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// This file is part of Substrate.

// Copyright (C) 2019-2021 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! In-memory implementation of offchain workers database.

use std::collections::hash_map::{HashMap, Entry};
use crate::offchain::OffchainStorage;
use std::iter::Iterator;

/// In-memory storage for offchain workers.
#[derive(Debug, Clone, Default)]
pub struct InMemOffchainStorage {
	storage: HashMap<Vec<u8>, Vec<u8>>,
}

impl InMemOffchainStorage {
	/// Consume the offchain storage and iterate over all key value pairs.
	pub fn into_iter(self) -> impl Iterator<Item=(Vec<u8>,Vec<u8>)> {
		self.storage.into_iter()
	}

	/// Iterate over all key value pairs by reference.
	pub fn iter<'a>(&'a self) -> impl Iterator<Item=(&'a Vec<u8>,&'a Vec<u8>)> {
		self.storage.iter()
	}

	/// Remove a key and its associated value from the offchain database.
	pub fn remove(&mut self, prefix: &[u8], key: &[u8]) {
		let key: Vec<u8> = prefix.iter().chain(key).cloned().collect();
		self.storage.remove(&key);
	}
}

impl OffchainStorage for InMemOffchainStorage {
	fn set(&mut self, prefix: &[u8], key: &[u8], value: &[u8]) {
		let key = prefix.iter().chain(key).cloned().collect();
		self.storage.insert(key, value.to_vec());
	}

	fn remove(&mut self, prefix: &[u8], key: &[u8]) {
		let key: Vec<u8> = prefix.iter().chain(key).cloned().collect();
		self.storage.remove(&key);
	}

	fn get(&self, prefix: &[u8], key: &[u8]) -> Option<Vec<u8>> {
		let key: Vec<u8> = prefix.iter().chain(key).cloned().collect();
		self.storage.get(&key).cloned()
	}

	fn compare_and_set(
		&mut self,
		prefix: &[u8],
		key: &[u8],
		old_value: Option<&[u8]>,
		new_value: &[u8],
	) -> bool {
		let key = prefix.iter().chain(key).cloned().collect();

		match self.storage.entry(key) {
			Entry::Vacant(entry) => if old_value.is_none() {
				entry.insert(new_value.to_vec());
				true
			} else { false },
			Entry::Occupied(ref mut entry) if Some(entry.get().as_slice()) == old_value => {
				entry.insert(new_value.to_vec());
				true
			},
			_ => false,
		}
	}
}