import {z} from 'zod'

export type GetApiFlagsArgs = {token?: string | undefined, project_id: number, context: string};

export type GetApiFlagsOptions = {baseUrl?: string | undefined, ProjectSecret?: {username: string, password: string} | undefined, fetch?: typeof fetch | undefined};

export const selectedVariant = z.object({variant_key: z.string(), variant_value: z.union([z.string(), z.number(), z.boolean(), z.object({})]), experiment_id: z.string().optional(), is_experiment_active: z.boolean().optional(), is_qa_tester: z.boolean().optional()});

export const evaluateFlagsResponse = z.object({flags: z.record(z.string(), selectedVariant)});

export const validateResponse = async <Output>(
  schema: {
    readonly '~standard': {
      readonly validate: (value: unknown) => ({ readonly value: Output; readonly issues?: undefined } | { readonly issues: ReadonlyArray<{ readonly message: string; readonly path?: ReadonlyArray<PropertyKey | { readonly key: PropertyKey }> | undefined }> }) | Promise<{ readonly value: Output; readonly issues?: undefined } | { readonly issues: ReadonlyArray<{ readonly message: string; readonly path?: ReadonlyArray<PropertyKey | { readonly key: PropertyKey }> | undefined }> }>
    }
  },
  value: unknown
): Promise<Output> => {
  const result = await schema['~standard'].validate(value)

  if (result.issues !== undefined) {
    const detail = result.issues
      .map(({ message, path }) =>
        path?.length
          ? `${path.map((segment) => String(typeof segment === 'object' ? segment.key : segment)).join('.')}: ${message}`
          : message
      )
      .join('; ')

    throw new Error(`Response does not match the schema: ${detail}`, { cause: { issues: result.issues } })
  }

  return result.value
};

/**
 * Evaluate Feature Flags (GET)
 * 
 * GET /flags
 * 
 * Also accepts auth: ServiceAccount
 */
export const getApiFlags = async (args: GetApiFlagsArgs, options?: GetApiFlagsOptions) => {
const {baseUrl = "https://mixpanel.com/api/query", fetch: fetchFn = fetch, ProjectSecret} = options ?? {}

const query = new URLSearchParams()
const headers = new Headers()
headers.set('accept', "application/json")

if (args.token != null) query.append("token", String(args.token))
if (args.context != null) query.append("context", String(args.context))
if (ProjectSecret !== undefined) headers.set('authorization', `Basic ${btoa(`${ProjectSecret.username}:${ProjectSecret.password}`)}`)

const url = `${baseUrl.replace(/\/+$/, '')}/flags${query.size > 0 ? `?${query}` : ''}`

const res = await fetchFn(url, {method: "GET", headers})

if (!res.ok) throw new Error(`Request failed with status ${res.status}`, {cause: {status: res.status, body: await res.text()}})

return validateResponse(evaluateFlagsResponse, await res.json())
};