/**
 * Shared payment/settlement math for invoices. Both the global
 * `BillingService.recordPayment` and the warehouse fee invoice flow apply a
 * payment the same way — accumulate `paidAmount`, derive the outstanding
 * `balanceAmount`, and decide whether the invoice is now fully settled. Keeping
 * it here means the two flows can never drift on rounding or the
 * partial-vs-full threshold.
 */

/** Round to 2 decimals, avoiding binary float drift. */
export const round2 = (n: number): number => Math.round(n * 100) / 100;

export interface SettlementResult {
  /** New cumulative amount paid. */
  paidAmount: number;
  /** Remaining balance (0 once fully paid). */
  balanceAmount: number;
  /** True once the balance reaches zero. */
  fullyPaid: boolean;
}

/**
 * Apply a single payment of `amount` to an invoice with `totalAmount` already
 * carrying `currentPaid`. Caller is responsible for validating `amount > 0` and
 * the invoice being in a payable state.
 */
export function applySettlement(
  totalAmount: number,
  currentPaid: number,
  amount: number,
): SettlementResult {
  const total = Number(totalAmount);
  const paidAmount = round2(Number(currentPaid) + Number(amount));
  const balanceAmount = Math.max(0, round2(total - paidAmount));
  return { paidAmount, balanceAmount, fullyPaid: paidAmount >= total };
}

/**
 * SQL for an invoice's settled payment method, normalised to one vocabulary.
 *
 * Two sources have to be merged: gateway settlements carry the real provider on
 * the linked `freight.payments` row (`cbe-bill`, `telebirr`, …) while the
 * invoice's own `payments` ledger only records a flat `"GATEWAY"`; manual
 * settlements have no payments row at all and the ledger is the ONLY source
 * (`BANK_TRANSFER`, `OFFLINE`, or whatever `PayInvoiceDto.method` carried).
 * So: provider first, newest ledger entry as the fallback.
 *
 * `-> -1` is the last ledger element — the ledger is appended newest-last.
 * `::text` is not cosmetic: `payments.method` is a real Postgres enum, and
 * COALESCE against a text fallback fails without the cast.
 *
 * Normalised UPPER_SNAKE so `cbe-bill` and a hand-typed `CBE_BILL` are one
 * value on screen, in the filter and in the export.
 */
export const invoicePaymentMethodExpr = (invoice: string, payment: string): string =>
  `UPPER(REPLACE(COALESCE(${payment}.method::text, ${invoice}.payments -> -1 ->> 'method'), '-', '_'))`;

/**
 * The methods the filter offers. Not exhaustive by construction — the manual
 * pay endpoint takes a free-form `method` string — so nothing validates against
 * this list; it is the pick-list, not a constraint.
 */
export const INVOICE_PAYMENT_METHODS = [
  "TELEBIRR",
  "CBE_BIRR",
  "CBE_BILL",
  "EBIRR",
  "WAAFI",
  "CARD",
  "DMONEY",
  "CAC_BANK",
  "BANK_TRANSFER",
  "OFFLINE",
  /** Settled at a gateway whose provider row is no longer linked. */
  "GATEWAY",
] as const;