《独立开发者的商业指南·收入与财务工程》13.1 三张表的横向对照

// file: src/fin/baseline.ts
// tier: L1
// verify: node --test test/fin/baseline.test.ts

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

export type BaselineInput = {
  name: string;
  revenueCents: Cents;
  variableCostsCents: Cents;
  operatingExpensesCents: Cents;
  founderSalaryCents: Cents;
  taxRateBps: Bps;
  operatingCashFlowCents: Cents;
};

export type BaselineRow = {
  name: string;
  revenueCents: Cents;
  grossProfitCents: Cents;
  grossMarginBps: Bps;
  sdeCents: Cents;
  sdeMarginBps: Bps;
  pretaxCents: Cents;
  taxCents: Cents;
  netIncomeCents: Cents;
  netMarginBps: Bps;
  cashConversionBps: Bps;
};

export type BalanceCheck = {
  assetsCents: Cents;
  claimsCents: Cents;
  balanced: boolean;
  differenceCents: Cents;
};

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;
}

/**
 * Reduce one business to the same five-line structure used across the book.
 * Gross profit, SDE, pretax income and net income are derived here so the
 * three cases can be compared without re-deriving formulas by hand.
 */
export function buildBaseline(input: BaselineInput): Result<BaselineRow> {
  const fields: Array<[Cents, string]> = [
    [input.revenueCents, "revenue"],
    [input.variableCostsCents, "variable costs"],
    [input.operatingExpensesCents, "operating expenses"],
    [input.founderSalaryCents, "founder salary"],
    [input.operatingCashFlowCents, "operating cash flow"],
  ];
  for (const [value, label] of fields) {
    const error = checkAmount(value, label);
    if (error) {
      return fail(error);
    }
  }
  if (
    !Number.isInteger(input.taxRateBps) ||
    input.taxRateBps < 0 ||
    input.taxRateBps > 10000
  ) {
    return fail("tax rate must be between 0 and 10000 bps");
  }
  if (input.variableCostsCents > input.revenueCents) {
    return fail("variable costs cannot exceed revenue");
  }

  const grossProfitCents = input.revenueCents - input.variableCostsCents;
  const sdeCents = grossProfitCents - input.operatingExpensesCents;
  const pretaxCents = sdeCents - input.founderSalaryCents;
  const taxCents = pretaxCents > 0 ? applyRate(pretaxCents, input.taxRateBps) : 0;
  const netIncomeCents = pretaxCents - taxCents;

  return ok({
    name: input.name,
    revenueCents: input.revenueCents,
    grossProfitCents,
    grossMarginBps: divide(grossProfitCents, input.revenueCents),
    sdeCents,
    sdeMarginBps: divide(sdeCents, input.revenueCents),
    pretaxCents,
    taxCents,
    netIncomeCents,
    netMarginBps: divide(netIncomeCents, input.revenueCents),
    cashConversionBps: divide(input.operatingCashFlowCents, netIncomeCents),
  });
}

/**
 * The balance sheet must satisfy assets = liabilities + equity. A non-zero
 * difference is almost always an unbooked accrual, a missing deferred balance
 * or an equity roll-forward that was never closed.
 */
export function checkBalanceSheet(
  assetsCents: Cents,
  liabilitiesCents: Cents,
  equityCents: Cents,
): Result<BalanceCheck> {
  for (const [value, label] of [
    [assetsCents, "assets"],
    [liabilitiesCents, "liabilities"],
    [equityCents, "equity"],
  ] as Array<[Cents, string]>) {
    const error = checkAmount(value, label);
    if (error) {
      return fail(error);
    }
  }
  const claimsCents = liabilitiesCents + equityCents;
  return ok({
    assetsCents,
    claimsCents,
    balanced: assetsCents === claimsCents,
    differenceCents: assetsCents - claimsCents,
  });
}

/**
 * Net income and operating cash flow differ by non-cash items and working
 * capital. This helper keeps the sign convention explicit: a deferred revenue
 * increase is a positive adjustment because cash arrived before revenue.
 */
export function cashBridge(
  netIncomeCents: Cents,
  nonCashCents: Cents,
  deferredRevenueChangeCents: Cents,
  receivableChangeCents: Cents,
): Cents {
  return (
    netIncomeCents + nonCashCents + deferredRevenueChangeCents - receivableChangeCents
  );
}