export interface MerchantJwtPayload {
  user_id: number | string
  username: string
  tenant_id: number | string
  operator_tenant_id?: number | string
  membership_id: number | string
  app_code: string
  client_type?: string
  exp: number
}

export class MerchantTokenExpiredError extends Error {
  constructor() {
    super('登录状态已过期')
    this.name = 'MerchantTokenExpiredError'
  }
}

function decodeBase64Url(value: string) {
  const normalized = value.replace(/-/g, '+').replace(/_/g, '/')
  const padded = normalized.padEnd(Math.ceil(normalized.length / 4) * 4, '=')
  const binary = atob(padded)
  const bytes = Uint8Array.from(binary, (character) => character.charCodeAt(0))
  return new TextDecoder().decode(bytes)
}

export function decodeMerchantToken(token: string): MerchantJwtPayload {
  const payloadPart = token.split('.')[1]
  if (!payloadPart) throw new Error('登录凭证格式无效')

  try {
    const value: unknown = JSON.parse(decodeBase64Url(payloadPart))
    if (!value || typeof value !== 'object') throw new Error()
    const payload = value as Partial<MerchantJwtPayload>
    if (!payload.user_id || !payload.username || !payload.tenant_id || !payload.membership_id || !payload.exp) throw new Error()
    if (payload.app_code !== 'MERCHANT') throw new Error('账号不属于当前应用端')
    if (payload.exp * 1000 <= Date.now()) throw new MerchantTokenExpiredError()
    return payload as MerchantJwtPayload
  } catch (error) {
    if (error instanceof Error && error.message === '账号不属于当前应用端') throw error
    if (error instanceof MerchantTokenExpiredError) throw error
    throw new Error('登录凭证无法解析，请重新登录')
  }
}