gistfile1.txt

import matter from 'gray-matter';
import {createHash} from 'crypto';
import _ from 'lodash';
import escapeStringRegexp from 'escape-string-regexp';
import fs from 'fs-extra';

import readline from 'readline';
import {once} from 'events';

function isSeparator(line: string) {
  // the '---' separator can have trailing whitespace but not leading whitespace
  return line[0] === "-" && line.trim() === "---";
}

export async function parseStream(filepath: string, highWaterMark: number = 1024) {
  try {
    const stream = fs.createReadStream(filepath, {
      encoding: "utf8",
      highWaterMark
    });
    const rl = readline.createInterface({
      input: stream,
      crlfDelay: Infinity
    });
      // Note: we use the crlfDelay option to recognize all instances of CR LF
  // ('\r\n') in input.txt as a single line break.

    let isFirstLine = true;
    let excerpt = "";
    let frontMatter: string[] = [];
    let insideFrontMatter = true;

    rl.on("line", line => {
      // Process the line.
      if (isFirstLine) {
        isFirstLine = false;
        if (isSeparator(line)) {
          frontMatter.push(line);
        } else {
          excerpt = line;
          rl.close();
          stream.destroy();
        }
      } else {
        if (insideFrontMatter) {
          frontMatter.push(line);
          // the next line is the first line of `body`
          if (isSeparator(line)) {
            insideFrontMatter = false;
          }
        } else if (line.length > 0 && excerpt === "") {
          excerpt = line;
          rl.close();
          stream.destroy();
        }
      }
    });

    await once(rl, "close");

    const { data } = matter(frontMatter.join("\n"));
    return { frontMatter: data, excerpt };
  } catch (err) {
    console.error(err);
    return { frontMatter: {}, excerpt: ""}
  }
}