#!/bin/bash
set -o errexit
set -o nounset
set -o pipefail

# For a tag to be considered suitable for release, it must start with
# the latter 'v' followed by a digit. Afterwards, any sequence of
# alphanumerics and '.', '+', '-', '~' are supported.
#
# Supported tag examples:
# v1.8-rc1
# v1.9~rc1
# v2
# v2.0
#
# Unsupported tag examples:
# 1.9
# 2.0
# release-test
TAG_REGEX='^v[[:digit:]][[:alnum:]\.\+\-\~]+$'

usage()
{
cat <<'EOF'
USAGE: get-version [OPTIONS]

DESCRIPTION:

OPTIONS:
  -h        Displays this help text.
  -p PREFIX Modify the version string for use with packages. Both Debian and
            Fedora packages have strict version requirements. If there exist
            no tags that reference this commit or the tags are not suitable
            for packages, use "$PREFIX-$GIT_SHORT_COMMIT" instead. The
            prefix must start with a number.
  -n        (Only works when used with -p). Use the nightly version format.
            This uses the format "$PREFIX-nightly-YYYYMMDD".
EOF
}

go_version()
{
  # `git describe --exact` will fail when no tags match the HEAD commit.
  # This is a supported scenario. So, this discards the return value.
  TAG=$(git describe --exact --tag HEAD 2>/dev/null || true)

  if [[ ${TAG} =~ ${TAG_REGEX} ]]
  then
    printf '%s\n' "${TAG}"
    return
  fi

  printf 'unknown\n'
}

package_version()
{
  # `git describe --exact` will fail when no tags match the HEAD commit.
  # This is a supported scenario. So, this discards the return value.
  TAG=$(git describe --exact --tag HEAD 2>/dev/null || true)

  if [[ ${TAG} =~ ${TAG_REGEX} ]]
  then
    # Debian package versions must start with a number; therefore, the
    # 'v' must be stripped from the tag.
    printf '%s\n' "${TAG:1}"
    return
  fi

  if [[ ${PACKAGE_VERSION_NIGHTLY:-} ]]
  then
    printf '%s-nightly-%s\n' "${PACKAGE_VERSION_PREFIX}" "$(date '+%Y%m%d')"
    return
  fi

  printf '%s-%s\n' "${PACKAGE_VERSION_PREFIX}" "$(git rev-parse --verify --short HEAD)"
}

while getopts 'hp:n' option
do
  case $option
  in
    n)
      PACKAGE_VERSION_NIGHTLY=1
      ;;
    p)
      PACKAGE_VERSION_PREFIX=${OPTARG}
      ;;
    h)
      usage && exit 0
      ;;
  esac
done

if [[ ${PACKAGE_VERSION_PREFIX:-} ]]
then
  package_version
else
  go_version
fi