package lib;

import haxe.Exception;

class LambdaExtender {
	/**
		Returns the first element if there are exectly one element present.
		Throws exception if not.
	**/
	static public function single<T>(it:Iterable<T>):T {
		var elem:T = null;
		for (t in it) {
			if (elem != null) {
				throw new Exception("Multiple elements found");
			}
			elem = t;
		}

		if (elem == null) {
			throw new Exception("No element found");
		}

		return elem;
	}

	/**
		Like `single` but when no element was found return the default value.
	**/
	static public function singleOrDefault<T>(it:Iterable<T>, defaultValue:T):T {
		var elem:T = null;
		for (t in it) {
			if (elem != null) {
				throw new Exception("Multiple elements found");
			}
			elem = t;
		}

		if (elem == null) {
			return defaultValue;
		}

		return elem;
	}

	/**
		Returns the first element.
		Throws execption if no first element found.
	**/
	static public function first<T>(it:Iterable<T>):T {
		for (t in it) {
			return t;
		}

		throw new Exception("No element found");
	}

	/**
		Like `first` only if no first element was found it returns the defalt value.
	**/
	static public function firstOrDefault<T>(it:Iterable<T>, defaultValue:T):T {
		var iter = it.iterator();

		if (iter.hasNext()) {
			return iter.next();
		}

		return defaultValue;
	}
}