#!/bin/bash

# How to setup the repository to make this correctly work
# 1. Clone repo and make sure you can correctly push to that
#    (example with openwrt main repo you need to use ssh remote url)
# 2. Make sure you can correctly push and force push to the github
#    repository
#
# Make sure to install the extra git-filter-repo package.
#
# Usage: github-merge-pr.sh PR_NUMBER BRANCH REPO_NAME
#
# BRANCH is optional and defaults to main.
# REPO_NAME is optional and defaults to openwrt. It does
# describe the repository name to use to pull PR info from.

# Script .config variables
# Github repository owner or organization name.
# By default set to openwrt, set this line in .config to overwrite
# the default value.
GITHUB_REPO_OWNER="openwrt"

# Your repository token, generate this token at your profile page:
# - Navigate to https://github.com/settings/tokens
# - Click on "Generate new token"
# - Enter a description, e.g. "pr.sh" and pick the "repo" scope
# - Hit "Generate token"
# Set this line in .config to provide a GITHUB_TOKEN and add comments
#GITHUB_TOKEN="d41d8cd98f00b204e9800998ecf8427e"
#
# Set this line in .config to use SSH key to rebase PR branch
# GITHUB_USE_SSH=1

SCRIPT_DIR="$(dirname $0)"
[ -h $0 ] && SCRIPT_DIR="$(dirname $(readlink $0))"

# Everything in .config will overwrite the default values set up
[ -f "$SCRIPT_DIR/.config" ] && source "$SCRIPT_DIR"/.config

PRID="$1"
BRANCH="${2:-main}"
GITHUB_REPO_NAME="${3:-openwrt}"
DRY_RUN="$4"

GIT=git
REPO="$GITHUB_REPO_OWNER"/"$GITHUB_REPO_NAME"

yesno() {
	local prompt="$1"
	local default="${2:-n}"
	local input

	while [ 1 ]; do
		printf "%s y/n [%s] > " "$prompt" "$default"
		read input
		case "${input:-$default}" in
			y*) return 0 ;;
			n*) return 1 ;;
		esac
	done
}

if ! command -v jq &> /dev/null; then
	echo "jq could not be found! This script require jq!"
	exit 1
fi

if [ -z "$PRID" -o -n "${PRID//[0-9]*/}" ]; then
	echo "Usage: $0 <PR-ID> [rebase-branch] [dry-run]" >&2
	exit 1
fi

if [ -n "$DRY_RUN" ]; then
	GIT="echo git"
fi

if [ -z "$(git branch --list "$BRANCH")" ]; then
	echo "Given rebase branch '$BRANCH' does not exist!" >&2
	exit 2
fi

if [ -n "$GITHUB_TOKEN" ]; then
	CURL_CMD=" --user \"$GITHUB_TOKEN:x-oauth-basic\" "
else
	CURL_CMD=" "
fi

if ! PR_INFO="$(curl $CURL_CMD -f -s "https://api.github.com/repos/$REPO/pulls/$PRID")"; then
	echo "Failed fetch PR #$PRID info" >&2
	exit 3
fi

if [ "$(echo "$PR_INFO" | jq -r ".maintainer_can_modify")" == "false" ]; then
	echo "PR #$PRID can't be force pushed by maintainers. Trying to merge as is!" >&2
fi

if [ "$(echo "$PR_INFO" | jq -r ".mergeable")" == "false" ]; then
	echo "PR #$PRID is not mergeable for Github.com. Check the PR!" >&2
	exit 5
fi

echo "Pulling current $BRANCH from origin"
$GIT checkout $BRANCH
$GIT fetch origin $BRANCH

if ! $GIT rebase origin/$BRANCH; then
	echo "Failed to rebase $BRANCH with origin/$BRANCH" >&2
	exit 7
fi

PR_USER="$(echo "$PR_INFO" | jq -r ".head.user.login")"
PR_BRANCH="$(echo "$PR_INFO" | jq -r ".head.ref")"
LOCAL_PR_BRANCH="$PR_BRANCH"-"$PR_USER"
if [ "$GITHUB_USE_SSH" = "1" ]; then
	PR_REPO="$(echo "$PR_INFO" | jq -r ".head.repo.ssh_url")"
else
	PR_REPO="$(echo "$PR_INFO" | jq -r ".head.repo.html_url")"
fi

if ! $GIT remote get-url $PR_USER &> /dev/null || [ -n "$DRY_RUN" ]; then
	echo "Adding $PR_USER with repo $PR_REPO to remote"
	$GIT remote add  $PR_USER $PR_REPO
fi

echo "Fetching remote $PR_USER"
$GIT fetch $PR_USER $PR_BRANCH

if [ "$(echo "$PR_INFO" | jq -r ".maintainer_can_modify")" == "true" ] || [ "$IGNORE_MERGEABLE" = "1" ]; then
	echo "Creating branch $LOCAL_PR_BRANCH for $PR_BRANCH"
	if ! $GIT checkout -b $LOCAL_PR_BRANCH $PR_USER/$PR_BRANCH; then
		echo "Failed to checkout new branch $PR_BRANCH from $PR_USER/$PR_BRANCH" >&2
		exit 8
	fi

	echo "Rebasing $LOCAL_PR_BRANCH on top of $BRANCH"
	if ! $GIT rebase origin/$BRANCH; then
		echo "Failed to rebase $PR_BRANCH with origin/$BRANCH" >&2
		exit 9
	fi

	# Remove any previous Link: https://github.com/$REPO/pull/$PRID tag
	if ! $GIT filter-repo --message-callback "
		return message.replace(b\"Link: https://github.com/$REPO/pull/$PRID\n\",b\"\")
	" --refs $BRANCH..$LOCAL_PR_BRANCH --force; then
		echo "Failed to remove previous Link: https://github.com/$REPO/pull/$PRID tag" >&2
		exit 9
	fi

	# Add to each commit Link: https://github.com/$REPO/pull/$PRID
	if ! $GIT filter-repo --message-callback "
		return message + b\"Link: https://github.com/$REPO/pull/$PRID\"
	" --refs $BRANCH..$LOCAL_PR_BRANCH --force; then
		echo "Failed to add Link: Pull Request tag" >&2
		exit 9
	fi

	# Remove any previous SoB tag if the Pull Request Author and Committer match
	if ! $GIT filter-repo --message-callback "
		return message.replace(b\"Signed-off-by: $(git config user.name) <$(git config user.email)>\n\",b\"\")
	" --refs $BRANCH..$LOCAL_PR_BRANCH --force; then
		echo "Failed to remove previous Committer SoB tag" >&2
		exit 9
	fi

	# Add Committer SoB to better reference who merged the thing last
	if ! $GIT rebase origin/$BRANCH $LOCAL_PR_BRANCH --exec "git commit -s --amend -C HEAD"; then
		echo "Failed to add Committer SoB tag" >&2
		exit 9
	fi

	if [ "$GITHUB_NO_PUSH" = "1" ]; then
		echo "next commands:"
		if [ "$(echo "$PR_INFO" | jq -r ".maintainer_can_modify")" == "true" ]; then
			echo "$GIT push $PR_USER HEAD:$PR_BRANCH --force"
			echo "$GIT checkout $BRANCH"
			echo "$GIT merge --ff-only $PR_USER/$PR_BRANCH"
		else
			echo "$GIT checkout $BRANCH"
			echo "$GIT merge --ff-only $LOCAL_PR_BRANCH"
		fi
		echo "$GIT push"
		echo "$GIT branch -D $LOCAL_PR_BRANCH"
		exit 20
	fi

	echo "Force pushing $LOCAL_PR_BRANCH to HEAD:$PR_BRANCH for $PR_USER"
	if ! $GIT push $PR_USER HEAD:$PR_BRANCH --force; then
		echo "Failed to force push HEAD to $PR_USER" >&2
		exit 10
	fi

	echo "Returning to $BRANCH"
	$GIT checkout $BRANCH
fi

if [ -n "$($GIT log origin/$BRANCH..HEAD)" ]; then
	echo "Working on dirty branch for $BRANCH! Please reset $BRANCH to origin/$BRANCH" >&2
	exit 11
fi

echo "Actually merging the PR #$PRID from branch $PR_USER/$PR_BRANCH"
if ! $GIT merge --ff-only $PR_USER/$PR_BRANCH; then
	echo "Failed to merge $PR_USER/$PR_BRANCH on $BRANCH" >&2
else
	if yesno "Push to openwrt $BRANCH" "y"; then
		echo "Pushing to openwrt git server"
		if ! $GIT push; then
			echo "Failed to push to $BRANCH but left branch as is." >&2
			exit 12
		fi

		# Default close comment
		COMMENT="Thanks! Rebased on top of $BRANCH and merged!"

		if [ -n "$GITHUB_TOKEN" ] && [ -z "$DRY_RUN" ]; then
			echo ""
			echo "Enter a comment and hit <enter> to close the PR at Github automatically now."
			echo "Hit <ctrl>-<c> to exit."
			echo ""
			echo "If you do not provide a comment, the default will be: "
			echo "[$COMMENT]"

			echo -n "Comment > "
			read usercomment

			echo "Sending message to PR..."

			comment="${usercomment:-$COMMENT}"
			comment="${comment//\\/\\\\}"
			comment="${comment//\"/\\\"}"
			comment="$(printf '{"body":"%s"}' "$comment")"

			if ! curl -s -o /dev/null -w "%{http_code} %{url_effective}\\n" --user "$GITHUB_TOKEN:x-oauth-basic" --request POST --data "$comment" "https://api.github.com/repos/$REPO/issues/$PRID/comments" || \
			! curl -s -o /dev/null -w "%{http_code} %{url_effective}\\n" --user "$GITHUB_TOKEN:x-oauth-basic" --request PATCH --data '{"state":"closed"}' "https://api.github.com/repos/$REPO/pulls/$PRID"
			then
				echo ""                                                     >&2
				echo "Something failed while sending comment to the PR via ">&2
				echo "the Github API, please review the state manually at " >&2
				echo "https://github.com/$REPO/pull/$PRID"                  >&2
				exit 6
			fi
		fi

		echo -e "\n"
		echo "The PR has been merged!"
		echo -e "\n"
	fi
fi

if [ "$(echo "$PR_INFO" | jq -r ".maintainer_can_modify")" == "true" ]; then
	echo "Deleting branch $LOCAL_PR_BRANCH"
	$GIT branch -D $LOCAL_PR_BRANCH
fi

exit 0