import { NO_TAG } from "./Histogram";
import { encodeIntoCompressedBase64 } from "./encoding";
import { floatFormatter } from "./formatters";
import Histogram from "./Histogram";

export interface Writable {
  (c: string): void;
}

const HISTOGRAM_LOG_FORMAT_VERSION = "1.3";
const timeFormatter = floatFormatter(5, 3);

class HistogramLogWriter {
  /**
   * Base time to subtract from supplied histogram start/end timestamps when
   * logging based on histogram timestamps.
   * Base time is expected to be in msec since the epoch, as histogram start/end times
   * are typically stamped with absolute times in msec since the epoch.
   */
  baseTime = 0;

  constructor(private log: Writable) {}

  /**
   * Output an interval histogram, with the given timestamp information and the [optional] tag
   * associated with the histogram, using a configurable maxValueUnitRatio. (note that the
   * specified timestamp information will be used, and the timestamp information in the actual
   * histogram will be ignored).
   * The max value reported with the interval line will be scaled by the given maxValueUnitRatio.
   * @param startTimeStampSec The start timestamp to log with the interval histogram, in seconds.
   * @param endTimeStampSec The end timestamp to log with the interval histogram, in seconds.
   * @param histogram The interval histogram to log.
   * @param maxValueUnitRatio The ratio by which to divide the histogram's max value when reporting on it.
   */
  outputIntervalHistogram(
    histogram: Histogram,
    startTimeStampSec = (histogram.startTimeStampMsec - this.baseTime) / 1000,
    endTimeStampSec = (histogram.endTimeStampMsec - this.baseTime) / 1000,
    maxValueUnitRatio = 1000
  ) {
    const base64 = encodeIntoCompressedBase64(histogram);
    const start = timeFormatter(startTimeStampSec);
    const duration = timeFormatter(endTimeStampSec - startTimeStampSec);
    const max = timeFormatter(histogram.maxValue / maxValueUnitRatio);
    const lineContent = `${start},${duration},${max},${base64}\n`;
    if (histogram.tag && histogram.tag !== NO_TAG) {
      this.log(`Tag=${histogram.tag},${lineContent}`);
    } else {
      this.log(lineContent);
    }
  }

  /**
   * Log a comment to the log.
   * Comments will be preceded with with the '#' character.
   * @param comment the comment string.
   */
  outputComment(comment: string) {
    this.log(`#${comment}\n`);
  }

  /**
   * Log a start time in the log.
   * @param startTimeMsec time (in milliseconds) since the absolute start time (the epoch)
   */
  outputStartTime(startTimeMsec: number) {
    this.outputComment(
      `[StartTime: ${floatFormatter(
        5,
        3
      )(startTimeMsec / 1000)} (seconds since epoch), ${new Date(
        startTimeMsec
      )}]\n`
    );
  }

  /**
   * Output a legend line to the log.
   */
  outputLegend() {
    this.log(
      '"StartTimestamp","Interval_Length","Interval_Max","Interval_Compressed_Histogram"\n'
    );
  }

  /**
   * Output a log format version to the log.
   */
  outputLogFormatVersion() {
    this.outputComment(
      "[Histogram log format version " + HISTOGRAM_LOG_FORMAT_VERSION + "]"
    );
  }
}

export default HistogramLogWriter;