mirror of
https://github.com/vale981/Vulcan
synced 2025-03-06 10:01:40 -05:00
43 lines
2 KiB
JavaScript
43 lines
2 KiB
JavaScript
updateScore = function (collection, item, forceUpdate) {
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var forceUpdate = typeof forceUpdate !== 'undefined' ? forceUpdate : false;
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// For performance reasons, the database is only updated if the difference between the old score and the new score
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// is meaningful enough. To find out, we calculate the "power" of a single vote after n days.
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// We assume that after n days, a single vote will not be powerful enough to affect posts' ranking order.
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// Note: sites whose posts regularly get a lot of votes can afford to use a lower n.
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// n = number of days after which a single vote will not have a big enough effect to trigger a score update
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// and posts can become inactive
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var n = 30;
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// x = score increase amount of a single vote after n days (for n=100, x=0.000040295)
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var x = 1/Math.pow(n*24+2,1.3);
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// time decay factor
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var f = 1.3;
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// use submitted timestamp if available, else (for pending posts) calculate score using createdAt
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var age = item.submitted || item.createdAt;
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// use baseScore if defined, if not just use the number of votes
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// note: for transition period, also use votes if there are more votes than baseScore
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// var baseScore = Math.max(item.votes || 0, item.baseScore || 0);
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var baseScore = item.baseScore;
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// now multiply by 'age' exponentiated
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// FIXME: timezones <-- set by server or is getTime() ok?
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var ageInHours = (new Date().getTime() - age) / (60 * 60 * 1000);
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// HN algorithm
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var newScore = baseScore / Math.pow(ageInHours + 2, f);
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// Note: before the first time updateScore runs on a new item, its score will be at 0
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var scoreDiff = Math.abs(item.score - newScore);
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// only update database if difference is larger than x to avoid unnecessary updates
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if (forceUpdate || scoreDiff > x){
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collection.update(item._id, {$set: {score: newScore, inactive: false}});
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return 1;
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}else if(ageInHours > n*24){
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// only set a post as inactive if it's older than n days
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collection.update(item._id, {$set: {inactive: true}});
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}
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return 0;
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};
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