"use strict";

const Promise = require("bluebird");
const defaultValue = require("default-value");
const chalk = require("chalk");
const util = require("util");
const syncpipe = require("syncpipe");

const rateLimit = require("@ppstreams/rate-limit");
const simpleSink = require("@promistream/simple-sink");
const pipe = require("@promistream/pipe");
const parallelize = require("@ppstreams/parallelize");

const initialize = require("./initialize");

// TODO: Publish this as a separate package
// Inverts an object of arrays, eg. {a: [x, y], b: [x, z]} becomes {x: [a, b], y: [a], z: [b]}
// Useful for eg. tag mappings
function invertMapping(object) {
	let newObject = {};
	
	for (let [ key, valueList ] of Object.entries(object)) {
		for (let value of valueList) {
			if (newObject[value] == null) {
				newObject[value] = [];
			}
			
			newObject[value].push(key);
		}
	}
	
	return newObject;
}

function log(value) {
	console.log(value);
	return value;
}

module.exports = function createKernel(configuration) {
	return Promise.try(() => {
		return initialize({
			knexfile: {
				client: "pg",
				connection: configuration.database
			}
		});
	}).then((state) => {
		const queries = require("./queries")(state);
		const createTaskStream = require("./task-stream")(state);

		let { knex } = state;
	
		function insertSeeds() {
			return Promise.map(configuration.seed, (item) => {
				return queries.createItem(knex, {
					... item,
					allowUpsert: false,
					failIfExists: false
				});
			});
		}

		function checkLockedTasks() {
			return Promise.try(() => {
				return queries.countLockedTasks(knex);
			}).then((lockedCount) => {
				if (lockedCount > 0) {
					console.log(`${chalk.bold.red("WARNING:")} There are ${lockedCount} tasks currently locked, and they will not be run! This may be caused by a process crash in the past. See the documentation for more details on how to solve this issue.`);
				}
			});
		}

		function runTaskStreams() {
			let tasks = invertMapping(configuration.tags);

			let attachToGlobalRateLimit = (configuration.taskInterval != null)
				? rateLimit.clonable(configuration.taskInterval)
				: undefined;

			console.log(`Starting ${Object.keys(tasks).length} tasks...`);

			return Promise.map(Object.entries(tasks), ([ task, tags ]) => {
				let taskConfiguration = configuration.tasks[task];

				if (taskConfiguration != null) {
					let taskStream = createTaskStream({
						task: task,
						tags: tags,
						taskVersion: defaultValue(taskConfiguration.version, "0"),
						ttl: taskConfiguration.ttl,
						run: taskConfiguration.run,
						globalRateLimiter: (attachToGlobalRateLimit != null)
							? attachToGlobalRateLimit()
							: null,
						globalParallelize: (configuration.parallelTasks != null)
							? parallelize(configuration.parallelTasks)
							: null,
						taskDependencies: defaultValue(taskConfiguration.dependsOn, []).map((task) => {
							return {
								task: task,
								taskVersion: defaultValue(configuration.tasks[task].taskVersion, "0")
							};
						})
					});

					return pipe([
						taskStream,
						simpleSink((completedItem) => {
							console.log(`[completed] ${completedItem.id}`);
						})
					]).read();
				} else {
					throw new Error(`Task '${task}' is defined to run for tags [${tags}], but no such task is defined`);
				}
			}).catch((error) => {
				console.dir(error, { depth: null, colors: true });
				throw error;
			});
		}
		
		function simulateTask(id, task) {
			let taskConfiguration = configuration.tasks[task];

			let methods = [ "createItem", "renameItem", "mergeItem", "deleteItem", "createAlias", "deleteAlias", "updateData", "updateMetadata", "expire" ];

			let simulatedMethods = syncpipe(methods, [
				(_) => _.map((method) => [ method, function() {
					console.log(`${chalk.bold.yellow.bgBlack(`${method} (simulated):`)} ${util.inspect(arguments, { colors: true, depth: null })}`);
				}]),
				(_) => Object.fromEntries(_)
			]);
			
			return Promise.try(() => {
				return queries.getItem(knex, id);
			}).then((item) => {
				return taskConfiguration.run({
					id: item.id,
					data: item.data,
					getItem: function (id) {
						return queries.getItem(knex, id);
					},
					... simulatedMethods
				});
			});
		}
	
		return {
			run: function runKernel() {
				return Promise.try(() => {
					return insertSeeds();
				}).then(() => {
					return checkLockedTasks();
				}).then(() => {
					return runTaskStreams();
				});
			},
			simulate: function simulate({ itemID, task }) {
				return Promise.try(() => {
					return insertSeeds();
				}).then(() => {
					return checkLockedTasks();
				}).then(() => {
					return simulateTask(itemID, task);
				});
			},
			shutdown: function () {
				// TODO: Properly lock all public methods after shutdown is called, and wait for any running tasks to have completed
				knex.destroy();
			}
		};
	});
};