A simplified state-machine like connection class

connection.ts

type ConnectionContext = {
  state: 'disconnected'
  methods: {
    connect: () => Promise<void>
  }
} | {
  state: 'connected',
  data: {
    endpoint: string
  },
  methods: {
    disconnect: () => Promise<void>,
    login: () => Promise<void>
  }
} | {
  state: 'authenticated',
  data: {
    endpoint: string,
    user: string
  },
  methods: {
    disconnect: () => Promise<void>,
    logout: () => Promise<void>
  }
}

class Connection {
  private _context: ConnectionContext

  constructor () {
    this._context = {
      state: 'disconnected',
      methods: {
        connect: () => this.connect()
      }
    }
  }

  get context (): ConnectionContext {
    return this._context
  }

  private connect () {
    this._context = {
      state: 'connected',
      methods: {
        disconnect: () => this.disconnect(),
        login: () => this.login()
      },
      data: {
        endpoint: 'http://abcde'
      }
    }
    return Promise.resolve()
  }

  private disconnect () {
    this._context = {
      state: 'disconnected',
      methods: {
        connect: () => this.connect()
      }
    }
    return Promise.resolve()
  }

  private login () {
    this._context = {
      state: 'authenticated',
      methods: {
        disconnect: () => this.disconnect(),
        logout: () => this.logout()
      },
      data: {
        endpoint: 'http://abcde',
        user: 'robot'
      }
    }
    return Promise.resolve()
  }

  private logout () {
    this._context = {
      state: 'connected',
      methods: {
        disconnect: () => this.disconnect(),
        login: () => this.login()
      },
      data: {
        endpoint: 'http://abcde'
      }
    }
    return Promise.resolve()
  }
}

async function example () {
  const connection = new Connection()
  
  console.log(connection.context.state)
  
  if (connection.context.state === 'disconnected') {
    await connection.context.methods.connect()
  }
  
  console.log(connection.context.state)
  
  if (connection.context.state === 'connected') {
    await connection.context.methods.login()
  }
  
  console.log(connection.context.state)
  
  if (connection.context.state === 'authenticated') {
    await connection.context.methods.logout()
  }
  
  console.log(connection.context.state)
  
  if (connection.context.state === 'connected') {
    await connection.context.methods.disconnect()
  }
  
  console.log(connection.context.state)
}

example()