《独立开发者的商业指南·资本与退出》11.1 关停决策：继续、出售、关停

继续经营 NPV = (34,320 − 24,000) × 3.6048 = 37,201

出售现值 = 77,220 ÷ 1.12^(4/12) = 74,357

关停净值 = 48,000 + 11,264 − 5,000 − 25,000 − 24,150 = 5,114

P × (1 − t) ÷ (1 + d)^(m/12) > S
P > S × (1 + d)^(m/12) ÷ (1 − t)

P* = 4,971 × 1.12^(4/12) ÷ 0.75 = 6,883

P* = 37,201 × 1.12^(4/12) ÷ 0.75 = 51,511

继续总现值 = 年度超额现金 × 年金系数 + 终值 × 折现因子
终值 3.0×：37,201 + 58,422 = 95,623
终值 1.5×：37,201 + 29,211 = 66,412

// file: src/capital/shutdown-decision.ts
// tier: L1
// verify: node --test test/capital/shutdown-decision.test.ts

import { type Cents } from "../core/money.ts";
import { type Bps } from "../core/rate.ts";
import { type Result, fail, ok } from "../core/result.ts";

export type ShutdownOption = "continue" | "sell" | "shutdown";

export type ShutdownInput = {
  annualSdeCents: Cents;
  annualOpportunityCostCents: Cents;
  continueYears: number;
  discountRateBps: Bps;
  salePriceCents: Cents;
  saleTaxBps: Bps;
  saleMonths: number;
  cashCents: Cents;
  receivablesCents: Cents;
  payablesCents: Cents;
  debtCents: Cents;
  refundCents: Cents;
  notificationCents: Cents;
  dataWinddownCents: Cents;
  deregistrationCents: Cents;
  transitionCents: Cents;
  winddownMonths: number;
};

export type ShutdownOutcome = {
  continueOwnerEarningsCents: Cents;
  continueNpvCents: Cents;
  saleAfterTaxCents: Cents;
  salePresentCents: Cents;
  shutdownCostCents: Cents;
  shutdownNetCents: Cents;
  shutdownPresentCents: Cents;
  saleVsShutdownCents: Cents;
  saleVsContinueCents: Cents;
  breakEvenSalePriceCents: Cents;
  bestOption: ShutdownOption;
};

function checkAmount(value: Cents, label: string): string | null {
  if (!Number.isInteger(value) || value < 0) {
    return `${label} must be a non-negative integer amount in cents`;
  }
  return null;
}

function checkBps(value: Bps, label: string): string | null {
  if (!Number.isInteger(value) || value < 0 || value > 10000) {
    return `${label} must be between 0 and 10000 bps`;
  }
  return null;
}

function discountFactor(rateBps: Bps, months: number): number {
  return Math.pow(1 + rateBps / 10000, months / 12);
}

function annuityFactor(rateBps: Bps, years: number): number {
  if (rateBps === 0) {
    return years;
  }
  const rate = rateBps / 10000;
  let factor = 0;
  for (let year = 1; year <= years; year += 1) {
    factor += 1 / Math.pow(1 + rate, year);
  }
  return factor;
}

/**
 * Three options are compared on the same present-value basis. Continue is the
 * SDE left after charging the founders' market wage, discounted as a finite
 * annuity with no terminal value. Sell is the offer after the combined
 * capital-gains tax assumption, discounted from closing. Shutdown is cash
 * plus collectible receivables minus payables, debt and wind-down costs; a
 * negative result means the owners must fund the gap. The break-even price
 * answers the narrow question: below what offer is shutting down better
 * than selling.
 */
export function shutdownDecision(
  input: ShutdownInput,
): Result<ShutdownOutcome> {
  const sdeError = checkAmount(input.annualSdeCents, "annual SDE");
  if (sdeError) {
    return fail(sdeError);
  }
  if (input.annualSdeCents === 0) {
    return fail("annual SDE must be positive");
  }
  for (const [value, label] of [
    [input.annualOpportunityCostCents, "annual opportunity cost"],
    [input.salePriceCents, "sale price"],
    [input.cashCents, "cash"],
    [input.receivablesCents, "receivables"],
    [input.payablesCents, "payables"],
    [input.debtCents, "debt"],
    [input.refundCents, "refund"],
    [input.notificationCents, "notification"],
    [input.dataWinddownCents, "data wind-down"],
    [input.deregistrationCents, "deregistration"],
    [input.transitionCents, "transition support"],
  ] as Array<[Cents, string]>) {
    const error = checkAmount(value, label);
    if (error) {
      return fail(error);
    }
  }
  for (const [value, label] of [
    [input.discountRateBps, "discount rate"],
    [input.saleTaxBps, "sale tax"],
  ] as Array<[Bps, string]>) {
    const error = checkBps(value, label);
    if (error) {
      return fail(error);
    }
  }
  if (
    !Number.isInteger(input.continueYears) ||
    input.continueYears < 1 ||
    input.continueYears > 10
  ) {
    return fail("continue years must be an integer between 1 and 10");
  }
  for (const [value, label] of [
    [input.saleMonths, "sale months"],
    [input.winddownMonths, "wind-down months"],
  ] as Array<[number, string]>) {
    if (!Number.isInteger(value) || value < 0 || value > 24) {
      return fail(`${label} must be an integer between 0 and 24`);
    }
  }

  const continueOwnerEarningsCents = Math.max(
    0,
    input.annualSdeCents - input.annualOpportunityCostCents,
  );
  const continueNpvCents = Math.round(
    continueOwnerEarningsCents * annuityFactor(input.discountRateBps, input.continueYears),
  );

  const saleAfterTaxCents = Math.round(
    input.salePriceCents * (1 - input.saleTaxBps / 10000),
  );
  const salePresentCents = Math.round(
    saleAfterTaxCents / discountFactor(input.discountRateBps, input.saleMonths),
  );

  const shutdownCostCents =
    input.refundCents +
    input.notificationCents +
    input.dataWinddownCents +
    input.deregistrationCents +
    input.transitionCents;
  const shutdownNetCents =
    input.cashCents +
    input.receivablesCents -
    input.payablesCents -
    input.debtCents -
    shutdownCostCents;
  const shutdownPresentCents = Math.round(
    shutdownNetCents /
      discountFactor(input.discountRateBps, input.winddownMonths / 2),
  );

  const breakEvenSalePriceCents =
    shutdownPresentCents <= 0
      ? 0
      : Math.ceil(
          (shutdownPresentCents *
            discountFactor(input.discountRateBps, input.saleMonths)) /
            (1 - input.saleTaxBps / 10000),
        );

  let bestOption: ShutdownOption = "continue";
  let bestValue = continueNpvCents;
  if (salePresentCents > bestValue) {
    bestOption = "sell";
    bestValue = salePresentCents;
  }
  if (shutdownPresentCents > bestValue) {
    bestOption = "shutdown";
  }

  return ok({
    continueOwnerEarningsCents,
    continueNpvCents,
    saleAfterTaxCents,
    salePresentCents,
    shutdownCostCents,
    shutdownNetCents,
    shutdownPresentCents,
    saleVsShutdownCents: salePresentCents - shutdownPresentCents,
    saleVsContinueCents: salePresentCents - continueNpvCents,
    breakEvenSalePriceCents,
    bestOption,
  });
}