69 lines
2.2 KiB
JavaScript
69 lines
2.2 KiB
JavaScript
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// @flow
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import * as REACTION_TYPES from 'constants/reactions';
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import { SORT_COMMENTS_NEW, SORT_COMMENTS_BEST, SORT_COMMENTS_CONTROVERSIAL } from 'constants/comment';
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// Mostly taken from Reddit's sorting functions
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// https://github.com/reddit-archive/reddit/blob/master/r2/r2/lib/db/_sorts.pyx
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export function sortComments(comments: ?Array<Comment>, reactionsById: {}, method: string): Array<Comment> {
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if (!comments) {
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return [];
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}
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return comments.slice().sort((a, b) => {
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if (method === SORT_COMMENTS_NEW) {
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return 0;
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}
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const aReactions = reactionsById[a.comment_id];
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const bReactions = reactionsById[b.comment_id];
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const aLikes = (aReactions && aReactions[REACTION_TYPES.LIKE]) || 0;
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const aDislikes = (aReactions && aReactions[REACTION_TYPES.DISLIKE]) || 0;
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const bLikes = (bReactions && bReactions[REACTION_TYPES.LIKE]) || 0;
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const bDislikes = (bReactions && bReactions[REACTION_TYPES.DISLIKE]) || 0;
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if (method === SORT_COMMENTS_CONTROVERSIAL) {
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if (aLikes === 0 && aDislikes === 0) {
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return 1;
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} else if (bLikes === 0 && bDislikes === 0) {
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return -1;
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}
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const aMagnitude = aLikes + aDislikes;
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const bMagnitude = bLikes + bDislikes;
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const aBalance = aLikes > aDislikes ? aDislikes / aLikes : aLikes / aDislikes;
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const bBalance = bLikes > bDislikes ? bDislikes / bLikes : bLikes / bDislikes;
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return bMagnitude ** bBalance - aMagnitude ** aBalance;
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}
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if (method === SORT_COMMENTS_BEST) {
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const aN = aLikes + aDislikes;
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const bN = bLikes + bDislikes;
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if (aN === 0) {
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return 1;
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} else if (bN === 0) {
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return -1;
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}
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const z = 1.281551565545; // 80% confidence
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const aP = aLikes / aN;
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const bP = bLikes / bN;
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const aLeft = aP + (1 / (2 * aN)) * z * z;
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const aRight = z * Math.sqrt((aP * (1 - aP)) / aN + (z * z) / (4 * aN * aN));
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const aUnder = 1 + (1 / aN) * z * z;
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const bLeft = bP + (1 / (2 * bN)) * z * z;
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const bRight = z * Math.sqrt((bP * (1 - bP)) / bN + (z * z) / (4 * bN * bN));
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const bUnder = 1 + (1 / bN) * z * z;
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return (bLeft - bRight) / bUnder - (aLeft - aRight) / aUnder;
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}
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return 0;
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});
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}
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