Add basic set of MailPoet exceptions

[MAILPOET-2900]

lib/exceptions.php

@@ -0,0 +1,75 @@
+<?php declare(strict_types = 1);
+
+// phpcs:ignoreFile PSR1.Classes.ClassDeclaration
+namespace MailPoet;
+
+/**
+ * Frames all MailPoet exceptions ("$e instanceof MailPoet\Exception").
+ */
+abstract class Exception extends \Exception {
+  /** @var string[] */
+  private $errors = [];
+
+  final public function __construct($message = '', $code = 0, \Throwable $previous = null) {
+    parent::__construct($message, $code, $previous);
+  }
+
+  public static function create(\Throwable $previous = null): self {
+    return new static('', 0, $previous);
+  }
+
+  public function withMessage(string $message): self {
+    $this->message = $message;
+    return $this;
+  }
+
+  public function withCode(int $code): self {
+    $this->code = $code;
+    return $this;
+  }
+
+  public function withErrors(array $errors): self {
+    $this->errors = $errors;
+    return $this;
+  }
+
+  public function getErrors(): array {
+    return $this->errors;
+  }
+}
+
+
+/**
+ * USE: Generic runtime error. When possible, use a more specific exception instead.
+ */
+class RuntimeException extends Exception {}
+
+
+/**
+ * USE: When wrong data VALUE is received.
+ */
+class UnexpectedValueException extends RuntimeException {}
+
+
+/**
+ * USE: When an action is forbidden for given actor (although generally valid).
+ */
+class AccessDeniedException extends UnexpectedValueException {}
+
+
+/**
+ * USE: When the main resource we're interested in doesn't exist.
+ */
+class NotFoundException extends UnexpectedValueException {}
+
+
+/**
+ * USE: When the main action produces conflict (i.e. duplicate key).
+ */
+class ConflictException extends UnexpectedValueException {}
+
+
+/**
+ * USE: An application state that should not occur. Can be subclassed for feature-specific exceptions.
+ */
+class InvalidStateException extends RuntimeException {}