WordPress simple validator class. Still in the work

errors.php

<?php if( isset( $_SESSION['errors'] ) ): ?>
    <div class="alert alert-danger">
        <a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
        <ul>
         <?php foreach ($_SESSION["errors"] as $error): ?>
              <li><?php echo $error; ?></li>
         <?php endforeach ?>
        </ul>
    </div>
<?php endif; ?>

example.md

Currently it only supports required, sometimes and date_format validation rules.

You need to pass the $_POST data, the validation rules and optionally custom error messages. If there's any error it will automatically redirect the user back to the form and preset the errors.

(new Validator($_POST, [
  'pr_title'       => 'required',
  'pr_description' => 'required',
  'company_name'   => 'required',
  'pr_date'        => 'required|date|date_format:m/d/Y',
], [
  'pr_title.required'       => 'The title field is required.',
  'pr_description.required' => 'The content field is required.',
  'pr_date.required'        => 'The date field is required.',
  'pr_date.date_format'     => 'The date field does not match the format mm/dd/yyyy.',
]))->pass_or_fail();

validator.php

<?php
class Validator {
	private $data;
	private $rules;
	private $messages;
	private $errors = [];

	public function __construct($data, array $rules, array $messages = []) {
		$this->data     = $data;
		$this->rules    = $rules;
		$this->messages = $messages;
	}

	public function pass_or_fail() {
		foreach ($this->rules as $attribute => $rules) {
			$this->validate_attribute($attribute, $rules);
		}
		if ( count( $this->errors ) ) {
			$_SESSION["errors"] = $this->errors;
			$_SESSION['old']    = $_POST;
			wp_safe_redirect( wp_get_referer() );
			exit;
		}
	}

	public function validate_attribute($attribute, $rules) {
		$rules     = explode('|', $rules);
		$required  = in_array( 'required', $rules );
		$sometimes = in_array( 'sometimes', $rules );
		$filled    = isset( $this->data[$attribute] ) && $this->data[$attribute];

		if ( ( $required && ( ! $filled ) ) || ( ( ! $sometimes ) && ( ! $filled ) ) ) {
			$this->errors[] = $this->messages["{$attribute}.required"] ?? "The ".str_replace('_', ' ', $attribute)." field is required.";
			return;
		}

		if ( $sometimes && ( ! $filled ) ) {
			return;
		}

		foreach ( $rules as $rule ) {
			if ( $rule === 'email' && ! is_email( $this->data[$attribute] ) ) {
				$this->errors[] = $this->messages["{$attribute}.email"] ?? "The ".str_replace('_', ' ', $attribute)." must be a valid email.";
				break;
			}

			if ( $rule === 'date' && ! $this->valid_date( $this->data[$attribute] ) ) {
				$this->errors[] = $this->messages["{$attribute}.date"] ?? "The ".str_replace('_', ' ', $attribute)." must be a valid date.";
				break;
			}

			if ( strncmp($rule, 'date_format', strlen('date_format')) === 0 ) {
				$format = str_replace( 'date_format:', '', $rule );
				$value  = $this->data[$attribute] ?? '';
				if ( ! $this->valid_date_format( $value, $format ) ) {
					$this->errors[] = $this->messages["{$attribute}.date_format"] ?? "The ".str_replace('_', ' ', $attribute)." does not match the format $format";
					break;
				}
			}
		}
	}

	protected function valid_date( $value ) {
		if ( $value instanceof DateTime ) {
			return true;
		}

		if ( ( ! is_string( $value ) && ! is_numeric( $value ) ) || strtotime( $value ) === false ) {
			return false;
		}

		$date = date_parse( $value );

		return checkdate( $date['month'], $date['day'], $date['year'] );
	}


	protected function valid_date_format( $value, $format ) {
		if ( ! is_string( $value ) && ! is_numeric( $value ) ) {
			return false;
		}
		$date = DateTime::createFromFormat($format, $value);
        return  $date && $date->format($format) == $value;
	}
}