Add PHP version check for plugin.

classifai.php

@@ -15,6 +15,49 @@
  * Domain Path:       /languages
  */
 
+/**
+ * Get the minimum version of PHP required by this plugin.
+ *
+ * @return string Minimum version required.
+ */
+function classifai_minimum_php_requirement() {
+	return '7.4';
+}
+
+/**
+ * Whether PHP installation meets the minimum requirements
+ *
+ * @return bool True if meets minimum requirements, false otherwise.
+ */
+function classifai_site_meets_php_requirements() {
+	return version_compare( phpversion(), classifai_minimum_php_requirement(), '>=' );
+}
+
+// Ensuring our PHP version requirement is met first before loading plugin.
+if ( ! classifai_site_meets_php_requirements() ) {
+	add_action(
+		'admin_notices',
+		function() {
+			?>
+			<div class="notice notice-error">
+				<p>
+					<?php
+					echo wp_kses_post(
+						sprintf(
+							/* translators: %s: Minimum required PHP version */
+							__( 'ClassifAI requires PHP version %s or later. Please upgrade PHP or disable the plugin.', 'classifai' ),
+							esc_html( classifai_minimum_php_requirement() )
+						)
+					);
+					?>
+				</p>
+			</div>
+			<?php
+		}
+	);
+	return;
+}
+
 /**
  * Small wrapper around PHP's define function. The defined constant is
  * ignored if it has already been defined. This allows the