package model

import (
	"crypto/rand"
	"fmt"
	"golang.org/x/crypto/nacl/secretbox"
	"io"
)


//Group defines and encapsulates Cwtch's conception of group chat. Which are sessions
// tied to a server under a given group key. Each group has a set of messages.
type Group struct {
	GroupID     string
	GroupKey    [32]byte
	GroupServer string
	Timeline    []Message
}

// NewGroup initializes a new group associated with a given CwtchServer
func NewGroup(server string) *Group {
	group := new(Group)
	group.GroupServer = server

	var groupID [16]byte
	if _, err := io.ReadFull(rand.Reader, groupID[:]); err != nil {
		panic(err)
	}
	group.GroupID = fmt.Sprintf("%x", groupID)

	var groupKey [32]byte
	if _, err := io.ReadFull(rand.Reader, groupKey[:]); err != nil {
		panic(err)
	}
	copy(group.GroupKey[:], groupKey[:])
	return group
}

// AddMember ...
func (g *Group) AddMember() {
	// TODO: Rotate Key
}

// RemoveMember ...
func (g *Group) RemoveMember() {
	// TODO: Rotate Key
}

//EncryptMessage takes a message and encrypts the message under the group key.
func (g *Group) EncryptMessage(message string) []byte {
	var nonce [24]byte
	if _, err := io.ReadFull(rand.Reader, nonce[:]); err != nil {
		panic(err)
	}
	encrypted := secretbox.Seal(nonce[:], []byte(message), &nonce, &g.GroupKey)
	return encrypted
}

// DecryptMessage takes a ciphertext and returns true and the decrypted message if the
// cipher text can be successfully decrypted,else false.
func (g *Group) DecryptMessage(ciphertext []byte) (bool, string) {
	var decryptNonce [24]byte
	copy(decryptNonce[:], ciphertext[:24])
	decrypted, ok := secretbox.Open(nil, ciphertext[24:], &decryptNonce, &g.GroupKey)
	if ok {
		return true, string(decrypted)
	}
	return false, ""
}