<?php

namespace alveolata\term;

// require_once(DIR_ALVEOLATA . '/definitions.php');
require_once(DIR_ALVEOLATA . '/list/functions.php');
require_once(DIR_ALVEOLATA . '/term/interface.php');
require_once(DIR_ALVEOLATA . '/term/implementation-variable.php');
require_once(DIR_ALVEOLATA . '/term/implementation-function.php');


/**
 * @param interface_term $term
 * @return string
 * @author Christian Fraß <frass@greenscale.de>
 */
function to_string(
	interface_term $term
) : string
{
	if ($term instanceof class_variable) {
		$variable = $term;
		return sprintf('$%s', $variable->name);
	}
	else if ($term instanceof class_function) {
		$function = $term;
		return sprintf(
			'%s(%s)',
			$function->head,
			implode(
				',',
				\alveolata\list_\map(
					$function->arguments,
					function ($argument) {
						return to_string($argument);
					}
				)
			)
		);
	}
	else {
		throw (new \Exception('unhandled'));
	}
}


/**
 * @param interface_term $term1
 * @param interface_term $term2
 * @return bool
 * @author Christian Fraß <frass@greenscale.de>
 */
function equal(
	interface_term $term1,
	interface_term $term2
) : bool
{
	if ($term1 instanceof class_variable) {
		if ($term2 instanceof class_variable) {
			return ($term1->name === $term2->name);
		}
		else if ($term2 instanceof class_function) {
			return false;
		}
		else {
			throw (new \Exception('unhandled'));
		}
	}
	else if ($term1 instanceof class_function) {
		if ($term2 instanceof class_variable) {
			return false;
		}
		else if ($term2 instanceof class_function) {
			return (
				($term1->head === $term2->head)
				&&
				(count($term1->arguments) === count($term2->arguments))
				&&
				\alveolata\list_\every(
					\alveolata\list_\sequence(count($term1->arguments)),
					function ($index) use (&$term1, &$term2) {
						return equal($term1->arguments[$index], $term2->arguments[$index]);
					}
				)
			);
		}
		else {
			throw (new \Exception('unhandled'));
		}
	}
	else {
		throw (new \Exception('unhandled'));
	}
}


/**
 * @param interface_term $term1
 * @param interface_term $term2
 * @return bool
 * @author Christian Fraß <frass@greenscale.de>
 */
function contains(
	interface_term $term1,
	interface_term $term2
) : bool
{
	if (equal($term1, $term2)) {
		return true;
	}
	else {
		if ($term1 instanceof class_variable) {
			return false;
		}
		else if ($term1 instanceof class_function) {
			return \alveolata\list_\some(
				$term1->arguments,
				function ($argument) use (&$term2) {
					return contains($argument, $term2);
				}
			);
		}
		else {
			throw (new \Exception('unhandled'));
		}
	}
}

 ?>