path: root/git-update-agent

#!/bin/sh

# GLOBAL VARIABLES:
# - AGENT:           Name of the project which is receiving updates (for display purposes)
# - UPSTREAM_BRANCH: The branch in the upstream repo used for updates (defaults to remote's head if set)
# - REMOTE:          Name of the remote used for updates
# - REMOTE_URL:      Name of URL used for synchronization

# USAGE:
#
# Initialize a project:
# git-update-agent --init https://git.mydomain.com
#
# Update:
# git-update-agent

CMD_PROMPT="[#] "
PROGRAM="${0##*/}"

die () {
  if [[ $# -eq 0 ]]; then
    echo -n "$PROGRAM: " 1>&2
    cat <&0 1>&2
  elif [[ $# -eq 1 ]]; then
    echo "$PROGRAM: $1" 1>&2
  fi

  exit 1
}

depends() {
  if ! type "$1" >/dev/null; then
    die "\"$1\" must be installed and in your \$PATH"
  fi
}

cmd() {
  echo "$CMD_PROMPT $*"
  "$@"
}

stash() {
  if ! git                                \
    -c "user.email=git-updater@localhost" \
    -c "user.name=git-updater"            \
    stash save --include-untracked &>/dev/null
  then

  die <<_EOF
Could not stash in $(pwd)
Please stash/commit manually if you need to keep your changes. If you would like to destroy all changes, run:
cd $(pwd)
git reset --hard origin/main
_EOF

  fi
}

current_version() {
  git rev-parse -q --verify HEAD
}
      
die_no_upstream_found() {
  die <<_EOF
origin/HEAD is used as the reference for updates
origin/HEAD is not set and UPSTREAM_BRANCH override not provided

You can set the upstream branch with:
git remote set-head <name> <branch>
_EOF
}

upstream_branch() {
  local upstream_branch
  local remote

  remote="$1"


  if [[ -z "$UPSTREAM_BRANCH" ]]; then
    upstream_branch="$(git symbolic-ref "refs/remotes/$remote/HEAD" 2>/dev/null)"
    upstream_branch="${upstream_branch#refs/remotes/$remote/}"
  else
    upstream_branch="$UPSTREAM_BRANCH"
  fi

  echo "$upstream_branch"
}

local_branch() {
  local branch

  branch="$(git symbolic-ref HEAD)"
  branch="${branch#refs/heads/}"

  echo "$branch"
}

merge() {
  local STASHED
  
  local remote
  local remote_branch 
  local local_branch

  remote="$1"
  remote_branch="$2"
  local_branch="$3"
  
  local remote_ref
  remote_ref="$remote/$remote_branch"


  if [[ -n "$(git status --untracked-files=all --porcelain 2>/dev/null)" ]]; then
    # Abort rebase or merge if initiated
    git merge --abort  &>/dev/null
    git rebase --abort &>/dev/null

    stash
    STASHED="1"
  fi

  # Attempt fetch to REMOTE/UPSTREAM_BRANCH
  if ! git fetch --tags --force "$remote" \
    "refs/heads/$remote_branch:refs/remotes/$remote_ref"
  then
    die "Cannot fetch from $remote_ref from $local_branch"
  fi

  # Try fast-forward merge
  git merge --no-edit --ff "$remote_ref" \
      --strategy=recursive \
      --strategy-option=ours \
      --strategy-option=ignore-all-space \
      >/dev/null

  if [[ -n "$STASHED" && -z "$NO_STASH_POP" ]]; then
    git stash pop &>/dev/null
  fi
}

remote() {
  local remote

  if [[ -z "$REMOTE" ]]; then
    remote="origin"
  else
    remote="$REMOTE"
  fi

  echo "$remote"
}

cd_or_die() {
  cd "$1" || die "Cannot enter directory $1. Exiting."
}

die_no_git_dir() {
  die <<_EOF
Cannot find a .git directory in $(pwd). Try initializing repo with:
$PROGRAM --init-with https://git.example.com

To automatically create a git repo, consider setting "REMOTE_URL"
_EOF
}

init_if_empty() {
  if [[ ! -d ".git" ]]; then

    if [[ -z "$REMOTE_URL" ]]; then 
      die_no_git_dir
    else
      init_repo "$REMOTE_URL"
    fi

  fi
}

update() {
  local dir
  local previous_version
  local next_version

  dir="$1"
  cd_or_die "$dir"

  previous_version="$(current_version)"

  if [[ -z "$AGENT" ]]; then
    AGENT="$(basename "$(pwd)")"
  fi

  depends git

  init_if_empty

  local remote
  local remote_branch
  local local_branch

  remote="$(remote)"
  
  remote_branch="$(upstream_branch "$remote")"

  if [[ -z "$remote_branch" ]]; then
    die_no_upstream_found
  fi

  local_branch="$(local_branch)"

  merge "$remote" "$remote_branch" "$local_branch"

  next_version="$(current_version)"

  if [[ "$previous_version" == "" ]]; then
    echo "Initialized $AGENT with \"$previous_version\""
  elif [[ "$previous_version" != "$next_version" ]]; then
    echo "Updated $AGENT from version \"$previous_version\" to \"$next_version\""
  else
    echo "$AGENT is already up to date."
  fi
}

print_usage() {
cat <<_EOF
Usage: ${PROGRAM} [OPTIONS]...
  -h, --help     output this help info
  -d, --dir      update in directory
  --init         initialize a project with the given URL
_EOF
}

init_repo() {
  local remote
  local remote_url
  local upstream_branch
  local remote_ref

  remote_url="$1"
  remote="$(remote)"

  DEFAULT_BRANCH="main"

  trap '{ rm -rf .git; exit 1; }' EXIT

  set -e
  git init &>/dev/null
  git branch -M "$DEFAULT_BRANCH"
  git config remote.origin.url "$remote_url"
  git config remote.origin.fetch "+refs/heads/*:refs/remotes/$remote/*"
  git fetch --force --tags "$remote" &>/dev/null
  git remote set-head "$remote" --auto >/dev/null
  
  upstream_branch="$(upstream_branch "$remote")"

  if [[ -z "$upstream_branch" ]]; then
    die_no_upstream_found
  fi

  remote_ref="$remote/$upstream_branch"

  git merge --ff --no-edit "$remote_ref"

  git branch --set-upstream-to="$remote_ref" "$DEFAULT_BRANCH"

  git reset --hard "$remote_ref" >/dev/null

  trap - EXIT

  set +e
}

git_update_agent() {
  local dir
  local option
  local remote_url

  while [[ $# -gt 0 ]]; do
    case "$1" in
      -h|-\?|--help|--usage) print_usage; exit 0 ;;
      --dir)
        
        shift

        if [[ $# -eq 0 ]]; then
          die "--dir requires an option"
        fi

        dir="$1"

        shift
      ;;
      --init-with)

        shift

        if [[ $# -eq 0 ]]; then
          die "--init requires an option"
        fi

        remote_url="$1"

        shift
      ;;
      *) die "$(print_usage)" ;;
    esac
  done

  if [[ -z "$dir" ]]; then
    dir="." 
  fi

  if [[ -z "$remote_url" ]]; then
    update "$dir"
  else
    init_repo "$remote_url"
  fi
}

git_update_agent "$@"