git-describe-always

#! /usr/bin/env bash

# Author:  Thomas DEBESSE <dev@illwieckz.net>
# License: MIT

set -e
set -u

delta='false'
case "${1:-}" in
    '-d'|'--delta')
        delta='true'
        shift
        ;;
esac

ref="${1:-HEAD}"

version="$(git describe --tags --match 'v[0-9]*' "${ref}" 2>/dev/null || true)"

if [ -n "${version}" ]
then
    if "${delta}"
    then
        tag="$(git describe --tags --abbrev=0 --match 'v[0-9]*')"

        if [ "${tag}" = "${version}" ]
        then
            version="$(git tag --contains "${ref}" 2>/dev/null | egrep '^v[0-9].*' | head -n1)"
        fi
    fi
else
    echo 'warning: no tag found' >&2
    tag='0'

    count="$(git rev-list --count "${ref}" 2>/dev/null || true)"
    count="${count:-0}"

    id="$(git rev-list --abbrev-commit --abbrev=9 -n1 "${ref}" 2>/dev/null || true)"
    if [ -n "${id}" ]
    then
        id="g${id}"
    else
        echo 'warning: no commit found' >&2
        id="$(date --utc '+%Y%m%d-%H%M%S')"
    fi

    version="${tag}-${count}-${id}"
fi

if ! git status >/dev/null 2>&1
then
    if [ "${ref}" != 'HEAD' ]
    then
        echo 'error: not a git repository' >&2
        exit 1
    fi

    echo 'warning: not a git repository' >&2
    version+='0'
elif ! git diff --quiet 2>/dev/null
then
    echo 'warning: uncommited changes' >&2
    version+='-dirty'
elif ! git ls-files --other --directory --exclude-standard 2>/dev/null | sed q1 >/dev/null
then
    echo 'warning: untracked files' >&2
    version+='-dirty'
fi

echo "${version}"