template.php

<?php
/*
Example usage:

$template = new Medium_Template( 'Hi, I am {{name|html}}.' );

echo $template->compile( array( 'name' => '<b>Evan</b>' ) );
// Hi, I am &lt;b&gt;Evan&lt;/b&gt;.

echo $template->compile( array( 'name' => 'someone else' ) );
// Hi, I am someone else.
*/

/**
 * A *very* simple mustache-style template utility.
 */
class Medium_Template {
	/**
	 * Create a template instance with an (uncompiled) template string. Templates
	 * are a very basic version of mustache-style, plus an optional pipe-delimited
	 * escape callback. Escape callbacks are prefixed with esc_ by default.
	 */
	function __construct( $template ) {
		$this->template = $template;
		$this->pattern = '/\{{2}(.+?)\}{2}/';
		$this->esc_delimiter = '|';
	}

	/**
	 * Return the compiled output of the template with the given data. Missing fields
	 * are interpretted as empty strings.
	 */
	function compile( $data ) {
		$tokens = $this->get_tokens();
		return $this->replace( $tokens, $data );
	}

	/**
	 * Get a list of replacement tokens without the surrounding identifiers.
	 */
	function get_tokens() {
		preg_match_all( $this->pattern, $this->template, $matches );
		return $matches[1];
	}

	/**
	 * Replace each token with its underlying data. Escape the data with its
	 * optional callback.
	 */
	function replace( $tokens, $data ) {
		$template = $this->template;

		foreach ( $tokens as $token ) {
			$target = $this->wrap_token( $token );

			$token_parts = $this->parse_token( $token );
			$escape      = $token_parts['escape'];

			if ( isset( $data[ $token_parts['name'] ] ) ) {
				$input = $data[ $token_parts['name'] ];
			} else {
				$input = '';
			}

			$replacement = $this->maybe_escape( $input, $escape );

			$template = str_replace( $target, $replacement, $template );
		}

		return $template;
	}

	/**
	 * Convert a token to a replacement string.
	 */
	function wrap_token( $token ) {
		return '{{' . $token . '}}';
	}

	/**
	 * Split a token into its name and optional escape callback.
	 */
	function parse_token( $token ) {
		$data = array();

		$parts = array_map( 'trim', explode( $this->esc_delimiter, $token ) );

		$data['name']   = $parts[0];
		$data['escape'] = count( $parts ) > 1 ? $parts[1] : false;

		return $data;
	}

	/**
	 * Escape data with a callback only when the callback is valid.
	 */
	function maybe_escape( $data, $callback ) {
		$callback = "esc_{$callback}";
		if ( ! is_callable( $callback ) ) {
			return $data;
		}

		return call_user_func( $callback, $data );
	}
}