// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum 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.

// OpenEthereum 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 OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

//! A minimal "state backend" trait: an abstraction over the sources of data
//! a blockchain state may draw upon.
//!
//! Currently assumes a very specific DB + cache structure, but
//! should become general over time to the point where not even a
//! merkle trie is strictly necessary.

use std::{
    collections::{HashMap, HashSet},
    sync::Arc,
};

use ethereum_types::{Address, H256};
use hash_db::{AsHashDB, HashDB};
use journaldb::AsKeyedHashDB;
use keccak_hasher::KeccakHasher;
use kvdb::DBValue;
use memory_db::MemoryDB;
use parking_lot::Mutex;
use state::Account;

/// State backend. See module docs for more details.
pub trait Backend: Send {
    /// Treat the backend as a read-only hashdb.
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue>;

    /// Treat the backend as a writeable hashdb.
    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue>;

    // t_nb 9.4 Add an account entry to the cache.
    fn add_to_account_cache(&mut self, addr: Address, data: Option<Account>, modified: bool);

    /// Add a global code cache entry. This doesn't need to worry about canonicality because
    /// it simply maps hashes to raw code and will always be correct in the absence of
    /// hash collisions.
    fn cache_code(&self, hash: H256, code: Arc<Vec<u8>>);

    /// Get basic copy of the cached account. Not required to include storage.
    /// Returns 'None' if cache is disabled or if the account is not cached.
    fn get_cached_account(&self, addr: &Address) -> Option<Option<Account>>;

    /// Get value from a cached account.
    /// `None` is passed to the closure if the account entry cached
    /// is known not to exist.
    /// `None` is returned if the entry is not cached.
    fn get_cached<F, U>(&self, a: &Address, f: F) -> Option<U>
    where
        F: FnOnce(Option<&mut Account>) -> U;

    /// Get cached code based on hash.
    fn get_cached_code(&self, hash: &H256) -> Option<Arc<Vec<u8>>>;
}

/// A raw backend used to check proofs of execution.
///
/// This doesn't delete anything since execution proofs won't have mangled keys
/// and we want to avoid collisions.
// TODO: when account lookup moved into backends, this won't rely as tenuously on intended
// usage.
#[derive(Clone, PartialEq)]
pub struct ProofCheck(MemoryDB<KeccakHasher, DBValue>);

impl ProofCheck {
    /// Create a new `ProofCheck` backend from the given state items.
    pub fn new(proof: &[DBValue]) -> Self {
        let mut db = journaldb::new_memory_db();
        for item in proof {
            db.insert(item);
        }
        ProofCheck(db)
    }
}

impl journaldb::KeyedHashDB for ProofCheck {
    fn keys(&self) -> HashMap<H256, i32> {
        self.0.keys()
    }
}

impl HashDB<KeccakHasher, DBValue> for ProofCheck {
    fn get(&self, key: &H256) -> Option<DBValue> {
        self.0.get(key)
    }

    fn contains(&self, key: &H256) -> bool {
        self.0.contains(key)
    }

    fn insert(&mut self, value: &[u8]) -> H256 {
        self.0.insert(value)
    }

    fn emplace(&mut self, key: H256, value: DBValue) {
        self.0.emplace(key, value)
    }

    fn remove(&mut self, _key: &H256) {}
}

impl AsHashDB<KeccakHasher, DBValue> for ProofCheck {
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue> {
        self
    }
    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue> {
        self
    }
}

impl Backend for ProofCheck {
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue> {
        self
    }
    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue> {
        self
    }
    fn add_to_account_cache(&mut self, _addr: Address, _data: Option<Account>, _modified: bool) {}
    fn cache_code(&self, _hash: H256, _code: Arc<Vec<u8>>) {}
    fn get_cached_account(&self, _addr: &Address) -> Option<Option<Account>> {
        None
    }
    fn get_cached<F, U>(&self, _a: &Address, _f: F) -> Option<U>
    where
        F: FnOnce(Option<&mut Account>) -> U,
    {
        None
    }
    fn get_cached_code(&self, _hash: &H256) -> Option<Arc<Vec<u8>>> {
        None
    }
}

/// Proving state backend.
/// This keeps track of all state values loaded during usage of this backend.
/// The proof-of-execution can be extracted with `extract_proof`.
///
/// This doesn't cache anything or rely on the canonical state caches.
pub struct Proving<H> {
    base: H,                                  // state we're proving values from.
    changed: MemoryDB<KeccakHasher, DBValue>, // changed state via insertions.
    proof: Mutex<HashSet<DBValue>>,
}

impl<AH: AsKeyedHashDB + Send + Sync> AsKeyedHashDB for Proving<AH> {
    fn as_keyed_hash_db(&self) -> &dyn journaldb::KeyedHashDB {
        self
    }
}

impl<AH: AsHashDB<KeccakHasher, DBValue> + Send + Sync> AsHashDB<KeccakHasher, DBValue>
    for Proving<AH>
{
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue> {
        self
    }
    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue> {
        self
    }
}

impl<H: AsKeyedHashDB + Send + Sync> journaldb::KeyedHashDB for Proving<H> {
    fn keys(&self) -> HashMap<H256, i32> {
        let mut keys = self.base.as_keyed_hash_db().keys();
        keys.extend(self.changed.keys());
        keys
    }
}

impl<H: AsHashDB<KeccakHasher, DBValue> + Send + Sync> HashDB<KeccakHasher, DBValue>
    for Proving<H>
{
    fn get(&self, key: &H256) -> Option<DBValue> {
        match self.base.as_hash_db().get(key) {
            Some(val) => {
                self.proof.lock().insert(val.clone());
                Some(val)
            }
            None => self.changed.get(key),
        }
    }

    fn contains(&self, key: &H256) -> bool {
        self.get(key).is_some()
    }

    fn insert(&mut self, value: &[u8]) -> H256 {
        self.changed.insert(value)
    }

    fn emplace(&mut self, key: H256, value: DBValue) {
        self.changed.emplace(key, value)
    }

    fn remove(&mut self, key: &H256) {
        // only remove from `changed`
        if self.changed.contains(key) {
            self.changed.remove(key)
        }
    }
}

impl<H: AsHashDB<KeccakHasher, DBValue> + Send + Sync> Backend for Proving<H> {
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue> {
        self
    }

    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue> {
        self
    }

    fn add_to_account_cache(&mut self, _: Address, _: Option<Account>, _: bool) {}

    fn cache_code(&self, _: H256, _: Arc<Vec<u8>>) {}

    fn get_cached_account(&self, _: &Address) -> Option<Option<Account>> {
        None
    }

    fn get_cached<F, U>(&self, _: &Address, _: F) -> Option<U>
    where
        F: FnOnce(Option<&mut Account>) -> U,
    {
        None
    }

    fn get_cached_code(&self, _: &H256) -> Option<Arc<Vec<u8>>> {
        None
    }
}

impl<H: AsHashDB<KeccakHasher, DBValue>> Proving<H> {
    /// Create a new `Proving` over a base database.
    /// This will store all values ever fetched from that base.
    pub fn new(base: H) -> Self {
        Proving {
            base: base,
            changed: journaldb::new_memory_db(),
            proof: Mutex::new(HashSet::new()),
        }
    }

    /// Consume the backend, extracting the gathered proof in lexicographical order
    /// by value.
    pub fn extract_proof(self) -> Vec<DBValue> {
        self.proof.into_inner().into_iter().collect()
    }
}

impl<H: AsHashDB<KeccakHasher, DBValue> + Clone> Clone for Proving<H> {
    fn clone(&self) -> Self {
        Proving {
            base: self.base.clone(),
            changed: self.changed.clone(),
            proof: Mutex::new(self.proof.lock().clone()),
        }
    }
}

/// A basic backend. Just wraps the given database, directly inserting into and deleting from
/// it. Doesn't cache anything.
pub struct Basic<H>(pub H);

impl<H: AsHashDB<KeccakHasher, DBValue> + Send + Sync> Backend for Basic<H> {
    fn as_hash_db(&self) -> &dyn HashDB<KeccakHasher, DBValue> {
        self.0.as_hash_db()
    }

    fn as_hash_db_mut(&mut self) -> &mut dyn HashDB<KeccakHasher, DBValue> {
        self.0.as_hash_db_mut()
    }

    fn add_to_account_cache(&mut self, _: Address, _: Option<Account>, _: bool) {}

    fn cache_code(&self, _: H256, _: Arc<Vec<u8>>) {}

    fn get_cached_account(&self, _: &Address) -> Option<Option<Account>> {
        None
    }

    fn get_cached<F, U>(&self, _: &Address, _: F) -> Option<U>
    where
        F: FnOnce(Option<&mut Account>) -> U,
    {
        None
    }

    fn get_cached_code(&self, _: &H256) -> Option<Arc<Vec<u8>>> {
        None
    }
}