// 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/>.

//! Disk-backed, ref-counted `JournalDB` implementation.

use std::collections::HashMap;
use std::sync::Arc;
use heapsize::HeapSizeOf;
use rlp::*;
use hashdb::*;
use overlaydb::OverlayDB;
use memorydb::MemoryDB;
use super::{DB_PREFIX_LEN, LATEST_ERA_KEY};
use super::traits::JournalDB;
use kvdb::{KeyValueDB, DBTransaction};
use bigint::hash::H256;
use error::UtilError;
use bytes::Bytes;

/// Implementation of the `HashDB` trait for a disk-backed database with a memory overlay
/// and latent-removal semantics.
///
/// Like `OverlayDB`, there is a memory overlay; `commit()` must be called in order to
/// write operations out to disk. Unlike `OverlayDB`, `remove()` operations do not take effect
/// immediately. Rather some age (based on a linear but arbitrary metric) must pass before
/// the removals actually take effect.
///
/// journal format:
/// ```
/// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
/// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
/// [era, n] => [ ... ]
/// ```
///
/// when we make a new commit, we journal the inserts and removes.
/// for each `end_era` that we journaled that we are no passing by,
/// we remove all of its removes assuming it is canonical and all
/// of its inserts otherwise.
// TODO: store last_era, reclaim_period.
pub struct RefCountedDB {
	forward: OverlayDB,
	backing: Arc<KeyValueDB>,
	latest_era: Option<u64>,
	inserts: Vec<H256>,
	removes: Vec<H256>,
	column: Option<u32>,
}

const PADDING : [u8; 10] = [ 0u8; 10 ];

impl RefCountedDB {
	/// Create a new instance given a `backing` database.
	pub fn new(backing: Arc<KeyValueDB>, col: Option<u32>) -> RefCountedDB {
		let latest_era = backing.get(col, &LATEST_ERA_KEY).expect("Low-level database error.").map(|val| decode::<u64>(&val));

		RefCountedDB {
			forward: OverlayDB::new(backing.clone(), col),
			backing: backing,
			inserts: vec![],
			removes: vec![],
			latest_era: latest_era,
			column: col,
		}
	}
}

impl HashDB for RefCountedDB {
	fn keys(&self) -> HashMap<H256, i32> { self.forward.keys() }
	fn get(&self, key: &H256) -> Option<DBValue> { self.forward.get(key) }
	fn contains(&self, key: &H256) -> bool { self.forward.contains(key) }
	fn insert(&mut self, value: &[u8]) -> H256 { let r = self.forward.insert(value); self.inserts.push(r.clone()); r }
	fn emplace(&mut self, key: H256, value: DBValue) { self.inserts.push(key.clone()); self.forward.emplace(key, value); }
	fn remove(&mut self, key: &H256) { self.removes.push(key.clone()); }
}

impl JournalDB for RefCountedDB {
	fn boxed_clone(&self) -> Box<JournalDB> {
		Box::new(RefCountedDB {
			forward: self.forward.clone(),
			backing: self.backing.clone(),
			latest_era: self.latest_era,
			inserts: self.inserts.clone(),
			removes: self.removes.clone(),
			column: self.column.clone(),
		})
	}

	fn mem_used(&self) -> usize {
		self.inserts.heap_size_of_children() + self.removes.heap_size_of_children()
 	}

	fn is_empty(&self) -> bool {
		self.latest_era.is_none()
	}

	fn backing(&self) -> &Arc<KeyValueDB> {
		&self.backing
	}

	fn latest_era(&self) -> Option<u64> { self.latest_era }

	fn state(&self, id: &H256) -> Option<Bytes> {
		self.backing.get_by_prefix(self.column, &id[0..DB_PREFIX_LEN]).map(|b| b.into_vec())
	}

	fn journal_under(&mut self, batch: &mut DBTransaction, now: u64, id: &H256) -> Result<u32, UtilError> {
		// record new commit's details.
		let mut index = 0usize;
		let mut last;

		while self.backing.get(self.column, {
			let mut r = RlpStream::new_list(3);
			r.append(&now);
			r.append(&index);
			r.append(&&PADDING[..]);
			last = r.drain();
			&last
		})?.is_some() {
			index += 1;
		}

		let mut r = RlpStream::new_list(3);
		r.append(id);
		r.append_list(&self.inserts);
		r.append_list(&self.removes);
		batch.put(self.column, &last, r.as_raw());

		let ops = self.inserts.len() + self.removes.len();

		trace!(target: "rcdb", "new journal for time #{}.{} => {}: inserts={:?}, removes={:?}", now, index, id, self.inserts, self.removes);

		self.inserts.clear();
		self.removes.clear();

		if self.latest_era.map_or(true, |e| now > e) {
			batch.put(self.column, &LATEST_ERA_KEY, &encode(&now));
			self.latest_era = Some(now);
		}

		Ok(ops as u32)
	}

	fn mark_canonical(&mut self, batch: &mut DBTransaction, end_era: u64, canon_id: &H256) -> Result<u32, UtilError> {
		// apply old commits' details
		let mut index = 0usize;
		let mut last;
		while let Some(rlp_data) = {
			self.backing.get(self.column, {
				let mut r = RlpStream::new_list(3);
				r.append(&end_era);
				r.append(&index);
				r.append(&&PADDING[..]);
				last = r.drain();
				&last
			})?
		} {
			let rlp = Rlp::new(&rlp_data);
			let our_id: H256 = rlp.val_at(0);
			let to_remove: Vec<H256> = rlp.list_at(if *canon_id == our_id {2} else {1});
			trace!(target: "rcdb", "delete journal for time #{}.{}=>{}, (canon was {}): deleting {:?}", end_era, index, our_id, canon_id, to_remove);
			for i in &to_remove {
				self.forward.remove(i);
			}
			batch.delete(self.column, &last);
			index += 1;
		}

		let r = self.forward.commit_to_batch(batch)?;
		Ok(r)
	}

	fn inject(&mut self, batch: &mut DBTransaction) -> Result<u32, UtilError> {
		self.inserts.clear();
		for remove in self.removes.drain(..) {
			self.forward.remove(&remove);
		}
		self.forward.commit_to_batch(batch)
	}

	fn consolidate(&mut self, mut with: MemoryDB) {
		for (key, (value, rc)) in with.drain() {
			for _ in 0..rc {
				self.emplace(key, value.clone());
			}

			for _ in rc..0 {
				self.remove(&key);
			}
		}
	}
}

#[cfg(test)]
mod tests {

	use keccak::keccak;
	use hashdb::{HashDB, DBValue};
	use super::*;
	use {JournalDB, kvdb_memorydb};

	fn new_db() -> RefCountedDB {
		let backing = Arc::new(kvdb_memorydb::create(0));
		RefCountedDB::new(backing, None)
	}

	#[test]
	fn long_history() {
		// history is 3
		let mut jdb = new_db();
		let h = jdb.insert(b"foo");
		jdb.commit_batch(0, &keccak(b"0"), None).unwrap();
		assert!(jdb.contains(&h));
		jdb.remove(&h);
		jdb.commit_batch(1, &keccak(b"1"), None).unwrap();
		assert!(jdb.contains(&h));
		jdb.commit_batch(2, &keccak(b"2"), None).unwrap();
		assert!(jdb.contains(&h));
		jdb.commit_batch(3, &keccak(b"3"), Some((0, keccak(b"0")))).unwrap();
		assert!(jdb.contains(&h));
		jdb.commit_batch(4, &keccak(b"4"), Some((1, keccak(b"1")))).unwrap();
		assert!(!jdb.contains(&h));
	}

	#[test]
	fn latest_era_should_work() {
		// history is 3
		let mut jdb = new_db();
		assert_eq!(jdb.latest_era(), None);
		let h = jdb.insert(b"foo");
		jdb.commit_batch(0, &keccak(b"0"), None).unwrap();
		assert_eq!(jdb.latest_era(), Some(0));
		jdb.remove(&h);
		jdb.commit_batch(1, &keccak(b"1"), None).unwrap();
		assert_eq!(jdb.latest_era(), Some(1));
		jdb.commit_batch(2, &keccak(b"2"), None).unwrap();
		assert_eq!(jdb.latest_era(), Some(2));
		jdb.commit_batch(3, &keccak(b"3"), Some((0, keccak(b"0")))).unwrap();
		assert_eq!(jdb.latest_era(), Some(3));
		jdb.commit_batch(4, &keccak(b"4"), Some((1, keccak(b"1")))).unwrap();
		assert_eq!(jdb.latest_era(), Some(4));
	}

	#[test]
	fn complex() {
		// history is 1
		let mut jdb = new_db();

		let foo = jdb.insert(b"foo");
		let bar = jdb.insert(b"bar");
		jdb.commit_batch(0, &keccak(b"0"), None).unwrap();
		assert!(jdb.contains(&foo));
		assert!(jdb.contains(&bar));

		jdb.remove(&foo);
		jdb.remove(&bar);
		let baz = jdb.insert(b"baz");
		jdb.commit_batch(1, &keccak(b"1"), Some((0, keccak(b"0")))).unwrap();
		assert!(jdb.contains(&foo));
		assert!(jdb.contains(&bar));
		assert!(jdb.contains(&baz));

		let foo = jdb.insert(b"foo");
		jdb.remove(&baz);
		jdb.commit_batch(2, &keccak(b"2"), Some((1, keccak(b"1")))).unwrap();
		assert!(jdb.contains(&foo));
		assert!(!jdb.contains(&bar));
		assert!(jdb.contains(&baz));

		jdb.remove(&foo);
		jdb.commit_batch(3, &keccak(b"3"), Some((2, keccak(b"2")))).unwrap();
		assert!(jdb.contains(&foo));
		assert!(!jdb.contains(&bar));
		assert!(!jdb.contains(&baz));

		jdb.commit_batch(4, &keccak(b"4"), Some((3, keccak(b"3")))).unwrap();
		assert!(!jdb.contains(&foo));
		assert!(!jdb.contains(&bar));
		assert!(!jdb.contains(&baz));
	}

	#[test]
	fn fork() {
		// history is 1
		let mut jdb = new_db();

		let foo = jdb.insert(b"foo");
		let bar = jdb.insert(b"bar");
		jdb.commit_batch(0, &keccak(b"0"), None).unwrap();
		assert!(jdb.contains(&foo));
		assert!(jdb.contains(&bar));

		jdb.remove(&foo);
		let baz = jdb.insert(b"baz");
		jdb.commit_batch(1, &keccak(b"1a"), Some((0, keccak(b"0")))).unwrap();

		jdb.remove(&bar);
		jdb.commit_batch(1, &keccak(b"1b"), Some((0, keccak(b"0")))).unwrap();

		assert!(jdb.contains(&foo));
		assert!(jdb.contains(&bar));
		assert!(jdb.contains(&baz));

		jdb.commit_batch(2, &keccak(b"2b"), Some((1, keccak(b"1b")))).unwrap();
		assert!(jdb.contains(&foo));
		assert!(!jdb.contains(&baz));
		assert!(!jdb.contains(&bar));
	}

	#[test]
	fn inject() {
		let mut jdb = new_db();
		let key = jdb.insert(b"dog");
		jdb.inject_batch().unwrap();

		assert_eq!(jdb.get(&key).unwrap(), DBValue::from_slice(b"dog"));
		jdb.remove(&key);
		jdb.inject_batch().unwrap();

		assert!(jdb.get(&key).is_none());
	}
}