'use strict';

const Promise = require("bluebird");
const bhttp = require("bhttp");
const promiseTaskQueue = require("promise-task-queue");
const createEventEmitter = require("create-event-emitter");
const defaultValue = require("default-value");
const debug = require("debug")("pastebinStream:scrapers:pastebinCom");

const promiseSetInterval = require("../promise-set-interval");
const errors = require("../errors");

function tryParseBody(body) {
	try {
		return JSON.parse(body);
	} catch (err) {
		throw new errors.HttpError(`Got rate-limited? Error message: ${body}`, {type: "rateLimited"});
	}
}

module.exports = function createPastebinComScraper(options = {}) {
	let queue = promiseTaskQueue();
	let knownPastes = [];
	let previousKnownPastes = [];

	queue.define("fetchPaste", (task) => {
		return Promise.try(() => {
			return bhttp.get(`http://pastebin.com/api_scrape_item.php?i=${task.pasteKey}`);
		}).then((response) => {
			if (response.statusCode !== 200) {
				// FIXME: Retry!
				throw new errors.HttpError(`Encountered a non-200 status code for Pastebin.com while retrieving a raw paste: ${response.statusCode}`, {type: "statusCode"});
			} else if (response.body.toString().indexOf("Please slow down, you are hitting our servers unnecessarily hard!") === 0) {
				throw new errors.HttpError("Got rate-limited!", {type: "rateLimited"});
			} else {
				return response.body.toString();
			}
		})
	}, {
		interval: options.pasteInterval
	});

	let loop;

	return createEventEmitter({
		stop: function stopScraper() {
			if (loop != null) {
				this.emit("stopped");
				loop.cancel();
			}
		},
		start: function startScraper() {
			loop = promiseSetInterval(() => {
				return Promise.try(() => {
					return bhttp.get(`http://pastebin.com/api_scraping.php?limit=${defaultValue(options.listLimit, 100)}`, {
						noDecode: true /* Because Pastebin.com errors aren't JSON... */
					});
				}).then((response) => {
					if (response.statusCode !== 200) {
						throw new errors.HttpError(`Encountered a non-200 status code for Pastebin.com while listing the most recent pastes: ${response.statusCode}`, {type: "statusCode"});
					} else {
						return tryParseBody(response.body).reverse();
					}
				}).tap((pastes) => {
					previousKnownPastes = knownPastes;
					knownPastes = pastes.map(paste => paste.key);
				}).filter((paste) => {
					return (!previousKnownPastes.includes(paste.key));
				}).tap((pastes) => {
					debug(`Found ${pastes.length} new pastes`);
				}).each((paste) => {
					/* We *intentionally* do not return the Promise chain below; we don't want to block the interval with queue items. */
					Promise.try(() => {
						return queue.push("fetchPaste", {
							pasteKey: paste.key
						});
					}).then((rawPaste) => {
						this.emit("paste", Object.assign({
							raw: rawPaste
						}, paste));
					}).catch((err) => {
						this.emit("error", err);
					});
				}).catch((err) => {
					/* This is where eg. rate-limiting errors will end up. */
					this.emit("error", err);
				});
			}, defaultValue(options.listInterval, 60) * 1000, {
				startImmediately: true
			});
		}
	});
};