/*
 * Copyright (c) 2017 Digital Bazaar, Inc. All rights reserved.
 */
'use strict';

const {
  isSubjectReference: _isSubjectReference
} = require('./graphTypes');

const {
  createMergedNodeMap: _createMergedNodeMap
} = require('./nodeMap');

const api = {};
module.exports = api;

/**
 * Performs JSON-LD flattening.
 *
 * @param input the expanded JSON-LD to flatten.
 *
 * @return the flattened output.
 */
api.flatten = input => {
  const defaultGraph = _createMergedNodeMap(input);

  // produce flattened output
  const flattened = [];
  const keys = Object.keys(defaultGraph).sort();
  for(let ki = 0; ki < keys.length; ++ki) {
    const node = defaultGraph[keys[ki]];
    // only add full subjects to top-level
    if(!_isSubjectReference(node)) {
      flattened.push(node);
    }
  }
  return flattened;
};