Add no cycle rule for workflow validation

[MAILPOET-4629]

mailpoet/lib/Automation/Engine/Validation/WorkflowRules/NoCycleRule.php

@@ -0,0 +1,35 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\WorkflowRules;
+
+use MailPoet\Automation\Engine\Data\Step;
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowNode;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowNodeVisitor;
+
+class NoCycleRule implements WorkflowNodeVisitor {
+  public function initialize(Workflow $workflow): void {
+  }
+
+  public function visitNode(Workflow $workflow, WorkflowNode $node): void {
+    $step = $node->getStep();
+    $parents = $node->getParents();
+    $parentIdsMap = array_combine(
+      array_map(function (Step $parent) {
+        return $parent->getId();
+      }, $node->getParents()),
+      $parents
+    ) ?: [];
+
+    foreach ($step->getNextSteps() as $nextStep) {
+      $nextStepId = $nextStep->getId();
+      if ($nextStepId === $step->getId() || isset($parentIdsMap[$nextStepId])) {
+        throw Exceptions::workflowStructureNotValid(__('Cycle found in workflow graph', 'mailpoet'));
+      }
+    }
+  }
+
+  public function complete(Workflow $workflow): void {
+  }
+}

mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/NoCycleRuleTest.php

@@ -0,0 +1,57 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation\WorkflowRules;
+
+require_once __DIR__ . '/WorkflowRuleTest.php';
+
+use MailPoet\Automation\Engine\Exceptions\UnexpectedValueException;
+use MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowWalker;
+
+class NoCycleRuleTest extends WorkflowRuleTest {
+  public function testItDetectsLongCycle(): void {
+    $workflow = $this->createWorkflow([
+      'root' => ['a'],
+      'a' => ['b'],
+      'b' => ['c'],
+      'c' => ['a'],
+    ]);
+
+    $this->expectException(UnexpectedValueException::class);
+    $this->expectExceptionMessage('Invalid workflow structure: Cycle found in workflow graph');
+    (new WorkflowWalker())->walk($workflow, [new NoCycleRule()]);
+  }
+
+  public function testItDetectsSelfCycle(): void {
+    $workflow = $this->createWorkflow([
+      'root' => ['root'],
+    ]);
+
+    $this->expectException(UnexpectedValueException::class);
+    $this->expectExceptionMessage('Invalid workflow structure: Cycle found in workflow graph');
+    (new WorkflowWalker())->walk($workflow, [new NoCycleRule()]);
+  }
+
+  public function testItPassesWithSimplePath(): void {
+    $workflow = $this->createWorkflow([
+      'root' => ['a'],
+      'a' => ['b'],
+      'b' => ['c'],
+      'c' => [],
+    ]);
+
+    (new WorkflowWalker())->walk($workflow, [new NoCycleRule()]);
+    // no exception thrown
+  }
+
+  public function testItPassesWithPathSplitAndJoin(): void {
+    $workflow = $this->createWorkflow([
+      'root' => ['a1', 'a2'],
+      'a1' => ['b'],
+      'a2' => ['b'],
+      'b' => [],
+    ]);
+
+    (new WorkflowWalker())->walk($workflow, [new NoCycleRule()]);
+    // no exception thrown
+  }
+}