/**
 * @license
 * Copyright Google LLC All Rights Reserved.
 *
 * Use of this source code is governed by an MIT-style license that can be
 * found in the LICENSE file at https://angular.io/license
 */

import * as Octokit from '@octokit/rest';
import {GitClient} from '../../utils/git/index';

/** Thirty seconds in milliseconds. */
const THIRTY_SECONDS_IN_MS = 30000;

/** State of a pull request in Github. */
export type PullRequestState = 'merged'|'closed'|'open';

/** Gets whether a given pull request has been merged. */
export async function getPullRequestState(
    api: GitClient<boolean>, id: number): Promise<PullRequestState> {
  const {data} = await api.github.pulls.get({...api.remoteParams, pull_number: id});
  if (data.merged) {
    return 'merged';
  }
  // Check if the PR was closed more than 30 seconds ago, this extra time gives Github time to
  // update the closed pull request to be associated with the closing commit.
  // Note: a Date constructed with `null` creates an object at 0 time, which will never be greater
  // than the current date time.
  if (data.closed_at !== null &&
      (new Date(data.closed_at).getTime() < Date.now() - THIRTY_SECONDS_IN_MS)) {
    return await isPullRequestClosedWithAssociatedCommit(api, id) ? 'merged' : 'closed';
  }
  return 'open';
}

/**
 * Whether the pull request has been closed with an associated commit. This is usually
 * the case if a PR has been merged using the autosquash merge script strategy. Since
 * the merge is not fast-forward, Github does not consider the PR as merged and instead
 * shows the PR as closed. See for example: https://github.com/angular/angular/pull/37918.
 */
async function isPullRequestClosedWithAssociatedCommit(api: GitClient<boolean>, id: number) {
  const request =
      api.github.issues.listEvents.endpoint.merge({...api.remoteParams, issue_number: id});
  const events: Octokit.IssuesListEventsResponse = await api.github.paginate(request);
  // Iterate through the events of the pull request in reverse. We want to find the most
  // recent events and check if the PR has been closed with a commit associated with it.
  // If the PR has been closed through a commit, we assume that the PR has been merged
  // using the autosquash merge strategy. For more details. See the `AutosquashMergeStrategy`.
  for (let i = events.length - 1; i >= 0; i--) {
    const {event, commit_id} = events[i];
    // If we come across a "reopened" event, we abort looking for referenced commits. Any
    // commits that closed the PR before, are no longer relevant and did not close the PR.
    if (event === 'reopened') {
      return false;
    }
    // If a `closed` event is captured with a commit assigned, then we assume that
    // this PR has been merged properly.
    if (event === 'closed' && commit_id) {
      return true;
    }
    // If the PR has been referenced by a commit, check if the commit closes this pull
    // request. Note that this is needed besides checking `closed` as PRs could be merged
    // into any non-default branch where the `Closes <..>` keyword does not work and the PR
    // is simply closed without an associated `commit_id`. For more details see:
    // https://docs.github.com/en/enterprise/2.16/user/github/managing-your-work-on-github/closing-issues-using-keywords#:~:text=non-default.
    if (event === 'referenced' && commit_id &&
        await isCommitClosingPullRequest(api, commit_id, id)) {
      return true;
    }
  }
  return false;
}

/** Checks whether the specified commit is closing the given pull request. */
async function isCommitClosingPullRequest(api: GitClient<boolean>, sha: string, id: number) {
  const {data} = await api.github.repos.getCommit({...api.remoteParams, ref: sha});
  // Matches the closing keyword supported in commit messages. See:
  // https://docs.github.com/en/enterprise/2.16/user/github/managing-your-work-on-github/closing-issues-using-keywords.
  return data.commit.message.match(
      new RegExp(`(?:close[sd]?|fix(?:e[sd]?)|resolve[sd]?):? #${id}(?!\\d)`, 'i'));
}