#![allow(dead_code)] // REMOVE THIS LINE after fully implementing this functionality

use std::ops::Bound;
use std::path::Path;
use std::sync::atomic::AtomicUsize;
use std::sync::Arc;

use anyhow::Result;
use bytes::Bytes;
use crossbeam_skiplist::SkipMap;
use ouroboros::self_referencing;

use crate::iterators::StorageIterator;
use crate::table::SsTableBuilder;
use crate::wal::Wal;

/// A basic mem-table based on crossbeam-skiplist.
///
/// An initial implementation of memtable is part of week 1, day 1. It will be incrementally implemented in other
/// chapters of week 1 and week 2.
pub struct MemTable {
    map: Arc<SkipMap<Bytes, Bytes>>,
    wal: Option<Wal>,
    id: usize,
    approximate_size: Arc<AtomicUsize>,
}

/// Create a bound of `Bytes` from a bound of `&[u8]`.
pub(crate) fn map_bound(bound: Bound<&[u8]>) -> Bound<Bytes> {
    match bound {
        Bound::Included(x) => Bound::Included(Bytes::copy_from_slice(x)),
        Bound::Excluded(x) => Bound::Excluded(Bytes::copy_from_slice(x)),
        Bound::Unbounded => Bound::Unbounded,
    }
}

impl MemTable {
    /// Create a new mem-table.
    pub fn create(_id: usize) -> Self {
        unimplemented!()
    }

    /// Create a new mem-table with WAL
    pub fn create_with_wal(_id: usize, _path: impl AsRef<Path>) -> Result<Self> {
        unimplemented!()
    }

    /// Create a memtable from WAL
    pub fn recover_from_wal(_id: usize, _path: impl AsRef<Path>) -> Result<Self> {
        unimplemented!()
    }

    /// Get a value by key.
    pub fn get(&self, _key: &[u8]) -> Option<Bytes> {
        unimplemented!()
    }

    /// Put a key-value pair into the mem-table.
    ///
    /// In week 1, day 1, simply put the key-value pair into the skipmap.
    /// In week 2, day 6, also flush the data to WAL.
    pub fn put(&self, _key: &[u8], _value: &[u8]) -> Result<()> {
        unimplemented!()
    }

    pub fn sync_wal(&self) -> Result<()> {
        if let Some(ref wal) = self.wal {
            wal.sync()?;
        }
        Ok(())
    }

    /// Get an iterator over a range of keys.
    pub fn scan(&self, _lower: Bound<&[u8]>, _upper: Bound<&[u8]>) -> MemTableIterator {
        unimplemented!()
    }

    /// Flush the mem-table to SSTable. Implement in week 1 day 6.
    pub fn flush(&self, _builder: &mut SsTableBuilder) -> Result<()> {
        unimplemented!()
    }

    pub fn id(&self) -> usize {
        self.id
    }

    pub fn approximate_size(&self) -> usize {
        self.approximate_size
            .load(std::sync::atomic::Ordering::Relaxed)
    }
}

type SkipMapRangeIter<'a> =
    crossbeam_skiplist::map::Range<'a, Bytes, (Bound<Bytes>, Bound<Bytes>), Bytes, Bytes>;

/// An iterator over a range of `SkipMap`. This is a self-referential structure and please refer to week 1, day 2
/// chapter for more information.
///
/// This is part of week 1, day 2.
#[self_referencing]
pub struct MemTableIterator {
    /// Stores a reference to the skipmap.
    map: Arc<SkipMap<Bytes, Bytes>>,
    /// Stores a skipmap iterator that refers to the lifetime of `MemTableIterator` itself.
    #[borrows(map)]
    #[not_covariant]
    iter: SkipMapRangeIter<'this>,
    /// Stores the current key-value pair.
    item: (Bytes, Bytes),
}

impl StorageIterator for MemTableIterator {
    fn value(&self) -> &[u8] {
        unimplemented!()
    }

    fn key(&self) -> &[u8] {
        unimplemented!()
    }

    fn is_valid(&self) -> bool {
        unimplemented!()
    }

    fn next(&mut self) -> Result<()> {
        unimplemented!()
    }
}