cwtch/model/message.go

package model

import (
	"encoding/json"
	"sort"
	"sync"
	"time"
)

// Timeline encapsulates a collection of ordered Messages, and a mechanism to access them
// in a threadsafe manner.
type Timeline struct {
	Messages      []Message
	SignedGroupID []byte
	lock          sync.Mutex
}

// Message is a local representation of a given message sent over a group chat channel.
type Message struct {
	Timestamp          time.Time
	Received           time.Time
	PeerID             string
	Message            string
	Signature          []byte
	PreviousMessageSig []byte
	ReceivedByServer   bool   // messages sent to a server
	Acknowledged       bool   // peer to peer
	Error              string `json:",omitempty"`
}

// MessageBaseSize is a rough estimate of the base number of bytes the struct uses before strings are populated
const MessageBaseSize = 104

func compareSignatures(a []byte, b []byte) bool {
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}

// GetMessages returns a copy of the entire timeline
func (t *Timeline) GetMessages() []Message {
	t.lock.Lock()
	messages := make([]Message, len(t.Messages))
	copy(messages[:], t.Messages[:])
	t.lock.Unlock()
	return messages
}

// GetCopy returns a duplicate of the Timeline
func (t *Timeline) GetCopy() *Timeline {
	t.lock.Lock()
	defer t.lock.Unlock()
	bytes, _ := json.Marshal(t)
	newt := &Timeline{}
	json.Unmarshal(bytes, newt)
	return newt
}

// SetMessages sets the Messages of this timeline. Only to be used in loading/initialization
func (t *Timeline) SetMessages(messages []Message) {
	t.lock.Lock()
	defer t.lock.Unlock()
	t.Messages = messages
}

// Len gets the length of the timeline
func (t *Timeline) Len() int {
	return len(t.Messages)
}

// Swap swaps 2 Messages on the timeline.
func (t *Timeline) Swap(i, j int) {
	t.Messages[i], t.Messages[j] = t.Messages[j], t.Messages[i]
}

// Less checks 2 Messages (i and j) in the timeline and returns true if i occurred before j, else false
func (t *Timeline) Less(i, j int) bool {

	if t.Messages[i].Timestamp.Before(t.Messages[j].Timestamp) {
		return true
	}

	// Short circuit false if j is before i, signature checks will give a wrong order in this case.
	if t.Messages[j].Timestamp.Before(t.Messages[i].Timestamp) {
		return false
	}

	if compareSignatures(t.Messages[i].PreviousMessageSig, t.SignedGroupID) {
		return true
	}

	if compareSignatures(t.Messages[i].Signature, t.Messages[j].PreviousMessageSig) {
		return true
	}

	return false
}

// Sort sorts the timeline in a canonical order.
// TODO: There is almost definitely a more efficient way of doing things that involve not calling this method on every timeline load.
func (t *Timeline) Sort() {
	t.lock.Lock()
	defer t.lock.Unlock()
	sort.Sort(t)
}

// Insert inserts a message into the timeline in a thread safe way.
func (t *Timeline) Insert(mi *Message) bool {
	t.lock.Lock()
	defer t.lock.Unlock()

	for _, m := range t.Messages {
		// If the message already exists, then we don't add it
		if compareSignatures(m.Signature, mi.Signature) {
			return true
		}
	}

	t.Messages = append(t.Messages, *mi)
	sort.Sort(t)
	return false
}