"use strict";

const util = require("util");

// TODO: Publish this as a stand-alone module

module.exports = function kahn(nodes) {
	let queue = [];
	let list = [];

	// Start with all the zero-dependency nodes
	for (let node of nodes) {
		if (node.parents.length === 0) {
			queue.push(node);
		}
	}

	while (queue.length > 0) {
		let current = queue.shift();
		
		list.push(current);
		
		// For each dependent/parent of this item
		for (let child of current.children) {
			child.parents.splice(child.parents.indexOf(current), 1);

			// If all its dependencies have been fully processed and removed
			if (child.parents.length === 0) {
				queue.push(child);
			} else {
				// TODO: Add a proper loop checker!
				if (child.children.some((item) => item === child) || child.parents.some((item) => item === child)) {
					throw new Error(`Dependency on self encountered: ${util.inspect(child)}`);
				}
			}
		}
	}

	return list;
};