#!/usr/bin/env bash

# ignore detached heads
if ! git symbolic-ref -q HEAD > /dev/null; then
  exit
fi

# ignore non-branch checkouts
if [[ "$3" != "1" ]]; then
  exit
fi

# skip if upstream is already set
if git rev-parse --verify --quiet '@{u}' > /dev/null 2>&1; then
  exit
fi

# use upstream/HEAD if it exists, otherwise origin/HEAD
if git show-ref --verify --quiet refs/remotes/upstream/HEAD; then
  git branch --set-upstream-to refs/remotes/upstream/HEAD
else
  git branch --set-upstream-to refs/remotes/origin/HEAD
fi