# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

"""
Support for optimizing tasks based on the set of files that have changed.
"""

import functools
import logging
import os
from subprocess import CalledProcessError

from mozpack.path import join as join_path
from mozpack.path import match as mozpackmatch
from mozversioncontrol import InvalidRepoPath, get_repository_object

from gecko_taskgraph import GECKO
from gecko_taskgraph.util.hg import get_json_pushchangedfiles

logger = logging.getLogger(__name__)


@functools.cache
def get_changed_files(repository, revision):
    """
    Get the set of files changed in the push headed by the given revision.
    Responses are cached, so multiple calls with the same arguments are OK.
    """
    try:
        return get_json_pushchangedfiles(repository, revision)["files"]
    except KeyError:
        # We shouldn't hit this error in CI.
        if os.environ.get("MOZ_AUTOMATION"):
            raise

        # We're likely on an unpublished commit, grab changed files from
        # version control.
        return get_locally_changed_files(GECKO)


def check(params, file_patterns):
    """Determine whether any of the files changed in the indicated push to
    https://hg.mozilla.org match any of the given file patterns."""
    repository = params.get("head_repository")
    revision = params.get("head_rev")
    if not repository or not revision:
        logger.warning(
            "Missing `head_repository` or `head_rev` parameters; "
            "assuming all files have changed"
        )
        return True

    changed_files = get_changed_files(repository, revision)

    if "comm_head_repository" in params:
        repository = params.get("comm_head_repository")
        revision = params.get("comm_head_rev")
        if not revision:
            logger.warning(
                "Missing `comm_head_rev` parameters; assuming all files have changed"
            )
            return True

        changed_files |= {
            join_path("comm", file) for file in get_changed_files(repository, revision)
        }

    for pattern in file_patterns:
        for path in changed_files:
            if mozpackmatch(path, pattern):
                return True

    return False


def _get_locally_changed_files(repo):
    try:
        vcs = get_repository_object(repo)
        s = set(vcs.get_outgoing_files("AM"))
        return s
    except (InvalidRepoPath, CalledProcessError):
        return set()


class PreloadedGetLocallyChangedFiles:
    """
    Function-like class that performs eager computation of _get_locally_changed_files
    for what looks the default repo.

    The rationale is the following:
    - computing _get_locally_changed_files is relatively slow (~600ms)
    - it's already done through an external command

    So we do that in a background thread as soon as possible, so that at the
    point when we need the result, it's already "prefetched".
    """

    def __init__(self):
        self.preloaded_repo = None
        self.preloading_thread = None
        self.preloaded_answer = None

    def preload(self, repo):
        """
        Fire off preloading of get_locally_changed_files(repo).

        For the sake of simplicity, there can be only one preloaded repo.
        """
        import threading
        from pathlib import Path

        if self.preloaded_repo is not None:
            raise ValueError("Can only preload one repo")

        self.preloaded_repo = Path(repo)

        def preloading():
            self.preloaded_answer = _get_locally_changed_files(self.preloaded_repo)

        self.preloading_thread = threading.Thread(target=preloading, daemon=True)
        self.preloading_thread.start()

    @functools.cache
    def __call__(self, repo):
        if repo == self.preloaded_repo:
            # A thread can be joined many times, but it's going to happen only
            # once, thanks to @memoize.
            self.preloading_thread.join()
            return self.preloaded_answer
        return _get_locally_changed_files(repo)


get_locally_changed_files = PreloadedGetLocallyChangedFiles()