Report Aggregator POC

AggregatorInterface.php

<?php

declare(strict_types=1);

namespace App\Reporting\Core\ReportAggregator;

interface AggregatorInterface
{
    /**
     * @param $value int|float
     */
    public function add($value): void;

    /**
     * @return int|float
     */
    public function getResult();
}

AvgAggregator.php

<?php

declare(strict_types=1);

namespace App\Reporting\Core\ReportAggregator;

class AvgAggregator implements AggregatorInterface
{
    /** @var int|float */
    private $total;
    private int $counter = 0;

    public function add($value): void
    {
        $this->counter++;
        $this->total += $value;
    }

    /**
     * @return float|int
     */
    public function getResult()
    {
        return $this->total / $this->counter;
    }
}

ReportAggregator.php

<?php

declare(strict_types=1);

namespace App\Reporting\Core\ReportAggregator;

abstract class ReportAggregator implements \IteratorAggregate
{
    private array $segmentFields;
    private array $sumFields = [];
    private array $avgFields = [];
    private array $aggregates = [];

    public function __construct()
    {
        $this->configure();
    }

    protected function configure(): void
    {
        // Configure report here: segments, sum, avg, etc
        // Ex: $this->setSegmentFields(['field_1',...]);
    }

    public function setSegmentFields(array $fields): self
    {
        $this->segmentFields = $fields;

        return $this;
    }

    public function setSumFields(array $sumFields): self
    {
        $this->sumFields = $sumFields;

        return $this;
    }

    public function setAvgFields(array $avgFields): self
    {
        $this->avgFields = $avgFields;

        return $this;
    }

    public function add(object $object): void
    {
        $data = $this->normalize($object);

        $segments = [];
        foreach ($this->segmentFields as $field) {
            $segments[$field] = $data[$field] ?? null;
        }

        $key = implode('~', $segments);

        // If the aggregate doesn't exist yet, we create one with the common fields: segments
        if (!$aggregate = $this->aggregates[$key] ?? false) {
            $aggregate = $segments;
        }

        // SUM aggregation
        foreach ($this->sumFields as $field) {
            $aggregate[$field] ??= 0;
            $aggregate[$field] += $data[$field] ?? 0;
        }

        // AVG aggregation
        foreach ($this->avgFields as $field) {
            $aggregate[$field] ??= new AvgAggregator();
            $aggregate[$field]->add($data[$field] ?? 0);
        }

        $this->aggregates[$key] = $aggregate;
    }

    /**
     * @param object $object
     * @return array<string, mixed>
     */
    abstract protected function normalize(object $object): array;

    public function getIterator(): \Generator
    {
        while (\count($this->aggregates) > 0) {
            yield $this->computeAggregate(array_shift($this->aggregates));
        }
    }

    /**
     * @param array<string, mixed> $aggregate
     * @return array<string, mixed>
     */
    protected function format(array $aggregate): array
    {
        // Override this method to format final aggregate.
        // Ex: $aggregate['my_field'] = round($aggregate['my_field']);

        return $aggregate;
    }

    /**
     * @param array<string, mixed> $aggregate
     * @return array<string, mixed>
     */
    private function computeAggregate(array $aggregate): array
    {
        return $this->format(array_map(function ($value) {
            if (is_object($value) && $value instanceof AggregatorInterface) {
                return $value->getResult();
            }

            return $value;
        }, $aggregate));
    }
}

ReportAggregatorTest.php

<?php

declare(strict_types=1);

namespace App\Tests\Reporting\Core\ReportAggregator;

use App\Reporting\Core\ReportAggregator\ReportAggregator;
use PHPUnit\Framework\TestCase;

class ReportAggregatorTest extends TestCase
{
    public function test()
    {
        $objects = [
            (object) [
                'date' => '2020-01-01',
                'product' => 'toilet paper',
                'sells' => 100,
                'price' => 79.99,
            ],
            (object) [
                'date' => '2020-01-01',
                'product' => 'toilet paper',
                'sells' => 50,
                'price' => 9,
            ],
            (object) [
                'date' => '2020-01-02',
                'product' => 'toilet paper',
                'sells' => 10,
                'price' => 9,
            ],
            (object) [
                'date' => '2020-01-02',
                'product' => 'hydro gel',
                'sells' => 1000,
                'price' => 99.9,
            ],
        ];

        $report = new class() extends ReportAggregator {
            protected function configure(): void
            {
                $this
                    ->setSegmentFields([
                        'date',
                        'product',
                    ])
                    ->setSumFields([
                        'sells',
                    ])
                    ->setAvgFields([
                        'price',
                    ]);
            }

            protected function normalize(object $object): array
            {
                return (array) $object;
            }

            protected function format(array $aggregate): array
            {
                $aggregate['price'] = round($aggregate['price'], 2);

                return $aggregate;
            }
        };

        foreach ($objects as $object) {
            $report->add($object);
        }

        $results = iterator_to_array($report);

        $this->assertSame([
            [
                'date' => '2020-01-01',
                'product' => 'toilet paper',
                'sells' => 150,
                'price' => 44.50,
            ],
            [
                'date' => '2020-01-02',
                'product' => 'toilet paper',
                'sells' => 10,
                'price' => 9.0,
            ],
            [
                'date' => '2020-01-02',
                'product' => 'hydro gel',
                'sells' => 1000,
                'price' => 99.9,
            ],
        ], $results);
    }
}