# Copyright 2012 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

"""Functionality for mangling repository checkouts that are shared

In particular, this in combination w/ enter_chroot's mount binding, allows
us to access the same repo from inside and outside a chroot at the same time
"""

__all__ = ("RebuildRepoCheckout",)

import errno
import math
import os
import shutil

from chromite.lib import commandline
from chromite.lib import cros_build_lib
from chromite.lib import git
from chromite.lib import osutils


_CACHE_NAME = ".cros_projects.list"


def _FilterNonExistentProjects(project_dir, projects):
    for project in projects:
        if os.path.exists(os.path.join(project_dir, project)):
            yield project


def _CleanAlternates(projects, alt_root):
    alt_root = os.path.normpath(alt_root)

    projects = set(projects)
    # Ignore our cache.
    projects.add(_CACHE_NAME)
    required_directories = set(os.path.dirname(x) for x in projects)

    for abs_root, dirs, files in os.walk(alt_root):
        rel_root = abs_root[len(alt_root) :].strip("/")

        if rel_root not in required_directories:
            shutil.rmtree(abs_root)
            dirs[:] = []
            continue

        if rel_root:
            for filename in files:
                if os.path.join(rel_root, filename) not in projects:
                    os.unlink(os.path.join(abs_root, filename))


def _UpdateAlternatesDir(alternates_root, reference_maps, projects):
    is_mirror = {}
    for reference in reference_maps:
        base = os.path.join(reference, ".repo", "manifests.git")
        result = git.RunGit(
            base, ["config", "--local", "--get", "repo.mirror"], check=False
        )
        is_mirror[reference] = (
            result.returncode == 0 and result.stdout.strip() == "true"
        )

    for project in projects:
        alt_path = os.path.join(alternates_root, project)
        paths = []
        for k, v in reference_maps.items():
            if is_mirror[k]:
                # The layout when the reference is a repo mirror (--mirror).
                suffix = os.path.join(project, "objects")
            else:
                # The layout when the reference is a normal repo checkout.
                suffix = os.path.join(
                    ".repo", "project-objects", project, "objects"
                )

            if os.path.exists(os.path.join(k, suffix)):
                paths.append(os.path.join(v, suffix))

        osutils.SafeMakedirs(os.path.dirname(alt_path))
        osutils.WriteFile(alt_path, "%s\n" % ("\n".join(paths),), atomic=True)


def _UpdateGitAlternates(proj_root, projects):
    for project in projects:
        alt_path = os.path.join(
            proj_root, project, "objects", "info", "alternates"
        )
        tmp_path = "%s.tmp" % alt_path

        # Clean out any tmp files that may have existed prior.
        osutils.SafeUnlink(tmp_path)

        # The pathway is written relative to the alternates files absolute path;
        # literally, .repo/projects/chromite.git/objects/info/alternates.
        relpath = "../" * (project.count("/") + 4)
        relpath = os.path.join(relpath, "alternates", project)

        osutils.SafeMakedirs(os.path.dirname(tmp_path))
        os.symlink(relpath, tmp_path)
        os.rename(tmp_path, alt_path)


def _GetProjects(repo_root):
    # Note that we cannot rely upon projects.list, nor repo list, nor repo
    # forall here to be authoritative.
    # if we rely on the manifest contents, the local tree may not yet be
    # updated - thus if we drop the alternate for that project, that project is
    # no longer usable (which can tick off repo sync).
    # Thus, we just iterate over the raw underlying projects store, and generate
    # alternates for that; we regenerate based on either the manifest changing,
    # local_manifest having changed, or projects.list having changed (which
    # occurs during partial local repo syncs; aka repo sync chromite for
    # example).
    # Finally, note we have to truncate our mtime awareness to just integers;
    # this is required since utime isn't guaranteed to set floats, despite our
    # being able to get a float back from stat'ing.

    manifest_xml = os.path.join(repo_root, "manifest.xml")
    times = [os.lstat(manifest_xml).st_mtime, os.stat(manifest_xml).st_mtime]
    for path in ("local_manifest.xml", "project.list"):
        path = os.path.join(repo_root, path)
        if os.path.exists(path):
            times.append(os.stat(path).st_mtime)

    # Truncate to seconds.
    manifest_time = math.trunc(max(times))

    cache_path = os.path.join(repo_root, _CACHE_NAME)

    try:
        if math.trunc(os.stat(cache_path).st_mtime) == manifest_time:
            return osutils.ReadFile(cache_path).split()
    except EnvironmentError as e:
        if e.errno != errno.ENOENT:
            raise

    # The -a ! section of this find invocation is to block descent
    # into the actual git repository; for IO constrained systems,
    # this avoids a fairly large amount of inode/dentry load up.
    # TLDR; It's faster, don't remove it ;)
    data = cros_build_lib.run(
        [
            "find",
            "./",
            "-type",
            "d",
            "-name",
            "*.git",
            "-a",
            "!",
            "-wholename",
            "*/*.git/*",
            "-prune",
        ],
        cwd=os.path.join(repo_root, "project-objects"),
        capture_output=True,
        encoding="utf-8",
    )

    # Drop the leading ./ and the trailing .git
    data = [x[2:-4] for x in data.stdout.splitlines() if x]

    with open(cache_path, "w", encoding="utf-8") as f:
        f.write("\n".join(sorted(data)))

    # Finally, mark the cache with the time of the manifest.xml we examined.
    os.utime(cache_path, (manifest_time, manifest_time))
    return data


class Failed(Exception):
    """Exception used to fail out for a bad environment."""


def _RebuildRepoCheckout(target_root, reference_map, alternates_dir):
    repo_root = os.path.join(target_root, ".repo")
    proj_root = os.path.join(repo_root, "project-objects")

    manifest_path = os.path.join(repo_root, "manifest.xml")
    if not os.path.exists(manifest_path):
        raise Failed(
            "%r does not exist, thus cannot be a repo checkout" % manifest_path
        )

    projects = ["%s.git" % x for x in _GetProjects(repo_root)]
    projects = _FilterNonExistentProjects(proj_root, projects)
    projects = list(sorted(projects))

    if not osutils.SafeMakedirs(alternates_dir, 0o775):
        # We know the directory exists; thus cleanse out
        # dead alternates.
        _CleanAlternates(projects, alternates_dir)

    _UpdateAlternatesDir(alternates_dir, reference_map, projects)
    _UpdateGitAlternates(proj_root, projects)


def WalkReferences(repo_root, max_depth=5, suppress=()):
    """Given a repo checkout root, find the repos it references up to max_depth.

    Args:
        repo_root: The root of a repo checkout to start from
        max_depth: Git internally limits the max alternates depth to 5;
            this option exists to adjust how deep we're willing to look.
        suppress: List of repos already seen (and so to ignore).

    Returns:
        List of repository roots required for this repo_root.
    """

    original_root = repo_root
    seen = set(os.path.abspath(x) for x in suppress)

    for _x in range(0, max_depth):
        repo_root = os.path.abspath(repo_root)

        if repo_root in seen:
            # Cyclic reference graph; break out of it, if someone induced this
            # the necessary objects should be in place.  If they aren't, really
            # isn't much that can be done.
            return

        yield repo_root
        seen.add(repo_root)
        base = os.path.join(repo_root, ".repo", "manifests.git")
        result = git.RunGit(base, ["config", "repo.reference"], check=False)

        if result.returncode not in (0, 1):
            raise Failed(
                "Unexpected returncode %i from examining %s git "
                "repo.reference configuration" % (result.returncode, base)
            )

        repo_root = result.stdout.strip()
        if not repo_root:
            break

    else:
        raise Failed(
            "While tracing out the references of %s, we recursed more "
            "than the allowed %i times ending at %s"
            % (original_root, max_depth, repo_root)
        )


def RebuildRepoCheckout(
    repo_root, initial_reference, chroot_reference_root=None
):
    """Rebuild a repo checkout's 'alternate tree' rewriting the repo to use it

    Args:
        repo_root: absolute path to the root of a repository checkout.
        initial_reference: absolute path to the root of the repository that is
            shared.
        chroot_reference_root: if given, repo_root will have it's chroot
            alternates tree configured with this pathway, enabling repo access
            to work from within the chroot.
    """

    reference_roots = list(
        WalkReferences(initial_reference, suppress=[repo_root])
    )

    # Always rebuild the external alternates for any operation; 1) we don't want
    # external out of sync from chroot, 2) if this is the first conversion, if
    # we only update chroot it'll break external access to the repo.
    reference_map = dict((x, x) for x in reference_roots)
    rebuilds = [("alternates", reference_map)]
    if chroot_reference_root:
        alternates_dir = "chroot/alternates"
        base = os.path.join(
            chroot_reference_root, ".repo", "chroot", "external"
        )
        reference_map = dict(
            (x, "%s%i" % (base, idx + 1))
            for idx, x in enumerate(reference_roots)
        )
        rebuilds += [("chroot/alternates", reference_map)]

    for alternates_dir, reference_map in rebuilds:
        alternates_dir = os.path.join(repo_root, ".repo", alternates_dir)
        _RebuildRepoCheckout(repo_root, reference_map, alternates_dir)
    return reference_roots


def get_parser():
    """Return a command line parser"""
    parser = commandline.ArgumentParser(description=__doc__)
    parser.add_argument("repository_root", type="path")
    parser.add_argument("referenced_repository", type="path")
    parser.add_argument("chroot_path", type="path", nargs="?")
    return parser


def main(argv):
    """The main func!"""
    parser = get_parser()
    opts = parser.parse_args(argv)
    opts.Freeze()

    ret = RebuildRepoCheckout(
        opts.repository_root,
        opts.referenced_repository,
        chroot_reference_root=opts.chroot_path,
    )
    print("\n".join(ret))