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/*
 * Copyright (c) 2024 Snowflake Computing Inc. All rights reserved.
 */
package net.snowflake.client.util;

import net.snowflake.client.core.SnowflakeJdbcInternalApi;

/** Stopwatch class used to calculate the time between start and stop. */
@SnowflakeJdbcInternalApi
public class Stopwatch {
  private boolean isStarted = false;
  private long startTime;
  private long elapsedTime;

  /**
   * Starts the Stopwatch.
   *
   * @throws IllegalStateException when Stopwatch is already running.
   */
  public void start() {
    if (isStarted) {
      throw new IllegalStateException("Stopwatch is already running");
    }

    isStarted = true;
    startTime = System.nanoTime();
  }

  /**
   * Stops the Stopwatch.
   *
   * @throws IllegalStateException when Stopwatch was not yet started or is already stopped.
   */
  public void stop() {
    if (!isStarted) {
      if (startTime == 0) {
        throw new IllegalStateException("Stopwatch has not been started");
      }
      throw new IllegalStateException("Stopwatch is already stopped");
    }

    isStarted = false;
    elapsedTime = System.nanoTime() - startTime;
  }

  /** Resets the instance to it's initial state. */
  public void reset() {
    isStarted = false;
    startTime = 0;
    elapsedTime = 0;
  }

  /** Restarts the instance. */
  public void restart() {
    isStarted = true;
    startTime = System.nanoTime();
    elapsedTime = 0;
  }

  /**
   * Get the elapsed time (in ms) between the stopTime and startTime.
   *
   * @return elapsed milliseconds between stopTime and startTime
   * @throws IllegalStateException when Stopwatch has not been started yet
   */
  public long elapsedMillis() {
    return elapsedNanos() / 1_000_000;
  }

  /**
   * Get the elapsed time (in nanoseconds) between the stopTime and startTime.
   *
   * @return elapsed nanoseconds between stopTime and startTime
   * @throws IllegalStateException when Stopwatch has not been started yet
   */
  public long elapsedNanos() {
    if (isStarted) {
      return (System.nanoTime() - startTime);
    }
    if (startTime == 0) {
      throw new IllegalStateException("Stopwatch has not been started");
    }
    return elapsedTime;
  }

  /**
   * Get the instance status.
   *
   * @return true if the stopwatch is running, false otherwise
   */
  public boolean isStarted() {
    return isStarted;
  }
}