// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity.  If not, see <http://www.gnu.org/licenses/>.

extern crate parking_lot;
extern crate kvdb;

use std::collections::{BTreeMap, HashMap};
use parking_lot::RwLock;
use kvdb::{DBValue, DBTransaction, KeyValueDB, DBOp, Result};

/// A key-value database fulfilling the `KeyValueDB` trait, living in memory.
/// This is generally intended for tests and is not particularly optimized.
#[derive(Default)]
pub struct InMemory {
	columns: RwLock<HashMap<Option<u32>, BTreeMap<Vec<u8>, DBValue>>>,
}

/// Create an in-memory database with the given number of columns.
/// Columns will be indexable by 0..`num_cols`
pub fn create(num_cols: u32) -> InMemory {
	let mut cols = HashMap::new();
	cols.insert(None, BTreeMap::new());

	for idx in 0..num_cols {
		cols.insert(Some(idx), BTreeMap::new());
	}

	InMemory {
		columns: RwLock::new(cols)
	}
}

impl KeyValueDB for InMemory {
	fn get(&self, col: Option<u32>, key: &[u8]) -> Result<Option<DBValue>> {
		let columns = self.columns.read();
		match columns.get(&col) {
			None => Err(format!("No such column family: {:?}", col).into()),
			Some(map) => Ok(map.get(key).cloned()),
		}
	}

	fn get_by_prefix(&self, col: Option<u32>, prefix: &[u8]) -> Option<Box<[u8]>> {
		let columns = self.columns.read();
		match columns.get(&col) {
			None => None,
			Some(map) =>
				map.iter()
					.find(|&(ref k ,_)| k.starts_with(prefix))
					.map(|(_, v)| v.to_vec().into_boxed_slice())
		}
	}

	fn write_buffered(&self, transaction: DBTransaction) {
		let mut columns = self.columns.write();
		let ops = transaction.ops;
		for op in ops {
			match op {
				DBOp::Insert { col, key, value } => {
					if let Some(col) = columns.get_mut(&col) {
						col.insert(key.into_vec(), value);
					}
				},
				DBOp::Delete { col, key } => {
					if let Some(col) = columns.get_mut(&col) {
						col.remove(&*key);
					}
				},
			}
		}
	}

	fn flush(&self) -> Result<()> {
		Ok(())
	}

	fn iter<'a>(&'a self, col: Option<u32>) -> Box<Iterator<Item=(Box<[u8]>, Box<[u8]>)> + 'a> {
		match self.columns.read().get(&col) {
			Some(map) => Box::new( // TODO: worth optimizing at all?
				map.clone()
					.into_iter()
					.map(|(k, v)| (k.into_boxed_slice(), v.into_vec().into_boxed_slice()))
			),
			None => Box::new(None.into_iter()),
		}
	}

	fn iter_from_prefix<'a>(&'a self, col: Option<u32>, prefix: &'a [u8])
		-> Box<Iterator<Item=(Box<[u8]>, Box<[u8]>)> + 'a>
	{
		match self.columns.read().get(&col) {
			Some(map) => Box::new(
				map.clone()
					.into_iter()
					.skip_while(move |&(ref k, _)| !k.starts_with(prefix))
					.map(|(k, v)| (k.into_boxed_slice(), v.into_vec().into_boxed_slice()))
			),
			None => Box::new(None.into_iter()),
		}
	}

	fn restore(&self, _new_db: &str) -> Result<()> {
		Err("Attempted to restore in-memory database".into())
	}
}