/*
 * This is a TypeScript port of the original Java version, which was written by
 * Gil Tene as described in
 * https://github.com/HdrHistogram/HdrHistogram
 * and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */
import { NO_TAG } from "./Histogram";
import { decodeFromCompressedBase64 } from "./encoding";
import Histogram, { BitBucketSize } from "./Histogram";

const TAG_PREFIX = "Tag=";
const TAG_PREFIX_LENGTH = "Tag=".length;

/**
 * A histogram log reader.
 * <p>
 * Histogram logs are used to capture full fidelity, per-time-interval
 * histograms of a recorded value.
 * <p>
 * For example, a histogram log can be used to capture high fidelity
 * reaction-time logs for some measured system or subsystem component.
 * Such a log would capture a full reaction time histogram for each
 * logged interval, and could be used to later reconstruct a full
 * HdrHistogram of the measured reaction time behavior for any arbitrary
 * time range within the log, by adding [only] the relevant interval
 * histograms.
 * <h3>Histogram log format:</h3>
 * A histogram log file consists of text lines. Lines beginning with
 * the "#" character are optional and treated as comments. Lines
 * containing the legend (starting with "Timestamp") are also optional
 * and ignored in parsing the histogram log. All other lines must
 * be valid interval description lines. Text fields are delimited by
 * commas, spaces.
 * <p>
 * A valid interval description line contains an optional Tag=tagString
 * text field, followed by an interval description.
 * <p>
 * A valid interval description must contain exactly four text fields:
 * <ul>
 * <li>StartTimestamp: The first field must contain a number parse-able as a Double value,
 * representing the start timestamp of the interval in seconds.</li>
 * <li>intervalLength: The second field must contain a number parse-able as a Double value,
 * representing the length of the interval in seconds.</li>
 * <li>Interval_Max: The third field must contain a number parse-able as a Double value,
 * which generally represents the maximum value of the interval histogram.</li>
 * <li>Interval_Compressed_Histogram: The fourth field must contain a text field
 * parse-able as a Base64 text representation of a compressed HdrHistogram.</li>
 * </ul>
 * The log file may contain an optional indication of a starting time. Starting time
 * is indicated using a special comments starting with "#[StartTime: " and followed
 * by a number parse-able as a double, representing the start time (in seconds)
 * that may be added to timestamps in the file to determine an absolute
 * timestamp (e.g. since the epoch) for each interval.
 */
class HistogramLogReader {
  startTimeSec: number;
  baseTimeSec: number;

  lines: string[];
  currentLineIndex: number;
  bitBucketSize: BitBucketSize;
  useWebAssembly: boolean;

  constructor(
    logContent: string,
    bitBucketSize: BitBucketSize = 32,
    useWebAssembly: boolean = false
  ) {
    this.lines = splitLines(logContent);
    this.currentLineIndex = 0;
    this.bitBucketSize = bitBucketSize;
    this.useWebAssembly = useWebAssembly;
  }

  /**
   * Read the next interval histogram from the log. Returns a Histogram object if
   * an interval line was found, or null if not.
   * <p>Upon encountering any unexpected format errors in reading the next interval
   * from the file, this method will return a null.
   * @return a DecodedInterval, or a null if no appropriate interval found
   */
  public nextIntervalHistogram(
    rangeStartTimeSec = 0,
    rangeEndTimeSec = Number.MAX_VALUE
  ): Histogram | null {
    while (this.currentLineIndex < this.lines.length) {
      const currentLine = this.lines[this.currentLineIndex];
      this.currentLineIndex++;
      if (currentLine.startsWith("#[StartTime:")) {
        this.parseStartTimeFromLine(currentLine);
      } else if (currentLine.startsWith("#[BaseTime:")) {
        this.parseBaseTimeFromLine(currentLine);
      } else if (
        currentLine.startsWith("#") ||
        currentLine.startsWith('"StartTimestamp"')
      ) {
        // skip legend & meta data for now
      } else if (currentLine.includes(",")) {
        const tokens = currentLine.split(",");
        const [firstToken] = tokens;
        let tag: string;
        if (firstToken.startsWith(TAG_PREFIX)) {
          tag = firstToken.substring(TAG_PREFIX_LENGTH);
          tokens.shift();
        } else {
          tag = NO_TAG;
        }

        const [
          rawLogTimeStampInSec,
          rawIntervalLengthSec,
          ,
          base64Histogram,
        ] = tokens;
        const logTimeStampInSec = Number.parseFloat(rawLogTimeStampInSec);

        if (!this.baseTimeSec) {
          // No explicit base time noted. Deduce from 1st observed time (compared to start time):
          if (logTimeStampInSec < this.startTimeSec - 365 * 24 * 3600.0) {
            // Criteria Note: if log timestamp is more than a year in the past (compared to
            // StartTime), we assume that timestamps in the log are not absolute
            this.baseTimeSec = this.startTimeSec;
          } else {
            // Timestamps are absolute
            this.baseTimeSec = 0.0;
          }
        }

        if (rangeEndTimeSec < logTimeStampInSec) {
          return null;
        }
        if (logTimeStampInSec < rangeStartTimeSec) {
          continue;
        }
        const histogram = decodeFromCompressedBase64(
          base64Histogram,
          this.bitBucketSize,
          this.useWebAssembly
        );
        histogram.startTimeStampMsec =
          (this.baseTimeSec + logTimeStampInSec) * 1000;
        const intervalLengthSec = Number.parseFloat(rawIntervalLengthSec);
        histogram.endTimeStampMsec =
          (this.baseTimeSec + logTimeStampInSec + intervalLengthSec) * 1000;

        histogram.tag = tag;

        return histogram;
      }
    }
    return null;
  }

  private parseStartTimeFromLine(line: string) {
    this.startTimeSec = Number.parseFloat(line.split(" ")[1]);
  }

  private parseBaseTimeFromLine(line: string) {
    this.baseTimeSec = Number.parseFloat(line.split(" ")[1]);
  }
}

const splitLines = (logContent: string) => logContent.split(/\r\n|\r|\n/g);

const shouldIncludeNoTag = (lines: string[]) =>
  lines.find(
    (line) =>
      !line.startsWith("#") &&
      !line.startsWith('"') &&
      !line.startsWith(TAG_PREFIX) &&
      line.includes(",")
  );

export const listTags = (content: string) => {
  const lines = splitLines(content);
  const tags = lines
    .filter((line) => line.includes(",") && line.startsWith(TAG_PREFIX))
    .map((line) => line.substring(TAG_PREFIX_LENGTH, line.indexOf(",")));
  const tagsWithoutDuplicates = new Set(tags);
  const result = Array.from(tagsWithoutDuplicates);
  if (shouldIncludeNoTag(lines)) {
    result.unshift("NO TAG");
  }
  return result;
};

export default HistogramLogReader;