Bump semver tag in git

#!/usr/bin/env bash
set -e

USAGE_TEXT="Bump and tag the current repository using semantic versioning (https://semver.org/).

Usage: git-bump [options] [major|minor|patch]

Default: patch

Options:
  -n|--no-update  Don't update repository before tagging.
  -d|--dry-run    Show what the next version will be but do not tag and push the next version.
  -h|--help       Show this message and exit.
"

DRY_RUN=''
NO_UPDATE=''
ACTION='patch'

while [[ "$#" -gt "0" ]]; do
  case "$1" in
    major|minor|patch)
      ACTION="$1"
      shift
      ;;
    -n|--no-update)
      NO_UPDATE='yes'
      shift
      ;;
    -d|--dry-run)
      DRY_RUN='yes'
      shift
      ;;
    -h|--help)
      echo "$USAGE_TEXT"
      exit 0
      ;;
    *)
      echo "> Unknown option: $1"
      echo "$USAGE_TEXT"
      exit 1
      ;;
  esac
done

if [[ -z "$NO_UPDATE" ]]; then
  echo "> Updating repository..."
  git pull --rebase
fi

CURRENT_VERSION=$(git tag --sort=-version:refname --list "v[0-9]*" | head -n 1)
if [[ -z "$CURRENT_VERSION" ]]; then
  CURRENT_VERSION='v0.0.0'
fi

echo "> Current version is ${CURRENT_VERSION}"

# strip the leading "v"
CURRENT_VERSION="${CURRENT_VERSION:1}"
# replace period and split into parts
CURRENT_VERSION_PARTS=(${CURRENT_VERSION//./ })

MAJOR_PART=${CURRENT_VERSION_PARTS[0]}
MINOR_PART=${CURRENT_VERSION_PARTS[1]}
PATCH_PART=${CURRENT_VERSION_PARTS[2]}

case "$ACTION" in
  major)
    MAJOR_PART=$((MAJOR_PART+1))
    MINOR_PART='0'
    PATCH_PART='0'
    ;;
  minor)
    MINOR_PART=$((MINOR_PART+1))
    PATCH_PART='0'
    ;;
  *)
    PATCH_PART=$((PATCH_PART+1))
    ;;
esac

NEW_VERSION="v${MAJOR_PART}.${MINOR_PART}.${PATCH_PART}"
echo "> New version is $NEW_VERSION"

if [[ -z "$DRY_RUN" ]]; then
  echo "> Tagging repository..."
  git tag "$NEW_VERSION"
  git push origin "$NEW_VERSION"
fi