export class SocketManager {
  constructor (app) {
    this._app = app
    this._hasRequestedHistoryGraph = false
    this._reconnectDelayBase = 0
  }

  reset () {
    this._hasRequestedHistoryGraph = false
  }

  createWebSocket () {
    this._webSocket = new WebSocket('ws://' + location.host)

    // The backend will automatically push data once connected
    this._webSocket.onopen = () => {
      this._app.caption.set('Loading...')

      // Reset reconnection scheduling since the WebSocket has been established
      this._reconnectDelayBase = 0
    }

    this._webSocket.onclose = (event) => {
      this._app.handleDisconnect()

      // Modify page state to display loading overlay
      // Code 1006 denotes "Abnormal closure", most likely from the server or client losing connection
      // See https://developer.mozilla.org/en-US/docs/Web/API/CloseEvent
      // Treat other codes as active errors (besides connectivity errors) when displaying the message
      if (event.code === 1006) {
        this._app.caption.set('Lost connection!')
      } else {
        this._app.caption.set('Disconnected due to error.')
      }

      // Reset modified DOM structures
      document.getElementById('big-graph-mobile-load-request').style.display = 'none'

      // Schedule socket reconnection attempt
      this.scheduleReconnect()
    }

    this._webSocket.onmessage = (message) => {
      const payload = JSON.parse(message.data)

      switch (payload.message) {
        case 'init':
          this._app.setPublicConfig(payload.config)

          // Display the main page component
          // Called here instead of syncComplete so the DOM can be drawn prior to the graphs being drawn
          // Otherwise flot.js will cause visual alignment bugs
          this._app.setPageReady(true)

          // Allow the graphDisplayManager to control whether or not the historical graph is loaded
          // Defer to isGraphVisible from the publicConfig to understand if the frontend will ever receive a graph payload
          if (this._app.publicConfig.isGraphVisible) {
            if (this._app.graphDisplayManager.isVisible) {
              this.sendHistoryGraphRequest()
            } else {
              document.getElementById('big-graph-mobile-load-request').style.display = 'block'
            }
          }

          payload.servers.forEach(this._app.addServer)

          if (payload.mojangServices) {
            this._app.mojangUpdater.updateStatus(payload.mojangServices)
          }

          // Init payload contains all data needed to render the page
          // Alert the app it is ready
          this._app.handleSyncComplete()

          break

        case 'updateServer': {
          // The backend may send "update" events prior to receiving all "add" events
          // A server has only been added once it's ServerRegistration is defined
          // Checking undefined protects from this race condition
          const serverRegistration = this._app.serverRegistry.getServerRegistration(payload.serverId)

          if (serverRegistration) {
            serverRegistration.updateServerStatus(payload, false, this._app.publicConfig.minecraftVersions)
          }

          // Use update payloads to conditionally append data to graph
          // Skip any incoming updates if the graph is disabled
          if (payload.updateHistoryGraph && this._app.graphDisplayManager.isVisible) {
            // Update may not be successful, safely append 0 points
            const playerCount = payload.result ? payload.result.players.online : 0

            this._app.graphDisplayManager.addGraphPoint(serverRegistration.serverId, payload.timestamp, playerCount)

            // Only redraw the graph if not mutating hidden data
            if (serverRegistration.isVisible) {
              this._app.graphDisplayManager.requestRedraw()
            }
          }
          break
        }

        case 'updateMojangServices': {
          this._app.mojangUpdater.updateStatus(payload)
          break
        }

        case 'historyGraph': {
          // Consider the graph visible since a payload has been received
          // This is used for the manual graph load request behavior
          this._app.graphDisplayManager.isVisible = true

          this._app.graphDisplayManager.buildPlotInstance(payload.graphData)

          // Build checkbox elements for graph controls
          let lastRowCounter = 0
          let controlsHTML = ''

          this._app.serverRegistry.getServerRegistrations()
            .map(serverRegistration => serverRegistration.data.name)
            .sort()
            .forEach(serverName => {
              const serverRegistration = this._app.serverRegistry.getServerRegistration(serverName)

              controlsHTML += '<td>' +
                '<input type="checkbox" class="graph-control" minetrack-server-id="' + serverRegistration.serverId + '" ' + (serverRegistration.isVisible ? 'checked' : '') + '>' +
                ' ' + serverName +
                '</input></td>'

              // Occasionally break table rows using a magic number
              if (++lastRowCounter % 6 === 0) {
                controlsHTML += '</tr><tr>'
              }
            })

          // Apply generated HTML and show controls
          document.getElementById('big-graph-checkboxes').innerHTML = '<table><tr>' +
            controlsHTML +
            '</tr></table>'

          document.getElementById('big-graph-controls').style.display = 'block'

          // Bind click event for updating graph data
          this._app.graphDisplayManager.initEventListeners()
          break
        }
      }
    }
  }

  scheduleReconnect () {
    // Release any active WebSocket references
    this._webSocket = undefined

    this._reconnectDelayBase++

    // Exponential backoff for reconnection attempts
    // Clamp ceiling value to 30 seconds
    this._reconnectDelaySeconds = Math.min((this._reconnectDelayBase * this._reconnectDelayBase), 30)

    const reconnectInterval = setInterval(() => {
      this._reconnectDelaySeconds--

      if (this._reconnectDelaySeconds === 0) {
        // Explicitly clear interval, this avoids race conditions
        // #clearInterval first to avoid potential errors causing pre-mature returns
        clearInterval(reconnectInterval)

        // Update displayed text
        this._app.caption.set('Reconnecting...')

        // Attempt reconnection
        // Only attempt when reconnectDelaySeconds === 0 and not <= 0, otherwise multiple attempts may be started
        this.createWebSocket()
      } else if (this._reconnectDelaySeconds > 0) {
        // Update displayed text
        this._app.caption.set('Reconnecting in ' + this._reconnectDelaySeconds + 's...')
      }
    }, 1000)
  }

  sendHistoryGraphRequest () {
    if (!this._hasRequestedHistoryGraph) {
      this._hasRequestedHistoryGraph = true

      // Send request as a plain text string to avoid the server needing to parse JSON
      // This is mostly to simplify the backend server's need for error handling
      this._webSocket.send('requestHistoryGraph')
    }
  }
}