<?php

// Immutable

class Path implements IteratorAggregate {
	
	public static function get ( $path ) {
		
		return new self($path);
		
	}
	
	public static function conv ( $path ) {
		
		if ( is_string($path) ) {
			
			if ( !$path )
				return array();
			
			$abs = $path[0] === DIRECTORY_SEPARATOR ? array(null) : array();
			$elements = array_filter(explode(DIRECTORY_SEPARATOR, $path));
			return array_merge($abs, $elements);
			
		} elseif ( is_array($path) )
			return $path;
		
		elseif ( $path instanceof self )
			return $path->elements;
		
		else throw new InvalidArgumentException();
		
	}
	
	private static function compute ( $elements, $target ) {
		
		foreach ( $target as $elem )
			if ( $elem === '.' );
			elseif ( $elem === '..' ) {
				if ( count($elements) && end($elements) && end($elements) !== '..' )
					array_pop($elements);
				elseif (!count($elements) || end($elements) === '..' ) $elements[] = $elem;
			} elseif ( $elem || !$elements )
				$elements[] = $elem;
		
		return $elements;
		
	}
	
	private $elements;
	
	public function __construct ( $path ) {
		
		$this->elements = self::compute(array(), self::conv($path));
		
	}
	
	public function getIterator () {
		
		return new ArrayIterator($this->elements);
		
	}
	
	public function isAbsolute () {
		
		return count($this->elements) && !$this->elements;
		
	}
	
	public function append ( $path ) {
		
		$source = $this->elements;
		foreach ( func_get_args() as $path )
			$source = self::compute($source, self::conv($path));
		
		return new self($source);
		
	}
	
	public function pop ( $path ) {
		
		$source = $this->elements;
		$target = self::compute(array(), self::conv($path));
		
		foreach ( func_get_args() as $path ) {
			
			while ( count($source) && count($target) && last($source) === last($target) ) {
				
				array_pop($source);
				array_pop($target);
				
			}
			
			if ( count($target) )
				return false;
			
		}
		
		return new self($source);
		
	}
	
	public function prepend ( $path ) {
		
		$source = $this->elements;
		foreach ( func_get_args() as $path )
			$source = self::compute(self::conv($path), $source);
		
		return new self($source);
		
	}
	
	public function shift ( $path ) {
		
		$source = $this->elements;
		$target = self::compute(array(), self::conv($path));
		
		foreach ( func_get_args() as $path ) {
			
			while ( count($source) && count($target) && reset($source) === reset($target) ) {
				
				array_shift($source);
				array_shift($target);
				
			}
			
			if ( count($target) )
				return false;
			
		}
		
		return new self($source);
		
	}
	
	public function absolute () {
		
		return array_key_exists(0, $this->elements) && !$this->elements[0];
		
	}
	
	public function __toString () {
		
		$abs = count($this->elements) === 1 && array_key_exists(0, $this->elements) && !$this->elements[0] ? DIRECTORY_SEPARATOR : '';
		
		return $abs . implode(DIRECTORY_SEPARATOR, $this->elements);
		
	}
	
}

?>