#!/bin/bash
set -euo pipefail

create_branch() {
    local base=$1
    local branch=$2
    git checkout -b $branch $base
    touch $branch
    git add $branch
    git commit $branch -m "Create $branch"
}

merge() {
    local branch=$1
    git merge --no-ff "$branch" -m "Merging $branch"
}

rm -rf demo
mkdir demo
cd demo

git init
touch README
git add README
git commit -m "Init" README

create_branch master topic1
create_branch topic1 topic1-1
create_branch master topic2

git checkout topic1
merge topic1-1

git checkout master
merge topic1

# Create two branches pointing to the same commit
create_branch master duplicate1
git branch duplicate2
git checkout master