text: from __future__ import annotations
  
  import pathlib
  import random
  import sys
  
  import typing
  from typing import (
      AbstractSet,
      Container,
      FrozenSet,
      Iterable,
      Tuple,
  )
  
  import gidgethub.abc
  import gidgethub.httpx
  import gidgethub.actions
  import httpx
  import trio
  import yaml
  
  
  class ConfigData(typing.TypedDict):
  
      """Dict representation of assign-reviers.yml."""
  
      numberOfReviewers: int
      team: list[str]
      reviewers: list[str]
  
  
  async def already_reviewed(gh: gidgethub.abc.GitHubAPI) -> FrozenSet[str]:
      """Get the list of people who have already left a review."""
      event = gidgethub.actions.event()
      reviews = gh.getiter(
          "/repos/{owner}/{repo}/pulls/{pull_number}/reviews",
          url_vars={
              "owner": event["repository"]["owner"]["login"],
              "repo": event["repository"]["name"],
              "pull_number": event["pull_request"]["number"],
          },
      )
      reviewers = set()
      # GitHub provides the complete history of reviews for a PR in
      # chronological order.
      async for review in reviews:
          reviewer = review["user"]["login"]
          # A comment is not a review.
          if review["state"] == "COMMENTED":
              continue
          else:
              reviewers.add(reviewer)
  
      return frozenset(reviewers)
  
  
  def select_reviewers(
      *,
      author: str,
      available_reviewers: AbstractSet[str],
      assigned_reviewers: AbstractSet[str],
      already_reviewers: AbstractSet[str],
      count: int,
  ) -> Tuple[FrozenSet[str], FrozenSet[str]]:
      """Select people to review the PR.
  
      If the author is a potential reviewer, remove them from contention. Also
      deduct the number of reviewers necessary based on any that have already
      been asked to review who are also eligible to review or have already
      reviewed.
  
      """
      already_reviewing = frozenset(
          (available_reviewers & assigned_reviewers)
          | (available_reviewers & already_reviewers)
      )
      potential_reviewers = set(available_reviewers)  # Mutable copy.
      potential_reviewers -= already_reviewing
      potential_reviewers.discard(author)
      print("Potential reviewers (left):", potential_reviewers)
      print(f"Want {count} reviewers")
      count -= len(already_reviewing)
      print(f"Need {count} more reviewers")
      selected_reviewers = []
      while count > 0 and potential_reviewers:
          selected = random.choice(list(potential_reviewers))
          potential_reviewers.discard(selected)
          selected_reviewers.append(selected)
          count -= 1
      selected_reviewers = frozenset(selected_reviewers)
      print("Reviewers to add:", select_reviewers)
      return already_reviewing | selected_reviewers, selected_reviewers
  
  
  async def add_assignee(
      gh: gidgethub.abc.GitHubAPI, team: Container[str], reviewers: Iterable[str]
  ) -> None:
      """Assign the PR.
  
      For team members, assign to themselves. For external PRs, randomly select
      one of the reviewers.
  
      """
      event = gidgethub.actions.event()
      if (assignee := event["pull_request"]["user"]["login"]) not in team:
          assignee = random.choice(list(reviewers))
      await gh.post(
          "/repos/{owner}/{repo}/issues/{issue_number}/assignees",
          url_vars={
              "owner": event["repository"]["owner"]["login"],
              "repo": event["repository"]["name"],
              "issue_number": event["pull_request"]["number"],
          },
          data={"assignees": [assignee]},
      )
  
  
  async def add_reviewers(
      gh: gidgethub.abc.GitHubAPI, reviewers_to_add: Iterable[str]
  ) -> None:
      """Add reviewers to a PR."""
      event = gidgethub.actions.event()
      await gh.post(
          "/repos/{owner}/{repo}/pulls/{pull_number}/requested_reviewers",
          url_vars={
              "owner": event["repository"]["owner"]["login"],
              "repo": event["repository"]["name"],
              "pull_number": event["pull_request"]["number"],
          },
          data={"reviewers": list(reviewers_to_add)},
      )
  
  
  async def main(token: str):
      config_file = pathlib.Path(__file__).parent.parent / "assign-reviewers.yml"
      with config_file.open(encoding="utf-8") as file:
          config: ConfigData = yaml.safe_load(file)
      event = gidgethub.actions.event()
      author = event["pull_request"]["user"]["login"]
      available_reviewers = frozenset(config["reviewers"])
      print("Available reviewers:", available_reviewers)
      assigned_reviewers = {
          reviewer["login"] for reviewer in event["pull_request"]["requested_reviewers"]
      }
      print("Reviewers already requested:", assigned_reviewers)
      async with httpx.AsyncClient(timeout=None) as client:
          gh = gidgethub.httpx.GitHubAPI(
              client, event["repository"]["full_name"], oauth_token=token
          )
          already_reviewers = await already_reviewed(gh)
          print("People who have already reviewed:", already_reviewers)
          team_reviewers, reviewers_to_add = select_reviewers(
              author=author,
              available_reviewers=available_reviewers,
              assigned_reviewers=assigned_reviewers,
              already_reviewers=already_reviewers,
              count=int(config["numberOfReviewers"]),
          )
          async with trio.open_nursery() as nursery:
              if not event["pull_request"]["assignee"]:
                  nursery.start_soon(
                      add_assignee, gh, frozenset(config["team"]), team_reviewers
                  )
              if reviewers_to_add and not event["pull_request"]["draft"]:
                  nursery.start_soon(add_reviewers, gh, reviewers_to_add)
              else:
                  print("No reviewers to add or PR is in draft")
  
  
  if __name__ == "__main__":
      trio.run(main, sys.argv[1])
  