// Copyright 2015, 2016 Ethcore (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/>.

//! Key-Value store abstraction with rocksb backend.

use rocksdb::{DB, Writable, WriteBatch, IteratorMode, DBVector, DBIterator,
	IndexType, Options, DBCompactionStyle, BlockBasedOptions, Direction};

/// Write transaction. Batches a sequence of put/delete operations for efficiency.
pub struct DBTransaction {
	batch: WriteBatch,
}

impl DBTransaction {
	/// Create new transaction.
	pub fn new() -> DBTransaction {
		DBTransaction { batch: WriteBatch::new() }
	}

	/// Insert a ket-value pair in the transaction. Any existing value value will be overwritten upon write.
    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<(), String> {
		self.batch.put(key, value)
	}

	/// Delete value by key.
    pub fn delete(&self, key: &[u8]) -> Result<(), String> {
		self.batch.delete(key)
	}
}

/// Database configuration
pub struct DatabaseConfig {
	/// Optional prefix size in bytes. Allows lookup by partial key.
	pub prefix_size: Option<usize>
}

/// Database iterator
pub struct DatabaseIterator<'a> {
    iter: DBIterator<'a>,
}

impl<'a> Iterator for DatabaseIterator<'a> {
    type Item = (Box<[u8]>, Box<[u8]>);

	#[allow(type_complexity)]
    fn next(&mut self) -> Option<(Box<[u8]>, Box<[u8]>)> {
		self.iter.next()
	}
}

/// Key-Value database.
pub struct Database {
	db: DB,
}

impl Database {
	/// Open database with default settings.
	pub fn open_default(path: &str) -> Result<Database, String> {
		Database::open(DatabaseConfig { prefix_size: None }, path) 
	}

	/// Open database file. Creates if it does not exist.
	pub fn open(config: DatabaseConfig, path: &str) -> Result<Database, String> {
		let mut opts = Options::new();
		opts.set_max_open_files(256);
		opts.create_if_missing(true);
		opts.set_use_fsync(false);
		opts.set_compaction_style(DBCompactionStyle::DBUniversalCompaction);
		/*
		opts.set_bytes_per_sync(8388608);
		opts.set_disable_data_sync(false);
		opts.set_block_cache_size_mb(1024);
		opts.set_table_cache_num_shard_bits(6);
		opts.set_max_write_buffer_number(32);
		opts.set_write_buffer_size(536870912);
		opts.set_target_file_size_base(1073741824);
		opts.set_min_write_buffer_number_to_merge(4);
		opts.set_level_zero_stop_writes_trigger(2000);
		opts.set_level_zero_slowdown_writes_trigger(0);
		opts.set_compaction_style(DBUniversalCompaction);
		opts.set_max_background_compactions(4);
		opts.set_max_background_flushes(4);
		opts.set_filter_deletes(false);
		opts.set_disable_auto_compactions(false);*/

		if let Some(size) = config.prefix_size {
			let mut block_opts = BlockBasedOptions::new();
			block_opts.set_index_type(IndexType::HashSearch);
			opts.set_block_based_table_factory(&block_opts);
			opts.set_prefix_extractor_fixed_size(size);
		}
		let db = try!(DB::open(&opts, path));
		Ok(Database { db: db })
	}

	/// Insert a ket-value pair in the transaction. Any existing value value will be overwritten.
    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<(), String> {
		self.db.put(key, value)
	}

	/// Delete value by key.
    pub fn delete(&self, key: &[u8]) -> Result<(), String> {
		self.db.delete(key)
	}

	/// Commit transaction to database.
    pub fn write(&self, tr: DBTransaction) -> Result<(), String> {
		self.db.write(tr.batch)
	}
	
	/// Get value by key.
    pub fn get(&self, key: &[u8]) -> Result<Option<DBVector>, String> {
		self.db.get(key)
	}

	/// Get value by partial key. Prefix size should match configured prefix size.
    pub fn get_by_prefix(&self, prefix: &[u8]) -> Option<Box<[u8]>> {
		let mut iter = self.db.iterator(IteratorMode::From(prefix, Direction::forward));
		match iter.next() {
			// TODO: use prefix_same_as_start read option (not availabele in C API currently)
			Some((k, v)) => if k[0 .. prefix.len()] == prefix[..] { Some(v) } else { None },
			_ => None
		}
	}

	/// Check if there is anything in the database.
	pub fn is_empty(&self) -> bool {
		self.db.iterator(IteratorMode::Start).next().is_none()
	}

	/// Check if there is anything in the database.
	pub fn iter(&self) -> DatabaseIterator {
		DatabaseIterator { iter: self.db.iterator(IteratorMode::Start) }
	}
}