import org.gradle.api.provider.ValueSourceParameters
import javax.inject.Inject

// Must wrap this in a ValueSource in order to get well-defined fail behavior without confusing Gradle on repeat builds.
abstract class GitShaValueSource implements ValueSource<String, ValueSourceParameters.None> {
    @Inject abstract ExecOperations getExecOperations()

    @Override String obtain() {
        try {
            def output = new ByteArrayOutputStream()

            execOperations.exec {
                it.commandLine 'git', 'rev-parse', '--short=8', 'HEAD'
                it.standardOutput = output
            }
            return output.toString().trim()
        } catch (GradleException ignore) {
            // Git executable unavailable, or we are not building in a git repo. Fall through:
        }
        return "unknown"
    }
}

// Export closure
ext.getGitSha = {
    providers.of(GitShaValueSource) {}.get()
}