use anyhow::Result;
    use jellyobject::Path;

    #[test]
    pub fn insert_get() -> Result<()> {
        let db = jellykv::memory::new();

        let mut bob_row = 0;
        db.transaction(&mut |txn| {
            bob_row = txn.insert(new_bob())?;
            Ok(())
        })?;

        let mut bob = None;
        db.transaction(&mut |txn| {
            bob = txn.get(bob_row)?;
            Ok(())
        })?;

        assert_eq!(bob.unwrap().as_object().get(NAME).unwrap(), "Bob");
        Ok(())
    }

    #[test]
    pub fn update() -> Result<()> {
        let db = jellykv::memory::new();

        let mut bob_row = 0;
        let mut bob = None;

        db.transaction(&mut |txn| {
            bob_row = txn.insert(new_bob())?;
            Ok(())
        })?;
        db.transaction(&mut |txn| {
            let better_bob = new_bob().as_object().insert(NAME, "Better Bob");
            txn.update(bob_row, better_bob)?;
            Ok(())
        })?;
        db.transaction(&mut |txn| {
            bob = txn.get(bob_row)?;
            Ok(())
        })?;

        assert_eq!(bob.unwrap().as_object().get(NAME).unwrap(), "Better Bob");
        Ok(())
    }

    #[test]
    pub fn filter() -> Result<()> {
        let db = jellykv::memory::new();

        let mut rows = [0, 0, 0];
        let mut result = None;

        db.transaction(&mut |txn| {
            rows = [
                txn.insert(new_bob())?,
                txn.insert(new_alice())?,
                txn.insert(new_charlie())?,
            ];
            Ok(())
        })?;
        db.transaction(&mut |txn| {
            result = txn.query_single(Query {
                filter: Filter::Match(Path(vec![AGE.0]), 35_u32.to_be_bytes().to_vec()),
                sort: Sort::None,
            })?;
            Ok(())
        })?;

        assert_eq!(result.unwrap(), 0);
        Ok(())
    }
}