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    // 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/>.

    //! This migration migrates the state db to use an accountdb which ensures uniqueness
    //! using an address' hash as opposed to the address itself.

    use std::collections::HashMap;

    use util::Bytes;
    use util::{Address, FixedHash, H256};
    use util::kvdb::Database;
    use util::migration::{Batch, Config, Error, Migration, SimpleMigration, Progress};
    use util::sha3::Hashable;
    use std::sync::Arc;

    use rlp::{decode, Rlp, RlpStream, Stream, View};

    // attempt to migrate a key, value pair. None if migration not possible.
    fn attempt_migrate(mut key_h: H256, val: &[u8]) -> Option<H256> {
    	let val_hash = val.sha3();

    	if key_h != val_hash {
    		// this is a key which has been xor'd with an address.
    		// recover the address.
    		let address = key_h ^ val_hash;

    		// check that the address is actually a 20-byte value.
    		// the leftmost 12 bytes should be zero.
    		if &address[0..12] != &[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] {
    			return None;
    		}

    		let address_hash = Address::from(address).sha3();

    		// create the xor'd key in place.
    		key_h.copy_from_slice(&*val_hash);
    		assert_eq!(key_h, val_hash);

    		{
    			let last_src: &[u8] = &*address_hash;
    			let last_dst: &mut [u8] = &mut *key_h;
    			for (k, a) in last_dst[12..].iter_mut().zip(&last_src[12..]) {
    				*k ^= *a;
    			}
    		}

    		Some(key_h)
    	} else {
    		None
    	}
    }

    /// Version for `ArchiveDB`.
    #[derive(Default)]
    pub struct ArchiveV7(Progress);

    impl SimpleMigration for ArchiveV7 {

    	fn columns(&self) -> Option<u32> { None }

    	fn version(&self) -> u32 { 7 }

    	fn simple_migrate(&mut self, key: Vec<u8>, value: Vec<u8>) -> Option<(Vec<u8>, Vec<u8>)> {
    		self.0.tick();

    		if key.len() != 32 {
    			// metadata key, ignore.
    			return Some((key, value));
    		}

    		let key_h = H256::from_slice(&key[..]);
    		if let Some(new_key) = attempt_migrate(key_h, &value[..]) {
    			Some((new_key[..].to_owned(), value))
    		} else {
    			Some((key, value))
    		}
    	}
    }

    // magic numbers and constants for overlay-recent at v6.
    // re-written here because it may change in the journaldb module.
    const V7_LATEST_ERA_KEY: &'static [u8] = &[ b'l', b'a', b's', b't', 0, 0, 0, 0, 0, 0, 0, 0 ];
    const V7_VERSION_KEY: &'static [u8] = &[ b'j', b'v', b'e', b'r', 0, 0, 0, 0, 0, 0, 0, 0 ];
    const DB_VERSION: u32 = 0x203;
    const PADDING : [u8; 10] = [0u8; 10];

    /// Version for `OverlayRecent` database.
    /// more involved than the archive version because of journaling.
    #[derive(Default)]
    pub struct OverlayRecentV7 {
    	migrated_keys: HashMap<H256, H256>,
    }

    impl OverlayRecentV7 {
    	// walk all journal entries in the database backwards.
    	// find migrations for any possible inserted keys.
    	fn walk_journal(&mut self, source: Arc<Database>) -> Result<(), Error> {
    		if let Some(val) = source.get(None, V7_LATEST_ERA_KEY).map_err(Error::Custom)? {
    			let mut era = decode::<u64>(&val);
    			loop {
    				let mut index: usize = 0;
    				loop {
    					let entry_key = {
    						let mut r = RlpStream::new_list(3);
    						r.append(&era).append(&index).append(&&PADDING[..]);
    						r.out()
    					};

    					if let Some(journal_raw) = source.get(None, &entry_key).map_err(Error::Custom)? {
    						let rlp = Rlp::new(&journal_raw);

    						// migrate all inserted keys.
    						for r in rlp.at(1).iter() {
    							let key: H256 = r.val_at(0);
    							let v: Bytes = r.val_at(1);

    							if self.migrated_keys.get(&key).is_none() {
    								if let Some(new_key) = attempt_migrate(key, &v) {
    									self.migrated_keys.insert(key, new_key);
    								}
    							}
    						}
    						index += 1;
    					} else {
    						break;
    					}
    				}

    				if index == 0 || era == 0 {
    					break;
    				}
    				era -= 1;
    			}
    		}
    		Ok(())
    	}

    	// walk all journal entries in the database backwards.
    	// replace all possible inserted/deleted keys with their migrated counterparts
    	// and commit the altered entries.
    	fn migrate_journal(&self, source: Arc<Database>, mut batch: Batch, dest: &mut Database) -> Result<(), Error> {
    		if let Some(val) = source.get(None, V7_LATEST_ERA_KEY).map_err(Error::Custom)? {
    			batch.insert(V7_LATEST_ERA_KEY.into(), val.clone().to_vec(), dest)?;

    			let mut era = decode::<u64>(&val);
    			loop {
    				let mut index: usize = 0;
    				loop {
    					let entry_key = {
    						let mut r = RlpStream::new_list(3);
    						r.append(&era).append(&index).append(&&PADDING[..]);
    						r.out()
    					};

    					if let Some(journal_raw) = source.get(None, &entry_key).map_err(Error::Custom)? {
    						let rlp = Rlp::new(&journal_raw);
    						let id: H256 = rlp.val_at(0);
    						let mut inserted_keys: Vec<(H256, Bytes)> = Vec::new();

    						// migrate all inserted keys.
    						for r in rlp.at(1).iter() {
    							let mut key: H256 = r.val_at(0);
    							let v: Bytes = r.val_at(1);

    							if let Some(new_key) = self.migrated_keys.get(&key) {
    								key = *new_key;
    							}

    							inserted_keys.push((key, v));
    						}

    						// migrate all deleted keys.
    						let mut deleted_keys: Vec<H256> = rlp.val_at(2);
    						for old_key in &mut deleted_keys {
    							if let Some(new) = self.migrated_keys.get(&*old_key) {
    								*old_key = new.clone();
    							}
    						}

    						// rebuild the journal entry rlp.
    						let mut stream = RlpStream::new_list(3);
    						stream.append(&id);
    						stream.begin_list(inserted_keys.len());
    						for (k, v) in inserted_keys {
    							stream.begin_list(2).append(&k).append(&v);
    						}

    						stream.append(&deleted_keys);

    						// and insert it into the new database.
    						batch.insert(entry_key, stream.out(), dest)?;

    						index += 1;
    					} else {
    						break;
    					}
    				}

    				if index == 0 || era == 0 {
    					break;
    				}
    				era -= 1;
    			}
    		}
    		batch.commit(dest)
    	}
    }

    impl Migration for OverlayRecentV7 {

    	fn columns(&self) -> Option<u32> { None }

    	fn version(&self) -> u32 { 7 }

    	// walk all records in the database, attempting to migrate any possible and
    	// keeping records of those that we do. then migrate the journal using
    	// this information.
    	fn migrate(&mut self, source: Arc<Database>, config: &Config, dest: &mut Database, col: Option<u32>) -> Result<(), Error> {
    		let mut batch = Batch::new(config, col);

    		// check version metadata.
    		match source.get(None, V7_VERSION_KEY).map_err(Error::Custom)? {
    			Some(ref version) if decode::<u32>(&*version) == DB_VERSION => {}
    			_ => return Err(Error::MigrationImpossible), // missing or wrong version
    		}

    		let mut count = 0;
    		for (key, value) in source.iter(None) {
    			count += 1;
    			if count == 100_000 {
    				count = 0;
    				flush!(".");
    			}

    			let mut key = key.into_vec();
    			if key.len() == 32 {
    				let key_h = H256::from_slice(&key[..]);
    				if let Some(new_key) = attempt_migrate(key_h.clone(), &value) {
    					self.migrated_keys.insert(key_h, new_key);
    					key.copy_from_slice(&new_key[..]);
    				}
    			}

    			batch.insert(key, value.into_vec(), dest)?;
    		}

    		self.walk_journal(source.clone())?;
    		self.migrate_journal(source, batch, dest)
    	}
    }

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