"use strict";

const defaultValue = require("default-value");
const syncpipe = require("syncpipe");

const arrayUnique = require("../util/array-unique");
const pickTaskResult = require("./pick-task-result");

function taskResultsToObject(taskResults) {
	return syncpipe(taskResults, [
		(_) => _.map((result) => [ result.taskName, result.metadata ]),
		(_) => Object.fromEntries(_)
	]);
}

module.exports = function mergeItems({ fromObj, intoObj, merge, mergeMetadata }) {
	let mergedData = merge(intoObj.data, fromObj.data);

	let fromTaskResults = taskResultsToObject(fromObj.taskResults);
	let intoTaskResults = taskResultsToObject(intoObj.taskResults);

	let allTaskKeys = arrayUnique([
		... Object.keys(fromTaskResults),
		... Object.keys(intoTaskResults)
	]);

	// TODO: Use merge-by-template here instead?

	let mergedTaskResults = allTaskKeys.map((key) => {
		let merger = mergeMetadata[key];
		let fromTask = fromTaskResults[key];
		let intoTask = intoTaskResults[key];

		if (merger != null) {
			// Generate a new TaskResult that includes data combined from both
			let newMetadata = merger(
				defaultValue(intoTask.metadata, {}),
				defaultValue(fromTask.metadata, {})
			);
			
			return {
				... intoTask,
				metadata: newMetadata,
				updatedAt: Date.now()
			};
		} else {
			// Take the newest known TaskResult and just make sure that it is pointing at the correct ID
			// TODO: Does this really belong in the semantics module? Or is this database-specific?
			return {
				... pickTaskResult(intoTask, fromTask),
				itemId: intoObj.id
			};
		}
	});

	return {
		id: intoObj.id,
		data: mergedData,
		taskResults: mergedTaskResults
	};
};