const VERSION = "2.2.1";

/**
 * Some “list” response that can be paginated have a different response structure
 *
 * They have a `total_count` key in the response (search also has `incomplete_results`,
 * /installation/repositories also has `repository_selection`), as well as a key with
 * the list of the items which name varies from endpoint to endpoint.
 *
 * Octokit normalizes these responses so that paginated results are always returned following
 * the same structure. One challenge is that if the list response has only one page, no Link
 * header is provided, so this header alone is not sufficient to check wether a response is
 * paginated or not.
 *
 * We check if a "total_count" key is present in the response data, but also make sure that
 * a "url" property is not, as the "Get the combined status for a specific ref" endpoint would
 * otherwise match: https://developer.github.com/v3/repos/statuses/#get-the-combined-status-for-a-specific-ref
 */
function normalizePaginatedListResponse(response) {
    const responseNeedsNormalization = "total_count" in response.data && !("url" in response.data);
    if (!responseNeedsNormalization)
        return response;
    // keep the additional properties intact as there is currently no other way
    // to retrieve the same information.
    const incompleteResults = response.data.incomplete_results;
    const repositorySelection = response.data.repository_selection;
    const totalCount = response.data.total_count;
    delete response.data.incomplete_results;
    delete response.data.repository_selection;
    delete response.data.total_count;
    const namespaceKey = Object.keys(response.data)[0];
    const data = response.data[namespaceKey];
    response.data = data;
    if (typeof incompleteResults !== "undefined") {
        response.data.incomplete_results = incompleteResults;
    }
    if (typeof repositorySelection !== "undefined") {
        response.data.repository_selection = repositorySelection;
    }
    response.data.total_count = totalCount;
    return response;
}

function iterator(octokit, route, parameters) {
    const options = typeof route === "function"
        ? route.endpoint(parameters)
        : octokit.request.endpoint(route, parameters);
    const requestMethod = typeof route === "function" ? route : octokit.request;
    const method = options.method;
    const headers = options.headers;
    let url = options.url;
    return {
        [Symbol.asyncIterator]: () => ({
            next() {
                if (!url) {
                    return Promise.resolve({ done: true });
                }
                return requestMethod({ method, url, headers })
                    .then(normalizePaginatedListResponse)
                    .then((response) => {
                    // `response.headers.link` format:
                    // '<https://api.github.com/users/aseemk/followers?page=2>; rel="next", <https://api.github.com/users/aseemk/followers?page=2>; rel="last"'
                    // sets `url` to undefined if "next" URL is not present or `link` header is not set
                    url = ((response.headers.link || "").match(/<([^>]+)>;\s*rel="next"/) || [])[1];
                    return { value: response };
                });
            },
        }),
    };
}

function paginate(octokit, route, parameters, mapFn) {
    if (typeof parameters === "function") {
        mapFn = parameters;
        parameters = undefined;
    }
    return gather(octokit, [], iterator(octokit, route, parameters)[Symbol.asyncIterator](), mapFn);
}
function gather(octokit, results, iterator, mapFn) {
    return iterator.next().then((result) => {
        if (result.done) {
            return results;
        }
        let earlyExit = false;
        function done() {
            earlyExit = true;
        }
        results = results.concat(mapFn ? mapFn(result.value, done) : result.value.data);
        if (earlyExit) {
            return results;
        }
        return gather(octokit, results, iterator, mapFn);
    });
}

/**
 * @param octokit Octokit instance
 * @param options Options passed to Octokit constructor
 */
function paginateRest(octokit) {
    return {
        paginate: Object.assign(paginate.bind(null, octokit), {
            iterator: iterator.bind(null, octokit),
        }),
    };
}
paginateRest.VERSION = VERSION;

export { paginateRest };
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