#!/usr/bin/env bash

set -euo pipefail

xgit() {
	git -c "user.name=Flake Update Bot" -c "user.email=flake-update-bot@clerie.de" -c "core.pager=cat" "$@"
}

xgit_merge_theirs() {
  # base branch is the one currently checked out

  # this is the branch we want to merge into the base branch
  OTHER_BRANCH="$1"

  # merge commit message
  COMMIT_MESSAGE="$2"

  # this branch gets used while merging
  TEMP_BRANCH="tempbranch"

  # create a merge commit between base branch and other branch, so it shows up correctly in git log
  # we use `ours` so we make sure there are no merge conflicts
  git merge -s ours "${OTHER_BRANCH}" -m "${COMMIT_MESSAGE}"

  # save our newly created merge commit in a seperate branch
  git branch "${TEMP_BRANCH}"

  # export contents of other branch to current working directory
  # this will change the last commit of our base branch too
  git reset --hard "${OTHER_BRANCH}"

  # return to our merge commit from the base branch
  # but without touching the current working directory
  git reset --soft "${TEMP_BRANCH}"

  # Add the changes to our merge commit
  git commit --amend --no-edit

  # we are now on our base branch again
  # so we can delete the temp branch
  git branch -D "${TEMP_BRANCH}"
}

NOW="$(date --utc +%Y-%m-%d-%H-%M)"

xgit status || xgit clone gitea@git.clerie.de:clerie/nixfiles.git .

echo "[!] Download changes"
xgit fetch --all

echo "[!] Chechout remote master"
xgit checkout origin/master

UPDATE_BRANCH="updated-inputs-${NOW}"
echo "[!] Create branch ${UPDATE_BRANCH}"
xgit checkout -b "${UPDATE_BRANCH}"

echo "[!] Update nixpkgs"
nix flake lock --update-input nixpkgs

echo "[!] Commit changes"
xgit add flake.lock

xgit commit -m "Update nixpkgs ${NOW}" || true

xgit diff --name-status origin/updated-inputs "${UPDATE_BRANCH}"

echo "[!] biep"
if xgit diff --quiet origin/updated-inputs "${UPDATE_BRANCH}"
then
	echo "[!] Nothing changed, removing branch"
	xgit checkout updated-inputs
	xgit branch -D "${UPDATE_BRANCH}"
	exit 0
fi

echo "[!] Publish ${UPDATE_BRANCH}"
xgit push --set-upstream origin "${UPDATE_BRANCH}"

echo "[!] Merge ${UPDATE_BRANCH} into updated-inputs"
xgit checkout updated-inputs
xgit_merge_theirs "${UPDATE_BRANCH}" "Update from ${UPDATE_BRANCH}"

echo "[!] Publish updated-inputs"
xgit push origin updated-inputs