set -eu

git init --object-format="$1" --ref-format="$2" --initial-branch=main source

git -C source commit --allow-empty -m 'Remote history'

for name in refs/heads/unborn REBASE_HEAD ORIG_HEAD refs/tags/missing refs/remotes/origin/missing; do

git -C source tag "$name"

git -C source tag -a nested/release -m 'Annotated release'

if [ "${3-}" = nested ]; then

git -C source tag -a nested/outer nested/release -m 'Nested annotated release'

git init --object-format="$1" --ref-format="$2" --initial-branch=unborn repo

git -C repo fetch ../source 'refs/tags/*:refs/tags/*'

if [ "${3-}" = symbolic ]; then

git -C repo symbolic-ref refs/tags/REBASE_HEAD refs/tags/refs/heads/unborn

if [ "${3-}" = shadowed ] || [ "${3-}" = reflog ]; then

# Fetched tags share the short names of a local branch and a remote-tracking branch.

git -C repo fetch ../source 'refs/heads/main:refs/tags/main' 'refs/heads/main:refs/tags/origin/main'

blob=$(printf 'local\n' | git -C repo hash-object -w --stdin)

tree=$(printf '100644 blob %s\tfile\n' "$blob" | git -C repo mktree)

commit=$(git -C repo commit-tree -m 'Local history' "$tree")

for path in refs/heads/main refs/remotes/origin/main; do

git -C repo update-ref "$path" "$commit"

done

git -C repo symbolic-ref HEAD refs/heads/main

if [ "${3-}" = reflog ]; then

old_tip=$(git -C repo commit-tree -p "$commit" -m 'Old tip' "$tree")

topic=$(git -C repo commit-tree -p "$old_tip" -m 'Topic history' "$tree")

git -C repo update-ref refs/heads/topic "$topic"

git -C repo tag topic refs/tags/main

for path in refs/heads/main refs/remotes/origin/main; do

git -C repo update-ref --create-reflog -m 'Advance upstream' "$path" "$old_tip"

git -C repo update-ref -m 'Rewind upstream' "$path" "$commit"

done

fi

if [ "${3-}" = existing ]; then

commit=$(git -C source rev-parse HEAD)

for path in refs/heads/unborn refs/stash ORIG_HEAD REBASE_HEAD; do

git -C repo update-ref "$path" "$commit"

done

printf '%s\n' "$commit" >repo/.git/MERGE_HEAD