#!/usr/bin/env bash
set -o errexit #abort if any command fails
me=$(basename "$0")

help_message="\
Usage: $me [-c FILE] [<options>]
Deploy generated files to a git branch.

Options:

  -h, --help               Show this help information.
  -v, --verbose            Increase verbosity. Useful for debugging.
  -e, --allow-empty        Allow deployment of an empty directory.
  -m, --message MESSAGE    Specify the message used when committing on the
                           deploy branch.
  -n, --no-hash            Don't append the source commit's hash to the deploy
                           commit's message.
      --source-only        Only build but not push
      --push-only          Only push but not build
"


run_build() {
  docker run --rm --name slate -v $(pwd)/build:/srv/slate/build -v $(pwd)/source:/srv/slate/source slatedocs/slate build
}

parse_args() {
  # Set args from a local environment file.
  if [ -e ".env" ]; then
    source .env
  fi

  # Parse arg flags
  # If something is exposed as an environment variable, set/overwrite it
  # here. Otherwise, set/overwrite the internal variable instead.
  while : ; do
    if [[ $1 = "-h" || $1 = "--help" ]]; then
      echo "$help_message"
      return 0
    elif [[ $1 = "-v" || $1 = "--verbose" ]]; then
      verbose=true
      shift
    elif [[ $1 = "-e" || $1 = "--allow-empty" ]]; then
      allow_empty=true
      shift
    elif [[ ( $1 = "-m" || $1 = "--message" ) && -n $2 ]]; then
      commit_message=$2
      shift 2
    elif [[ $1 = "-n" || $1 = "--no-hash" ]]; then
      GIT_DEPLOY_APPEND_HASH=false
      shift
    else
      break
    fi
  done

  # Set internal option vars from the environment and arg flags. All internal
  # vars should be declared here, with sane defaults if applicable.

  # Source directory & target branch.
  deploy_directory=build
  deploy_branch=gh-pages

  #if no user identity is already set in the current git environment, use this:
  default_username=${GIT_DEPLOY_USERNAME:-deploy.sh}
  default_email=${GIT_DEPLOY_EMAIL:-}

  #repository to deploy to. must be readable and writable.
  repo=origin

  #append commit hash to the end of message by default
  append_hash=${GIT_DEPLOY_APPEND_HASH:-true}
}

main() {
  parse_args "$@"

  enable_expanded_output

  if ! git diff --exit-code --quiet --cached; then
    echo Aborting due to uncommitted changes in the index >&2
    return 1
  fi

  commit_title=`git log -n 1 --format="%s" HEAD`
  commit_hash=` git log -n 1 --format="%H" HEAD`

  #default commit message uses last title if a custom one is not supplied
  if [[ -z $commit_message ]]; then
    commit_message="publish: $commit_title"
  fi

  #append hash to commit message unless no hash flag was found
  if [ $append_hash = true ]; then
    commit_message="$commit_message"$'\n\n'"generated from commit $commit_hash"
  fi

  previous_branch=`git rev-parse --abbrev-ref HEAD`

  if [ ! -d "$deploy_directory" ]; then
    echo "Deploy directory '$deploy_directory' does not exist. Aborting." >&2
    return 1
  fi

  # must use short form of flag in ls for compatibility with OS X and BSD
  if [[ -z `ls -A "$deploy_directory" 2> /dev/null` && -z $allow_empty ]]; then
    echo "Deploy directory '$deploy_directory' is empty. Aborting. If you're sure you want to deploy an empty tree, use the --allow-empty / -e flag." >&2
    return 1
  fi

  if git ls-remote --exit-code $repo "refs/heads/$deploy_branch" ; then
    # deploy_branch exists in $repo; make sure we have the latest version

    disable_expanded_output
    git fetch --force $repo $deploy_branch:$deploy_branch
    enable_expanded_output
  fi

  # check if deploy_branch exists locally
  if git show-ref --verify --quiet "refs/heads/$deploy_branch"
  then incremental_deploy
  else initial_deploy
  fi

  restore_head
}

initial_deploy() {
  git --work-tree "$deploy_directory" checkout --orphan $deploy_branch
  git --work-tree "$deploy_directory" add --all
  commit+push
}

incremental_deploy() {
  #make deploy_branch the current branch
  git symbolic-ref HEAD refs/heads/$deploy_branch
  #put the previously committed contents of deploy_branch into the index
  git --work-tree "$deploy_directory" reset --mixed --quiet
  git --work-tree "$deploy_directory" add --all

  set +o errexit
  diff=$(git --work-tree "$deploy_directory" diff --exit-code --quiet HEAD --)$?
  set -o errexit
  case $diff in
    0) echo No changes to files in $deploy_directory. Skipping commit.;;
    1) commit+push;;
    *)
      echo git diff exited with code $diff. Aborting. Staying on branch $deploy_branch so you can debug. To switch back to master, use: git symbolic-ref HEAD refs/heads/master && git reset --mixed >&2
      return $diff
      ;;
  esac
}

commit+push() {
  set_user_id
  git --work-tree "$deploy_directory" commit -m "$commit_message"

  disable_expanded_output
  #--quiet is important here to avoid outputting the repo URL, which may contain a secret token
  git push --quiet $repo $deploy_branch
  enable_expanded_output
}

#echo expanded commands as they are executed (for debugging)
enable_expanded_output() {
  if [ $verbose ]; then
    set -o xtrace
    set +o verbose
  fi
}

#this is used to avoid outputting the repo URL, which may contain a secret token
disable_expanded_output() {
  if [ $verbose ]; then
    set +o xtrace
    set -o verbose
  fi
}

set_user_id() {
  if [[ -z `git config user.name` ]]; then
    git config user.name "$default_username"
  fi
  if [[ -z `git config user.email` ]]; then
    git config user.email "$default_email"
  fi
}

restore_head() {
  if [[ $previous_branch = "HEAD" ]]; then
    #we weren't on any branch before, so just set HEAD back to the commit it was on
    git update-ref --no-deref HEAD $commit_hash $deploy_branch
  else
    git symbolic-ref HEAD refs/heads/$previous_branch
  fi

  git reset --mixed
}

filter() {
  sed -e "s|$repo|\$repo|g"
}

sanitize() {
  "$@" 2> >(filter 1>&2) | filter
}

if [[ $1 = --source-only ]]; then
  run_build
elif [[ $1 = --push-only ]]; then
  main "$@"
else
  run_build
  main "$@"
fi