/*
 * ZeroTier One - Network Virtualization Everywhere
 * Copyright (C) 2011-2016  ZeroTier, Inc.  https://www.zerotier.com/
 *
 * This program 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.
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef ZT_CERTIFICATEOFMEMBERSHIP_HPP
#define ZT_CERTIFICATEOFMEMBERSHIP_HPP

#include <stdint.h>
#include <string.h>

#include <string>
#include <stdexcept>
#include <algorithm>

#include "Constants.hpp"
#include "Buffer.hpp"
#include "Address.hpp"
#include "C25519.hpp"
#include "Identity.hpp"
#include "Utils.hpp"

/**
 * Default window of time for certificate agreement
 *
 * Right now we use time for 'revision' so this is the maximum time divergence
 * between two certs for them to agree. It comes out to five minutes, which
 * gives a lot of margin for error if the controller hiccups or its clock
 * drifts but causes de-authorized peers to fall off fast enough.
 */
#define ZT_NETWORK_COM_DEFAULT_REVISION_MAX_DELTA (ZT_NETWORK_AUTOCONF_DELAY * 5)

/**
 * Maximum number of qualifiers in a COM
 */
#define ZT_NETWORK_COM_MAX_QUALIFIERS 16

namespace ZeroTier {

/**
 * Certificate of network membership
 *
 * The COM contains a sorted set of three-element tuples called qualifiers.
 * These contain an id, a value, and a maximum delta.
 *
 * The ID is arbitrary and should be assigned using a scheme that makes
 * every ID globally unique. IDs beneath 65536 are reserved for global
 * assignment by ZeroTier Networks.
 *
 * The value's meaning is ID-specific and isn't important here. What's
 * important is the value and the third member of the tuple: the maximum
 * delta. The maximum delta is the maximum difference permitted between
 * values for a given ID between certificates for the two certificates to
 * themselves agree.
 *
 * Network membership is checked by checking whether a peer's certificate
 * agrees with your own. The timestamp provides the fundamental criterion--
 * each member of a private network must constantly obtain new certificates
 * often enough to stay within the max delta for this qualifier. But other
 * criteria could be added in the future for very special behaviors, things
 * like latitude and longitude for instance.
 *
 * This is a memcpy()'able structure and is safe (in a crash sense) to modify
 * without locks.
 */
class CertificateOfMembership
{
public:
	/**
	 * Certificate type codes, used in serialization
	 *
	 * Only one so far, and only one hopefully there shall be for quite some
	 * time.
	 */
	enum Type
	{
		COM_UINT64_ED25519 = 1 // tuples of unsigned 64's signed with Ed25519
	};

	/**
	 * Reserved qualifier IDs
	 *
	 * IDs below 65536 should be considered reserved for future global
	 * assignment here.
	 *
	 * Addition of new required fields requires that code in hasRequiredFields
	 * be updated as well.
	 */
	enum ReservedId
	{
		/**
		 * Revision number of certificate
		 *
		 * Certificates may differ in revision number by a designated max
		 * delta. Differences wider than this cause certificates not to agree.
		 */
		COM_RESERVED_ID_REVISION = 0,

		/**
		 * Network ID for which certificate was issued
		 *
		 * maxDelta here is zero, since this must match.
		 */
		COM_RESERVED_ID_NETWORK_ID = 1,

		/**
		 * ZeroTier address to whom certificate was issued
		 *
		 * maxDelta will be 0xffffffffffffffff here since it's permitted to differ
		 * from peers obviously.
		 */
		COM_RESERVED_ID_ISSUED_TO = 2
	};

	/**
	 * Create an empty certificate
	 */
	CertificateOfMembership() :
		_qualifierCount(0)
	{
		memset(_signature.data,0,_signature.size());
	}

	CertificateOfMembership(const CertificateOfMembership &c)
	{
		memcpy(this,&c,sizeof(CertificateOfMembership));
	}

	/**
	 * Create from required fields common to all networks
	 *
	 * @param revision Revision number of certificate
	 * @param timestampMaxDelta Maximum variation between timestamps on this net
	 * @param nwid Network ID
	 * @param issuedTo Certificate recipient
	 */
	CertificateOfMembership(uint64_t revision,uint64_t revisionMaxDelta,uint64_t nwid,const Address &issuedTo)
	{
		_qualifiers[0].id = COM_RESERVED_ID_REVISION;
		_qualifiers[0].value = revision;
		_qualifiers[0].maxDelta = revisionMaxDelta;
		_qualifiers[1].id = COM_RESERVED_ID_NETWORK_ID;
		_qualifiers[1].value = nwid;
		_qualifiers[1].maxDelta = 0;
		_qualifiers[2].id = COM_RESERVED_ID_ISSUED_TO;
		_qualifiers[2].value = issuedTo.toInt();
		_qualifiers[2].maxDelta = 0xffffffffffffffffULL;
		_qualifierCount = 3;
		memset(_signature.data,0,_signature.size());
	}

	inline CertificateOfMembership &operator=(const CertificateOfMembership &c)
	{
		memcpy(this,&c,sizeof(CertificateOfMembership));
		return *this;
	}

#ifdef ZT_SUPPORT_OLD_STYLE_NETCONF
	/**
	 * Create from string-serialized data
	 *
	 * @param s String-serialized COM
	 */
	CertificateOfMembership(const char *s) { fromString(s); }

	/**
	 * Create from string-serialized data
	 *
	 * @param s String-serialized COM
	 */
	CertificateOfMembership(const std::string &s) { fromString(s.c_str()); }
#endif // ZT_SUPPORT_OLD_STYLE_NETCONF

	/**
	 * Create from binary-serialized COM in buffer
	 *
	 * @param b Buffer to deserialize from
	 * @param startAt Position to start in buffer
	 */
	template<unsigned int C>
	CertificateOfMembership(const Buffer<C> &b,unsigned int startAt = 0)
	{
		deserialize(b,startAt);
	}

	/**
	 * @return True if there's something here
	 */
	inline operator bool() const throw() { return (_qualifierCount != 0); }

	/**
	 * Check for presence of all required fields common to all networks
	 *
	 * @return True if all required fields are present
	 */
	inline bool hasRequiredFields() const
	{
		if (_qualifierCount < 3)
			return false;
		if (_qualifiers[0].id != COM_RESERVED_ID_REVISION)
			return false;
		if (_qualifiers[1].id != COM_RESERVED_ID_NETWORK_ID)
			return false;
		if (_qualifiers[2].id != COM_RESERVED_ID_ISSUED_TO)
			return false;
		return true;
	}

	/**
	 * @return Maximum delta for mandatory revision field or 0 if field missing
	 */
	inline uint64_t revisionMaxDelta() const
	{
		for(unsigned int i=0;i<_qualifierCount;++i) {
			if (_qualifiers[i].id == COM_RESERVED_ID_REVISION)
				return _qualifiers[i].maxDelta;
		}
		return 0ULL;
	}

	/**
	 * @return Revision number for this cert
	 */
	inline uint64_t revision() const
	{
		for(unsigned int i=0;i<_qualifierCount;++i) {
			if (_qualifiers[i].id == COM_RESERVED_ID_REVISION)
				return _qualifiers[i].value;
		}
		return 0ULL;
	}

	/**
	 * @return Address to which this cert was issued
	 */
	inline Address issuedTo() const
	{
		for(unsigned int i=0;i<_qualifierCount;++i) {
			if (_qualifiers[i].id == COM_RESERVED_ID_ISSUED_TO)
				return Address(_qualifiers[i].value);
		}
		return Address();
	}

	/**
	 * @return Network ID for which this cert was issued
	 */
	inline uint64_t networkId() const
	{
		for(unsigned int i=0;i<_qualifierCount;++i) {
			if (_qualifiers[i].id == COM_RESERVED_ID_NETWORK_ID)
				return _qualifiers[i].value;
		}
		return 0ULL;
	}

	/**
	 * Add or update a qualifier in this certificate
	 *
	 * Any signature is invalidated and signedBy is set to null.
	 *
	 * @param id Qualifier ID
	 * @param value Qualifier value
	 * @param maxDelta Qualifier maximum allowed difference (absolute value of difference)
	 */
	void setQualifier(uint64_t id,uint64_t value,uint64_t maxDelta);
	inline void setQualifier(ReservedId id,uint64_t value,uint64_t maxDelta) { setQualifier((uint64_t)id,value,maxDelta); }

#ifdef ZT_SUPPORT_OLD_STYLE_NETCONF
	/**
	 * @return String-serialized representation of this certificate
	 */
	std::string toString() const;

	/**
	 * Set this certificate equal to the hex-serialized string
	 *
	 * Invalid strings will result in invalid or undefined certificate
	 * contents. These will subsequently fail validation and comparison.
	 * Empty strings will result in an empty certificate.
	 *
	 * @param s String to deserialize
	 */
	void fromString(const char *s);
#endif // ZT_SUPPORT_OLD_STYLE_NETCONF

	/**
	 * Compare two certificates for parameter agreement
	 *
	 * This compares this certificate with the other and returns true if all
	 * paramters in this cert are present in the other and if they agree to
	 * within this cert's max delta value for each given parameter.
	 *
	 * Tuples present in other but not in this cert are ignored, but any
	 * tuples present in this cert but not in other result in 'false'.
	 *
	 * @param other Cert to compare with
	 * @return True if certs agree and 'other' may be communicated with
	 */
	bool agreesWith(const CertificateOfMembership &other) const;

	/**
	 * Sign this certificate
	 *
	 * @param with Identity to sign with, must include private key
	 * @return True if signature was successful
	 */
	bool sign(const Identity &with);

	/**
	 * Verify certificate against an identity
	 *
	 * @param id Identity to verify against
	 * @return True if certificate is signed by this identity and verification was successful
	 */
	bool verify(const Identity &id) const;

	/**
	 * @return True if signed
	 */
	inline bool isSigned() const throw() { return (_signedBy); }

	/**
	 * @return Address that signed this certificate or null address if none
	 */
	inline const Address &signedBy() const throw() { return _signedBy; }

	template<unsigned int C>
	inline void serialize(Buffer<C> &b) const
	{
		b.append((unsigned char)COM_UINT64_ED25519);
		b.append((uint16_t)_qualifierCount);
		for(unsigned int i=0;i<_qualifierCount;++i) {
			b.append(_qualifiers[i].id);
			b.append(_qualifiers[i].value);
			b.append(_qualifiers[i].maxDelta);
		}
		_signedBy.appendTo(b);
		if (_signedBy)
			b.append(_signature.data,(unsigned int)_signature.size());
	}

	template<unsigned int C>
	inline unsigned int deserialize(const Buffer<C> &b,unsigned int startAt = 0)
	{
		unsigned int p = startAt;

		_qualifierCount = 0;
		_signedBy.zero();

		if (b[p++] != COM_UINT64_ED25519)
			throw std::invalid_argument("invalid type");

		unsigned int numq = b.template at<uint16_t>(p); p += sizeof(uint16_t);
		uint64_t lastId = 0;
		for(unsigned int i=0;i<numq;++i) {
			const uint64_t qid = b.template at<uint64_t>(p);
			if (qid < lastId)
				throw std::invalid_argument("qualifiers not sorted");
			else lastId = qid;
			if (_qualifierCount < ZT_NETWORK_COM_MAX_QUALIFIERS) {
				_qualifiers[_qualifierCount].id = qid;
				_qualifiers[_qualifierCount].value = b.template at<uint64_t>(p + 8);
				_qualifiers[_qualifierCount].maxDelta = b.template at<uint64_t>(p + 16);
				p += 24;
				++_qualifierCount;
			} else {
				throw std::invalid_argument("too many qualifiers");
			}
		}

		_signedBy.setTo(b.field(p,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH);
		p += ZT_ADDRESS_LENGTH;

		if (_signedBy) {
			memcpy(_signature.data,b.field(p,(unsigned int)_signature.size()),_signature.size());
			p += (unsigned int)_signature.size();
		}

		return (p - startAt);
	}

	inline bool operator==(const CertificateOfMembership &c) const
		throw()
	{
		if (_signedBy != c._signedBy)
			return false;
		if (_qualifierCount != c._qualifierCount)
			return false;
		for(unsigned int i=0;i<_qualifierCount;++i) {
			const _Qualifier &a = _qualifiers[i];
			const _Qualifier &b = c._qualifiers[i];
			if ((a.id != b.id)||(a.value != b.value)||(a.maxDelta != b.maxDelta))
				return false;
		}
		return (_signature == c._signature);
	}
	inline bool operator!=(const CertificateOfMembership &c) const throw() { return (!(*this == c)); }

private:
	struct _Qualifier
	{
		_Qualifier() : id(0),value(0),maxDelta(0) {}
		uint64_t id;
		uint64_t value;
		uint64_t maxDelta;
		inline bool operator<(const _Qualifier &q) const throw() { return (id < q.id); } // sort order
	};

	Address _signedBy;
	_Qualifier _qualifiers[ZT_NETWORK_COM_MAX_QUALIFIERS];
	unsigned int _qualifierCount;
	C25519::Signature _signature;
};

} // namespace ZeroTier

#endif