#!/bin/bash -eu
#
# Blender: modified version of update.sample in hooks directory to:
# - Deny merge commits to release branches
# - Deny merge of non-release branches to main
#
# This indirectly checks for accidentally merging main into release
# branches, as main is almost certain to contain merge commits not
# in the release branch.
#
# To enable this hook, rename this file to "pre-receive" or place it in
# an "pre-receive.d" folder.

# No revision indicator.
zero_revision="0000000000000000000000000000000000000000"

# Check if we need to verify merge commits for this branch.
need_verify_merge_commit()
{
  local branch="$1"
  local old_revision="$2"

  if [ "$old_revision" = "$zero_revision" ]; then
    # New branch, always ok to push.
    false
  elif [ "$branch" = "main" ]; then
    # Some merge commits allowed in main branch.
    true
  elif (echo "${branch}" | grep -Eq ^blender-v[0-9]\.[0-9][0-9]?-release$); then
    # No merge commits in release branch.
    true
  else
    false
  fi
}

# Check if this is an invalid merge commit.
is_invalid_merge_commit()
{
  local branch="$1"
  local revision="$2"

  # Detect if this revision is a merge commit. It's based on the commit merge
  # message which is weak, but not clear how to do it otherwise.
  if git show -s --format=%B ${revision} | grep -Eq "Merge (remote-tracking )?branch '"; then
    if (echo "${branch}" | grep -Eq ^blender-v[0-9]\.[0-9][0-9]?-release$); then
      # In release branch, all merge commits are invalid.
      true
    elif [ "$branch" = "main" ]; then
      # In main branch, only merge commits from release branches.
      if git show -s --format=%B ${revision} | grep -Eq "Merge (remote-tracking )?branch '(origin\/)?blender-v[0-9]\.[0-9][0-9]?-release'"; then
        false
      else
        true
      fi
    else
      false
    fi
  else
    false
  fi
}

# Read stdin for ref information.
while read oldrev newrev refname; do
    # Detect type of update.
    if [ "$newrev" = "$zero_revision" ]; then
      newrev_type=delete
    else
      newrev_type=$(git cat-file -t $newrev)
    fi

    case "$refname","$newrev_type" in
      refs/tags/*,commit)
        # un-annotated tag
        ;;
      refs/tags/*,delete)
        # delete tag
        ;;
      refs/tags/*,tag)
        # annotated tag
        ;;
      refs/heads/*,commit)
        # branch
        branch=${refname##refs/heads/}

        if need_verify_merge_commit "$branch" "$oldrev"; then
          for r in $(test "$oldrev" = $zero_revision \
                 && git rev-list $newrev \
                 || git rev-list $newrev ^$oldrev); do
            is_invalid_merge_commit ${branch} ${r} && {
              printf "error: *** %s\n" \
            "You may only merge release branches into main, no other merge commits are allowed." \
            "See Blender's release branch developer documentation for details." >&2
            exit 1
            }
          done
        fi

        ;;
      refs/heads/*,delete)
        # delete branch
        ;;
      refs/remotes/*,commit)
        # tracking branch
        ;;
      refs/remotes/*,delete)
        # delete tracking branch
        ;;
      *)
        # Anything else (is there anything else?)
        ;;
    esac
done

exit 0