<?php

class XmlTreeBuilder
{

	private $parser;
	private $node_stack;
	private $cur_node;
	private $cur_val;

	//TAG=0, VALUE=1, ELEMENTS=2

	public function &ParseFile($filename, &$err)
	{
		if (!is_file($filename)) {
			$err = $filename . ' is not a valid file.';
			return null;
		}
		$fd = fopen($filename, 'r');
		if (!$fd) {
			$err = 'failed to open file ' . $filename;
			return null;
		}
		$len = filesize($filename);
		if ($len > 0) {
			$contents = fread($fd, $len);
			fclose($fd);
			$root = $this->parseString($contents, $err);
		} else {
			$root = [];
			fclose($fd);
		}

		if ($err != null) {
			$err .= '<br> Failed to parse file ' . $filename;
			return null;
		}

		return $root;
	}

	private function parseString($xmlstring, &$err)
	{
		$this->parser = xml_parser_create();
		xml_set_object($this->parser, $this);
		xml_parser_set_option($this->parser, XML_OPTION_CASE_FOLDING, false);
		xml_set_element_handler($this->parser, 'startElement', 'endElement');
		xml_set_character_data_handler($this->parser, 'characterData');

		// Build a Root node and initialize the node_stack...
		$this->node_stack = [];
		$this->cur_node = null;
		$this->startElement(null, 'root', []);

		// parse the data and free the parser...
		$result = xml_parse($this->parser, $xmlstring);
		if (!$result) {
			$err = 'XML error: ' . xml_error_string(xml_get_error_code($this->parser))
					. ' at line ' . xml_get_current_line_number($this->parser);
		}
		xml_parser_free($this->parser);
		if (!$result) {
			return null;
		}

		// return the root node...

		return $this->cur_node[2][0];
	}

	private function startElement($parser, $name, $attrs)
	{
		if ($this->cur_node != null) {
			$this->node_stack[] = $this->cur_node;
		}
		$this->cur_node = [];
		$this->cur_node[0] = $name; //'TAG'=0
//		foreach ($attrs as $key => $value) 
//		{
//			$node[$key] = $value;
//		}  //no attributes used in xml

		$this->cur_val = '';
		$this->cur_node[2] = []; //'ELEMENTS'=2
	}

	private function endElement($parser, $name)
	{
		$this->cur_node[1] = trim($this->cur_val); //'VALUE'=1
		$node = $this->cur_node;
		// and add it an element of the last node in the stack...
		$this->cur_node = array_pop($this->node_stack);
		$this->cur_node[2][] = $node;
	}

	private function characterData($parser, $data)
	{
		// add this data to the last node in the stack...
		$this->cur_val .= $data;
	}

	private function xmlNodeOutput(&$node, $space)
	{
		$output = str_repeat('  ', $space);
		$attrs = [];
		foreach (array_keys($node) as $key) {
			if ($key == 0) { //'TAG'
				$name = &$node[0];
			} elseif ($key == 1) { //'VALUE'
				$data = &$node[1];
			} elseif ($key == 2) { //'ELEMENTS'
				$elements = &$node[2];
			} else {
				$attrs[$key] = $node[$key];
			}
		}
		$name = $node[0]; //'TAG'
		$output .= "<$name";
		if (count($attrs) > 0) {
			foreach ($attrs as $key => $value) {
				$output .= " $key=\"$value\"";
			}
		}
		$output .= '>';

		if (count($elements) == 0) {
			$output .= "$data</$name>\n";
		} else {
			$output .= "\n";
			if ($data) {
				$output .= str_repeat('  ', $space + 1);
				$output .= $data . "\n";
			}

			foreach (array_keys($elements) as $key) {
				$output .= $this->xmlNodeOutput($elements[$key], $space + 1);
			}

			$output .= str_repeat('  ', $space);
			$output .= "</$name>\n";
		}
		return $output;
	}

}