Introduce the NProc finder (#13)

Introduce `NProcFinder`, inspired from Infection.

src/Exec/ExecException.php

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+<?php
+
+/*
+ * This file is part of the Fidry CPUCounter Config package.
+ *
+ * (c) Théo FIDRY <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Fidry\CpuCounter\Exec;
+
+use ErrorException;
+use function error_get_last;
+
+// see https://github.com/thecodingmachine/safe/blob/master/generated/Exceptions/ExecException.php
+final class ExecException extends ErrorException
+{
+    public static function createFromPhpError(): self
+    {
+        $error = error_get_last();
+
+        return new self($error['message'] ?? 'An error occured', 0, $error['type'] ?? 1);
+    }
+}

src/Exec/ShellExec.php

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+<?php
+
+/*
+ * This file is part of the Fidry CPUCounter Config package.
+ *
+ * (c) Théo FIDRY <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Fidry\CpuCounter\Exec;
+
+use function error_clear_last;
+use function shell_exec;
+
+/**
+ * Mimicks Safe\shell_exec: this is to avoid to add an extra dependency to this
+ * micro package.
+ *
+ * @see https://github.com/thecodingmachine/safe/blob/0653752f6c2d45e0640fa24bf789cae367a501d3/generated/exec.php#L114
+ */
+final class ShellExec
+{
+    private function __construct()
+    {
+    }
+
+    /**
+     * @throws ExecException
+     */
+    public static function execute(string $command): string
+    {
+        error_clear_last();
+
+        $safeResult = shell_exec($command);
+
+        if (null === $safeResult || false === $safeResult) {
+            throw ExecException::createFromPhpError();
+        }
+
+        return $safeResult;
+    }
+}

src/NProcFinder.php

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+<?php
+
+/*
+ * This file is part of the Fidry CPUCounter Config package.
+ *
+ * (c) Théo FIDRY <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Fidry\CpuCounter;
+
+use Fidry\CpuCounter\Exec\ExecException;
+use Fidry\CpuCounter\Exec\ShellExec;
+use function filter_var;
+use function is_int;
+use function trim;
+use const FILTER_VALIDATE_INT;
+
+/**
+ * @see https://github.com/infection/infection/blob/fbd8c44/src/Resource/Processor/CpuCoresCountProvider.php#L69-L82
+ * @see https://unix.stackexchange.com/questions/146051/number-of-processors-in-proc-cpuinfo
+ */
+final class NProcFinder
+{
+    private function __construct()
+    {
+    }
+
+    /**
+     * @return positive-int|null
+     */
+    public static function find(): ?int
+    {
+        if (!self::supportsNproc()) {
+            return null;
+        }
+
+        try {
+            $nproc = ShellExec::execute('nproc --all');
+        } catch (ExecException $nprocFailed) {
+            return null;
+        }
+
+        return self::countCpuCores($nproc);
+    }
+
+    private static function supportsNproc(): bool
+    {
+        try {
+            $commandNproc = ShellExec::execute('command -v nproc');
+        } catch (ExecException $noNprocCommand) {
+            return false;
+        }
+
+        return '' !== trim($commandNproc);
+    }
+
+    /**
+     * @return positive-int|null
+     */
+    public static function countCpuCores(string $nproc): ?int
+    {
+        $cpuCount = filter_var(trim($nproc), FILTER_VALIDATE_INT);
+
+        return is_int($cpuCount) && $cpuCount > 0 ? $cpuCount : null;
+    }
+}

tests/NProcFinderTest.php

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+<?php
+
+/*
+ * This file is part of the Fidry CPUCounter Config package.
+ *
+ * (c) Théo FIDRY <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Fidry\CpuCounter\Test;
+
+use Fidry\CpuCounter\NProcFinder;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @covers \Fidry\CpuCounter\NProcFinder
+ *
+ * @internal
+ */
+final class NProcFinderTest extends TestCase
+{
+    /**
+     * @dataProvider nprocProvider
+     */
+    public function test_it_can_count_the_number_of_cpu_cores(
+        string $nproc,
+        ?int $expected
+    ): void {
+        $actual = NProcFinder::countCpuCores($nproc);
+
+        self::assertSame($expected, $actual);
+    }
+
+    public static function nprocProvider(): iterable
+    {
+        yield 'empty' => [
+            <<<'EOF'
+
+                EOF,
+            null,
+        ];
+
+        // $ docker run  --tty --rm --platform linux/amd64 alpine:3.14 nproc --all
+        yield 'example from an alpine Docker image' => [
+            <<<'EOF'
+                3
+
+                EOF,
+            3,
+        ];
+
+        yield 'no processor' => [
+            <<<'EOF'
+                0
+
+                EOF,
+            null,
+        ];
+    }
+}