HistogramMetric.php

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<?php
declare( strict_types=1 );
 
namespace Wikimedia\Stats\Metrics;
 
use InvalidArgumentException;
use Wikimedia\Stats\StatsFactory;
 
class HistogramMetric {
 
    private const MAX_BUCKETS = 10;
 
    private StatsFactory $statsFactory;
    private string $name;
    private array $buckets;
    private array $labels = [];
 
    public function __construct( StatsFactory $statsFactory, string $name, array $buckets ) {
        $this->statsFactory = $statsFactory;
        $this->name = $name;
        if ( !$buckets ) {
            throw new InvalidArgumentException( 'Stats: Histogram buckets cannot be an empty array.' );
        }
        $bucketCount = count( $buckets );
        if ( $bucketCount > self::MAX_BUCKETS ) {
            throw new InvalidArgumentException(
                "Stats: Too many buckets defined. Got:{$bucketCount}, Max:" . self::MAX_BUCKETS
            );
        }
        foreach ( $buckets as $bucket ) {
            if ( !( is_float( $bucket ) || is_int( $bucket ) ) ) {
                throw new InvalidArgumentException( 'Stats: Histogram buckets can only be float or int.' );
            }
        }
        $normalizedBuckets = array_unique( $buckets );
        sort( $normalizedBuckets, SORT_NUMERIC );
        if ( $buckets !== $normalizedBuckets ) {
            throw new InvalidArgumentException(
                'Stats: Histogram buckets must be unique and in order of least to greatest.'
            );
        }
        $this->buckets = $buckets;
    }
 
    private function preloadBuckets( CounterMetric $metric ): void {
        $metric->setBucket( '+Inf' );
        $metric->incrementBy( 0 );
        foreach ( $this->buckets as $bucket ) {
            $metric->setBucket( $bucket );
            $metric->incrementBy( 0 );
        }
    }
 
    public function observe( float $value ): void {
        $count = $this->statsFactory->getCounter( "{$this->name}_count" );
        $bucket = $this->statsFactory->getCounter( "{$this->name}_bucket" );
        $sum = $this->statsFactory->getCounter( "{$this->name}_sum" );
 
        foreach ( $this->labels as $k => $v ) {
            $count->setLabel( $k, $v );
            $bucket->setLabel( $k, $v );
            $sum->setLabel( $k, $v );
        }
 
        if ( $bucket->getSampleCount() === 0 ) {
            $this->preloadBuckets( $bucket );
        }
 
        $bucket->setBucket( '+Inf' )->increment();
        foreach ( $this->buckets as $le ) {
            if ( $value <= $le ) {
                $bucket->setBucket( $le )->increment();
            }
        }
 
        $count->increment();
        $sum->incrementBy( $value );
    }
 
    public function setLabel( string $key, string $value ): self {
        // each metric will run its own validation logic
        $this->labels[$key] = $value;
        return $this;
    }
 
    public function fresh(): self {
        $this->labels = [];
        return $this;
    }
}