/** Token amount needed for route economics calculations. */
export type Amount = {
  /** Quantity in the token's smallest unit. */
  baseUnits: string
  /** Monetary denomination represented by the token. */
  currency: string
  /** Number of decimal places used by the token. */
  decimals: number
}

/** Returns the signed basis-point difference from a reference amount. */
export function differenceBps(options: differenceBps.Options): number | undefined {
  if (options.reference.currency !== options.value.currency) return undefined
  const decimals = Math.max(options.reference.decimals, options.value.decimals)
  const reference = scale(options.reference, decimals)
  const value = scale(options.value, decimals)
  if (reference <= 0n) return undefined
  const precision = 1_000n
  const measured = Number(((reference - value) * 10_000n * precision) / reference) / 1_000
  return Number.isFinite(measured) ? measured : undefined
}

export declare namespace differenceBps {
  /** Reference and observed values in the same monetary denomination. */
  type Options = {
    /** Amount treated as the zero-cost reference. */
    reference: Amount
    /** Amount compared with the reference. */
    value: Amount
  }
}

/** Returns a finite USD amount, or undefined for non-USD denominations. */
export function usd(amount: Amount): number | undefined {
  if (amount.currency !== 'USD') return undefined
  return units(amount)
}

/** Returns a finite amount expressed in whole token units. */
export function units(amount: Amount): number | undefined {
  const value = Number(amount.baseUnits) / 10 ** amount.decimals
  return Number.isFinite(value) ? value : undefined
}

function scale(amount: Amount, decimals: number) {
  return BigInt(amount.baseUnits) * 10n ** BigInt(decimals - amount.decimals)
}