Interest-Coverage Ratio

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/** Deterministic TypeScript reference calculations for D18-F01. */

type Inputs = Record<string, unknown>;
type Output = Record<string, unknown>;

function numberValue(name: string, value: unknown): number {
  if (typeof value !== "number" || !Number.isFinite(value)) throw new RangeError(`${name} must be a finite number`);
  return value;
}

function positive(name: string, value: unknown): number {
  const parsed = numberValue(name, value);
  if (parsed <= 0) throw new RangeError(`${name} must be positive`);
  return parsed;
}

function booleanValue(name: string, value: unknown): boolean {
  if (typeof value !== "boolean") throw new RangeError(`${name} must be boolean`);
  return value;
}

const average = (beginning: number, ending: number): number => (beginning + ending) / 2;
const clean = (value: number): number => {
  const rounded = Math.round((value + Number.EPSILON) * 1e12) / 1e12;
  return Object.is(rounded, -0) ? 0 : rounded;
};

export function dupontDecomposition(input: Inputs): Output {
  const income = numberValue("net_income", input.net_income);
  const revenue = numberValue("revenue", input.revenue);
  const averageAssets = average(numberValue("beginning_assets", input.beginning_assets), numberValue("ending_assets", input.ending_assets));
  const averageEquity = average(numberValue("beginning_equity", input.beginning_equity), numberValue("ending_equity", input.ending_equity));
  if (revenue === 0 || averageAssets <= 0 || averageEquity <= 0) {
    const reasons: string[] = [];
    if (revenue === 0) reasons.push("zero-revenue");
    if (averageAssets <= 0) reasons.push("nonpositive-average-assets");
    if (averageEquity <= 0) reasons.push("nonpositive-average-equity");
    return { net_profit_margin: null, asset_turnover: null, equity_multiplier: null, dupont_roe: null, direct_roe: null, identity_gap: null,
      average_assets: clean(averageAssets), average_equity: clean(averageEquity), state: "not-meaningful", reason: reasons.join("+") };
  }
  const margin = income / revenue;
  const turnover = revenue / averageAssets;
  const multiplier = averageAssets / averageEquity;
  const dupontRoe = margin * turnover * multiplier;
  const directRoe = income / averageEquity;
  return { net_profit_margin: clean(margin), asset_turnover: clean(turnover), equity_multiplier: clean(multiplier), dupont_roe: clean(dupontRoe),
    direct_roe: clean(directRoe), identity_gap: clean(dupontRoe - directRoe), average_assets: clean(averageAssets), average_equity: clean(averageEquity),
    state: income < 0 ? "loss" : "calculated", reason: "three-factor-identity-reconciles" };
}

export function roicCalculation(input: Inputs): Output {
  const profit = numberValue("operating_profit", input.operating_profit);
  const taxRate = numberValue("normalized_tax_rate", input.normalized_tax_rate);
  if (taxRate < 0 || taxRate > 1) throw new RangeError("normalized_tax_rate must be between 0 and 1");
  const capitalBegin = numberValue("beginning_operating_assets", input.beginning_operating_assets) - numberValue("beginning_operating_liabilities", input.beginning_operating_liabilities);
  const capitalEnd = numberValue("ending_operating_assets", input.ending_operating_assets) - numberValue("ending_operating_liabilities", input.ending_operating_liabilities);
  const averageCapital = average(capitalBegin, capitalEnd);
  const nopat = profit * (1 - taxRate);
  if (averageCapital <= 0) return { nopat: clean(nopat), beginning_invested_capital: clean(capitalBegin), ending_invested_capital: clean(capitalEnd),
    average_invested_capital: clean(averageCapital), roic: null, state: "not-meaningful", reason: "nonpositive-average-invested-capital" };
  return { nopat: clean(nopat), beginning_invested_capital: clean(capitalBegin), ending_invested_capital: clean(capitalEnd),
    average_invested_capital: clean(averageCapital), roic: clean(nopat / averageCapital), state: nopat < 0 ? "loss" : "calculated",
    reason: "package-operating-capital-definition" };
}

export function cashConversionCycle(input: Inputs): Output {
  const revenue = numberValue("revenue", input.revenue);
  const cogs = numberValue("cost_of_goods_sold", input.cost_of_goods_sold);
  const days = positive("day_count", input.day_count);
  const receivablesBegin = numberValue("beginning_receivables", input.beginning_receivables);
  const receivablesEnd = numberValue("ending_receivables", input.ending_receivables);
  const inventoryBegin = numberValue("beginning_inventory", input.beginning_inventory);
  const inventoryEnd = numberValue("ending_inventory", input.ending_inventory);
  const payablesBegin = numberValue("beginning_trade_payables", input.beginning_trade_payables);
  const payablesEnd = numberValue("ending_trade_payables", input.ending_trade_payables);
  if (Math.min(receivablesBegin, receivablesEnd, inventoryBegin, inventoryEnd, payablesBegin, payablesEnd) < 0) throw new RangeError("working-capital balances must be nonnegative");
  const receivables = average(receivablesBegin, receivablesEnd);
  const inventory = average(inventoryBegin, inventoryEnd);
  const payables = average(payablesBegin, payablesEnd);
  if (revenue <= 0 || cogs <= 0) return { average_receivables: clean(receivables), average_inventory: clean(inventory), average_trade_payables: clean(payables),
    days_sales_outstanding: null, days_inventory_outstanding: null, days_payables_outstanding: null, cash_conversion_cycle_days: null,
    state: "not-meaningful", reason: revenue <= 0 ? "nonpositive-revenue" : "nonpositive-cogs" };
  const dso = receivables / revenue * days;
  const dio = inventory / cogs * days;
  const dpo = payables / cogs * days;
  const ccc = dio + dso - dpo;
  return { average_receivables: clean(receivables), average_inventory: clean(inventory), average_trade_payables: clean(payables),
    days_sales_outstanding: clean(dso), days_inventory_outstanding: clean(dio), days_payables_outstanding: clean(dpo),
    cash_conversion_cycle_days: clean(ccc), state: ccc < 0 ? "negative-cycle" : "calculated", reason: "dio-plus-dso-minus-dpo" };
}

export function interestCoverageRatio(input: Inputs): Output {
  const ebit = numberValue("ebit", input.ebit);
  const interest = numberValue("gross_interest_expense", input.gross_interest_expense);
  if (interest <= 0) return { ebit: clean(ebit), gross_interest_expense: clean(interest), interest_coverage_ratio: null,
    coverage_shortfall: null, state: "not-meaningful", reason: "nonpositive-gross-interest-expense" };
  const ratio = ebit / interest;
  return { ebit: clean(ebit), gross_interest_expense: clean(interest), interest_coverage_ratio: clean(ratio),
    coverage_shortfall: clean(Math.max(0, interest - ebit)), state: ratio >= 1 ? "covered" : "not-covered",
    reason: "ebit-divided-by-gross-interest-expense" };
}

export function netDebtToEbitda(input: Inputs): Output {
  const income = numberValue("net_income", input.net_income);
  const interest = numberValue("interest_expense", input.interest_expense);
  const tax = numberValue("income_tax_expense", input.income_tax_expense);
  const da = numberValue("depreciation_and_amortization", input.depreciation_and_amortization);
  const currentDebt = numberValue("current_borrowings", input.current_borrowings);
  const noncurrentDebt = numberValue("noncurrent_borrowings", input.noncurrent_borrowings);
  const leases = numberValue("lease_liabilities", input.lease_liabilities);
  const cash = numberValue("cash_and_cash_equivalents", input.cash_and_cash_equivalents);
  const includeLeases = booleanValue("include_lease_liabilities", input.include_lease_liabilities);
  if (Math.min(interest, da, currentDebt, noncurrentDebt, leases, cash) < 0) throw new RangeError("debt, cash, interest, and D&A inputs must be nonnegative");
  const ebitda = income + interest + tax + da;
  const grossDebt = currentDebt + noncurrentDebt + (includeLeases ? leases : 0);
  const netDebt = grossDebt - cash;
  if (ebitda <= 0) return { ebitda: clean(ebitda), gross_debt: clean(grossDebt), net_debt: clean(netDebt), net_debt_to_ebitda: null,
    lease_policy: includeLeases ? "included" : "excluded", state: "not-meaningful", reason: "nonpositive-ebitda" };
  return { ebitda: clean(ebitda), gross_debt: clean(grossDebt), net_debt: clean(netDebt), net_debt_to_ebitda: clean(netDebt / ebitda),
    lease_policy: includeLeases ? "included" : "excluded", state: netDebt < 0 ? "net-cash" : "net-debt", reason: "net-debt-divided-by-ebitda" };
}

interface Item { label: string; value: number }
interface Period { period: string; items: Item[] }

export function commonSizeStatements(input: Inputs): Output {
  const statementType = input.statement_type;
  if (statementType !== "income" && statementType !== "balance") throw new RangeError("statement_type must be 'income' or 'balance'");
  const baseLabel = input.base_label;
  const focusLabel = input.focus_label;
  if (typeof baseLabel !== "string" || !baseLabel.trim()) throw new RangeError("base_label must be a nonempty string");
  if (typeof focusLabel !== "string" || !focusLabel.trim()) throw new RangeError("focus_label must be a nonempty string");
  if (!Array.isArray(input.periods) || input.periods.length < 2) throw new RangeError("periods must contain at least two period objects");
  let expectedLabels: string[] | null = null;
  let previousFocus: number | null = null;
  const normalizedPeriods = (input.periods as unknown[]).map((rawPeriod, periodIndex) => {
    if (!rawPeriod || typeof rawPeriod !== "object") throw new RangeError(`periods[${periodIndex}] must be an object`);
    const period = rawPeriod as Record<string, unknown>;
    if (typeof period.period !== "string" || !period.period.trim()) throw new RangeError(`periods[${periodIndex}].period must be a nonempty string`);
    if (!Array.isArray(period.items) || period.items.length < 4) throw new RangeError(`periods[${periodIndex}].items must contain at least four rows`);
    const seen = new Set<string>();
    const parsed = (period.items as unknown[]).map((rawItem, itemIndex): Item => {
      if (!rawItem || typeof rawItem !== "object") throw new RangeError(`periods[${periodIndex}].items[${itemIndex}] must be an object`);
      const item = rawItem as Record<string, unknown>;
      if (typeof item.label !== "string" || !item.label.trim() || seen.has(item.label)) throw new RangeError("statement item labels must be nonempty and unique within a period");
      seen.add(item.label);
      return { label: item.label, value: numberValue(`${period.period}.${item.label}`, item.value) };
    });
    const labels = parsed.map((item) => item.label);
    if (expectedLabels === null) expectedLabels = labels;
    else if (labels.join("\u0000") !== expectedLabels.join("\u0000")) throw new RangeError("every period must use the same ordered line-item labels");
    const values = Object.fromEntries(parsed.map((item) => [item.label, item.value]));
    if (!(baseLabel in values) || !(focusLabel in values)) throw new RangeError("base_label and focus_label must exist in every period");
    const base = values[baseLabel];
    if (base === 0 || (statementType === "balance" && base < 0)) throw new RangeError("the common-size base must be nonzero and positive for balance sheets");
    const focusPercentage = values[focusLabel] / base * 100;
    const result = { period: (period.period as string).trim(), base_value: clean(base), focus_percentage: clean(focusPercentage),
      focus_change_pp: previousFocus === null ? null : clean(focusPercentage - previousFocus),
      items: parsed.map((item) => ({ label: item.label, value: clean(item.value), common_size_pct: clean(item.value / base * 100) })) };
    previousFocus = focusPercentage;
    return result;
  });
  const latest = normalizedPeriods[normalizedPeriods.length - 1];
  return { statement_type: statementType, base_label: baseLabel, focus_label: focusLabel, period_count: normalizedPeriods.length,
    line_item_count: normalizedPeriods[0].items.length, focus_percentage: latest.focus_percentage, focus_change_pp: latest.focus_change_pp,
    periods: normalizedPeriods, state: "calculated", reason: "signed-line-items-divided-by-period-base" };
}

export function calculate(topicId: string, input: Inputs): Output {
  if (!input || typeof input !== "object" || Array.isArray(input)) throw new RangeError("inputs must be an object");
  switch (topicId) {
    case "D18-F01-A01": return dupontDecomposition(input);
    case "D18-F01-A02": return roicCalculation(input);
    case "D18-F01-A03": return cashConversionCycle(input);
    case "D18-F01-A04": return interestCoverageRatio(input);
    case "D18-F01-A05": return netDebtToEbitda(input);
    case "D18-F01-A06": return commonSizeStatements(input);
    default: throw new RangeError(`unsupported topic_id: ${topicId}`);
  }
}