#!/usr/bin/env bash

# We want to catch any unexpected failure, and exit immediately
set -e

# Download helper for git, to be called from the download wrapper script
#
# Options:
#   -q          Be quiet.
#   -r          Clone and archive sub-modules.
#   -o FILE     Generate archive in FILE.
#   -u URI      Clone from repository at URI.
#   -c CSET     Use changeset CSET.
#   -n NAME     Use basename NAME.
#
# Environment:
#   GIT      : the git command to call

verbose=
recurse=0
while getopts "${BR_BACKEND_DL_GETOPTS}" OPT; do
    case "${OPT}" in
    q)  verbose=-q; exec >/dev/null;;
    r)  recurse=1;;
    o)  output="${OPTARG}";;
    u)  uri="${OPTARG}";;
    c)  cset="${OPTARG}";;
    d)  dl_dir="${OPTARG}";;
    n)  basename="${OPTARG}";;
    :)  printf "option '%s' expects a mandatory argument\n" "${OPTARG}"; exit 1;;
    \?) printf "unknown option '%s'\n" "${OPTARG}" >&2; exit 1;;
    esac
done

shift $((OPTIND-1)) # Get rid of our options

# We want to check if a cache of the git clone of this repo already exists.
git_cache="${dl_dir}/git"

# Caller needs to single-quote its arguments to prevent them from
# being expanded a second time (in case there are spaces in them)
_git() {
    eval GIT_DIR="${git_cache}/.git" ${GIT} "${@}"
}

# Initialise a repository in the git cache. If the repository already
# existed, this is a noop, unless the repository was broken, in which
# case this magically restores it to working conditions. In the latter
# case, we might be missing blobs, but that's not a problem: we'll
# fetch what we need later anyway.
#
# We can still go through the wrapper, because 'init' does not use the
# path pointed to by GIT_DIR, but really uses the directory passed as
# argument.
_git init "'${git_cache}'"

pushd "${git_cache}" >/dev/null

# Ensure the repo has an origin (in case a previous run was killed).
if ! _git remote |grep -q -E '^origin$'; then
    _git remote add origin "'${uri}'"
fi

_git remote set-url origin "'${uri}'"

# Try to fetch with limited depth, since it is faster than a full clone - but
# that only works if the version is a ref (tag or branch). Before trying to do
# a shallow clone we check if ${cset} is in the list provided by git ls-remote.
# If not we fallback to a full fetch.
#
# Messages for the type of clone used are provided to ease debugging in
# case of problems
git_done=0
if [ -n "$(_git ls-remote origin "'${cset}'" 2>&1)" ]; then
    printf "Doing a shallow fetch\n"
    if _git fetch "${@}" --depth 1 origin "'${cset}'"; then
        git_done=1
    else
        printf "Shallow fetch failed, falling back to fetching all refs\n"
    fi
fi
if [ ${git_done} -eq 0 ]; then
    printf "Fetching all references\n"
    _git fetch origin
    _git fetch origin -t
fi

# Try to get the special refs exposed by some forges (pull-requests for
# github, changes for gerrit...). There is no easy way to know whether
# the cset the user passed us is such a special ref or a tag or a sha1
# or whatever else. We'll eventually fail at checking out that cset,
# below, if there is an issue anyway. Since most of the cset we're gonna
# have to clone are not such special refs, consign the output to oblivion
# so as not to alarm unsuspecting users, but still trace it as a warning.
if ! _git fetch origin "'${cset}:${cset}'" >/dev/null 2>&1; then
    printf "Could not fetch special ref '%s'; assuming it is not special.\n" "${cset}"
fi

# Checkout the required changeset, so that we can update the required
# submodules.
_git checkout -q "'${cset}'"

# Get date of commit to generate a reproducible archive.
# %cD is RFC2822, so it's fully qualified, with TZ and all.
date="$( _git log -1 --pretty=format:%cD )"

# There might be submodules, so fetch them.
if [ ${recurse} -eq 1 ]; then
    _git submodule update --init --recursive
fi

# Generate the archive, sort with the C locale so that it is reproducible.
# We do not want the .git dir; we keep other .git files, in case they are the
# only files in their directory.
# The .git dir would generate non reproducible tarballs as it depends on
# the state of the remote server. It also would generate large tarballs
# (gigabytes for some linux trees) when a full clone took place.
find . -not -type d \
	-and -not -path "./.git/*" >"${output}.list"
LC_ALL=C sort <"${output}.list" >"${output}.list.sorted"

# Create GNU-format tarballs, since that's the format of the tarballs on
# sources.buildroot.org and used in the *.hash files
tar cf - --transform="s#^\./#${basename}/#" \
         --numeric-owner --owner=0 --group=0 --mtime="${date}" --format=gnu \
         -T "${output}.list.sorted" >"${output}.tar"
gzip -6 -n <"${output}.tar" >"${output}"

rm -f "${output}.list"
rm -f "${output}.list.sorted"

popd >/dev/null