#!/bin/sh
#
# Copyright © 2018 Nick Bowler
#
# Simple git post-receive hook to deploy a nanoc site
#
# License WTFPL2: Do What The Fuck You Want To Public License, version 2.
# This is free software: you are free to do what the fuck you want to.
# There is NO WARRANTY, to the extent permitted by law.

GIT=/usr/bin/git
worktreedir=/var/cache/git-worktrees

master_update=
while read old new ref x; do
  case $ref in
  refs/heads/master) master_update=$new ;;
  esac
done

worktree_remove() {
  # welp, git doesn't appear to have a way to ONLY remove worktree tracking
  # files, it removes the work tree itself which we don't want to do.  So do
  # this manually.

  for f in worktrees/*/gitdir; do
    exec 3<"$f" || continue
    read l <&3 || continue

    if test x"$l" = x"$1/.git"; then
      rm -f "$f"
      $GIT worktree prune -v
      break
    fi
  done

  exec 3<&-
}

cd_to_worktree_ () {
  tmpfile=`mktemp`
  exec 3>"$tmpfile" 4<"$tmpfile"
  rm -f "$tmpfile"

  branch=${1##*/}

  repodir=`pwd`
  reponame=${repodir##*/}
  worktree=/no/where

  # Remove any stale worktrees...
  $GIT worktree prune -v

  # First just try to add a new worktree
  tmp_worktree=`mktemp -d "${worktreedir%/}/$reponame-$branch-XXXXXXXX"`
  $GIT worktree add "$tmp_worktree" "$branch" 2>/dev/null ||
    rmdir "$tmp_worktree"

  $GIT worktree list --porcelain >&3
  exec 3<&-

  while read a b x <&4; do
    case $a in
    worktree) worktree=${b:-/no/where} ;;
    branch) if test x"$b" = x"refs/heads/$branch"; then
      if cd "$worktree"; then
        test x"`pwd -P`" != x"$worktree" || { exec 4<&-; return 0; }
        cd -
      fi

      # Clean up
      worktree_remove "$worktree"
    fi ;;
    esac
  done

  # Failed?
  exec 4<&-
  return 1
}

# Usage: cd_to_worktree branch
#
# Change the current working directory to the worktree for the specified
# branch, creating it if necessary.
cd_to_worktree () {
  # Try twice: stale entries might be removed by first pass and 2nd will work
  if cd_to_worktree_ "$@" || cd_to_worktree_ "$@"; then
    printf 'using worktree %s\n' "`pwd -P`"
    unset GIT_DIR
  fi
}

deploy_branch () {
  printf 'Deploying %s\n' "$1"
  ( cd_to_worktree $1
    { flock -w 60 9 || exit
      git reset --hard || exit
      git clean -qfd -e gitlock || exit
      nanoc || exit
      nanoc deploy master || exit
    } 9>gitlock
  )
}

ret=true
if test ${master_update:+y}; then
  deploy_branch master || ret=false
fi

$ret