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/**
 * @example caching.js
 *
 * This example demonstrates how to add a cache to an aspect engine.
 * The fiftyone.pipeline.engines module comes with an implementation
 * of a Least Recently Used (lru) cache that can be used in
 * place of the custom cache created in this example.
 *
 * To construct the lru cache pass in a size (in entries)
 * parameter to its constructor.
 *
 * let lruCache = new engine.lruCache(100);
 *
 */

const pipeline = require('fiftyone.pipeline.core');

// Note that this example is designed to be run from within the
// source repository. If this code has been copied to run standalone
// then you'll need to replace the require below with the commented
// out version below it.
const engine = require('..');
// const engine = require("fiftyone.pipeline.engines");

// This is a very simple cache that uses an in memory JavaScript object
class MyCustomCache extends engine.DataKeyedCache {
  constructor (size) {
    super();

    this.cache = {};
  }

  get (cachekey) {
    if (this.cache[cachekey]) {
      // Log out whether something has been fetched
      // from cache to demonstrate the example
      console.log('Fetched from cache');
      return this.cache[cachekey];
    }
  }

  put (cachekey, value) {
    this.cache[cachekey] = value;
  }
}

// A custom engine to test the caching, note the instance of the
// evidenceKeyFilter class which is used to determine which evidence
// is used by the flowElement and in turn the pipeline.

const cacheTest = new engine.Engine({
  dataKey: 'cacheTest',
  cache: new MyCustomCache(),
  evidenceKeyFilter: new pipeline
    .BasicListEvidenceKeyFilter(['cookie.my-user-id']),
  processInternal: function (flowData) {
    const engine = this;

    return new Promise(function (resolve, reject) {
      const data = new pipeline
        .ElementDataDictionary(
          { flowElement: engine, contents: { hello: 'world' } });

      flowData.setElementData(data);

      resolve();
    });
  },
  properties: {
    hello: {
      type: 'string'
    }
  }
});

const cachePipeline = new pipeline.PipelineBuilder().add(cacheTest).build();

const flowData = cachePipeline.createFlowData();

const processFlowDataWithUserId = function (userID) {
  flowData.evidence.add('cookie.my-user-id', userID);

  return flowData.process();
};

// Run the same evidence through the pipeline twice,
// second time should be fetched from the cache
processFlowDataWithUserId('112').then(() => processFlowDataWithUserId('112'));