#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright 2020 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Checks for various upstream events with the Rust toolchain.

Sends an email if something interesting (probably) happened.
"""

import argparse
import itertools
import json
import logging
import pathlib
import re
import shutil
import subprocess
import sys
import time
from typing import Any, Dict, Iterable, List, NamedTuple, Optional, Tuple

from cros_utils import bugs
from cros_utils import email_sender
from cros_utils import tiny_render


def gentoo_sha_to_link(sha: str) -> str:
    """Gets a URL to a webpage that shows the Gentoo commit at `sha`."""
    return f"https://gitweb.gentoo.org/repo/gentoo.git/commit?id={sha}"


def send_email(subject: str, body: List[tiny_render.Piece]) -> None:
    """Sends an email with the given title and body to... whoever cares."""
    email_sender.EmailSender().SendX20Email(
        subject=subject,
        identifier="rust-watch",
        well_known_recipients=["cros-team"],
        text_body=tiny_render.render_text_pieces(body),
        html_body=tiny_render.render_html_pieces(body),
    )


class RustReleaseVersion(NamedTuple):
    """Represents a version of Rust's stable compiler."""

    major: int
    minor: int
    patch: int

    @staticmethod
    def from_string(version_string: str) -> "RustReleaseVersion":
        m = re.match(r"(\d+)\.(\d+)\.(\d+)", version_string)
        if not m:
            raise ValueError(f"{version_string!r} isn't a valid version string")
        return RustReleaseVersion(*[int(x) for x in m.groups()])

    def __str__(self) -> str:
        return f"{self.major}.{self.minor}.{self.patch}"

    def to_json(self) -> str:
        return str(self)

    @staticmethod
    def from_json(s: str) -> "RustReleaseVersion":
        return RustReleaseVersion.from_string(s)


class State(NamedTuple):
    """State that we keep around from run to run."""

    # The last Rust release tag that we've seen.
    last_seen_release: RustReleaseVersion

    # We track Gentoo's upstream Rust ebuild. This is the last SHA we've seen
    # that updates it.
    last_gentoo_sha: str

    def to_json(self) -> Dict[str, Any]:
        return {
            "last_seen_release": self.last_seen_release.to_json(),
            "last_gentoo_sha": self.last_gentoo_sha,
        }

    @staticmethod
    def from_json(s: Dict[str, Any]) -> "State":
        return State(
            last_seen_release=RustReleaseVersion.from_json(
                s["last_seen_release"]
            ),
            last_gentoo_sha=s["last_gentoo_sha"],
        )


def parse_release_tags(lines: Iterable[str]) -> Iterable[RustReleaseVersion]:
    """Parses `git ls-remote --tags` output into Rust stable release versions."""
    refs_tags = "refs/tags/"
    for line in lines:
        _sha, tag = line.split(None, 1)
        tag = tag.strip()
        # Each tag has an associated 'refs/tags/name^{}', which is the actual
        # object that the tag points to. That's irrelevant to us.
        if tag.endswith("^{}"):
            continue

        if not tag.startswith(refs_tags):
            continue

        short_tag = tag[len(refs_tags) :]
        # There are a few old versioning schemes. Ignore them.
        if short_tag.startswith("0.") or short_tag.startswith("release-"):
            continue
        yield RustReleaseVersion.from_string(short_tag)


def fetch_most_recent_release() -> RustReleaseVersion:
    """Fetches the most recent stable `rustc` version."""
    result = subprocess.run(
        ["git", "ls-remote", "--tags", "https://github.com/rust-lang/rust"],
        check=True,
        stdin=None,
        capture_output=True,
        encoding="utf-8",
    )
    tag_lines = result.stdout.strip().splitlines()
    return max(parse_release_tags(tag_lines))


class GitCommit(NamedTuple):
    """Represents a single git commit."""

    sha: str
    subject: str


def update_git_repo(git_dir: pathlib.Path) -> None:
    """Updates the repo at `git_dir`, retrying a few times on failure."""
    for i in itertools.count(start=1):
        result = subprocess.run(
            ["git", "fetch", "origin"],
            check=False,
            cwd=str(git_dir),
            stdin=None,
        )

        if not result.returncode:
            break

        if i == 5:
            # 5 attempts is too many. Something else may be wrong.
            result.check_returncode()

        sleep_time = 60 * i
        logging.error(
            "Failed updating gentoo's repo; will try again in %ds...",
            sleep_time,
        )
        time.sleep(sleep_time)


def get_new_gentoo_commits(
    git_dir: pathlib.Path, most_recent_sha: str
) -> List[GitCommit]:
    """Gets commits to dev-lang/rust since `most_recent_sha`.

    Older commits come earlier in the returned list.
    """
    commits = subprocess.run(
        [
            "git",
            "log",
            "--format=%H %s",
            f"{most_recent_sha}..origin/master",  # nocheck
            "--",
            "dev-lang/rust",
        ],
        capture_output=True,
        check=False,
        cwd=str(git_dir),
        encoding="utf-8",
    )

    if commits.returncode:
        logging.error(
            "Error getting new gentoo commits; stderr:\n%s", commits.stderr
        )
        commits.check_returncode()

    results = []
    for line in commits.stdout.strip().splitlines():
        sha, subject = line.strip().split(None, 1)
        results.append(GitCommit(sha=sha, subject=subject))

    # `git log` outputs things in newest -> oldest order.
    results.reverse()
    return results


def setup_gentoo_git_repo(git_dir: pathlib.Path) -> str:
    """Sets up a gentoo git repo at the given directory. Returns HEAD."""
    subprocess.run(
        [
            "git",
            "clone",
            "https://anongit.gentoo.org/git/repo/gentoo.git",
            str(git_dir),
        ],
        stdin=None,
        check=True,
    )

    head_rev = subprocess.run(
        ["git", "rev-parse", "HEAD"],
        cwd=str(git_dir),
        check=True,
        stdin=None,
        capture_output=True,
        encoding="utf-8",
    )
    return head_rev.stdout.strip()


def read_state(state_file: pathlib.Path) -> State:
    """Reads state from the given file."""
    with state_file.open(encoding="utf-8") as f:
        return State.from_json(json.load(f))


def atomically_write_state(state_file: pathlib.Path, state: State) -> None:
    """Writes state to the given file."""
    temp_file = pathlib.Path(str(state_file) + ".new")
    with temp_file.open("w", encoding="utf-8") as f:
        json.dump(state.to_json(), f)
    temp_file.rename(state_file)


def file_bug(title: str, body: str) -> None:
    """Files update bugs with the given title/body."""
    # (component, optional_assignee)
    targets = (
        (bugs.WellKnownComponents.CrOSToolchainPublic, "gbiv@google.com"),
        (bugs.WellKnownComponents.AndroidRustToolchain, None),
    )
    for component, assignee in targets:
        bugs.CreateNewBug(component, title, body, assignee)


def maybe_compose_bug(
    old_state: State,
    newest_release: RustReleaseVersion,
) -> Optional[Tuple[str, str]]:
    """Creates a bug to file about the new release, if doing is desired."""
    if newest_release == old_state.last_seen_release:
        return None

    title = f"[Rust] Update to {newest_release}"
    body = (
        "A new Rust stable release has been detected; we should probably roll "
        "to it.\n"
        "\n"
        "The regression-from-stable-to-stable tag might be interesting to "
        "keep an eye on: https://github.com/rust-lang/rust/labels/"
        "regression-from-stable-to-stable\n"
        "\n"
        "For questions about this bot, please contact chromeos-toolchain@ and "
        "CC gbiv@."
    )
    return title, body


def maybe_compose_email(
    new_gentoo_commits: List[GitCommit],
) -> Optional[Tuple[str, List[tiny_render.Piece]]]:
    """Creates an email given our new state, if doing so is appropriate."""
    if not new_gentoo_commits:
        return None

    subject_pieces = []
    body_pieces = []

    # Separate the sections a bit for prettier output.
    if body_pieces:
        body_pieces += [tiny_render.line_break, tiny_render.line_break]

    if len(new_gentoo_commits) == 1:
        subject_pieces.append("new rust ebuild commit detected")
        body_pieces.append("commit:")
    else:
        subject_pieces.append("new rust ebuild commits detected")
        body_pieces.append("commits (newest first):")

    commit_lines = []
    for commit in new_gentoo_commits:
        commit_lines.append(
            [
                tiny_render.Link(
                    gentoo_sha_to_link(commit.sha),
                    commit.sha[:12],
                ),
                f": {commit.subject}",
            ]
        )

    body_pieces.append(tiny_render.UnorderedList(commit_lines))

    subject = "[rust-watch] " + "; ".join(subject_pieces)
    return subject, body_pieces


def main(argv: List[str]) -> None:
    logging.basicConfig(level=logging.INFO)

    parser = argparse.ArgumentParser(
        description=__doc__,
        formatter_class=argparse.RawDescriptionHelpFormatter,
    )
    parser.add_argument(
        "--state_dir", required=True, help="Directory to store state in."
    )
    parser.add_argument(
        "--skip_side_effects",
        action="store_true",
        help="Don't send an email or file a bug.",
    )
    parser.add_argument(
        "--skip_state_update",
        action="store_true",
        help="Don't update the state file. Doesn't apply to initial setup.",
    )
    opts = parser.parse_args(argv)

    state_dir = pathlib.Path(opts.state_dir)
    state_file = state_dir / "state.json"
    gentoo_subdir = state_dir / "upstream-gentoo"
    if not state_file.exists():
        logging.info("state_dir isn't fully set up; doing that now.")

        # Could be in a partially set-up state.
        if state_dir.exists():
            logging.info("incomplete state_dir detected; removing.")
            shutil.rmtree(str(state_dir))

        state_dir.mkdir(parents=True)
        most_recent_release = fetch_most_recent_release()
        most_recent_gentoo_commit = setup_gentoo_git_repo(gentoo_subdir)
        atomically_write_state(
            state_file,
            State(
                last_seen_release=most_recent_release,
                last_gentoo_sha=most_recent_gentoo_commit,
            ),
        )
        # Running through this _should_ be a nop, but do it anyway. Should make any
        # bugs more obvious on the first run of the script.

    prior_state = read_state(state_file)
    logging.info("Last state was %r", prior_state)

    most_recent_release = fetch_most_recent_release()
    logging.info("Most recent Rust release is %s", most_recent_release)

    logging.info("Fetching new commits from Gentoo")
    update_git_repo(gentoo_subdir)
    new_commits = get_new_gentoo_commits(
        gentoo_subdir, prior_state.last_gentoo_sha
    )
    logging.info("New commits: %r", new_commits)

    maybe_bug = maybe_compose_bug(prior_state, most_recent_release)
    maybe_email = maybe_compose_email(new_commits)

    if maybe_bug is None:
        logging.info("No bug to file")
    else:
        title, body = maybe_bug
        if opts.skip_side_effects:
            logging.info(
                "Skipping sending bug with title %r and contents\n%s",
                title,
                body,
            )
        else:
            logging.info("Writing new bug")
            file_bug(title, body)

    if maybe_email is None:
        logging.info("No email to send")
    else:
        title, body = maybe_email
        if opts.skip_side_effects:
            logging.info(
                "Skipping sending email with title %r and contents\n%s",
                title,
                tiny_render.render_html_pieces(body),
            )
        else:
            logging.info("Sending email")
            send_email(title, body)

    if opts.skip_state_update:
        logging.info("Skipping state update, as requested")
        return

    newest_sha = (
        new_commits[-1].sha if new_commits else prior_state.last_gentoo_sha
    )
    atomically_write_state(
        state_file,
        State(
            last_seen_release=most_recent_release,
            last_gentoo_sha=newest_sha,
        ),
    )


if __name__ == "__main__":
    sys.exit(main(sys.argv[1:]))