// Code generated by @openmeter/typespec-typescript. DO NOT EDIT.

import { unwrap, type RequestOptions, type Result } from './types.js'

// A misbehaving server — inconsistent `meta.page.total`/`size`, or a
// `meta.page.next` cursor that never resolves to an empty page — would
// otherwise make these generators loop forever. 10,000 pages is far beyond
// any real OpenMeter list, so hitting it means the server's pagination
// contract broke, not that the caller has a legitimately large list.
const MAX_PAGINATION_PAGES = 10_000

export class PaginationLimitExceededError extends Error {
  constructor(limit: number) {
    super(
      `pagination exceeded the maximum of ${limit} pages; the server may be returning inconsistent pagination metadata`,
    )
    this.name = 'PaginationLimitExceededError'
  }
}

interface PageNumberEnvelope<TItem> {
  data: TItem[]
  meta: { page: { number: number; size: number; total: number } }
}

interface PageNumberRequest {
  page?: { number?: number; size?: number }
}

/**
 * Iterates every item of a page-number-paginated list operation, advancing
 * `page.number` from wherever the caller's own request starts. Every other
 * field on `request` — filters, sort, page.size — is sent unchanged on every
 * page fetch; only the page number advances. Stops on a page shorter than
 * the server's own reported `size` (including an empty page) or once the
 * running item count reaches the server's reported `total`, whichever comes
 * first — so a final page that exactly fills `total` does not trigger one
 * more, empty request.
 */
export async function* paginatePages<TItem, TReq extends PageNumberRequest>(
  fetchPage: (
    req: TReq,
    options?: RequestOptions,
  ) => Promise<Result<PageNumberEnvelope<TItem>>>,
  request: TReq,
  options?: RequestOptions,
): AsyncGenerator<TItem, void, undefined> {
  let req = request
  let seen = 0
  for (let page = 0; page < MAX_PAGINATION_PAGES; page++) {
    const res = unwrap(await fetchPage(req, options))
    yield* res.data
    seen += res.data.length
    const { number, size, total } = res.meta.page
    if (res.data.length === 0 || res.data.length < size || seen >= total) {
      return
    }
    req = { ...req, page: { ...req.page, number: number + 1 } } as TReq
  }
  throw new PaginationLimitExceededError(MAX_PAGINATION_PAGES)
}

interface CursorEnvelope<TItem> {
  data: TItem[]
  meta: { page: { next: string | null } }
}

interface CursorRequest {
  page?: { after?: string; before?: string; size?: number }
}

/**
 * Iterates every item of a cursor-paginated list operation, following
 * `meta.page.next` until the server stops returning one. Despite carrying a
 * `format: uri` annotation in the spec, `next` is the opaque cursor token the
 * API expects back verbatim in `page.after` on the following request — not a
 * URI to fetch directly. Every other field on `request` is sent unchanged on
 * every page fetch; only `page.after` advances.
 */
export async function* paginateCursor<TItem, TReq extends CursorRequest>(
  fetchPage: (
    req: TReq,
    options?: RequestOptions,
  ) => Promise<Result<CursorEnvelope<TItem>>>,
  request: TReq,
  options?: RequestOptions,
): AsyncGenerator<TItem, void, undefined> {
  let req = request
  for (let page = 0; page < MAX_PAGINATION_PAGES; page++) {
    const res = unwrap(await fetchPage(req, options))
    yield* res.data
    const next = res.meta.page.next
    if (!next) {
      return
    }
    req = { ...req, page: { ...req.page, after: next } } as TReq
  }
  throw new PaginationLimitExceededError(MAX_PAGINATION_PAGES)
}