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util.js
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util.js
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/**
* Copyright 2020 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
const fs = require('fs');
const axios = require('axios');
const jsonld = require('jsonld');
const n3 = require('n3');
const Store = n3.Store;
const RdfaParser = require('rdfa-streaming-parser').RdfaParser;
const errors = require('./errors');
/**
* Loads related data (shapes, context, etc.) from remote or local source
* @param {string} link url to the remote source or local path
* @return {*}
*/
async function loadData(link) {
if (link.match("^https?://")) {
return (await axios.get(link)).data;
}
return fs.readFileSync(link).toString();
}
/**
* Removes duplicates from objects array
* @param {[object]} items
* @param {[string]} keys
* @returns {[object]}
*/
function uniqueBy(items, keys) {
const seen = {};
return items.filter(function (item) {
let val = '';
keys.forEach(key => val += item[key]);
return seen.hasOwnProperty(val) ? false : (seen[val] = true);
})
}
/**
* Generates random URL as base
* @param {number} length
* @return {string}
*/
function randomUrl(length = 16) {
let result = 'https://example.org/';
const characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
for (let i = 0; i < length; i++) {
result += characters.charAt(Math.floor(Math.random() * characters.length));
}
return result;
}
/**
* Finds strongly connected components in the data graph
* @param {Store} store
* @return {Map<string, number>} - map from subject uris to
* component ids
*/
function stronglyConnectedComponents(store) {
const nodes = [...new Set(store.getSubjects()
.map(x => x.id))];
const order = [];
let component = [];
let componentIdx = 0;
const components = new Map();
const used = new Map();
const forwardDfs = (v) => {
used.set(v, true);
for (const quad of store.getQuads(v, undefined, undefined)) {
if (nodes.includes(quad.object.id) && !used.get(quad.object.id))
forwardDfs(quad.object.id);
}
order.push(v);
}
const backwardDfs = (v) => {
used.set(v, true);
component.push(v);
for (const quad of store.getQuads(undefined, undefined, v)) {
if (!used.get(quad.subject.id))
backwardDfs(quad.subject.id);
}
}
for (const node of nodes) used.set(node, false);
for (const node of nodes) {
if (!used.get(node))
forwardDfs(node);
}
for (const node of nodes) used.set(node, false);
for (let i = 0; i < nodes.length; i++) {
const node = order[nodes.length-1-i];
if (!used.get(node)) {
backwardDfs(node);
component.forEach(x => components.set(x, componentIdx));
componentIdx++;
component = [];
}
}
return components;
}
/**
* Parses quads to multiple stores which represent root nodes
* in the data graph
* @param {Store} store
*/
function quadsToShapes(store) {
const components = stronglyConnectedComponents(store);
const notRoot = new Set();
for (const quad of store.getQuads()) {
if (components.has(quad.subject.id) &&
components.has(quad.object.id) &&
components.get(quad.subject.id) !== components.get(quad.object.id)) {
notRoot.add(components.get(quad.object.id));
}
}
const shapes = new Map();
for (const [node, component] of components.entries()) {
if (!notRoot.has(component)) {
shapes.set(node, getShape(node, store, shapes, []));
notRoot.add(component);
}
}
return shapes;
}
/**
* Recursively gets all triples, related to the shape
* @param {any} id - id of the constructed shape
* @param {Store} store - store, containing all the triples
* @param {Map<any, Store>} shapes - map [id -> shape Store]
* @param {Array<any>} parsed - array for tracking recursive loops
*/
function getShape(id, store, shapes, parsed) {
const shapeQuads = store.getQuads(id, undefined, undefined);
if (shapeQuads.length === 0) return;
parsed.push(id);
for (const quad of store.getQuads(id, undefined, undefined)) {
if (parsed.includes(quad.object.id)) {
shapeQuads.push(quad);
continue;
}
let nestedStore;
if (shapes.get(quad.object)) {
nestedStore = shapes.get(quad.object.id);
} else {
nestedStore = getShape(quad.object.id, store, shapes, parsed);
}
if (nestedStore && nestedStore.getQuads().length > 0) {
shapeQuads.push(...nestedStore.getQuads());
}
}
const shapeStore = new Store();
for (const quad of shapeQuads) {
shapeStore.addQuad(quad);
}
return shapeStore;
}
module.exports = {
randomUrl: randomUrl,
loadData: loadData,
uniqueBy: uniqueBy,
quadsToShapes: quadsToShapes,
};