#!/usr/bin/env python3

import base64
import json
import os
import re
import time
import urllib.parse
from datetime import datetime
from dataclasses import dataclass
from urllib.request import urlopen, Request
from urllib.error import HTTPError
from typing import Iterable, cast, Any, Callable, Dict, List, Optional, Tuple, Union
from gitutils import get_git_remote_name, get_git_repo_dir, patterns_to_regex, GitRepo
from functools import lru_cache
from warnings import warn


GH_PR_REVIEWS_FRAGMENT = """
fragment PRReviews on PullRequestReviewConnection {
  nodes {
    author {
      login
    }
    state
  }
  pageInfo {
    startCursor
    hasPreviousPage
  }
}
"""

GH_CHECKSUITES_FRAGMENT = """
fragment PRCheckSuites on CheckSuiteConnection {
  edges {
    node {
      app {
        name
        databaseId
      }
      workflowRun {
        workflow {
          name
        }
      }
      checkRuns(first: 50) {
        nodes {
          name
          conclusion
          detailsUrl
        }
        pageInfo {
          endCursor
          hasNextPage
        }
      }
      conclusion
      url
    }
    cursor
  }
  pageInfo {
    hasNextPage
  }
}
"""

GH_COMMIT_AUTHORS_FRAGMENT = """
fragment CommitAuthors on PullRequestCommitConnection {
  nodes {
    commit {
      author {
        user {
          login
        }
        email
        name
      }
      oid
    }
  }
  pageInfo {
    endCursor
    hasNextPage
  }
}
"""

GH_GET_PR_INFO_QUERY = GH_PR_REVIEWS_FRAGMENT + GH_CHECKSUITES_FRAGMENT + GH_COMMIT_AUTHORS_FRAGMENT + """
query ($owner: String!, $name: String!, $number: Int!) {
  repository(owner: $owner, name: $name) {
    pullRequest(number: $number) {
      closed
      isCrossRepository
      author {
        login
      }
      title
      body
      headRefName
      headRepository {
        nameWithOwner
      }
      baseRefName
      baseRepository {
        nameWithOwner
        isPrivate
        defaultBranchRef {
          name
        }
      }
      mergeCommit {
        oid
      }
      commits_with_authors:commits(first: 100) {
        ...CommitAuthors
        totalCount
      }
      commits(last: 1) {
        nodes {
          commit {
            checkSuites(first: 10) {
              ...PRCheckSuites
            }
            pushedDate
            oid
          }
        }
      }
      changedFiles
      files(first: 100) {
        nodes {
          path
        }
        pageInfo {
          endCursor
          hasNextPage
        }
      }
      reviews(last: 100) {
       ...PRReviews
      }
      comments(last: 5) {
        nodes {
          bodyText
          author {
            login
          }
          authorAssociation
          editor {
            login
          }
          databaseId
        }
        pageInfo {
          startCursor
          hasPreviousPage
        }
      }
    }
  }
}
"""

GH_GET_PR_NEXT_FILES_QUERY = """
query ($owner: String!, $name: String!, $number: Int!, $cursor: String!) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      files(first: 100, after: $cursor) {
        nodes {
          path
        }
        pageInfo {
          endCursor
          hasNextPage
        }
      }
    }
  }
}
"""

GH_GET_PR_NEXT_CHECKSUITES = GH_CHECKSUITES_FRAGMENT + """
query ($owner: String!, $name: String!, $number: Int!, $cursor: String!) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      commits(last: 1) {
        nodes {
          commit {
            oid
            checkSuites(first: 10, after: $cursor) {
              ...PRCheckSuites
            }
          }
        }
      }
    }
  }
}
"""

GH_GET_PR_NEXT_CHECK_RUNS = """
query ($owner: String!, $name: String!, $number: Int!, $cs_cursor: String, $cr_cursor: String!) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      commits(last: 1) {
        nodes {
          commit {
            oid
            checkSuites(first: 1, after: $cs_cursor) {
              nodes {
                checkRuns(first: 100, after: $cr_cursor) {
                  nodes {
                    name
                    conclusion
                    detailsUrl
                  }
                  pageInfo {
                    endCursor
                    hasNextPage
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}
"""


GH_GET_PR_PREV_COMMENTS = """
query ($owner: String!, $name: String!, $number: Int!, $cursor: String!) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      comments(last: 100, before: $cursor) {
        nodes {
          bodyText
          author {
            login
          }
          authorAssociation
          editor {
            login
          }
          databaseId
        }
        pageInfo {
          startCursor
          hasPreviousPage
        }
      }
    }
  }
}
"""

# This query needs read-org permission
GH_GET_TEAM_MEMBERS_QUERY = """
query($org: String!, $name: String!, $cursor: String) {
  organization(login: $org) {
    team(slug: $name) {
      members(first: 100, after: $cursor) {
        nodes {
          login
        }
        pageInfo {
          hasNextPage
          endCursor
        }
      }
    }
  }
}
"""

GH_GET_PR_NEXT_AUTHORS_QUERY = GH_COMMIT_AUTHORS_FRAGMENT + """
query ($owner: String!, $name: String!, $number: Int!, $cursor: String) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      commits_with_authors: commits(first: 100, after: $cursor) {
        ...CommitAuthors
      }
    }
  }
}
"""

GH_GET_PR_PREV_REVIEWS_QUERY = GH_PR_REVIEWS_FRAGMENT + """
query ($owner: String!, $name: String!, $number: Int!, $cursor: String!) {
  repository(name: $name, owner: $owner) {
    pullRequest(number: $number) {
      reviews(last: 100, before: $cursor) {
        ...PRReviews
      }
    }
  }
}
"""

RE_GHSTACK_HEAD_REF = re.compile(r"^(gh/[^/]+/[0-9]+/)head$")
RE_GHSTACK_DESC = re.compile(r'Stack.*:\r?\n(\* [^\r\n]+\r?\n)+', re.MULTILINE)
RE_PULL_REQUEST_RESOLVED = re.compile(
    r'Pull Request resolved: '
    r'https://github.com/(?P<owner>[^/]+)/(?P<repo>[^/]+)/pull/(?P<number>[0-9]+)',
    re.MULTILINE
)
RE_REVERT_CMD = re.compile(r"@pytorch(merge|)bot\s+revert\s+this")
RE_REVERT_CMD_CLI = re.compile(r"@pytorch(merge|)bot\s+revert\s+(-m.*-c.*|-c.*-m.*)")
RE_DIFF_REV = re.compile(r'^Differential Revision:.+?(D[0-9]+)', re.MULTILINE)

def _fetch_url(url: str, *,
               headers: Optional[Dict[str, str]] = None,
               data: Optional[Dict[str, Any]] = None,
               method: Optional[str] = None,
               reader: Callable[[Any], Any] = lambda x: x.read()) -> Any:
    if headers is None:
        headers = {}
    token = os.environ.get("GITHUB_TOKEN")
    if token is not None and url.startswith('https://api.github.com/'):
        headers['Authorization'] = f'token {token}'
    data_ = json.dumps(data).encode() if data is not None else None
    try:
        with urlopen(Request(url, headers=headers, data=data_, method=method)) as conn:
            return reader(conn)
    except HTTPError as err:
        if err.code == 403 and all(key in err.headers for key in ['X-RateLimit-Limit', 'X-RateLimit-Used']):
            print(f"Rate limit exceeded: {err.headers['X-RateLimit-Used']}/{err.headers['X-RateLimit-Limit']}")
        raise

def fetch_json(url: str,
               params: Optional[Dict[str, Any]] = None,
               data: Optional[Dict[str, Any]] = None) -> List[Dict[str, Any]]:
    headers = {'Accept': 'application/vnd.github.v3+json'}
    if params is not None and len(params) > 0:
        url += '?' + '&'.join(f"{name}={urllib.parse.quote(str(val))}" for name, val in params.items())
    return cast(List[Dict[str, Any]], _fetch_url(url, headers=headers, data=data, reader=json.load))

def fetch_json_dict(url: str,
                    params: Optional[Dict[str, Any]] = None,
                    data: Optional[Dict[str, Any]] = None) -> Dict[str, Any] :
    headers = {'Accept': 'application/vnd.github.v3+json'}
    if params is not None and len(params) > 0:
        url += '?' + '&'.join(f"{name}={urllib.parse.quote(str(val))}" for name, val in params.items())
    return cast(Dict[str, Any], _fetch_url(url, headers=headers, data=data, reader=json.load))

def _gh_post_comment(url: str, comment: str, dry_run: bool = False) -> List[Dict[str, Any]]:
    if dry_run:
        print(comment)
        return []
    return fetch_json(url, data={"body": comment})


def gh_post_pr_comment(org: str, project: str, pr_num: int, comment: str, dry_run: bool = False) -> List[Dict[str, Any]]:
    return _gh_post_comment(f'https://api.github.com/repos/{org}/{project}/issues/{pr_num}/comments', comment, dry_run)


def gh_post_commit_comment(org: str, project: str, sha: str, comment: str, dry_run: bool = False) -> List[Dict[str, Any]]:
    return _gh_post_comment(f'https://api.github.com/repos/{org}/{project}/commits/{sha}/comments', comment, dry_run)


def gh_add_labels(org: str, project: str, pr_num: int, labels: Union[str, List[str]]) -> None:
    fetch_json(f'https://api.github.com/repos/{org}/{project}/issues/{pr_num}/labels',
               data={"labels": labels})


def gh_graphql(query: str, **kwargs: Any) -> Dict[str, Any]:
    rc = _fetch_url("https://api.github.com/graphql", data={"query": query, "variables": kwargs}, reader=json.load)
    if "errors" in rc:
        raise RuntimeError(f"GraphQL query {query}, args {kwargs} failed: {rc['errors']}")
    return cast(Dict[str, Any], rc)


def gh_get_pr_info(org: str, proj: str, pr_no: int) -> Any:
    rc = gh_graphql(GH_GET_PR_INFO_QUERY, name=proj, owner=org, number=pr_no)
    return rc["data"]["repository"]["pullRequest"]


@lru_cache(maxsize=None)
def gh_get_team_members(org: str, name: str) -> List[str]:
    rc: List[str] = []
    team_members: Dict[str, Any] = {"pageInfo": {"hasNextPage": "true", "endCursor": None}}
    while bool(team_members["pageInfo"]["hasNextPage"]):
        query = gh_graphql(GH_GET_TEAM_MEMBERS_QUERY, org=org, name=name, cursor=team_members["pageInfo"]["endCursor"])
        team = query["data"]["organization"]["team"]
        if team is None:
            warn(f"Requested non-existing team {org}/{name}")
            return []
        team_members = team["members"]
        rc += [member["login"] for member in team_members["nodes"]]
    return rc


def parse_args() -> Any:
    from argparse import ArgumentParser
    parser = ArgumentParser("Merge PR into default branch")
    parser.add_argument("--dry-run", action="store_true")
    parser.add_argument("--on-green", action="store_true")
    parser.add_argument("--on-mandatory", action="store_true")
    parser.add_argument("--land-checks", action="store_true")
    parser.add_argument("--revert", action="store_true")
    parser.add_argument("--force", action="store_true")
    parser.add_argument("--comment-id", type=int)
    parser.add_argument("--reason", type=str)
    parser.add_argument("pr_num", type=int)
    return parser.parse_args()

def can_skip_internal_checks(pr: "GitHubPR", comment_id: Optional[int] = None) -> bool:
    if comment_id is None:
        return False
    comment = pr.get_comment_by_id(comment_id)
    if comment.editor_login is not None:
        return False
    return comment.author_login == "facebook-github-bot"


@dataclass
class GitHubComment:
    body_text: str
    author_login: str
    author_association: str
    editor_login: Optional[str]
    database_id: int


class GitHubPR:
    def __init__(self, org: str, project: str, pr_num: int) -> None:
        assert isinstance(pr_num, int)
        self.org = org
        self.project = project
        self.pr_num = pr_num
        self.info = gh_get_pr_info(org, project, pr_num)
        self.changed_files: Optional[List[str]] = None
        self.conclusions: Optional[Dict[str, Tuple[str, str]]] = None
        self.comments: Optional[List[GitHubComment]] = None
        self._authors: Optional[List[Tuple[str, str]]] = None
        self._reviews: Optional[List[Tuple[str, str]]] = None

    def is_closed(self) -> bool:
        return bool(self.info["closed"])

    def is_cross_repo(self) -> bool:
        return bool(self.info["isCrossRepository"])

    def base_ref(self) -> str:
        return cast(str, self.info["baseRefName"])

    def default_branch(self) -> str:
        return cast(str, self.info["baseRepository"]["defaultBranchRef"]["name"])

    def head_ref(self) -> str:
        return cast(str, self.info["headRefName"])

    def is_ghstack_pr(self) -> bool:
        return RE_GHSTACK_HEAD_REF.match(self.head_ref()) is not None

    def is_base_repo_private(self) -> bool:
        return bool(self.info["baseRepository"]["isPrivate"])

    def get_changed_files_count(self) -> int:
        return int(self.info["changedFiles"])

    def last_pushed_at(self) -> datetime:
        return datetime.fromisoformat(self.last_commit()['pushedDate'][:-1])

    def last_commit(self) -> Any:
        return self.info["commits"]["nodes"][-1]["commit"]

    def get_changed_files(self) -> List[str]:
        if self.changed_files is None:
            info = self.info
            self.changed_files = []
            # Do not try to fetch more than 10K files
            for _ in range(100):
                self.changed_files += [x["path"] for x in info["files"]["nodes"]]
                if not info["files"]["pageInfo"]["hasNextPage"]:
                    break
                rc = gh_graphql(GH_GET_PR_NEXT_FILES_QUERY,
                                name=self.project,
                                owner=self.org,
                                number=self.pr_num,
                                cursor=info["files"]["pageInfo"]["endCursor"])
                info = rc["data"]["repository"]["pullRequest"]

        if len(self.changed_files) != self.get_changed_files_count():
            raise RuntimeError("Changed file count mismatch")
        return self.changed_files

    def _get_reviews(self) -> List[Tuple[str, str]]:
        if self._reviews is None:
            self._reviews = []
            info = self.info
            for _ in range(100):
                nodes = info["reviews"]["nodes"]
                self._reviews = [(node["author"]["login"], node["state"]) for node in nodes] + self._reviews
                if not info["reviews"]["pageInfo"]["hasPreviousPage"]:
                    break
                rc = gh_graphql(GH_GET_PR_PREV_REVIEWS_QUERY,
                                name=self.project,
                                owner=self.org,
                                number=self.pr_num,
                                cursor=info["reviews"]["pageInfo"]["startCursor"])
                info = rc["data"]["repository"]["pullRequest"]
        reviews = {}
        for (author, state) in self._reviews:
            if state != "COMMENTED":
                reviews[author] = state
        return list(reviews.items())

    def get_approved_by(self) -> List[str]:
        return [login for (login, state) in self._get_reviews() if state == "APPROVED"]

    def get_commit_count(self) -> int:
        return int(self.info["commits_with_authors"]["totalCount"])

    def get_pr_creator_login(self) -> str:
        return cast(str, self.info["author"]["login"])

    def _fetch_authors(self) -> List[Tuple[str, str]]:
        if self._authors is not None:
            return self._authors
        authors: List[Tuple[str, str]] = []

        def add_authors(info: Dict[str, Any]) -> None:
            for node in info["commits_with_authors"]["nodes"]:
                author_node = node["commit"]["author"]
                user_node = author_node["user"]
                author = f"{author_node['name']} <{author_node['email']}>"
                if user_node is None:
                    # If author is not github user, user node will be null
                    authors.append(("", author))
                else:
                    authors.append((cast(str, user_node["login"]), author))

        info = self.info
        for _ in range(100):
            add_authors(info)
            if not info["commits_with_authors"]["pageInfo"]["hasNextPage"]:
                break
            rc = gh_graphql(GH_GET_PR_NEXT_AUTHORS_QUERY,
                            name=self.project,
                            owner=self.org,
                            number=self.pr_num,
                            cursor=info["commits_with_authors"]["pageInfo"]["endCursor"])
            info = rc["data"]["repository"]["pullRequest"]
        self._authors = authors
        return authors

    def get_committer_login(self, num: int = 0) -> str:
        return self._fetch_authors()[num][0]

    def get_committer_author(self, num: int = 0) -> str:
        return self._fetch_authors()[num][1]

    def get_checkrun_conclusions(self) -> Dict[str, Tuple[str, str]]:
        """ Returns dict of checkrun -> [conclusion, url] """
        if self.conclusions is not None:
            return self.conclusions
        orig_last_commit = self.info["commits"]["nodes"][-1]["commit"]
        checksuites = orig_last_commit["checkSuites"]
        conclusions = {}

        def add_conclusions(edges: List[Dict[str, Dict[str, Any]]]) -> None:
            for edge_idx, edge in enumerate(edges):
                node = edge["node"]
                workflow_run = node["workflowRun"]
                checkruns = node["checkRuns"]
                if workflow_run is not None:
                    conclusions[workflow_run["workflow"]["name"]] = (node["conclusion"], node["url"])
                has_failing_check = False
                while checkruns is not None:
                    for checkrun_node in checkruns["nodes"]:
                        if checkrun_node["conclusion"] == 'FAILURE':
                            has_failing_check = True
                        conclusions[checkrun_node["name"]] = (checkrun_node["conclusion"], checkrun_node["detailsUrl"])
                    if bool(checkruns["pageInfo"]["hasNextPage"]):
                        rc = gh_graphql(GH_GET_PR_NEXT_CHECK_RUNS,
                                        name=self.project,
                                        owner=self.org,
                                        number=self.pr_num,
                                        cs_cursor=edges[edge_idx - 1]["cursor"] if edge_idx > 0 else None,
                                        cr_cursor=checkruns["pageInfo"]["endCursor"])
                        last_commit = rc["data"]["repository"]["pullRequest"]["commits"]["nodes"][-1]["commit"]
                        checkruns = last_commit["checkSuites"]["nodes"][-1]["checkRuns"]
                    else:
                        checkruns = None
                # Github doesn't set conclusion to failure if a job is still pending
                if workflow_run is not None and has_failing_check:
                    conclusions[workflow_run["workflow"]["name"]] = ("FAILURE", node["url"])

        add_conclusions(checksuites["edges"])
        while bool(checksuites["pageInfo"]["hasNextPage"]):
            rc = gh_graphql(GH_GET_PR_NEXT_CHECKSUITES,
                            name=self.project,
                            owner=self.org,
                            number=self.pr_num,
                            cursor=checksuites["edges"][-1]["cursor"])
            info = rc["data"]["repository"]["pullRequest"]
            last_commit = info["commits"]["nodes"][-1]["commit"]
            if last_commit["oid"] != orig_last_commit["oid"]:
                raise RuntimeError("Last commit changed on PR")
            checksuites = last_commit["checkSuites"]
            add_conclusions(checksuites["edges"])
        self.conclusions = conclusions
        return conclusions

    def get_authors(self) -> Dict[str, str]:
        rc = {}
        # TODO: replace with  `self.get_commit_count()` when GraphQL pagination can be used
        # to fetch all commits, see https://gist.github.com/malfet/4f35321b0c9315bcd7116c7b54d83372
        # and https://support.github.com/ticket/enterprise/1642/1659119
        if self.get_commit_count() <= 250:
            assert len(self._fetch_authors()) == self.get_commit_count()
        for idx in range(len(self._fetch_authors())):
            rc[self.get_committer_login(idx)] = self.get_committer_author(idx)

        return rc

    def get_author(self) -> str:
        authors = self.get_authors()
        if len(authors) == 1:
            return next(iter(authors.values()))
        creator = self.get_pr_creator_login()
        # If PR creator is not among authors
        # Assume it was authored by first commit author
        if creator not in authors:
            return self.get_committer_author(0)
        return authors[creator]

    def get_title(self) -> str:
        return cast(str, self.info["title"])

    def get_body(self) -> str:
        return cast(str, self.info["body"])

    def get_merge_commit(self) -> Optional[str]:
        mc = self.info["mergeCommit"]
        return mc["oid"] if mc is not None else None

    def get_pr_url(self) -> str:
        return f"https://github.com/{self.org}/{self.project}/pull/{self.pr_num}"

    @staticmethod
    def _comment_from_node(node: Any) -> GitHubComment:
        editor = node["editor"]
        return GitHubComment(body_text=node["bodyText"],
                             author_login=node["author"]["login"],
                             author_association=node["authorAssociation"],
                             editor_login=editor["login"] if editor else None,
                             database_id=node["databaseId"]
                             )

    def get_comments(self) -> List[GitHubComment]:
        if self.comments is not None:
            return self.comments
        self.comments = []
        info = self.info["comments"]
        # Do not try to fetch more than 10K comments
        for _ in range(100):
            self.comments = [self._comment_from_node(node) for node in info["nodes"]] + self.comments
            if not info["pageInfo"]["hasPreviousPage"]:
                break
            rc = gh_graphql(GH_GET_PR_PREV_COMMENTS,
                            name=self.project,
                            owner=self.org,
                            number=self.pr_num,
                            cursor=info["pageInfo"]["startCursor"])
            info = rc["data"]["repository"]["pullRequest"]["comments"]
        return self.comments

    def get_last_comment(self) -> GitHubComment:
        return self._comment_from_node(self.info["comments"]["nodes"][-1])

    def get_comment_by_id(self, database_id: int) -> GitHubComment:
        if self.comments is None:
            # Fastpath - try searching in partial prefetched comments
            for node in self.info["comments"]["nodes"]:
                comment = self._comment_from_node(node)
                if comment.database_id == database_id:
                    return comment

        for comment in self.get_comments():
            if comment.database_id == database_id:
                return comment
        raise RuntimeError(f"Comment with id {database_id} not found")

    def get_diff_revision(self) -> Optional[str]:
        rc = RE_DIFF_REV.search(self.get_body())
        return rc.group(1) if rc is not None else None

    def has_internal_changes(self) -> bool:
        checkrun_name = "Meta Internal-Only Changes Check"
        if self.get_diff_revision() is None:
            return False
        checks = self.get_checkrun_conclusions()
        if checks is None or checkrun_name not in checks:
            return False
        return checks[checkrun_name][0] != "SUCCESS"

    def merge_ghstack_into(self, repo: GitRepo, force: bool, comment_id: Optional[int] = None) -> None:
        assert self.is_ghstack_pr()
        approved_by = self.get_approved_by()
        # For ghstack, cherry-pick commits based from origin
        orig_ref = f"{repo.remote}/{re.sub(r'/head$', '/orig', self.head_ref())}"
        rev_list = repo.revlist(f"{self.default_branch()}..{orig_ref}")
        for idx, rev in enumerate(reversed(rev_list)):
            msg = repo.commit_message(rev)
            m = RE_PULL_REQUEST_RESOLVED.search(msg)
            if m is None:
                raise RuntimeError(f"Could not find PR-resolved string in {msg} of ghstacked PR {self.pr_num}")
            if self.org != m.group('owner') or self.project != m.group('repo'):
                raise RuntimeError(f"PR {m.group('number')} resolved to wrong owner/repo pair")
            pr_num = int(m.group('number'))
            commit_msg = self.gen_commit_message(filter_ghstack=True)
            if pr_num != self.pr_num:
                pr = GitHubPR(self.org, self.project, pr_num)
                if pr.is_closed():
                    print(f"Skipping {idx+1} of {len(rev_list)} PR (#{pr_num}) as its already been merged")
                    continue
                commit_msg = pr.gen_commit_message(filter_ghstack=True)
                # Raises exception if matching rule is not found
                find_matching_merge_rule(pr, repo, force=force, skip_internal_checks=can_skip_internal_checks(self, comment_id))

            repo.cherry_pick(rev)
            repo.amend_commit_message(commit_msg)

    def gen_commit_message(self, filter_ghstack: bool = False) -> str:
        """ Fetches title and body from PR description
            adds reviewed by, pull request resolved and optionally
            filters out ghstack info """
        # Adding the url here makes it clickable within the Github UI
        approved_by_urls = ', '.join(prefix_with_github_url(login) for login in self.get_approved_by())
        msg = self.get_title() + f" (#{self.pr_num})\n\n"
        msg += self.get_body() if not filter_ghstack else re.sub(RE_GHSTACK_DESC, "", self.get_body())
        msg += f"\nPull Request resolved: {self.get_pr_url()}\n"
        msg += f"Approved by: {approved_by_urls}\n"
        return msg

    def merge_into(self, repo: GitRepo, *,
                   force: bool = False,
                   dry_run: bool = False,
                   comment_id: Optional[int] = None) -> None:
        # Raises exception if matching rule is not found
        find_matching_merge_rule(self, repo, force=force, skip_internal_checks=can_skip_internal_checks(self, comment_id))
        self.merge_changes(repo, force, comment_id)

        repo.push(self.default_branch(), dry_run)
        gh_post_pr_comment(self.org, self.project, self.pr_num,
                           f"@{self.get_pr_creator_login()} your PR has been successfully merged.", dry_run)
        if not dry_run:
            gh_add_labels(self.org, self.project, self.pr_num, ["merged"])

    def merge_changes(self,
                      repo: GitRepo,
                      force: bool = False,
                      comment_id: Optional[int] = None,
                      branch: Optional[str] = None) -> None:
        branch_to_merge_into = self.default_branch() if branch is None else branch
        if repo.current_branch() != branch_to_merge_into:
            repo.checkout(branch_to_merge_into)
        if not self.is_ghstack_pr():
            msg = self.gen_commit_message()
            pr_branch_name = f"__pull-request-{self.pr_num}__init__"
            repo.fetch(f"pull/{self.pr_num}/head", pr_branch_name)
            repo._run_git("merge", "--squash", pr_branch_name)
            repo._run_git("commit", f"--author=\"{self.get_author()}\"", "-m", msg)
        else:
            self.merge_ghstack_into(repo, force, comment_id=comment_id)

    def create_land_time_check_branch(self,
                                      repo: GitRepo,
                                      branch: str,
                                      force: bool = False,
                                      comment_id: Optional[int] = None,) -> str:
        self.merge_changes(repo, branch=branch, force=force, comment_id=comment_id)
        land_check_branch = f'landchecks/{self.pr_num}'
        try:
            repo._run_git('branch', "-D", land_check_branch)
        except Exception:
            pass
        repo._run_git('checkout', "-b", land_check_branch)
        repo._run_git('push', '-u', 'origin', land_check_branch, '--force')
        commit = repo.get_commit('HEAD').commit_hash
        gh_post_pr_comment(self.org, self.project, self.pr_num,
                           'Successfully started land time checks.' +
                           f' See progress here: https://hud.pytorch.org/{self.org}/{self.project}/commit/{commit}')
        return commit


class MandatoryChecksMissingError(Exception):
    pass


@dataclass
class MergeRule:
    name: str
    patterns: List[str]
    approved_by: List[str]
    mandatory_checks_name: Optional[List[str]]


def read_merge_rules(repo: Optional[GitRepo], org: str, project: str) -> List[MergeRule]:
    from pathlib import Path

    repo_relative_rules_path = Path(".github") / "merge_rules.json"
    if repo is None:
        json_data = _fetch_url(
            f"https://api.github.com/repos/{org}/{project}/contents/{repo_relative_rules_path}",
            headers={'Accept': 'application/vnd.github.v3+json'},
            reader=json.load,
        )
        content = base64.b64decode(json_data["content"])
        return cast(List[MergeRule], json.loads(content, object_hook=lambda x: MergeRule(**x)))
    else:
        rules_path = Path(repo.repo_dir) / repo_relative_rules_path
        if not rules_path.exists():
            print(f"{rules_path} does not exist, returning empty rules")
            return []
        with open(rules_path) as fp:
            rc = json.load(fp, object_hook=lambda x: MergeRule(**x))
        return cast(List[MergeRule], rc)


def find_matching_merge_rule(pr: GitHubPR,
                             repo: Optional[GitRepo] = None,
                             force: bool = False,
                             skip_internal_checks: bool = False
                             ) -> MergeRule:
    """Returns merge rule matching to this pr or raises an exception"""
    changed_files = pr.get_changed_files()
    approved_by = set(pr.get_approved_by())
    rules = read_merge_rules(repo, pr.org, pr.project)
    reject_reason = f"PR {pr.pr_num} does not match merge rules"
    #  Used to determine best rejection reason
    # Score 0 to 10K - how many files rule matched
    # Score 10K - matched all files, but no overlapping approvers
    # Score 20K - matched all files and approvers, but mandatory checks are pending
    # Score 30k - Matched all files and approvers, but mandatory checks failed
    reject_reason_score = 0
    for rule in rules:
        rule_name = rule.name
        patterns_re = patterns_to_regex(rule.patterns)
        non_matching_files = []
        for fname in changed_files:
            if not patterns_re.match(fname):
                non_matching_files.append(fname)
        if len(non_matching_files) > 0:
            num_matching_files = len(changed_files) - len(non_matching_files)
            if num_matching_files > reject_reason_score:
                reject_reason_score = num_matching_files
                reject_reason = (f"{num_matching_files} files matched rule {rule_name}, but there are still non-matching files: " +
                                 f"{','.join(non_matching_files[:5])}{', ...' if len(non_matching_files) > 5 else ''}")
            continue
        # If rule needs approvers but PR has not been reviewed, skip it
        if len(rule.approved_by) > 0 and len(approved_by) == 0:
            if reject_reason_score < 10000:
                reject_reason_score = 10000
                reject_reason = f"Matched rule {rule_name}, but PR #{pr.pr_num} has not been reviewed yet"
            continue

        rule_approvers_set = set()
        for approver in rule.approved_by:
            if "/" in approver:
                org, name = approver.split("/")
                rule_approvers_set.update(gh_get_team_members(org, name))
            else:
                rule_approvers_set.add(approver)
        approvers_intersection = approved_by.intersection(rule_approvers_set)
        # If rule requires approvers but they aren't the ones that reviewed PR
        if len(approvers_intersection) == 0 and len(rule_approvers_set) > 0:
            if reject_reason_score < 10000:
                reject_reason_score = 10000
                reject_reason = (f"Matched rule {rule_name}, but PR #{pr.pr_num} was not reviewed yet by any of: " +
                                 f"{', '.join(list(rule_approvers_set)[:5])}{', ...' if len(rule_approvers_set) > 5 else ''}")
            continue
        mandatory_checks = rule.mandatory_checks_name if rule.mandatory_checks_name is not None else []
        checks = pr.get_checkrun_conclusions()
        required_checks = filter(lambda x: force is False or "CLA Check" in x, mandatory_checks)
        [pending_checks, failed_checks] = categorize_checks(checks, required_checks)

        if len(failed_checks) > 0:
            if reject_reason_score < 30000:
                reject_reason_score = 30000
                reject_reason = ("Refusing to merge as mandatory check(s) " +
                                 checks_to_str(failed_checks) + f" failed for rule {rule_name}")
            continue
        elif len(pending_checks) > 0:
            if reject_reason_score < 20000:
                reject_reason_score = 20000
                reject_reason = f"Refusing to merge as mandatory check(s) {checks_to_str(pending_checks)}"
                reject_reason += f" are pending/not yet run for rule {rule_name}"
            continue
        if not skip_internal_checks and pr.has_internal_changes():
            raise RuntimeError("This PR has internal changes and must be landed via Phabricator")
        return rule
    if reject_reason_score == 20000:
        raise MandatoryChecksMissingError(reject_reason)
    raise RuntimeError(reject_reason)


def checks_to_str(checks: List[Tuple[str, Optional[str]]]) -> str:
    return ", ".join(f"[{c[0]}]({c[1]})" if c[1] is not None else c[0] for c in checks)

def pr_get_checks_with_lambda(pr: GitHubPR, status_check: Callable[[Optional[str]], bool]) -> List[Tuple[str, str]]:
    checks = pr.get_checkrun_conclusions()
    return [(name, status[1]) for name, status in checks.items() if status_check(status[0])]


def pr_get_pending_checks(pr: GitHubPR) -> List[Tuple[str, str]]:
    return pr_get_checks_with_lambda(pr, lambda x: x is None)


def pr_get_failed_checks(pr: GitHubPR) -> List[Tuple[str, str]]:
    return pr_get_checks_with_lambda(pr, lambda x: x == "FAILURE")


def try_revert(repo: GitRepo, pr: GitHubPR, *,
               dry_run: bool = False,
               comment_id: Optional[int] = None,
               reason: Optional[str] = None) -> None:
    def post_comment(msg: str) -> None:
        gh_post_pr_comment(pr.org, pr.project, pr.pr_num, msg, dry_run=dry_run)
    if not pr.is_closed():
        return post_comment(f"Can't revert open PR #{pr.pr_num}")
    comment = pr.get_last_comment() if comment_id is None else pr.get_comment_by_id(comment_id)
    if not RE_REVERT_CMD.match(comment.body_text) and not RE_REVERT_CMD_CLI.match(comment.body_text):
        raise RuntimeError(f"Comment {comment.body_text} does not seem to be a valid revert command")
    if comment.editor_login is not None:
        return post_comment("Don't want to revert based on edited command")
    author_association = comment.author_association
    author_login = comment.author_login
    # For some reason, one can not be a member of private repo, only CONTRIBUTOR
    expected_association = "CONTRIBUTOR" if pr.is_base_repo_private() else "MEMBER"
    if author_association != expected_association and author_association != "OWNER":
        return post_comment(f"Will not revert as @{author_login} is not a {expected_association}, but {author_association}")
    skip_internal_checks = can_skip_internal_checks(pr, comment_id)

    # Raises exception if matching rule is not found, but ignores all status checks
    find_matching_merge_rule(pr, repo, force=True, skip_internal_checks=skip_internal_checks)
    commit_sha = pr.get_merge_commit()
    if commit_sha is None:
        commits = repo.commits_resolving_gh_pr(pr.pr_num)
        if len(commits) == 0:
            raise RuntimeError("Can't find any commits resolving PR")
        commit_sha = commits[0]
    msg = repo.commit_message(commit_sha)
    rc = RE_DIFF_REV.search(msg)
    if rc is not None and not can_skip_internal_checks:
        raise RuntimeError(f"Can't revert PR that was landed via phabricator as {rc.group(1)}")
    revert_msg = f"\nReverted {pr.get_pr_url()} on behalf of {prefix_with_github_url(author_login)}"
    revert_msg += f" due to {reason}\n" if reason is not None else "\n"
    repo.checkout(pr.default_branch())
    repo.revert(commit_sha)
    msg = repo.commit_message("HEAD")
    msg = re.sub(RE_PULL_REQUEST_RESOLVED, "", msg)
    msg += revert_msg
    repo.amend_commit_message(msg)
    repo.push(pr.default_branch(), dry_run)
    post_comment(f"@{pr.get_pr_creator_login()} your PR has been successfully reverted.")
    if not dry_run:
        gh_add_labels(pr.org, pr.project, pr.pr_num, ["reverted"])
        gh_post_commit_comment(pr.org, pr.project, commit_sha, revert_msg)


def prefix_with_github_url(suffix_str: str) -> str:
    return f"https://github.com/{suffix_str}"

def check_for_sev(org: str, project: str, force: bool) -> None:
    if force:
        return
    response = cast(
        Dict[str, Any],
        fetch_json(
            "https://api.github.com/search/issues",
            params={"q": f'repo:{org}/{project} is:open is:issue label:"ci: sev"'},
        ),
    )
    if response["total_count"] != 0:
        for item in response["items"]:
            if "merge blocking" in item["body"].lower():
                raise RuntimeError(
                    "Not merging any PRs at the moment because there is a "
                    + "merge blocking https://github.com/pytorch/pytorch/labels/ci:%20sev issue open at: \n"
                    + f"{item['html_url']}"
                )
    return

def fetch_check_run_conclusions(repo: GitRepo, commit: str) -> Dict[str, Tuple[str, str]]:
    [owner, name] = repo.gh_owner_and_name()
    checks = fetch_json_dict(f'https://api.github.com/repos/{owner}/{name}/commits/{commit}/check-runs')
    check_run_conclusions = {}
    if len(checks) == 0:
        raise MandatoryChecksMissingError("Refusing to merge as land check(s) are not yet run")
    for check_run in checks['check_runs']:
        check_run_conclusions[check_run['name']] = (check_run['conclusion'],
                                                    check_run['html_url'])
    return check_run_conclusions

def validate_land_time_checks(repo: GitRepo, commit: str) -> None:
    checks = fetch_check_run_conclusions(repo, commit)
    [pending_checks, failed_checks] = categorize_checks(checks, checks)

    if len(failed_checks) > 0:
        raise RuntimeError(f"Failed to merge; some land checks failed: {checks_to_str(failed_checks)}")
    if len(pending_checks) > 0:
        raise MandatoryChecksMissingError(f"Refusing to merge as land check(s) {checks_to_str(pending_checks)} are not yet run")

def categorize_checks(check_runs: Dict[str, Tuple[str, str]],
                      required_checks: Iterable[str]) -> Tuple[List[Tuple[str, Optional[str]]], List[Tuple[str, Optional[str]]]]:
    pending_checks: List[Tuple[str, Optional[str]]] = []
    failed_checks: List[Tuple[str, Optional[str]]] = []
    for checkname in required_checks:
        if checkname not in check_runs:
            pending_checks.append((checkname, None))
        elif check_runs[checkname][0] is None:
            pending_checks.append((checkname, check_runs[checkname][1]))
        elif check_runs[checkname][0].upper() != 'SUCCESS' and check_runs[checkname][0].upper() != 'SKIPPED':
            failed_checks.append((checkname, check_runs[checkname][1]))
    return (pending_checks, failed_checks)

def merge(pr_num: int, repo: GitRepo,
          dry_run: bool = False,
          force: bool = False,
          comment_id: Optional[int] = None,
          mandatory_only: bool = False,
          on_green: bool = False,
          land_checks: bool = False,
          timeout_minutes: int = 400,
          stale_pr_days: int = 3) -> None:
    repo = GitRepo(get_git_repo_dir(), get_git_remote_name())
    org, project = repo.gh_owner_and_name()
    pr = GitHubPR(org, project, pr_num)
    initial_commit_sha = pr.last_commit()['oid']
    check_for_sev(org, project, force)
    if force or can_skip_internal_checks(pr, comment_id):
        # do not wait for any pending signals if PR is closed as part of co-development process
        return pr.merge_into(repo, dry_run=dry_run, force=force, comment_id=comment_id)
    if (datetime.utcnow() - pr.last_pushed_at()).days > stale_pr_days:
        raise RuntimeError("This PR is too stale; the last push date was more than 3 days ago. Please rebase and try again.")

    if land_checks:
        commit = pr.create_land_time_check_branch(repo, 'viable/strict', force=force, comment_id=comment_id)

    start_time = time.time()
    last_exception = ''
    elapsed_time = 0.0
    while elapsed_time < timeout_minutes * 60:
        check_for_sev(org, project, force)
        current_time = time.time()
        elapsed_time = current_time - start_time
        print(f"Attempting merge of https://github.com/{org}/{project}/pull/{pr_num} ({elapsed_time / 60} minutes elapsed)")
        pr = GitHubPR(org, project, pr_num)
        if initial_commit_sha != pr.last_commit()['oid']:
            raise RuntimeError("New commits were pushed while merging. Please rerun the merge command.")
        try:
            find_matching_merge_rule(pr, repo)
            pending = pr_get_pending_checks(pr)
            failing = pr_get_failed_checks(pr)

            if (not mandatory_only and on_green) and len(failing) > 0:
                raise RuntimeError(f"{len(failing)} additional jobs have failed, first few of them are: " +
                                   ' ,'.join(f"[{x[0]}]({x[1]})" for x in failing[:5]))
            if (not mandatory_only and on_green) and len(pending) > 0:
                raise MandatoryChecksMissingError(f"Still waiting for {len(pending)} additional jobs to finish, " +
                                                  f"first few of them are: {' ,'.join(x[0] for x in pending[:5])}")
            if land_checks:
                validate_land_time_checks(repo, commit)

            return pr.merge_into(repo, dry_run=dry_run, force=force, comment_id=comment_id)
        except MandatoryChecksMissingError as ex:
            last_exception = str(ex)
            print(f"Merge of https://github.com/{org}/{project}/pull/{pr_num} failed due to: {ex}. Retrying in 5 min")
            time.sleep(5 * 60)
    # Finally report timeout back
    msg = f"Merged timed out after {timeout_minutes} minutes. Please contact the pytorch_dev_infra team."
    msg += f"The last exception was: {last_exception}"
    if not dry_run:
        gh_add_labels(org, project, pr_num, ["land-failed"])
    raise RuntimeError(msg)

def main() -> None:
    args = parse_args()
    repo = GitRepo(get_git_repo_dir(), get_git_remote_name())
    org, project = repo.gh_owner_and_name()
    pr = GitHubPR(org, project, args.pr_num)

    def handle_exception(e: Exception, msg: str = "Merge failed") -> None:
        msg += f" due to {e}"
        run_url = os.getenv("GH_RUN_URL")
        if run_url is not None:
            msg += f"\nRaised by {run_url}"
        gh_post_pr_comment(org, project, args.pr_num, msg, dry_run=args.dry_run)
        import traceback
        traceback.print_exc()

    msg = f"@pytorchbot successfully started a {'revert' if args.revert else 'merge'} job."
    msg += f" Check the current status [here]({os.getenv('GH_RUN_URL')})"
    gh_post_pr_comment(org, project, args.pr_num, msg, dry_run=args.dry_run)

    if args.revert:
        try:
            try_revert(repo, pr, dry_run=args.dry_run, comment_id=args.comment_id, reason=args.reason)
        except Exception as e:
            handle_exception(e, f"Reverting PR {args.pr_num} failed")
        return

    if pr.is_closed():
        gh_post_pr_comment(org, project, args.pr_num, f"Can't merge closed PR #{args.pr_num}", dry_run=args.dry_run)
        return

    if pr.is_cross_repo() and pr.is_ghstack_pr():
        gh_post_pr_comment(org, project, args.pr_num, "Cross-repo ghstack merges are not supported", dry_run=args.dry_run)
        return

    try:
        merge(args.pr_num, repo,
              dry_run=args.dry_run,
              force=args.force,
              comment_id=args.comment_id,
              on_green=args.on_green,
              mandatory_only=args.on_mandatory,
              land_checks=args.land_checks)
    except Exception as e:
        handle_exception(e)


if __name__ == "__main__":
    main()