Rebases a branch and manages history when the target branch rebases itself off another one

git-smart-rebase

#!/usr/bin/env bash

# Fail on first non-zero exit code
set -e

setup_colors() {
  if [[ -t 2 ]] && [[ -z "${NO_COLOR-}" ]] && [[ "${TERM-}" != "dumb" ]]; then
    NOFORMAT='\033[0m' RED='\033[0;31m' GREEN='\033[0;32m' ORANGE='\033[0;33m' BLUE='\033[0;34m' PURPLE='\033[0;35m' CYAN='\033[0;36m' YELLOW='\033[1;33m'
  else
    NOFORMAT='' RED='' GREEN='' ORANGE='' BLUE='' PURPLE='' CYAN='' YELLOW=''
  fi
}

msg() {
  PREFIX=
  [[ "$1" == "-n" ]] && { PREFIX=$1; shift; }
  echo >&2 -e $PREFIX "${1-}"
}

setup_colors

# This will also issue a warning if we are not currently in a git repository
git_dir=$(git rev-parse --absolute-git-dir)
# Get the first argument of the script
rebase_branch="$1"
# Display a warning if the argument wasn't provided
if [[ -z "$rebase_branch" ]]; then
    msg "${RED}⚠️ Please provide a branch name to rebase onto${NOFORMAT}"
    exit 1
fi
# Exit if $rebase_branch contains whitespaces
if [[ "$rebase_branch" =~ \  ]]; then
  msg "${RED}Are you sure you want whitespaces in the branch name? 🧐${NOFORMAT}"
  exit 1
fi

current_branch=$(git branch --show-current)

# Filename matching the current branch with the one provided
file=$git_dir/rebase-$current_branch-on-$rebase_branch

prompt_last_commit_hash() {
  msg "${BLUE}What is the last commit hash of ${YELLOW}$rebase_branch${BLUE} you have on your branch (${YELLOW}$current_branch${BLUE})?${NOFORMAT}"
  read -r -p ">> " last_hash
  msg "${BLUE}Saving hash in $file...${NOFORMAT}"
  echo $last_hash > $file
}

# Record the last hash the branch was rebased on if we did not save it last time
if [[ ! -f "$file" ]]; then
  prompt_last_commit_hash
else
  last_hash=$(cat $file)
  msg "${BLUE}Hello back! It seems your branch was last rebased on this commit:${NOFORMAT}"
  git --no-pager log -1 --oneline $last_hash
  read -r -p "Can you confirm? [Y/N] " answer
  if [[ "$answer" =~ ^([yY][eE][sS]|[yY])$ ]]; then
    msg "${BLUE}Great! ✨${NOFORMAT}"
  elif [[ "$answer" =~ ^([nN][oO]|[nN])$ ]]; then
    prompt_last_commit_hash
  else
    msg "${RED}Invalid answer!${NOFORMAT}"
    exit 1
  fi
fi

msg "${PURPLE}[1/3] Fetching remote changes...${NOFORMAT}"
git fetch -p

# Do the actual rebase
msg "${PURPLE}[2/3] Rebasing ${YELLOW}$current_branch${PURPLE} onto ${YELLOW}origin/$rebase_branch${PURPLE} based on commit ${YELLOW}$last_hash${PURPLE}...${NOFORMAT}"
git rebase --onto origin/$rebase_branch $last_hash

# Remember what is the last commit of origin/$rebase_branch for next time
msg "${BLUE}[3/3] Saving the last commit hash of origin/$rebase_branch for next time...${NOFORMAT}"
msg "${BLUE}      (in $file)${NOFORMAT}"
origin_last_hash=$(git rev-parse origin/$rebase_branch)
echo $origin_last_hash > $file

msg "${GREEN}Rebase successful! 🎉${NOFORMAT}"