render_template.php

<?php
if (!function_exists('render_template')) {
	/**
	 * Setup replacements and find and replace them in a specific template
	 *
	 * @param string $filename the filename of the template including extension
	 * @param string $dir (optional) the directory where the file is hosted relative to your theme
	 * @param string $open the opening wrapper for the placeholder
	 * @param string $close the closing wrapper for the placeholder
	 * @return string
	 */
	function render_template($filename, $dir = '', $open = '', $close = '') {
		// Put all common post data in the list of replacements
		$replacements = [
			'post_id' => get_the_ID(),
			'post_title' => get_the_title(),
			'post_content' => get_the_content(),
			'post_excerpt' => get_the_excerpt(),
			'post_permalink' => get_permalink(),
			'post_thumbnail' => get_the_post_thumbnail(),
			'post_date' => get_the_date(),
			'post_format' => get_post_format(),
			'post_status' => get_post_status(),
			'post_edit_link' => get_edit_post_link(),
		];

		// Retrieve the post's custom meta and filter out the WordPress internally used custom meta
		$post_meta_keys = get_post_custom_keys();
		$post_meta_keys = array_diff($post_meta_keys, array_filter($post_meta_keys, function ($v) {
			return substr(trim($v), 0, 1) === '_';
		}));

		// Add the retrieved post custom meta to the list of replacements if they aren't already
		foreach ($post_meta_keys as $meta_key) {
			$replacements_key = 'post_meta_' . trim($meta_key);
			if (array_key_exists($replacements_key, $replacements)) continue;
			$replacements[$replacements_key] = get_post_meta(get_the_ID(), $meta_key, true);
		}

		/**
		 * Filter replacements for a specific template
		 *
		 * @since 4.9.9
		 *
		 * @param array $replacements Array of replacements for the template file, the key is a descriptive
		 *                            placeholder and the value is the actual value to be rendered as well.
		 * @param string $filename The filename of the template to be rendered including the extension.
		 */
		$replacements = apply_filters('render_template_replacements', $replacements, $filename);

		/**
		 * Filter replacements for a specific template
		 *
		 * @since 4.9.9
		 *
		 * @param array $replacements Array of replacements for the template file, the key is a descriptive
		 *                            placeholder and the value is the actual value to be rendered as well.
		 */
		$replacements = apply_filters("render_template_replacements_{$filename}", $replacements);

		// Load the template from the a sub directory, define the constant to change the default
		$template_dir = !empty($dir) ? $dir : (defined('WP_TEMPLATE_DIR') ? WP_TEMPLATE_DIR : 'tpl');

		// Determine what file to load preferring the
		$filename = '/' . $template_dir . '/' . $filename;
		$file = (file_exists(get_stylesheet_directory() . $filename) ?
				get_stylesheet_directory() : get_template_directory()) . $filename;

		// Load the template
		if (array_key_exists('wp_render_templates', $GLOBALS)
			&& is_array($GLOBALS['wp_render_templates'])
			&& array_key_exists($file, $GLOBALS['wp_render_templates'])) {
			$template = $GLOBALS['wp_render_templates'][$file];
		} else {
			ob_start();
			if (file_exists($file)) {
				require_once $file;
			}
			$template = ob_get_clean();
			$GLOBALS['wp_render_templates'][$file] = $template;
		}

		// Prepare the replacement placeholders and values
		$keys = array_keys($replacements);
		$values = array_values($replacements);

		// Setup the placeholder identifiers
		$open = !empty($open) ? $open : (defined('WP_TEMPLATE_OPEN') ? WP_TEMPLATE_OPEN : '{');
		$close = !empty($close) ? $close : (defined('WP_TEMPLATE_CLOSE') ? WP_TEMPLATE_CLOSE : '}');

		$keys = array_map(function ($v) use ($open, $close) {
			// Escape the un-escaped '/'
			$v = preg_replace("/(?<!\\\\)(?:\\\\\\\\)*\K\\//", '\/', $v);

			// Format the key to a regex pattern enclosed in curly braces
			return '/' . $open . $v . $close . '/';
		}, $keys);

		return preg_replace($keys, $values, $template);
	}
}