/**
*    Copyright (C) 2014 10gen Inc.
*
*    This program is free software: you can redistribute it and/or  modify
*    it under the terms of the GNU Affero General Public License, version 3,
*    as published by the Free Software Foundation.
*
*    This program 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 Affero General Public License for more details.
*
*    You should have received a copy of the GNU Affero General Public License
*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*
*    As a special exception, the copyright holders give permission to link the
*    code of portions of this program with the OpenSSL library under certain
*    conditions as described in each individual source file and distribute
*    linked combinations including the program with the OpenSSL library. You
*    must comply with the GNU Affero General Public License in all respects for
*    all of the code used other than as permitted herein. If you modify file(s)
*    with this exception, you may extend this exception to your version of the
*    file(s), but you are not obligated to do so. If you do not wish to do so,
*    delete this exception statement from your version. If you delete this
*    exception statement from all source files in the program, then also delete
*    it in the license file.
*/

#pragma once

#include <string>

#include "mongo/base/secure_allocator.h"
#include "mongo/base/status.h"
#include "mongo/crypto/sha1_block.h"
#include "mongo/db/jsobj.h"

namespace mongo {
namespace scram {

const std::string serverKeyConst = "Server Key";
const std::string clientKeyConst = "Client Key";

const std::string iterationCountFieldName = "iterationCount";
const std::string saltFieldName = "salt";
const std::string storedKeyFieldName = "storedKey";
const std::string serverKeyFieldName = "serverKey";

/*
 * The precursors necessary to perform the computation which produces SCRAMSecrets.
 * These are the original password, its salt, and the number of times it must be
 * hashed to produce the SaltedPassword used to generate the rest of the SCRAMSecrets.
 */
struct SCRAMPresecrets {
    SCRAMPresecrets(std::string hashedPassword,
                    std::vector<std::uint8_t> salt_,
                    size_t iterationCount_)
        : hashedPassword(std::move(hashedPassword)),
          salt(std::move(salt_)),
          iterationCount(iterationCount_) {
        uassert(ErrorCodes::BadValue,
                "Invalid salt for SCRAM mechanism",
                salt.size() >= kSaltLengthMin);
    }

    std::string hashedPassword;
    std::vector<std::uint8_t> salt;
    size_t iterationCount;

private:
    static const size_t kSaltLengthMin = 16;
};

inline bool operator==(const SCRAMPresecrets& lhs, const SCRAMPresecrets& rhs) {
    return lhs.hashedPassword == rhs.hashedPassword && lhs.salt == rhs.salt &&
        lhs.iterationCount == rhs.iterationCount;
}

/*
 * Computes the SaltedPassword from password, salt and iterationCount.
 */
SHA1Block generateSaltedPassword(const SCRAMPresecrets& presecrets);

/*
 * Stores all of the keys, generated from a password, needed for a client or server to perform a
 * SCRAM handshake.
 * These keys are reference counted, and allocated using the SecureAllocator.
 * May be unpopulated. SCRAMSecrets created via the default constructor are unpopulated.
 * The behavior is undefined if the accessors are called when unpopulated.
 */
class SCRAMSecrets {
private:
    struct SCRAMSecretsHolder {
        SHA1Block clientKey;
        SHA1Block storedKey;
        SHA1Block serverKey;
    };

public:
    // Creates an unpopulated SCRAMSecrets object.
    SCRAMSecrets() = default;

    // Creates a populated SCRAMSecrets object. First, allocates secure storage, then provides it
    // to a callback, which fills the memory.
    template <typename T>
    explicit SCRAMSecrets(T initializationFun)
        : _ptr(std::make_shared<SecureHandle<SCRAMSecretsHolder>>()) {
        initializationFun((*this)->clientKey, (*this)->storedKey, (*this)->serverKey);
    }

    // Returns true if the underlying shared_pointer is populated.
    explicit operator bool() const {
        return static_cast<bool>(_ptr);
    }

    const SecureHandle<SCRAMSecretsHolder>& operator*() const& {
        invariant(_ptr);
        return *_ptr;
    }
    void operator*() && = delete;

    const SecureHandle<SCRAMSecretsHolder>& operator->() const& {
        invariant(_ptr);
        return *_ptr;
    }
    void operator->() && = delete;

private:
    std::shared_ptr<SecureHandle<SCRAMSecretsHolder>> _ptr;
};

/*
 * Computes the SCRAM secrets clientKey, storedKey, and serverKey using the salt 'salt'
 * and iteration count 'iterationCount' as defined in RFC5802 (server side).
 */
SCRAMSecrets generateSecrets(const SCRAMPresecrets& presecrets);

/*
 * Computes the ClientKey and StoredKey from SaltedPassword (client side).
 */
SCRAMSecrets generateSecrets(const SHA1Block& saltedPassword);

/*
 * Generates the user salt and the SCRAM secrets storedKey and serverKey as
 * defined in RFC5802 (server side).
 */
BSONObj generateCredentials(const std::string& hashedPassword, int iterationCount);

/*
 * Computes the ClientProof from ClientKey, StoredKey, and authMessage (client side).
 */
std::string generateClientProof(const SCRAMSecrets& clientCredentials,
                                const std::string& authMessage);

/*
 * Validates that the provided password 'hashedPassword' generates the serverKey
 * 'serverKey' given iteration count 'iterationCount' and salt 'salt'.
 */
bool validatePassword(const std::string& hashedPassword,
                      int iterationCount,
                      const std::string& salt,
                      const std::string& storedKey);

/*
 * Verifies ServerSignature (client side).
 */
bool verifyServerSignature(const SCRAMSecrets& clientCredentials,
                           const std::string& authMessage,
                           const std::string& serverSignature);

/*
 * Verifies ClientProof (server side).
 */
bool verifyClientProof(StringData clientProof, StringData storedKey, StringData authMessage);

}  // namespace scram
}  // namespace mongo
