backend/src/modules/investments/brokerage-accounts/brokerage-accounts.service.ts

import { Injectable } from '@nestjs/common';
import { createHash } from 'node:crypto';

import {
  decimalFromString,
  divide,
  formatDecimal,
  isZero,
  multiply,
} from '../../../common/decimal';
import { investmentResourceMeta } from '../investment-resource.mapper';
import { sumMoneyByCurrency } from '../portfolio/domain/portfolio-totals';
import { PortfolioPositionDto, PortfolioService } from '../portfolio/portfolio.api';
import { hourlyAttempt, TbankSyncRepository } from '../tbank-sync/tbank-sync.api';
import {
  BrokerageAccountDto,
  BrokerageAccountsResourceDto,
  UnrealizedReturnDto,
} from './brokerage-account.dto';

const PERCENT_DECIMAL_PLACES = 2;
const ZERO_QUANTITY = 0n;

function unrealizedReturns(positions: PortfolioPositionDto[]): UnrealizedReturnDto[] {
  // Cash-like CURRENCY positions must not duplicate the separately returned cash balances.
  const investments = positions.filter((position) => position.type !== 'CURRENCY');
  const absolute = sumMoneyByCurrency(
    investments.flatMap((position) => position.absoluteReturn ? [position.absoluteReturn] : []),
  );
  const costs = sumMoneyByCurrency(
    investments.flatMap((position) =>
      position.absoluteReturn && position.averagePurchasePrice
        ? [{
            currency: position.absoluteReturn.currency,
            value: formatDecimal(multiply(
              decimalFromString(position.averagePurchasePrice.value),
              decimalFromString(position.quantity),
            )),
          }]
        : [],
    ),
  );
  const partial = new Set(
    investments.flatMap((position) => {
      const money = position.absoluteReturn
        ? null
        : position.averagePurchasePrice ?? position.currentValue;
      return money ? [money.currency] : [];
    }),
  );
  // A short position has negative cost basis, so a percent would flip sign or net out.
  const withShorts = new Set(
    investments.flatMap((position) => {
      const money = position.absoluteReturn ?? position.averagePurchasePrice ?? position.currentValue;
      return money && decimalFromString(position.quantity).value < ZERO_QUANTITY ? [money.currency] : [];
    }),
  );
  const currencies = new Set([...absolute, ...costs].map((money) => money.currency));
  return [...new Set([...currencies, ...partial])]
    .sort((left, right) => left.localeCompare(right))
    .map((currency) => {
      const absoluteReturn = absolute.find((money) => money.currency === currency)?.value ?? '0';
      const costBasis = costs.find((money) => money.currency === currency)?.value ?? '0';
      const cost = decimalFromString(costBasis);
      return {
        currency,
        absolute: absoluteReturn,
        costBasis,
        percent: isZero(cost) || withShorts.has(currency)
          ? null
          : formatDecimal(divide(
              multiply(decimalFromString(absoluteReturn), decimalFromString('100')),
              cost,
              PERCENT_DECIMAL_PLACES,
            )),
        partial: partial.has(currency),
      };
    });
}

@Injectable()
export class BrokerageAccountsService {
  constructor(
    private readonly portfolio: PortfolioService,
    private readonly sync: TbankSyncRepository,
  ) {}

  async list(userId: string): Promise<BrokerageAccountsResourceDto> {
    const saved = await this.portfolio.saved(userId, 'all');
    const data: BrokerageAccountDto[] | null =
      saved.membership.completeness === 'incomplete'
        ? null
        : saved.accounts.map((account) => ({
            id: account.id,
            name: account.name,
            type: account.type as BrokerageAccountDto['type'],
            openedOn: account.openedOn,
            portfolioSummary: account.snapshot
              ? {
                  totalsByCurrency: account.snapshot.totalsByCurrency,
                  cashBalances: account.snapshot.cashBalances,
                  structure: account.snapshot.structure,
                  unrealizedReturnByCurrency: unrealizedReturns(account.snapshot.positions),
                  stockPositionCount: account.snapshot.positions.filter(
                    (position) => position.type === 'STOCK',
                  ).length,
                  bondPositionCount: account.snapshot.positions.filter(
                    (position) => position.type === 'BOND',
                  ).length,
                  fundPositionCount: account.snapshot.positions.filter(
                    (position) => position.type === 'FUND',
                  ).length,
                  // The snapshot mapper already drops zero-quantity positions.
                  totalPositionCount: account.snapshot.positions.length,
                }
              : null,
          }));
    // The read-only result of the last hourly walk; never starts one.
    const hourly = await this.sync.hourly(userId);
    return {
      data,
      meta: investmentResourceMeta({
        resourceKey: 'accounts',
        dataRevision: createHash('sha256')
          .update(
            JSON.stringify([
              saved.membership.dataRevision,
              saved.accounts.map((account) => [
                account.id,
                account.meta.dataRevision,
              ]),
            ]),
          )
          .digest('base64url'),
        availability:
          data === null
            ? 'missing'
            : 'complete',
        fetchedAt: saved.membership.lastSuccessfulAt
          ? new Date(saved.membership.lastSuccessfulAt)
          : null,
        freshForMs: 3_600_000,
        work: null,
        lastAttempt: hourlyAttempt(hourly, ['membership', 'portfolio']),
        dependencies: saved.accounts.map((account) => account.meta),
      }),
      sync: hourly
        ? {
            state: hourly.state,
            startedAt: hourly.startedAt.toISOString(),
            finishedAt: hourly.finishedAt?.toISOString() ?? null,
            problems: hourly.sections.map((section) => ({
              ...section,
              accountId: section.accountId ?? null,
            })),
          }
        : null,
    };
  }
}