wp-calypso/client/reader/search-stream/suggestion-provider.jsx

import { map, sampleSize, times } from 'lodash';
import { Component } from 'react';
import { connect } from 'react-redux';
import { getLocaleSlug } from 'calypso/lib/i18n-utils';
import { suggestions } from 'calypso/reader/search-stream/suggestions';
import { getReaderFollowedTags } from 'calypso/state/reader/tags/selectors';

function createRandomId( randomBytesLength = 9 ) {
	// 9 * 4/3 = 12
	// this is to avoid getting padding of a random byte string when it is base64 encoded
	let randomBytes;

	if ( window.crypto && window.crypto.getRandomValues ) {
		randomBytes = new Uint8Array( randomBytesLength );
		window.crypto.getRandomValues( randomBytes );
	} else {
		randomBytes = times( randomBytesLength, () => Math.floor( Math.random() * 256 ) );
	}

	return window.btoa( String.fromCharCode.apply( String, randomBytes ) );
}

/**
 * Build suggestions from subscribed tags
 * @param  {number} count The number of suggestions required
 * @param  {Array} tags  An array of subscribed tags
 * @returns {Array}       An array of suggestions, or null if no tags where provided
 */
function suggestionsFromTags( count, tags ) {
	if ( tags ) {
		if ( tags.length <= count ) {
			return [];
		}
		return map( sampleSize( tags, count ), ( tag, i ) => {
			const text = ( tag.displayName || tag.slug ).replace( /-/g, ' ' );
			const ui_algo = 'read:search-suggestions:tags/1';
			return suggestionWithRailcar( text, ui_algo, i );
		} );
	}
	return null;
}

/**
 * Maps trending tags to tags
 * @param {Array} trendingTags Trending tag results from the API.
 * @returns {Array} An array of tag objects
 */
function trendingTagsToTags( trendingTags ) {
	return map( trendingTags, ( tag ) => ( {
		displayName: tag.tag.display_name,
		slug: tag.tag.slug,
	} ) );
}

function suggestionsFromPicks( count ) {
	const lang = getLocaleSlug().split( '-' )[ 0 ];
	if ( suggestions[ lang ] ) {
		return map( sampleSize( suggestions[ lang ], count ), ( tag, i ) => {
			const ui_algo = 'read:search-suggestions:picks/1';
			return suggestionWithRailcar( tag, ui_algo, i );
		} );
	}
	return null;
}

function suggestionWithRailcar( text, ui_algo, position ) {
	return {
		text: text,
		railcar: {
			railcar: createRandomId() + '-' + position,
			ui_algo: ui_algo,
			ui_position: position,
			rec_result: text,
		},
	};
}

function getSuggestions( count, tags, trendingTags ) {
	// trendingTags will be requested if the user is logged out
	const tagSuggestions = tags
		? suggestionsFromTags( count, tags )
		: suggestionsFromTags( count, trendingTagsToTags( trendingTags ) );

	// return null to suppress showing any suggestions until tag subscriptions load.
	if ( tagSuggestions === null ) {
		return null;
	}

	const newSuggestions = tagSuggestions.length ? tagSuggestions : suggestionsFromPicks( count );
	return newSuggestions;
}

const SuggestionsProvider = ( Element, count = 3 ) =>
	class extends Component {
		// never let the suggestions change once its been set to non-null so that suggestions
		// don't keep getting recalulated every redux-store change
		memoizedSuggestions = null;
		getFirstSuggestions = ( state ) =>
			this.memoizedSuggestions
				? this.memoizedSuggestions
				: ( this.memoizedSuggestions = getSuggestions(
						count,
						getReaderFollowedTags( state ),
						this.props.trendingTags
				  ) );

		componentWillUnmount() {
			// when unmounted, let the suggestions refresh
			this.memoizedSuggestions = null;
		}

		EnhancedComponent = connect( ( state ) => ( {
			suggestions: this.getFirstSuggestions( state ),
		} ) )( Element );

		render() {
			const EnhancedComponent = this.EnhancedComponent;
			return <EnhancedComponent { ...this.props } />;
		}
	};

export default SuggestionsProvider;