gulpfile.js

var gulp = require("gulp");
var replace = require("gulp-replace");
var inject = require("gulp-inject");
var fs = require("fs");
var gulpImports = require("gulp-imports");

gulp.task("imports", function (done) {
  gulp.src(["./src/js/code.js"]).pipe(gulpImports()).pipe(gulp.dest("./dist"));
  done();
});

gulp.task("add-styles", function () {
  var target = gulp.src("./src/html/*.html");
  var sources = gulp.src(["./src/css/*.css"], {});
  return target.pipe(inject(sources)).pipe(gulp.dest("./dist"));
});

function getCSSFilename(linkTag) {
  var hrefValue = /href\=\"([A-Za-z0-9/._]*)\"/g;
  var cssFilename = linkTag.match(hrefValue);
  cssFilename = cssFilename[0].replace('href="', "").replace('"', "");
  return cssFilename;
}

gulp.task("inject", function () {
  return gulp
    .src("./dist/*.html")
    .pipe(
      replace(/<link rel="stylesheet" href="[^"]*" \/>/g, function (linkTag) {
        var style = fs.readFileSync(`.${getCSSFilename(linkTag)}`, "utf8");
        return "<style>\n" + style + "\t</style>";
      })
    )
    .pipe(
      replace(/<script src=".\/papaparse.min.js"><\/script>/g, function () {
        var papaparseContent = fs.readFileSync(`./src/js/papaparse.min.js`, "utf8");
        return "<script>\n" + papaparseContent + "\t</script>";
      })
    )
    .pipe(gulp.dest("./dist"));
});

gulp.task("watch", function () {
  gulp.watch(["./src/**/*.*", "./*.*"], gulp.series("build"));
});

gulp.task("build", gulp.series("imports", "add-styles", "inject"));