"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 ({ db, knex }) {
	return function processTaskSafely(task, processHandler) {
		let lockStream = mapFilter((item) => {
			return Promise.try(() => {
				return db.TaskInProgress.query(knex).insert({
					task: task,
					item_id: item.id
				});
			}).then(() => {
				return item;
			}).catch({ name: "UniqueViolationError" }, () => {
				return mapFilter.NoValue;
			});
		});

		let processUnlockStream = map((item) => {
			return Promise.try(() => {
				return knex.transaction((tx) => {
					return processHandler(item, tx);
				}, { doNotRejectOnRollback: false });
			}).finally(() => {
				return db.TaskInProgress.query(knex)
					.delete()
					.where({
						task: task,
						item_id: item.id
					});
			}).then(() => {
				return item;
			});
		});
		
		return pipe([
			lockStream,
			processUnlockStream
		]);
	};
};