// Copyright 2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

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

use std::collections::hash_map::{HashMap, Entry};

/// Offchain workers local storage.
pub trait OffchainStorage: Clone + Send + Sync {
	/// Persist a value in storage under given key and prefix.
	fn set(&mut self, prefix: &[u8], key: &[u8], value: &[u8]);

	/// Retrieve a value from storage under given key and prefix.
	fn get(&self, prefix: &[u8], key: &[u8]) -> Option<Vec<u8>>;

	/// Replace the value in storage if given old_value matches the current one.
	///
	/// Returns `true` if the value has been set and false otherwise.
	fn compare_and_set(
		&mut self,
		prefix: &[u8],
		key: &[u8],
		old_value: Option<&[u8]>,
		new_value: &[u8],
	) -> bool;
}

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

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 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,
		}
	}
}