preBuild.doLast {
    // get the current commit hash in git
    def git_version = new ByteArrayOutputStream()
    exec {
        commandLine 'git', 'log', '-1', '--format=%h'
        standardOutput = git_version
    }
    git_version = git_version.toString().trim()

    // get the current git branch, if any
    def git_branch = new ByteArrayOutputStream()
    exec {
        commandLine 'git', 'symbolic-ref', '--short', '-q', 'HEAD'
        standardOutput = git_branch
        // ignore error output as we might not be on a branch
        ignoreExitValue = true
    }

    // if we are not on a branch, try to get a tag for the commit
    def git_branch_or_tag
    if (git_branch.size() > 0) {
        git_branch_or_tag = git_branch.toString().trim()
    } else {
        def git_tag = new ByteArrayOutputStream()
        exec {
            commandLine 'git', 'describe', '--tags', '--exact-match'
            standardOutput = git_tag
            // ignore error output
            errorOutput = new ByteArrayOutputStream()
            ignoreExitValue = true
        }

        git_branch_or_tag = git_tag.toString().trim()
    }

    if (git_branch_or_tag.size() == 0) {
        git_branch_or_tag = "HEAD"
    }

    def build_time = new Date().toString()

    // save the combined build info into assets/build.info file
    def result_line = git_branch_or_tag + "-" + git_version + " (" +
            build_time + ")\n"
    def assetsDir = android.sourceSets.main.assets.srcDirs.toArray()[0]
    def buildInfoFile = new File(assetsDir, 'build.info').getAbsolutePath()
    new File(buildInfoFile).write(result_line)
}