export const GENERATION_PURPOSE_HEADER = 'X-D3RO-Generation-Purpose'
export const GENERATION_ID_HEADER = 'X-D3RO-Generation-Id'

export type GenerationPurpose = 'talk_response' | 'command_response' | 'action_response'

const GENERATION_PURPOSES = new Set<string>([
  'talk_response',
  'command_response',
  'action_response',
])

const UUID_PATTERN = /^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i

export class GenerationReceiptError extends Error {
  constructor(readonly code: string) {
    super(code)
    this.name = 'GenerationReceiptError'
  }
}

export function parseGenerationPurpose(value: string | null): GenerationPurpose | null {
  if (value === null) return null
  const normalized = value.trim()
  if (!GENERATION_PURPOSES.has(normalized)) {
    throw new GenerationReceiptError('invalid_generation_purpose')
  }
  return normalized as GenerationPurpose
}

export function parseGenerationReceiptId(value: unknown): string {
  if (
    typeof value !== 'object'
    || value === null
    || Array.isArray(value)
    || typeof (value as Record<string, unknown>).generationId !== 'string'
  ) {
    throw new GenerationReceiptError('invalid_generation_receipt')
  }
  const generationId = ((value as Record<string, unknown>).generationId as string).toLowerCase()
  if (!UUID_PATTERN.test(generationId)) {
    throw new GenerationReceiptError('invalid_generation_receipt')
  }
  return generationId
}