import { getToken, invalidateToken } from './token.js';

export interface RateLimitInfo {
  cost: number;
  remaining: number;
  resetAt: string;
}

export class GithubError extends Error {}

let lastRateLimit: RateLimitInfo | null = null;

export function getLastRateLimit(): RateLimitInfo | null {
  return lastRateLimit;
}

export async function graphql<T>(
  query: string,
  variables: Record<string, unknown>,
): Promise<T> {
  for (let attempt = 0; ; attempt++) {
    const res = await fetch('https://api.github.com/graphql', {
      method: 'POST',
      headers: {
        authorization: `bearer ${getToken()}`,
        'content-type': 'application/json',
        'user-agent': 'pr-monitor',
      },
      body: JSON.stringify({ query, variables }),
    });

    if (res.status === 401 && attempt === 0) {
      invalidateToken();
      continue;
    }
    if (!res.ok) {
      throw new GithubError(`GitHub API ${res.status}: ${(await res.text()).slice(0, 300)}`);
    }

    const body = (await res.json()) as {
      data?: T & { rateLimit?: RateLimitInfo };
      errors?: { message: string }[];
    };
    // Partial data with errors (e.g. one inaccessible node) is usable; only fail when
    // there is no data at all.
    if (!body.data) {
      const msg = body.errors?.map((e) => e.message).join('; ') ?? 'no data returned';
      throw new GithubError(`GraphQL error: ${msg.slice(0, 500)}`);
    }
    if (body.data.rateLimit) {
      lastRateLimit = body.data.rateLimit;
      console.log(
        `[github] cost=${lastRateLimit.cost} remaining=${lastRateLimit.remaining}`,
      );
    }
    return body.data;
  }
}