// Copyright 2016 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package messenger defines interfaces for peer-to-peer messaging where the
// originator of the message and its recipient don't necessarily have a direct
// network connection.
//
// Messages are opportunistically relayed from device to device until they
// reach their destination.
package ifc

import (
	"time"
	"v.io/v23/security"
)

// Messenger defines the interface to talk to nodes that can relay messages.
// This interface is EXPERIMENTAL and can change at any time.
type Messenger interface {
	// Diff compares the set of messages on the sender with the set of
	// messages on the receiver. The sender streams batches of message IDs
	// and the receiver reponds with one bool for each message ID. A true
	// value means the receiver has the message, a false value means it
	// doesn't.
	Diff() stream<[]string,[]bool> error
	// Push accepts a message. The receiver may be the final recipient
	// or a relay. If the receiver has already seen this message or
	// if it cannot relay the message, it should return a error.
	//
	// The message content is streamed to the receiver. The content is
	// opaque to everyone except the final recipient.
	Push(Msg Message, Offset int64) stream<[]byte,_> error
	// ResumeOffset returns the size of the partially transferred message.
	// The caller will use it to resume the transfer. If the message doesn't
	// exist yet, the returned offset will be 0.
	ResumeOffset(Msg Message) (Offset int64 | error)
}

// MessageRepository defines the interface to talk to a node that holds
// messages.
// This interface is EXPERIMENTAL and can change at any time.
type MessageRepository interface {
	// Manifest shows all messages in the receiver's repository.
	Manifest() stream<_, Message> error
	// Pull retrieves the message with the given ID. The message content
	// is streamed to the caller.
	Pull(Id string, Offset int64) stream<_, []byte> (Message | error)
}

// MessengerRepository combines the Messenger and MessageRepository interfaces.
type MessengerRepository interface {
	Messenger
	MessageRepository
}

// Message contains the metadata of a message, not the content of the message.
// It is EXPERIMENTAL and can change at any time.
type Message struct {
	// The list of nodes that have relayed this message. Each node
	// must add its own name to the list before sending it to another
	// node, either via Push() or Pull().
	Hops []string
	// The identity of the sender. Can be used to both authenticate
	// the message and to authorize sending or relaying it. 
	SenderBlessings security.WireBlessings
	// Any required discharges to prove the sender blessings are still
	// valid.
	SenderDischarges map[string]security.WireDischarge
	// Proof that the sender sent this message. The signature covers
	// all the fields below.
	Signature security.Signature
	// The unique ID of this message.
	Id string
	// The intended recipient of the message.
	// TBD: blessing pattern or email? Or something else?
	Recipient string
	// When the message was created.
	CreationTime time.Time
	// The lifespan of the message. The message can be deleted by everyone
	// when CreationTime + Lifespan has been reached.
	Lifespan time.Duration
	// The length of the message's content.
	Length int64
	// The sha256 hash of the message's content.
	Sha256 []byte
}

error (
	AlreadySeen(Id string) {"en": "message id already seen: {Id}"}
	Busy(Id string) {RetryBackoff, "en": "message is already opened"}
	ContentMismatch() {"en": "the sha256 hash doesn't match the message content"}
	Expired(CreationTime time.Time, Lifespan time.Duration, Now time.Time) {"en": "message lifespan expired: {CreationTime} + {Lifespan} < {Now}"}
	IncorrectOffset(Offset, Size int64) {"en": "the specified file offset is incorrect ({Offset} != {Size})"}
	InvalidSignature() {"en": "message signature is invalid"}
	MessageIdCollision(Id string) {"en": "message id already seen with different content: {Id}"}
	NoRoute(Recipient string) {"en": "no route for recipient: {Recipient}"}
	RateLimitExceeded(Limit float32) {RetryBackoff, "en": "request rate limit exceeded: {Limit} req/s"}
	TooBig(Limit int64) {"en": "message is too big, limit: {Limit}"}
	TooManyHops(Limit int32) {"en": "too many hops, limit: {Limit}"}
)