"use strict";

const assert = require("assert");
const unreachable = require("@joepie91/unreachable")("zapdb-kv");

const integerCoder = require("./integer");

function decimalToInteger(value, precision = 0) {
	let multiplier = 10n ** BigInt(precision);
	let match = /^(-?)([0-9]+)(?:\.([0-9]+))?$/.exec(value);
	
	if (match != null) {
		let isNegative = (match[1] !== "");
		let whole = BigInt(match[2]) * multiplier;

		let fraction = (match[3] != null)
			? BigInt(match[3].slice(0, precision))
			: BigInt(0);
		
		let signMultiplier = (isNegative)
			? -1n
			: 1n;

		return (whole + fraction) * signMultiplier;
	} else {
		throw unreachable("Decimal regex did not match");
	}
}

function integerToDecimal(integer, precision = 0) {
	let multiplier = 10n ** BigInt(precision);

	let wholes = integer / multiplier; // this is integer division!
	let fraction = integer - (wholes * multiplier); // modulo

	// TODO: Support float mode? Or maybe custom transforms on a database level, eg. to feed this through a user-specified decimal library?
	return `${wholes}.${fraction}`;
}

module.exports = {
	encode: function (value, asIndexKey, { precision }) {
		let integer = decimalToInteger(value, precision);
		return integerCoder.encode(integer, asIndexKey);
	},
	decode: function (buffer, offset, { precision }) {
		let result = integerCoder.decode(buffer, offset);
		assert(result.blobID === undefined);

		let decimal = integerToDecimal(result.value, precision);

		return {
			bytesRead: result.bytesRead,
			value: decimal,
			auxiliaryBlob: undefined
		};
	}
};