frontend/src/pages/account/model/positions.ts

import { formatShare, type Portfolio } from "@/entities/portfolio";
import { formatDecimal, formatMoney, instrumentLogoUrl } from "@/shared/lib";

type AccountPagePosition = Portfolio["positions"][number] & {
	instrumentTo?: string;
	logoSrc: null | string;
	returnPercent: null | string;
	returnPercentText: null | string;
	returnText: null | string;
	returnTone?: AccountPageReturnTone;
	shareText: null | string;
};

type AccountPagePositionGroup = {
	key: string;
	positions: [AccountPagePosition, ...AccountPagePosition[]];
};

type AccountPagePositionSection = {
	groups: AccountPagePositionGroup[];
	kind: PositionSectionKind;
};

type AccountPageReturnTone = "negative" | "positive";

type Decimal = { scale: number; value: bigint };

type Money = NonNullable<Portfolio["positions"][number]["absoluteReturn"]>;

type PositionSectionKind = "bonds"
	| "other"
	| "stocks";

const RADIX = 10n;
const DECIMAL_PARTS = 2;
const PERCENT_SCALE = 6;
const DISPLAY_PERCENT_SCALE = 2;
const PERCENT_FACTOR = 100n;
const ROUNDING_FACTOR = 2n;

function decimalFromString(value: string): Decimal {
	const [whole = "0", fraction = ""] = value.split(".", DECIMAL_PARTS);

	return { scale: fraction.length, value: BigInt(`${whole}${fraction}`) };
}

function decimalToString(decimal: Decimal): string {
	const sign = decimal.value < 0n ? "-" : "";

	const digits = (decimal.value < 0n ? -decimal.value : decimal.value)
		.toString()
		.padStart(decimal.scale + 1, "0");

	const whole = decimal.scale
		? digits.slice(0, -decimal.scale)
		: digits;

	let fraction = decimal.scale ? digits.slice(-decimal.scale) : "";

	while (fraction.endsWith("0")) fraction = fraction.slice(0, -1);

	const suffix = fraction ? `.${fraction}` : "";

	return `${sign}${whole}${suffix}`;
}

function formatPositionReturnPercent(value: string): string {
	const decimal = decimalFromString(value);
	let rounded = decimal.value;

	if (decimal.scale > DISPLAY_PERCENT_SCALE) {
		const divisor = RADIX ** BigInt(decimal.scale - DISPLAY_PERCENT_SCALE);
		const remainder = rounded % divisor;
		const absoluteRemainder = remainder < 0n ? -remainder : remainder;
		rounded /= divisor;

		if (absoluteRemainder * ROUNDING_FACTOR >= divisor) {
			rounded += decimal.value < 0n ? -1n : 1n;
		}
	}
	else {
		rounded *= RADIX ** BigInt(DISPLAY_PERCENT_SCALE - decimal.scale);
	}

	const sign = rounded > 0n ? "+" : "";

	return `${sign}${decimalToString({
		scale: DISPLAY_PERCENT_SCALE,
		value: rounded,
	})}`;
}

function groupPositions(
	positions: AccountPagePosition[],
): AccountPagePositionGroup[] {
	const groups = new Map<string, AccountPagePositionGroup>();

	for (const [index, position] of positions.entries()) {
		const identity = positionIdentity(position);
		const rowKey = JSON.stringify(["row", position.account?.id, index]);

		const key
			= identity && position.account
				? JSON.stringify([position.type, ...identity])
				: rowKey;

		const group = groups.get(key);

		if (
			group
			&& group.positions.every(
				item => item.account?.id !== position.account?.id,
			)
		) {
			group.positions.push(position);
		}
		else {
			const uniqueKey = group ? rowKey : key;
			groups.set(uniqueKey, { key: uniqueKey, positions: [position] });
		}
	}

	// eslint-disable-next-line unicorn/prefer-iterator-to-array -- Production targets ES2023; Iterator helpers require a newer browser baseline.
	return [...groups.values()];
}

function positionIdentity(position: AccountPagePosition) {
	if (position.instrumentUid?.trim())
		return ["uid", position.instrumentUid.trim()];
	if (position.figi?.trim()) return ["figi", position.figi.trim()];

	return position.isin?.trim() ? ["isin", position.isin.trim()] : undefined;
}

function returnPercent(
	position: Portfolio["positions"][number],
): null | string {
	const result = position.absoluteReturn;
	const price = position.averagePurchasePrice;
	if (!result || !price || result.currency !== price.currency) return null;

	const quantity = decimalFromString(position.quantity);
	const purchasePrice = decimalFromString(price.value);

	const cost = {
		scale: quantity.scale + purchasePrice.scale,
		value: quantity.value * purchasePrice.value,
	};

	if (quantity.value <= 0n || cost.value <= 0n) return null;

	const absoluteReturn = decimalFromString(result.value);

	const numerator = absoluteReturn.value * PERCENT_FACTOR
		* RADIX ** BigInt(cost.scale + PERCENT_SCALE);

	const denominator = cost.value * RADIX ** BigInt(absoluteReturn.scale);
	const remainder = numerator % denominator;

	const isRoundsUp = (remainder < 0n ? -remainder : remainder) * ROUNDING_FACTOR
		>= denominator;

	const rounding = isRoundsUp ? 1n : 0n;
	const signedRounding = numerator < 0n ? -rounding : rounding;
	const rounded = numerator / denominator + signedRounding;

	return decimalToString({ scale: PERCENT_SCALE, value: rounded });
}

function sumDecimals(values: Decimal[]): Decimal {
	const scale = Math.max(...values.map(value => value.scale));

	const sum = values.reduce(
		(total, value) => total
			+ value.value * RADIX ** BigInt(scale - value.scale),
		0n,
	);

	return { scale, value: sum };
}

function toAccountPagePositionSections(
	portfolio: Portfolio,
): AccountPagePositionSection[] {
	const denominators = new Map<string, number>();

	for (const position of portfolio.positions) {
		if (!position.currentValue) continue;
		const currency = position.currentValue.currency;
		denominators.set(
			currency,
			(denominators.get(currency) ?? 0) + Number(position.currentValue.value),
		);
	}

	const stocks = toSection(
		"stocks",
		portfolio,
		denominators,
	);

	const bonds = toSection("bonds", portfolio, denominators);
	const other = toSection("other", portfolio, denominators);

	return [stocks, bonds, other].filter(section => section.groups.length > 0);
}

function toPosition(
	position: Portfolio["positions"][number],
	denominators: Map<string, number>,
	kind: PositionSectionKind,
): AccountPagePosition {
	const isExpanded = kind !== "other";

	const returnValue = position.absoluteReturn
		? Number(position.absoluteReturn.value)
		: null;

	let returnTone: AccountPageReturnTone | undefined;
	if (returnValue !== null && returnValue !== 0)
		returnTone = returnValue > 0 ? "positive" : "negative";

	const returnPrefix
		= isExpanded && returnValue !== null && returnValue > 0 ? "+" : "";

	const percent = returnPercent(position);

	return {
		...position,
		instrumentTo:
			(kind === "stocks" || kind === "bonds") && position.instrumentUid
				? `/${kind}/${encodeURIComponent(position.instrumentUid)}`
				: undefined,
		logoSrc: isExpanded
			? instrumentLogoUrl(position.logoName)
			: null,
		returnPercent: percent,
		returnPercentText: percent
			? `${formatDecimal(formatPositionReturnPercent(percent))} %`
			: null,
		returnText: position.absoluteReturn
			? `${returnPrefix}${formatMoney(position.absoluteReturn)}`
			: null,
		returnTone,
		shareText: position.currentValue?.currency
			? formatShare(position.currentValue, {
					currency: position.currentValue.currency,
					value: String(denominators.get(position.currentValue.currency) ?? 0),
				})
			: null,
	};
}

function toSection(
	kind: PositionSectionKind,
	portfolio: Portfolio,
	denominators: Map<string, number>,
): AccountPagePositionSection {
	return {
		groups: groupPositions(
			portfolio.positions
				.filter((position) => {
					if (kind === "stocks") return position.type === "STOCK";

					return kind === "bonds"
						? position.type === "BOND"
						: position.type !== "STOCK"
							&& position.type !== "BOND"
							&& position.type !== "CURRENCY";
				})
				.map(position =>
					toPosition(
						position,
						denominators,
						kind,
					),
				),
		),
		kind,
	};
}

function toUnrealizedReturns(
	positions: Portfolio["positions"],
): Money[] {
	const totals = new Map<string, {
		complete: boolean;
		values: Decimal[];
	}>();

	for (const position of positions) {
		const currencies = position.absoluteReturn
			? [position.absoluteReturn.currency]
			: [...new Set([
					position.averagePurchasePrice?.currency,
					position.currentValue?.currency,
				].filter((currency): currency is string => !!currency))];

		for (const currency of currencies) {
			const total = totals.get(currency) ?? { complete: true, values: [] };

			if (position.absoluteReturn) {
				total.values.push(decimalFromString(position.absoluteReturn.value));
			}
			else {
				total.complete = false;
			}

			totals.set(currency, total);
		}
	}

	return [...totals].flatMap(([currency, total]) => total.complete
		? [{ currency, value: decimalToString(sumDecimals(total.values)) }]
		: []);
}

export {
	type AccountPagePosition,
	type AccountPagePositionGroup,
	type AccountPagePositionSection,
	formatPositionReturnPercent,
	toAccountPagePositionSections,
	toUnrealizedReturns,
};