index.js

var Writer      = require('broccoli-caching-writer');
var walkSync    = require('walk-sync');
var path        = require('path');
var mkdirp      = require('mkdirp');
var matter      = require('gray-matter');
var objectMerge = require('object-merge');
var fs          = require('fs');

var copyDereferenceSync = require('copy-dereference').sync;

module.exports = FrontMatterFilter;

FrontMatterFilter.prototype = Object.create(Writer.prototype);
FrontMatterFilter.prototype.constructor = FrontMatterFilter;

function FrontMatterFilter (inputTree, options) {
  if (!(this instanceof FrontMatterFilter)) return new FrontMatterFilter(inputTree, options);

  var defaultOptions = {
    stripFrontMatter:      false,
    removeIfNoFrontMatter: false,
    grayMatter: {}
  };

  this.options   = objectMerge(defaultOptions, (options || {}));
  this.inputTree = inputTree;
}

FrontMatterFilter.prototype.updateCache = function(srcDir, destDir) {
  var includeCB             = this.options.include;
  var strip                 = this.options.stripFrontMatter;
  var removeIfNoFrontMatter = this.options.removeIfNoFrontMatter;
  var grayMatterOptions     = this.options.grayMatter;

  var hasIncludeCB = (typeof(includeCB) === 'function');

  var filePaths = walkSync(srcDir);

  filePaths.forEach(function(filePath) {
    var srcFilePath  = path.join(srcDir, filePath);
    var destFilePath = path.join(destDir, filePath);

    // handle directories
    if (filePath.slice(-1) === '/') {
      mkdirp.sync(destFilePath);
      return;
    }

    var content = fs.readFileSync(srcFilePath, {encoding: 'utf8'});
    var hasFrontMatter = matter.exists(content, grayMatterOptions);

    if (!hasFrontMatter) {
      if (!removeIfNoFrontMatter) {
        // fs.writeFileSync(destFilePath, content);
        _copyFile(srcFilePath, destFilePath)
      }
    } else {
      var parsed = matter(content, grayMatterOptions);
      if (hasIncludeCB && includeCB(parsed.data)) {
        // fs.writeFileSync(destFilePath, (strip ? parsed.content : content));
        _copyFile(srcFilePath, destFilePath, parsed.content, strip);
      } else if (!hasIncludeCB) {
        // pass through if include callback not provided
        // fs.writeFileSync(destFilePath, (strip ? parsed.content : content));
        _copyFile(srcFilePath, destFilePath, parsed.content, strip);
      }
    }
  });

  return destDir;
};

function _copyFile(srcFilePath, destFilePath, parsedContent, strip) {
  if (strip) {
    // Need to implement caching still
    fs.writeFileSync(destFilePath, parsedContent);
  } else {
    copyDereferenceSync(srcFilePath, destFilePath);
  }
}