JS: Group chat messages based on criteria (initial code for Care.tv)

index.ts

interface AppPartyLog {
  id: number
  party_id: number
  type: 'activity' | 'message'
  activity?: {
    id: string
    text: string
    user: AppUser
  }
  message?: {
    id: string
    text: string
    user: AppUser
  }
  created_at: string
  updated_at: string
}

interface GroupedLog {
  type: 'activity' | 'message'
  user: AppUser
  logs: AppPartyLog[]
}

/**
 * This will group chat based on the criteria:
 * 
 * Suceeding logs
 * Succeeding messages sent by the same user
 */
function groupPartyLogs(logs: AppPartyLog[]): GroupedLog[] {
  if (logs.length === 0) {
    return []
  }

  const first: AppPartyLog = logs[0]

  const groups: GroupedLog[] = [{
    type: first.type,
    user: first[first.type].user,
    logs: [first]
  }]

  // Since we've initialized the group with the first log, we'll start with the second log.
  logs.slice(1).forEach(log => {
    const recent = last(groups)

    // We'll group it together based on the criteria
    if (recent.type === 'activity' || recent.user.id === log.message.user.id) {
      recent.logs.push(log)
    } else {
      // Otherwise, it probably belongs to its own group
      groups.push({
        type: log.type,
        user: log[log.type].user,
        logs: [log]
      })
    }
  })

  return groups
}