import { Hex } from 'ox'

// Tempo gas prices (`maxFeePerGas`, `effectiveGasPrice`, block base fee) are
// denominated in attodollars (10^-18 USD) per gas, while fee-token balances
// use 6 decimals (microdollars, 10^-6 USD). The charged fee is
// `ceil(gas × gasPrice / 10^12)`, mirroring `calc_gas_balance_spending` in
// tempoxyz/tempo.

/** Attodollar exponent gas prices use (10^-18 USD per gas), fixed by the fee spec. */
const attoDecimals = 18

/** Fee-token decimals: TIP-20 fixes 6 (1 token unit = 1 microdollar). */
export const tokenDecimals = 6

/** Scaling between attodollar gas math and fee-token units, derived from the exponents. */
export const scalingFactor = 10n ** BigInt(attoDecimals - tokenDecimals)

/**
 * Fee in fee-token base units for a gas amount priced in attodollars per gas
 * (ceiling division). Works for actual fees (`gasUsed × effectiveGasPrice`)
 * and signed caps (`gas × maxFeePerGas`) alike.
 *
 * @param gas - Gas amount.
 * @param gasPrice - Price in attodollars per gas.
 * @returns The fee in fee-token base units.
 */
export function fromGas(gas: bigint, gasPrice: bigint): bigint {
  return (gas * gasPrice + scalingFactor - 1n) / scalingFactor
}

/**
 * Signed fee cap of a candidate transaction in fee-token base units:
 * `gas × maxFeePerGas` (attodollars) scaled through {@link fromGas}. Undefined
 * when either field is missing or unparseable, so callers can fail closed.
 *
 * @param request - Transaction-shaped fee fields.
 * @returns The cap in base units, or undefined.
 */
export function maxOf(request: { gas?: unknown; maxFeePerGas?: unknown }): bigint | undefined {
  const gas = toBigInt(request.gas)
  const maxFeePerGas = toBigInt(request.maxFeePerGas)
  if (gas === undefined || maxFeePerGas === undefined) return undefined
  return fromGas(gas, maxFeePerGas)
}

/** Fee fields arrive as bigints (raw envelopes) or hex quantities (fills). */
function toBigInt(value: unknown): bigint | undefined {
  if (typeof value === 'bigint') return value
  if (typeof value === 'string' && Hex.validate(value)) return Hex.toBigInt(value)
  return undefined
}