pre-commit Hook which formats your kotlin file with ktling

ktlint_pre_commit_hook.rb

#!/usr/bin/env ruby
require 'open3'

class KtlintPreCommitHook
  def self.run
    puts "Running pre commit hook"
    check_ktlint_availability
    files_needs_formatting = check_changed_files
    auto_format_changed_files(files_needs_formatting)
  end

  private

  def self.check_ktlint_availability
    puts "\nCheck if ktlint is installed...."
    if !`which ktlint`.strip
      raise 'Ktlint is not available in the PATH. Please install ktlint or add it to your PATH.'
    end
    puts "Ktlint is installed\n"
  end

  def self.get_all_changed_kotlin_files
    puts "\nChecking if there are any changed kotlin files - ignoring deleted files"
    # this parameter  --diff-filter=d filters all the deleted files a way from the change list
    changed_files = `git diff --name-only --diff-filter=d HEAD`.split("\n")

    ktlint_files = changed_files.select { |file| file.end_with?('.kt') }
    if ktlint_files.empty?
        puts "It seams no Kotlin files has been change skipping format checking"
    end
    puts "Found #{ktlint_files.length} Kotlin file(s) that has changed"
    return ktlint_files
  end

  

  def self.auto_format_changed_files(files_needs_formatting)
    if files_needs_formatting.empty? 
        return
    end

    files_needs_formatting.each do | file |
      cmd = "ktlint -F #{file}"
      Open3.popen3(cmd) do |stdin, stdout, stderr|
        if stderr.read.strip != '' or stdout.read.strip != ''
          raise "Ktlint found errors in file #{file} run 'ktlint -F #{file}' to see whats the excate issue"
        end
      end
      `git add #{file}`
    end
  end


    

  def self.check_changed_files
    ktfiles_need_formatting = []
    ktlint_files = get_all_changed_kotlin_files
    if ktlint_files.empty?
        return ktfiles_need_formatting
    end
    puts "\nChecking if any of the changed files needs reformatting"
    
    ktlint_files.each do |file|
      cmd = "ktlint #{file}"
      Open3.popen3(cmd) do |stdin, stdout, stderr|
        if stderr.read.strip != '' or stdout.read.strip != ''
          ktfiles_need_formatting.push(file)  
          puts "Added file '#{file}' to formatting list"
        end
      end
    end
    return ktlint_files
  end
end

KtlintPreCommitHook.run