/**
 * The models that may draft a listing, and what each one costs.
 *
 * One catalogue rather than two lists. The Admin settings dropdown needs the
 * models, `costMicros` needs their rates, and the price shown beside a model in
 * Admin has to be the price it is actually billed at — which it cannot be if
 * the list and the rates are maintained separately.
 *
 * Rates are dollars per million tokens, confirmed against the pricing page on
 * 2026-08-31 rather than recalled. Worth checking again when a model is added:
 * an increase to $3/$15 had been scheduled for 2026-09-01 and was cancelled,
 * with Sonnet's $2/$10 made permanent.
 */
export interface DraftingModel {
  id: string;
  /** Shown in the Admin dropdown. */
  label: string;
  /** Dollars per million input tokens. */
  inputRate: number;
  /** Dollars per million output tokens. */
  outputRate: number;
}

export const DRAFTING_MODELS: readonly DraftingModel[] = [
  { id: 'claude-sonnet-5', label: 'Claude Sonnet 5', inputRate: 2, outputRate: 10 },
  { id: 'claude-opus-5', label: 'Claude Opus 5', inputRate: 5, outputRate: 25 },
  { id: 'claude-haiku-4-5', label: 'Claude Haiku 4.5', inputRate: 1, outputRate: 5 }
];

/**
 * Sonnet, not Opus. The task is writing a description from a photograph rather
 * than reasoning, and this runs once per submission on a route a stranger with
 * a link can trigger. Opus costs two and a half times as much per item.
 */
export const DEFAULT_DRAFTING_MODEL = 'claude-sonnet-5';

export function isDraftingModel(id: string): boolean {
  return DRAFTING_MODELS.some((model) => model.id === id);
}

/**
 * Deliberately not zero. An unrecognised model pricing at nothing would make a
 * budget read as unspent however much was really spent, which is the one
 * failure a spend guard must not have. Set to the most expensive rate here, so
 * an unknown model errs towards over- rather than under-reporting.
 */
const FALLBACK_RATE = { inputRate: 5, outputRate: 25 };

/**
 * Whole micros, so a cost never carries a floating-point fraction into the
 * database. Rates are per million tokens and a micro is a millionth of a
 * dollar, so the two cancel and the arithmetic is just tokens times rate.
 */
export function costMicros(model: string, inputTokens: number, outputTokens: number): number {
  const rate = DRAFTING_MODELS.find((m) => m.id === model) ?? FALLBACK_RATE;
  return Math.round(inputTokens * rate.inputRate + outputTokens * rate.outputRate);
}