// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

/*
Package whisper implements the Whisper PoC-1.

(https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec)

Whisper combines aspects of both DHTs and datagram messaging systems (e.g. UDP).
As such it may be likened and compared to both, not dissimilar to the
matter/energy duality (apologies to physicists for the blatant abuse of a
fundamental and beautiful natural principle).

Whisper is a pure identity-based messaging system. Whisper provides a low-level
(non-application-specific) but easily-accessible API without being based upon
or prejudiced by the low-level hardware attributes and characteristics,
particularly the notion of singular endpoints.
*/
package whisperv5

import (
	"fmt"
	"time"
)

const (
	EnvelopeVersion    = uint64(0)
	ProtocolVersion    = uint64(5)
	ProtocolVersionStr = "5.0"
	ProtocolName       = "shh"

	statusCode           = 0
	messagesCode         = 1
	p2pCode              = 2
	mailRequestCode      = 3
	NumberOfMessageCodes = 32

	paddingMask   = byte(3)
	signatureFlag = byte(4)

	TopicLength       = 4
	signatureLength   = 65
	aesKeyLength      = 32
	saltLength        = 12
	AESNonceMaxLength = 12

	MaxMessageLength = 0xFFFF // todo: remove this restriction after testing in morden and analizing stats. this should be regulated by MinimumPoW.
	MinimumPoW       = 10.0   // todo: review

	padSizeLimitLower = 128 // it can not be less - we don't want to reveal the absence of signature
	padSizeLimitUpper = 256 // just an arbitrary number, could be changed without losing compatibility

	expirationCycle   = time.Second
	transmissionCycle = 300 * time.Millisecond

	DefaultTTL     = 50 // seconds
	SynchAllowance = 10 // seconds
)

type unknownVersionError uint64

func (e unknownVersionError) Error() string {
	return fmt.Sprintf("invalid envelope version %d", uint64(e))
}

// MailServer represents a mail server, capable of
// archiving the old messages for subsequent delivery
// to the peers. Any implementation must ensure that both
// functions are thread-safe. Also, they must return ASAP.
// DeliverMail should use directMessagesCode for delivery,
// in order to bypass the expiry checks.
type MailServer interface {
	Archive(env *Envelope)
	DeliverMail(whisperPeer *Peer, data []byte)
}