"use strict";

const consumable = require("@joepie91/consumable");

const mapFilter = require("@promistream/map-filter");
const parseXML = require("@promistream/parse-xml");
const pipe = require("@promistream/pipe");

// NOTE: This is not a 100% strict parser. It assumes that the sitemap XML is well-formed, and tags appearing in strange places are ignored.

module.exports = function createSitemapParsingStream() {
	// The consumable is always filled with an object, so that mutating operations never fail. However, if a tag appears outside of an expected item context, its value will be stored on a placeholder object that gets thrown away as soon as an item context is encountered, effectively throwing away the tag's data itself.
	let currentItem = consumable({});
	let currentTag;

	return pipe([
		parseXML({ events: [ "opentag", "closetag", "text" ] }),
		mapFilter((event) => {
			if (event.type === "opentag") {
				let tag = event.value;

				if (tag.name === "sitemap") {
					currentItem.replace({
						type: "sitemap",
						url: undefined,
						lastModified: undefined
					});
				} else if (tag.name === "url") {
					currentItem.replace({
						type: "url",
						url: undefined,
						priority: undefined
					});
				}

				currentTag = tag.name;

				return mapFilter.NoValue;
			} else if (event.type === "closetag") {
				let tag = event.value;

				// We need to ensure that we unset the currentTag once we're done with it, otherwise text elements *between* tags might erroneously end up in our items. Technically this is not correct as we've just moved to the parent tag, but since we're only interested in text which *directly* exists within a tag uninterrupted, we can cut some corners here.
				currentTag = undefined;

				if (tag.name === "sitemap" || tag.name === "url") {
					return currentItem.replace({});
				} else {
					return mapFilter.NoValue;
				}
			} else {
				let text = event.value;

				if (currentTag === "loc") {
					currentItem.peek().url = text;
				} else if (currentTag === "lastmod") {
					currentItem.peek().lastModified = text;
				} else if (currentTag === "priority") {
					currentItem.peek().currentTag = text;
				}

				return mapFilter.NoValue;
			}
		})
	]);
};