<?php

/**
 * A Mustache Partial filesystem loader.
 *
 * @author Justin Hileman {@link http://justinhileman.com}
 */
class MustacheLoader implements ArrayAccess {

	protected $baseDir;
	protected $partialsCache = array();
	protected $extension;

	/**
	 * MustacheLoader constructor.
	 *
	 * @access public
	 * @param  string $baseDir   Base template directory.
	 * @param  string $extension File extension for Mustache files (default: 'mustache')
	 * @return void
	 */
	public function __construct( $baseDir, $extension = 'mustache' ) {
		if ( ! is_dir( $baseDir ) ) {
			throw new InvalidArgumentException( '$baseDir must be a valid directory, ' . $baseDir . ' given.' );
		}

		$this->baseDir   = $baseDir;
		$this->extension = $extension;
	}

	/**
	 * @param  string $offset Name of partial
	 * @return boolean
	 */
	public function offsetExists( $offset ) {
		return ( isset( $this->partialsCache[ $offset ] ) || file_exists( $this->pathName( $offset ) ) );
	}

	/**
	 * @throws InvalidArgumentException if the given partial doesn't exist
	 * @param  string $offset Name of partial
	 * @return string Partial template contents
	 */
	public function offsetGet( $offset ) {
		if ( ! $this->offsetExists( $offset ) ) {
			throw new InvalidArgumentException( 'Partial does not exist: ' . $offset );
		}

		if ( ! isset( $this->partialsCache[ $offset ] ) ) {
			$this->partialsCache[ $offset ] = file_get_contents( $this->pathName( $offset ) );
		}

		return $this->partialsCache[ $offset ];
	}

	/**
	 * MustacheLoader is an immutable filesystem loader. offsetSet throws a LogicException if called.
	 *
	 * @throws LogicException
	 * @return void
	 */
	public function offsetSet( $offset, $value ) {
		throw new LogicException( 'Unable to set offset: MustacheLoader is an immutable ArrayAccess object.' );
	}

	/**
	 * MustacheLoader is an immutable filesystem loader. offsetUnset throws a LogicException if called.
	 *
	 * @throws LogicException
	 * @return void
	 */
	public function offsetUnset( $offset ) {
		throw new LogicException( 'Unable to unset offset: MustacheLoader is an immutable ArrayAccess object.' );
	}

	/**
	 * An internal helper for generating path names.
	 *
	 * @param  string $file Partial name
	 * @return string File path
	 */
	protected function pathName( $file ) {
		return $this->baseDir . '/' . $file . '.' . $this->extension;
	}
}