main.js

const fs = require("fs");
var childProcess = require("child_process");

function run(cwd) {
  const cmd = "git";
  const args = ["log", "--pretty=format:metadata:%aD,%an,%ae", "--name-only"];

  const perFile = {};
  const lastModified = {};
  // const lastModified = new Set();

  function add(files, metadata) {
    if (!metadata) {
      console.log({ files, metadata });
      throw new Error("!");
    }
    for (let file of files) {
      if (!(file in lastModified)) {
        lastModified[file] = metadata.date;
      }
      // if (!(file in perFile)) {
      //   perFile[file] = [];
      // }
      // perFile[file].push(metadata);
    }
    // files.length = 0; // empty the array trick
  }

  var spawned = childProcess.spawnSync(cmd, args, {
    cwd,
    maxBuffer: 1024 * 1024 * 10 // 10 MB, good enough??
  });
  if (spawned.error) {
    console.error("crap!!");
    console.log(spawned.error);
  } else {
    console.log("done!");
    let metadata = null;
    const files = [];
    spawned.stdout
      .toString()
      .split("\n")
      .forEach(line => {
        // console.log(line);
        if (line.startsWith("metadata:")) {
          if (files.length) {
            add(files, metadata);
          }
          metadata = {
            date: line.split(",")[1].trim()
            // author: {
            //   name: line.split(",")[2],
            //   email: line.split(",")[3]
            // }
          };
        } else if (line) {
          files.push(line);
        }
      });
    if (files.length) {
      add(files, metadata);
    }
    //for (let line of spawned.stdout.toString().split('\n')) {
    //  console.log(i, line);
    //}
  }

  // Object.entries(perFile).forEach(([file, metadatas]) => {
  //   lastModified[file] = metadatas.date;
  // });
  // console.log(JSON.stringify(perFile, null, 2));
  // console.log(JSON.stringify(lastModified, null, 2));
  fs.writeFileSync(
    "lastmodified.json",
    JSON.stringify(lastModified, null, 2),
    "utf8"
  );
  console.log(`${Object.keys(lastModified).length.toLocaleString()} keys`);
}
run("/Users/peterbe/dev/MOZILLA/MDN/kuma");