# Chat

# Smart Contract

A chat is just a smart object with a property messages of type string[]. Like all smart objects it has an _owners property set to the current data owner. The _readers property can be used to restrict read access.

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) {
    this._readers = this._readers.filter(o => o !== publicKey)
    this._owners_ = this._owners_.filter(o => o !== publicKey)
  }
}

# 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 to the _owners array and _readers array by Alice 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.

Eve was never part of the _readers array so she cannot read the content of the chat, nor write to it.

// Create and fund wallets
const alice = new Computer()
const bob = new Computer()
const eve = 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()].sort()
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) as Chat
await bobsChat.post('Yo')
expect(bobsChat.messages).deep.eq(['Hi', 'Yo'])

// Eve was not invited and can neither read nor write
try {
  // This line throws an error
  await eve.sync(alicesChat._rev)
  expect(true).eq(false)
} catch(err) {
  expect(err.message).not.undefined
}

// 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
}