#!/usr/bin/env bash

set -euo pipefail

if [[ $# -eq 0 ]]; then
  targetBranch=$(git rev-parse --abbrev-ref HEAD)
else
  targetBranch=$1
  git checkout "$targetBranch"
fi

git for-each-ref refs/heads/ "--format=%(refname:short)" | while read -r branch; do
    mergeBase=$(git merge-base "$targetBranch" "$branch")

    if [[ $(git cherry "$targetBranch" "$(git commit-tree "$(git rev-parse "$branch^{tree}")" -p "$mergeBase" -m _)") == "-"* ]]; then
        git branch -D "$branch"
    fi
done