'use strict';

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

const validateSync = require("./validate-sync");

let originAliases = {
	top: 0,
	left: 0,
	center: "50%",
	bottom: "100%",
	right: "100%"
}

function tryAlias(value) {
	if (originAliases[value] != null) {
		return originAliases[value];
	} else {
		return value;
	}
}

function calculateOffset(value, origin) {
	if (typeof origin === "number") {
		return -origin;
	} else {
		let match = /^(-?[0-9]+(?:\.[0-9]+)?)%$/.exec(origin);

		if (match == null) {
			throw new Error(`Encountered invalid origin value: ${origin}`);
		} else {
			let percentage = match[1];
			return -(value * (parseFloat(percentage) / 100));
		}
	}
}

module.exports = function calculateOriginOffsets(options) {
	validateSync(options, {
		width: "required",
		height: "required",
		originX: "required",
		originY: "required"
	});

	let originX = tryAlias(options.originX);
	let originY = tryAlias(options.originY);

	return {
		x: calculateOffset(options.width, originX),
		y: calculateOffset(options.height, originY)
	}
}