pre-commit hook for running SwiftLint and SwiftFormat on changed files

pre-commit.sh

#!/bin/bash

SWIFT_LINT=/opt/homebrew/bin/swiftlint
SWIFT_LINT_CONFIG=.swiftlint.yml
SWIFT_FORMAT=/opt/homebrew/bin/swiftformat
CHANGED_FILES="$(git --no-pager diff --name-status --no-color --cached | awk '$1 != "D" && $NF ~ /\.swift?$/ { print $NF }')"

if [[ -e "${SWIFT_LINT}" || -e "${SWIFT_FORMAT}" ]]; then
    count=0

    if [ -z "$CHANGED_FILES" ]; then
        echo "No Swift staged files."
        exit 0
    fi

    for file_path in $CHANGED_FILES; do
        export SCRIPT_INPUT_FILE_$count=$file_path
        count=$((count + 1))
    done
    export SCRIPT_INPUT_FILE_COUNT=$count

    echo "Running SwiftLint over these files:"
    echo "$CHANGED_FILES"

    diff=.git/unstaged-swiftlint-git-hook.diff
    git diff --color=never > $diff
    if [ -s $diff ]; then
        git apply -R $diff
    fi

    $SWIFT_FORMAT $CHANGED_FILES
    format_command_exit_code=$?
    echo "Completed SwiftFormat run."

    $SWIFT_LINT lint --use-script-input-files --quiet --fix --config $SWIFT_LINT_CONFIG
    lint_command_exit_code=$?
    echo "Completed SwiftLint run."

    echo "$CHANGED_FILES" | while read -r file; do
        if [ -f $file ]; then
            git add $file
        fi
    done

    if [ -s $diff ]; then
        git apply --ignore-whitespace $diff
    fi
    rm $diff
    unset diff

    combined_exit_code=$(($format_command_exit_code + $lint_command_exit_code))
    echo "Completed hook."
    exit $combined_exit_code
else
    echo "ERROR: SwiftLint or SwiftFormat not found."
    exit 1
fi