#!/usr/bin/env bash

set -u # don't expand unbound variable
set -f # disable pathname expansion
set -C # noclobber

readonly BASE_BRANCH_NAME="upstream-merge-"
readonly BASE_PULL_URL="https://api.github.com/repos/tgstation/tgstation/pulls"

# Ensure the current directory is a git directory
if [ ! -d .git ]; then
    echo "Error: must run this script from the root of a git repository"
    exit 1
fi

# Ensure all given parameters exist
if [ $# -eq 0 ]; then
    echo "Error: No arguments have been given, the first argument needs to be a pull ID, the second argument needs to be the commit message"
    exit 1
fi

# Ensure curl exists and is available in the current context
type curl >/dev/null 2>&1 || { echo >&2 "Error: This script requires curl, please ensure curl is installed and exists in the current PATH"; exit 1; }

# Ensure jq exists and is available in the current context
type jq >/dev/null 2>&1 || { echo >&2 "Error: This script requires jq, please ensure jq is installed and exists in the current PATH"; exit 1; }

# Make sure we have our upstream remote
if ! git remote | grep tgstation > /dev/null; then
   git remote add tgstation https://github.com/tgstation/tgstation.git
fi

# We need to make sure we are always on a clean master when creating the new branch.
# So we forcefully reset, clean and then checkout the master branch
git fetch --all
git checkout master
git reset --hard origin/master
git clean -f

# Remove the other branches
git branch | grep -v "master" | xargs git branch -D

# Create a new branch
git checkout -b "$BASE_BRANCH_NAME$1"

# Grab the SHA of the merge commit
readonly MERGE_SHA=$(curl --silent "$BASE_PULL_URL/$1" | jq '.merge_commit_sha' -r)

# Get the commits
readonly COMMITS=$(curl "$BASE_PULL_URL/$1/commits" | jq '.[].sha' -r)

# Cherry pick onto the new branch
CHERRY_PICK_OUTPUT=$(git cherry-pick -m 1 "$MERGE_SHA" 2>&1)
echo "$CHERRY_PICK_OUTPUT"

# If it's a squash commit, you can't use -m 1, you need to remove it
# You also can't use -m 1 if it's a rebase and merge...
if echo "$CHERRY_PICK_OUTPUT" | grep 'error: mainline was specified but commit'; then
  echo "Commit was a squash, retrying"
  for commit in $COMMITS; do
  	echo "Cherry-picking: $commit"
	git cherry-pick "$commit"
	# Add all files onto this branch
	git add -A .
	git cherry-pick --continue
  done
else
  # Add all files onto this branch
  git add -A .
fi

# Commit these changes
git commit --allow-empty -m "$2"

# Push them onto the branch
git push -u origin "$BASE_BRANCH_NAME$1"
