#! /usr/bin/env bash

build_jekyll_site() {
  # $1 is the expected source branch
  local source_br; source_br=$1
  # $2 is the name of the target branch
  local tgt_br; tgt_br=$2

  local cur_branch; cur_branch=$(git rev-parse --symbolic-full-name HEAD) || return 1

  # skip execution on other branches
  [[ $cur_branch == "refs/heads/$source_br" ]] || return 0

  # create message
  local message; message="Jekyll build from $source_br:$(git rev-parse --verify 'HEAD^{commit}' | cut -c1-7)"$'\n'$'\n'"$(git cat-file commit HEAD | sed '1,/^$/d')"

  # import git utils: needed for die, require_clean_work_tree
  . "$(git --exec-path)/git-sh-setup" || return 1

  # ensure target branch exists
  local not_a_branch_msg; not_a_branch_msg="$tgt_br is not a branch; this script can only update branches named $tgt_br (try: git checkout -t origin/$tgt_br)"
  local target_branch; target_branch=$(git rev-parse --symbolic-full-name "$tgt_br" 2>/dev/null) || die "fatal: $not_a_branch_msg"
  case "$target_branch" in
    refs/heads/*)
      true
      ;;
    *)
      die "fatal: $not_a_branch_msg"
      ;;
  esac

  # don't build what's not checked in
  require_clean_work_tree

  # check gem versions
  bundle check >/dev/null || die "fatal: gems are out of date; run 'bundle install'"

  # prep the working location
  local workdir; workdir=$(mktemp -d /tmp/jekyll-XXXXXXXXXX) || die "fatal: unable to allocate a temporary directory"
  trap "rm -rf '""$workdir""'" 0 1 2 3 15

  # actually generate the site
  bundle exec jekyll build --destination "$workdir/_site" || die "fatal: jekyll build failure"

  # prepare and commit to the target branch
  export GIT_INDEX_FILE="$workdir/index"
  rm -f "$workdir/_site/Gemfile" "$workdir/_site/Gemfile.lock"
  git --work-tree="$workdir/_site" add . || die "fatal: error adding $workdir/_site"
  local tree; tree=$(git write-tree) || die "fatal: error writing tree"
  local commit; commit=$(git commit-tree "$tree" -p "$target_branch" -m "$message") || die "fatal: error writing commit"
  git update-ref -m "$message" "$target_branch" "$commit" || die "fatal: error updating ref"

  return 0
}

build_jekyll_site 'master' 'asf-site'
rm -rf .jekyll-cache/