#https://shiny.rstudio.com/gallery/chat-room.html


# Create a spot for reactive variables specific to this particular session
sessionVars <- reactiveValues(username = "")

# Track whether or not this session has been initialized. We'll use this to
# assign a username to unininitialized sessions.
init <- FALSE

# When a session is ended, remove the user and note that they left the room.
session$onSessionEnded(function() {
  isolate({
    vars$users <- vars$users[vars$users != sessionVars$username]
    vars$chat <- c(vars$chat, paste0(linePrefix(),
                                     tags$span(class="user-exit",
                                               sessionVars$username,
                                               "left the room.")))
  })
})

# Observer to handle changes to the username
observe({
  # We want a reactive dependency on this variable, so we'll just list it here.
  input$user

  if (!init){
    # Seed initial username
    sessionVars$username <- ifelse(userId == "", paste0("User", round(runif(1, 10000, 99999))) , paste0(userId, round(runif(1, 10000, 99999))))

    isolate({
      vars$chat <<- c(vars$chat, paste0(linePrefix(),
                                        tags$span(class="user-enter",
                                                  sessionVars$username,
                                                  "entered the room.")))
    })
    init <<- TRUE

  } else{
    # A previous username was already given
    isolate({
      if (input$user == sessionVars$username || input$user == ""){
        # No change. Just return.
        return()
      }

      # Updating username
      # First, remove the old one
      vars$users <- vars$users[vars$users != sessionVars$username]

      # Note the change in the chat log
      vars$chat <<- c(vars$chat, paste0(linePrefix(),
                                        tags$span(class="user-change",
                                                  paste0("\"", sessionVars$username, "\""),
                                                  " -> ",
                                                  paste0("\"", input$user, "\""))))

      # Now update with the new one
      sessionVars$username <- input$user
    })
  }
  # Add this user to the global list of users
  isolate(vars$users <- c(vars$users, sessionVars$username))
})

# Keep the username updated with whatever sanitized/assigned username we have
observe({
  updateTextInput(session, "user",
                  value=sessionVars$username)
})

# Keep the list of connected users updated
output$userList <- renderUI({
  tagList(tags$ul( lapply(vars$users, function(user){
    return(tags$li(user))
  })))
})

# Listen for input$send changes (i.e. when the button is clicked)
observe({
  if(input$send < 1){
    # The code must be initializing, b/c the button hasn't been clicked yet.
    return()
  }
  isolate({
    # Add the current entry to the chat log.
    if(input$entry != "")
      vars$chat <<- c(vars$chat,
                      paste0(
                        linePrefix(),
                        tags$span(class = "username",
                                  tags$abbr(title = Sys.time(), sessionVars$username)),
                        ": ",
                        tagList(input$entry)
                      ))

  })
  # Clear out the text entry field.
  updateTextInput(session, "entry", value="")
})

# Dynamically create the UI for the chat window.
output$chat <- renderUI({
  if (length(vars$chat) > 500){
    # Too long, use only the most recent 500 lines
    vars$chat <- vars$chat[(length(vars$chat)-500):(length(vars$chat))]
  }
  # Save the chat object so we can restore it later if needed.
  if(userId == "")
    saveRDS(vars$chat, "./chat/chat.Rds")
  else
    saveRDS(vars$chat, "/root/MA_Trix_App/chat/chat.Rds")


  # Pass the chat log through as HTML
  HTML(vars$chat)
})