broccoli.js

class Plugin
{
  shouldBuild() {
    return this.inputs.hasChanges();
  }
  
  build() {
    for (let input of this.inputs) {
      input.readFileSync('path/to/file');
    }
    
    this.output.writeFileSync('path/to/file', 'content'); // here we know about changes
  }
}

class DirectoryArray {
  
  construct(directories) {
    this.directories = directories;
  }
  
  hasChanges() {
    for (let directory of this.directories) {
      if (directory.hasChanges()) {
        return true;
      }
    }
    
    return false;
  }
}

// brocfile.js
const source = 'src';

const funnel1 = funnel(source, {files: ['index.html', 'index.js']});
// funnel1.outputPath == '/tmp/assdasdas/funnel-1-out'

const funnel2 = funnel('public', {files: ['index.css']});
// funnel2.outputPath == '/tmp/assdasdas/funnel-2-out'

const funnel3 = funnel(funnel1, {files: ['index.html']});
// funnel3.inputPaths[0] = /tmp/assdasdas/funnel-1-out
// funnel3.outputPath == '/tmp/assdasdas/funnel-3-out'

const funnel4 = merge([funnel1, funnel2, funnel3]);
// funnel4.inputPaths[0] = /tmp/assdasdas/funnel-1-out

return funnel3;



class DirectoryRevision
{
  construct(directory) {
    this.directory = directory;
    this.revision = 0;
  }
  
  hasChanges() {
    return patch.length > 0;
  }
  
  getChanges() {
    const current = FSTree.fromEntries(walkSync.entries(inputPath));
    return current.calculatePatch(this.previous);
  }
  
  settleState() {
    const changes = this.getChanges();
    if (changes.length > 0) {
      this.previous = changes;
      this.revision++;
      return true;
    }
    
    return false;
  }

  getRevision() {
    return this.revision;
  }
}