export type Workload = {
  requestsPerSecond: number
  meanInputTokens: number
  meanOutputTokens: number
  meanOccupiedSeconds: number
  burstMultiplier: number
}

function positive(name: string, value: number): number {
  if (!Number.isFinite(value) || value <= 0) throw new Error(name + " must be positive")
  return value
}

export function tokenDemandPerSecond(workload: Workload): number {
  positive("requestsPerSecond", workload.requestsPerSecond)
  positive("meanInputTokens", workload.meanInputTokens)
  positive("meanOutputTokens", workload.meanOutputTokens)
  positive("burstMultiplier", workload.burstMultiplier)
  return (
    workload.requestsPerSecond *
    (workload.meanInputTokens + workload.meanOutputTokens) *
    workload.burstMultiplier
  )
}

export function expectedConcurrency(workload: Workload): number {
  positive("requestsPerSecond", workload.requestsPerSecond)
  positive("meanOccupiedSeconds", workload.meanOccupiedSeconds)
  positive("burstMultiplier", workload.burstMultiplier)
  return workload.requestsPerSecond * workload.meanOccupiedSeconds * workload.burstMultiplier
}

export function estimatedHourlyCost(
  workload: Workload,
  inputUsdPerMillion: number,
  outputUsdPerMillion: number
): number {
  if (inputUsdPerMillion < 0 || outputUsdPerMillion < 0) {
    throw new Error("prices must be non-negative")
  }
  const requestsPerHour = workload.requestsPerSecond * 3600 * workload.burstMultiplier
  return (
    (requestsPerHour * workload.meanInputTokens * inputUsdPerMillion) / 1_000_000 +
    (requestsPerHour * workload.meanOutputTokens * outputUsdPerMillion) / 1_000_000
  )
}