generate_pr_commit_message

#!/bin/bash
#/
# @license Apache-2.0
#
# Copyright (c) 2024 The Stdlib Authors.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#/

# Script to generate a commit message for a pull request.
#
# Usage: generate_pr_commit_message PR_NUMBER
#
# Arguments:
#
#   PR_NUMBER    Pull request number.
#
# Environment variables:
#
#   GITHUB_TOKEN   GitHub token for authentication.

# Ensure that the exit status of pipelines is non-zero in the event that at least one of the commands in a pipeline fails:
set -o pipefail


# VARIABLES #

# Get the pull request number:
pr_number="$1"

# GitHub API base URL
GITHUB_API_URL="https://api.github.com"

# Repository owner and name
REPO_OWNER="stdlib-js"
REPO_NAME="stdlib"


# FUNCTIONS #

# Error handler.
#
# $1 - error status
on_error() {
	echo 'ERROR: An error was encountered during execution.' >&2
	exit "$1"
}

# Resolves a name and email using .mailmap via `git check-mailmap`, falling back to the provided values if no match is found.
#
# $1 - name
# $2 - email
resolve_name_email() {
	local name="$1"
	local email="$2"
	local resolved

	resolved=$(git check-mailmap "$name <$email>" 2>/dev/null)
	if [ -n "$resolved" ]; then
		echo "$resolved"
	else
		echo "$name <$email>"
	fi
}

# Resolves GitHub handle to name and email using .mailmap.
#
# $1 - GitHub handle
resolve_user() {
	local github_handle="$1"
	local mailmap_file=".mailmap"
	local name_email

	# Try to find a match for the GitHub handle:
	name_email=$(grep -i "$github_handle" "$mailmap_file" | head -n 1)

	if [ -n "$name_email" ]; then
		# Extract only the first name and email pair:
		echo "$name_email" | sed -E 's/^([^<]+)<([^>]+)>.*/\1<\2>/' | xargs
	else
		# If no match found, use the GitHub handle as is:
		echo "$github_handle <$github_handle@users.noreply.github.com>"
	fi
}

# Makes GitHub API requests.
#
# $1 - HTTP method (GET or POST)
# $2 - API endpoint
# $3 - data for POST requests
github_api() {
	local method="$1"
	local endpoint="$2"
	local data="$3"

	# Initialize an array to hold curl headers:
	local headers=()

	# If GITHUB_TOKEN is set, add the Authorization header:
	if [ -n "$GITHUB_TOKEN" ]; then
		headers+=("-H" "Authorization: token $GITHUB_TOKEN")
	fi

	# Determine the HTTP method and construct the curl command accordingly...
	case "$method" in
		GET)
			curl -s "${headers[@]}" "$GITHUB_API_URL$endpoint"
			;;
		POST)
			# For POST requests, always set the Content-Type header:
			headers+=("-H" "Content-Type: application/json")

			# If data is provided, include it in the request:
			if [ -n "$data" ]; then
				curl -s -X POST "${headers[@]}" -d "$data" "$GITHUB_API_URL$endpoint"
			else
				# Handle cases where POST data is required but not provided:
				echo "POST request requires data."
				on_error 1
			fi
			;;
		*)
			echo "Invalid HTTP method: $method"
			on_error 1
			;;
	esac
}

# Main execution sequence.
main() {
	# Fetch pull request details:
	pr_details=$(github_api "GET" "/repos/$REPO_OWNER/$REPO_NAME/pulls/$pr_number")
	pr_title=$(echo "$pr_details" | jq -r '.title')
	pr_body=$(echo "$pr_details" | jq -r '.body // ""')
	pr_url=$(echo "$pr_details" | jq -r '.html_url')
	pr_author_login=$(echo "$pr_details" | jq -r '.user.login')

	# Resolve the PR author's name and email using .mailmap:
	pr_author_resolved=$(resolve_user "$pr_author_login")

	# Extract reviewers:
	pr_reviews=$(github_api "GET" "/repos/$REPO_OWNER/$REPO_NAME/pulls/$pr_number/reviews")
	reviewers=$(echo "$pr_reviews" | jq -r '.[] | select(.state == "APPROVED" ) | .user.login' | sort -u)

	# Fetch commits in the PR:
	pr_commits=$(github_api "GET" "/repos/$REPO_OWNER/$REPO_NAME/pulls/$pr_number/commits")

	# Extract co-authors from commit messages:
	co_authors=$(echo "$pr_commits" | jq -r '.[].commit.message' | grep -Eio 'Co-authored-by:.*' | sort -u)
	processed_co_authors=""
	while IFS= read -r co_author_line; do
		# Skip empty lines:
		if [ -z "$co_author_line" ]; then
			continue
		fi
		name_email=$(echo "$co_author_line" | sed -E 's/Co-authored-by:[[:space:]]*(.*)/\1/')
		name=$(echo "$name_email" | sed -E 's/^(.*)<.*>$/\1/' | xargs)
		email=$(echo "$name_email" | sed -E 's/^.*<(.*)>$/\1/' | xargs)
		resolved_author=$(resolve_name_email "$name" "$email")

		# Skip if the resolved author matches the resolved PR author:
		if [ "$resolved_author" == "$pr_author_resolved" ]; then
			continue
		fi
		processed_co_authors+="Co-authored-by: $resolved_author"$'\n'
	done <<< "$co_authors"

	# Extract commit authors:
	authors_info=$(echo "$pr_commits" | jq -r '.[] | .commit.author | "\(.name) <\(.email)>"' | sort -u | sed '/^ *<.*>/d' | sed '/^$/d')

	# Process commit authors:
	commit_authors=""
	while IFS= read -r author_line; do
		# Skip empty lines:
		if [ -z "$author_line" ]; then
			continue
		fi

		# Extract name and email:
		name=$(echo "$author_line" | sed -E 's/^(.*)<.*>$/\1/' | xargs)
		email=$(echo "$author_line" | sed -E 's/^.*<(.*)>$/\1/' | xargs)

		# Resolve name and email using .mailmap:
		resolved_author=$(resolve_name_email "$name" "$email")

		# Skip if the resolved author matches the resolved PR author:
		if [ "$resolved_author" == "$pr_author_resolved" ]; then
			continue
		fi

		commit_authors+="$resolved_author"$'\n'
	done <<< "$authors_info"

	# Remove any empty lines and duplicates:
	commit_authors=$(echo "$commit_authors" | sort -u | sed '/^$/d')

	# Prefix with 'Co-authored-by: ' if not empty:
	if [ -n "$commit_authors" ]; then
		commit_authors=$(echo "$commit_authors" | sed 's/^/Co-authored-by: /' | sort -u)
	fi

	# Combine co-authors and commit authors, removing empty lines:
	all_co_authors=$(echo -e "$processed_co_authors\n$commit_authors" | sed '/^\s*$/d' | sort -u)

	# Extract 'Signed-off-by' lines from commits:
	signed_off_bys=$(echo "$pr_commits" | jq -r '.[].commit.message' | grep -Eio 'Signed-off-by:.*' | sort -u)

	# Extract linked issues from PR body (e.g., #123):
	issue_numbers=$(echo "$pr_body" | grep -oE '#[0-9]+' | grep -oE '[0-9]+' | sort | uniq)
	closes_issues=""
	ref_issues=""

	# GitHub-supported closing keywords:
	closing_keywords=("close" "closes" "closed" "fix" "fixes" "fixed" "resolve" "resolves" "resolved")

	# Create a regex pattern from the keywords:
	keywords_pattern=$(IFS='|'; echo "${closing_keywords[*]}")

	for issue in $issue_numbers; do
		if echo "$pr_body" | grep -Eiq "(${keywords_pattern})([[:space:]]+|:)[[:space:]]*#${issue}\b"; then
			closes_issues+="Closes: https://github.com/$REPO_OWNER/$REPO_NAME/issues/$issue\n"
		else
			ref_issues+="Ref: https://github.com/$REPO_OWNER/$REPO_NAME/issues/$issue\n"
		fi
	done
	closes_issues=$(echo -e "$closes_issues" | sed '$ s/\n$//')
	ref_issues=$(echo -e "$ref_issues" | sed '$ s/\n$//')

	# Assemble commit message components:
	commit_subject="$pr_title"
	commit_body="PR-URL: $pr_url"

	if [ -n "$closes_issues" ]; then
		commit_body+="\n$closes_issues"
	fi
	if [ -n "$ref_issues" ]; then
		commit_body+="\n$ref_issues"
	fi
	commit_body+="\n"
	if [ -n "$all_co_authors" ]; then
		commit_body+="\n$all_co_authors"
	fi
	for reviewer in $reviewers; do
		resolved_reviewer=$(resolve_user "$reviewer")
		commit_body+="\nReviewed-by: $resolved_reviewer"
	done

	# Include Signed-off-by lines if present in the commits:
	if [ -n "$signed_off_bys" ]; then
		commit_body+="\n$signed_off_bys"
	fi

	# Combine subject and body:
	commit_message="$commit_subject\n\n$commit_body"

	# Output the commit message:
	echo -e "$commit_message"
}

# Call main with all command-line arguments:
main "$@"