// 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/>.

use std::collections::BTreeSet;
use ethkey::{KeyPair, Signature, Error as EthKeyError};
use bigint::hash::H256;
use types::all::{Error, Public, ServerKeyId, MessageHash, EncryptedMessageSignature, RequestSignature, EncryptedDocumentKey,
	EncryptedDocumentKeyShadow, NodeId};

/// Node key pair.
pub trait NodeKeyPair: Send + Sync {
	/// Public portion of key.
	fn public(&self) -> &Public;
	/// Sign data with node key.
	fn sign(&self, data: &H256) -> Result<Signature, EthKeyError>;
	/// Compute shared key to encrypt channel between two nodes.
	fn compute_shared_key(&self, peer_public: &Public) -> Result<KeyPair, EthKeyError>;
}

/// Server key (SK) generator.
pub trait ServerKeyGenerator {
	/// Generate new SK.
	/// `key_id` is the caller-provided identifier of generated SK.
	/// `signature` is `key_id`, signed with caller public key.
	/// `threshold + 1` is the minimal number of nodes, required to restore private key.
	/// Result is a public portion of SK.
	fn generate_key(&self, key_id: &ServerKeyId, signature: &RequestSignature, threshold: usize) -> Result<Public, Error>;
}

/// Document key (DK) server.
pub trait DocumentKeyServer: ServerKeyGenerator {
	/// Store externally generated DK.
	/// `key_id` is identifier of previously generated SK.
	/// `signature` is key_id, signed with caller public key. Caller must be the same as in the `generate_key` call.
	/// `common_point` is a result of `k * T` expression, where `T` is generation point and `k` is random scalar in EC field.
	/// `encrypted_document_key` is a result of `M + k * y` expression, where `M` is unencrypted document key (point on EC),
	///   `k` is the same scalar used in `common_point` calculation and `y` is previously generated public part of SK.
	fn store_document_key(&self, key_id: &ServerKeyId, signature: &RequestSignature, common_point: Public, encrypted_document_key: Public) -> Result<(), Error>;
	/// Generate and store both SK and DK. This is a shortcut for consequent calls of `generate_key` and `store_document_key`.
	/// The only difference is that DK is generated by DocumentKeyServer (which might be considered unsafe).
	/// `key_id` is the caller-provided identifier of generated SK.
	/// `signature` is `key_id`, signed with caller public key.
	/// `threshold + 1` is the minimal number of nodes, required to restore private key.
	/// Result is a DK, encrypted with caller public key.
	fn generate_document_key(&self, key_id: &ServerKeyId, signature: &RequestSignature, threshold: usize) -> Result<EncryptedDocumentKey, Error>;
	/// Restore previously stored DK.
	/// DK is decrypted on the key server (which might be considered unsafe), and then encrypted with caller public key.
	/// `key_id` is identifier of previously generated SK.
	/// `signature` is key_id, signed with caller public key. Caller must be on ACL for this function to succeed.
	/// Result is a DK, encrypted with caller public key.
	fn restore_document_key(&self, key_id: &ServerKeyId, signature: &RequestSignature) -> Result<EncryptedDocumentKey, Error>;
	/// Restore previously stored DK.
	/// To decrypt DK on client:
	/// 1) use requestor secret key to decrypt secret coefficients from result.decrypt_shadows
	/// 2) calculate decrypt_shadows_sum = sum of all secrets from (1)
	/// 3) calculate decrypt_shadow_point: decrypt_shadows_sum * result.common_point
	/// 4) calculate decrypted_secret: result.decrypted_secret + decrypt_shadow_point
	/// Result is a DK shadow.
	fn restore_document_key_shadow(&self, key_id: &ServerKeyId, signature: &RequestSignature) -> Result<EncryptedDocumentKeyShadow, Error>;
}

/// Message signer.
pub trait MessageSigner: ServerKeyGenerator {
	/// Sign message with previously generated SK.
	/// `key_id` is the caller-provided identifier of generated SK.
	/// `signature` is `key_id`, signed with caller public key.
	/// `message` is the message to be signed.
	/// Result is a signed message, encrypted with caller public key.
	fn sign_message(&self, key_id: &ServerKeyId, signature: &RequestSignature, message: MessageHash) -> Result<EncryptedMessageSignature, Error>;
}

/// Administrative sessions server.
pub trait AdminSessionsServer {
	/// Change servers set so that nodes in new_servers_set became owners of shares for all keys.
	/// And old nodes (i.e. cluste nodes except new_servers_set) have clear databases.
	/// WARNING: newly generated keys will be distributed among all cluster nodes. So this session
	/// must be followed with cluster nodes change (either via contract, or config files).
	fn change_servers_set(&self, old_set_signature: RequestSignature, new_set_signature: RequestSignature, new_servers_set: BTreeSet<NodeId>) -> Result<(), Error>;
}

/// Key server.
pub trait KeyServer: AdminSessionsServer + DocumentKeyServer + MessageSigner + Send + Sync {
}