import { logger } from "@coder/logger"
import { promises as fs } from "fs"

/**
 * Provides a heartbeat using a local file to indicate activity.
 */
export class Heart {
  private heartbeatTimer?: NodeJS.Timeout
  private heartbeatInterval = 60000
  public lastHeartbeat = 0

  public constructor(private readonly heartbeatPath: string, private readonly isActive: () => Promise<boolean>) {}

  public alive(): boolean {
    const now = Date.now()
    return now - this.lastHeartbeat < this.heartbeatInterval
  }
  /**
   * Write to the heartbeat file if we haven't already done so within the
   * timeout and start or reset a timer that keeps running as long as there is
   * activity. Failures are logged as warnings.
   */
  public beat(): void {
    if (this.alive()) {
      return
    }

    logger.trace("heartbeat")
    fs.writeFile(this.heartbeatPath, "").catch((error) => {
      logger.warn(error.message)
    })
    this.lastHeartbeat = Date.now()
    if (typeof this.heartbeatTimer !== "undefined") {
      clearTimeout(this.heartbeatTimer)
    }
    this.heartbeatTimer = setTimeout(() => {
      this.isActive()
        .then((active) => {
          if (active) {
            this.beat()
          }
        })
        .catch((error) => {
          logger.warn(error.message)
        })
    }, this.heartbeatInterval)
  }
}