# Chat

# Smart Contract

The smart contract below creates a chat that can be initialized with an array of participants. All messages are encrypted so that only the members can read the messages. It is not possible to add a new participant, but any current participant can remove another participant from the chat.

class Chat extends Contract {
  messages: string[]
  _owners: string[]
  _readers: string[]

  constructor(publicKeys: string[]) {
    super({
      messages: [],
      _owners: publicKeys,
      _readers: publicKeys,
    })
  }

  post(message) {
    this.messages.push(message)
  }

  remove(publicKey: string) {
    const isNotPublicKey = (o) => o !== publicKey
    this._readers = this._readers.filter(isNotPublicKey)
    this._owners = this._owners.filter(isNotPublicKey)
  }
}

# Usage

A new chat can be created using the new function. Note that Bob can initially post to the chat and read it's state as Bob's public key was added by Alice to the _owners array and to the _readers array upon creation of the chat.

Later, Alice called the remove function removing Bob's public key from these arrays. After this point Bob cannot read or write anymore.

// Create and fund wallets
const alice = new Computer()
const bob = new Computer()
await alice.faucet(0.01e8)
await bob.faucet(0.01e8)

// Alice creates a chat with Bob and posts a message
const publicKeys = [alice.getPublicKey(), bob.getPublicKey()]
const alicesChat = await alice.new(Chat, [publicKeys])

// Alice can post to the chat
await alicesChat.post('Hi')

// Bob can read the current state of the chat and post a message
const bobsChat = await bob.sync(alicesChat._rev)
await bobsChat.post('Yo')
expect(bobsChat.messages).deep.eq(['Hi', 'Yo'])

// Alice removes Bob's public key from the _readers array
await alicesChat.remove(bob.getPublicKey())

// Now Bob cannot read the latest state of the chat anymore
try {
  // This line throws an error
  await bob.sync(alicesChat._rev)
  expect(true).eq(false)
} catch (err) {
  expect(err.message).not.undefined
}

# Code

You can find the code here.