"use strict";

const Promise = require("bluebird");
// const { UniqueViolationError } = require("objection");

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

module.exports = function ({ backend }) {
	return function processTaskSafely(task, processHandler) {
		let lockStream = mapFilter((item) => {
			return Promise.try(() => {
				return backend.lock(null, { id: item.id, task: task });
			}).then((success) => {
				if (success) {
					return item;
				} else {
					return mapFilter.NoValue;
				}
			});
		});

		let processUnlockStream = map((item) => {
			return Promise.try(() => {
				return backend.runInTransaction((tx) => {
					return processHandler(item, tx);
				});
			}).finally(() => {
				// NOTE: The unlock deliberately happens outside of a transaction, so that it can always succeed, even if a task and its associated database changes failed
				return backend.unlock(null, { id: item.id, task: task });
			}).then(() => {
				return item;
			});
		});
		
		return pipe([
			lockStream,
			processUnlockStream
		]);
	};
};