fizzy/bin/bundle-drift

#!/usr/bin/env ruby
# Checks that Gemfile.lock and Gemfile.saas.lock are in sync for shared dependencies.
# Since Gemfile.saas evals Gemfile, shared gems should have identical versions.
#
# Usage:
#   bin/bundle-drift [check]   # check for drift (default subcommand)
#   bin/bundle-drift correct   # restore alignment (Gemfile.saas.lock is authoritative)
#   bin/bundle-drift forward   # push Gemfile.lock changes into Gemfile.saas.lock
require "bundler"
require "fileutils"

GEMFILE_LOCK = "Gemfile.lock"
GEMFILE_SAAS_LOCK = "Gemfile.saas.lock"

class GemfileDriftChecker
  def initialize
    @oss_lockfile = parse_lockfile(GEMFILE_LOCK)
    @saas_lockfile = parse_lockfile(GEMFILE_SAAS_LOCK)
  end

  def check
    find_drift.tap do
      report it
    end
  end

  private
    def parse_lockfile(path)
      Bundler::LockfileParser.new(File.read(path))
    end

    def find_drift
      oss_specs, saas_specs = specs_hash(@oss_lockfile), specs_hash(@saas_lockfile)
      shared_gems = oss_specs.keys & saas_specs.keys

      shared_gems.filter_map do |name|
        oss_version, saas_version = oss_specs[name], saas_specs[name]
        if oss_version != saas_version
          { name: name, oss: oss_version, saas: saas_version }
        end
      end.sort_by { |d| d[:name] }
    end

    def specs_hash(lockfile)
      lockfile.specs.to_h { |spec| [ spec.name, spec.version.to_s ] }
    end

    def report(drift)
      if drift.empty?
        puts "✓ Gemfile.lock and Gemfile.saas.lock are in sync"
      else
        puts "✗ Gemfile lock files have drifted!\n\n"

        name_width = [ drift.map { |d| d[:name].length }.max, "Gem".length ].max
        oss_width = [ drift.map { |d| d[:oss].length }.max, "Gemfile.lock".length ].max
        saas_width = [ drift.map { |d| d[:saas].length }.max, "Gemfile.saas.lock".length ].max

        puts "  #{"Gem".ljust(name_width)}  #{"Gemfile.lock".ljust(oss_width)}  Gemfile.saas.lock"
        puts "  #{"-" * name_width}  #{"-" * oss_width}  #{"-" * saas_width}"

        drift.each do |d|
          puts "  #{d[:name].ljust(name_width)}  #{d[:oss].ljust(oss_width)}  #{d[:saas]}"
        end

        puts "\nRun 'bin/bundle-drift correct' to restore alignment."
      end
    end
end

class GemfileDriftCorrector
  def correct
    drift = GemfileDriftChecker.new.check
    return puts "\nNothing to correct." if drift.empty?

    puts "\nRestoring alignment (Gemfile.saas.lock is authoritative)...\n\n"

    # Save original for diff
    original_content = File.read(GEMFILE_LOCK)

    # Seed Gemfile.lock with Gemfile.saas.lock - Bundler will use these as version hints
    FileUtils.cp(GEMFILE_SAAS_LOCK, GEMFILE_LOCK)

    # Re-lock: Bundler prunes SaaS-only gems while preserving shared versions
    puts "▸ Re-locking Gemfile (seeded from Gemfile.saas.lock)"
    unless system("BUNDLE_GEMFILE=Gemfile bundle lock")
      File.write(GEMFILE_LOCK, original_content)
      abort("Failed to lock Gemfile. Restored original.")
    end

    puts "\n▸ Verifying alignment"
    new_drift = GemfileDriftChecker.new.check

    if new_drift.empty?
      puts "\n✓ Lock files are now in sync"
      show_diff(original_content, File.read(GEMFILE_LOCK))
    else
      puts "\n✗ Lock files still have drift after correction."
      puts "  Bundler couldn't resolve to matching versions."
      puts "  Restoring original Gemfile.lock."
      File.write(GEMFILE_LOCK, original_content)
      exit 1
    end
  end

  private
    def show_diff(original, corrected)
      require "tempfile"

      Tempfile.create("gemfile-lock-original") do |f|
        f.write(original)
        f.flush

        diff = `diff -u #{f.path} #{GEMFILE_LOCK} 2>/dev/null`
        unless diff.empty?
          puts "\nChanges made to Gemfile.lock:"
          puts diff
        end
      end
    end
end

class GemfileDriftForwarder
  def forward
    drift = GemfileDriftChecker.new.check
    return puts "\nNothing to forward." if drift.empty?

    puts "\nForwarding Gemfile.lock versions into Gemfile.saas.lock...\n\n"

    original_content = File.read(GEMFILE_SAAS_LOCK)
    patched_content = original_content.dup

    drift.each do |d|
      old_entry = "#{d[:name]} (#{d[:saas]})"
      new_entry = "#{d[:name]} (#{d[:oss]})"
      puts "  #{old_entry} → #{new_entry}"
      patched_content.gsub!(old_entry, new_entry)
    end

    File.write(GEMFILE_SAAS_LOCK, patched_content)

    puts "\n▸ Verifying alignment"
    new_drift = GemfileDriftChecker.new.check

    if new_drift.empty?
      puts "\n✓ Lock files are now in sync"
      show_diff(original_content, patched_content)
    else
      puts "\n✗ Lock files still have drift after forwarding."
      puts "  Restoring original Gemfile.saas.lock."
      File.write(GEMFILE_SAAS_LOCK, original_content)
      exit 1
    end
  end

  private
    def show_diff(original, patched)
      require "tempfile"

      Tempfile.create("gemfile-saas-lock-original") do |f|
        f.write(original)
        f.flush

        diff = `diff -u #{f.path} #{GEMFILE_SAAS_LOCK} 2>/dev/null`
        unless diff.empty?
          puts "\nChanges made to Gemfile.saas.lock:"
          puts diff
        end
      end
    end
end

case command = ARGV[0] || "check"
when "check"
  exit 1 unless GemfileDriftChecker.new.check.empty?
when "correct"
  GemfileDriftCorrector.new.correct
when "forward"
  GemfileDriftForwarder.new.forward
else
  abort "Usage: bin/bundle-drift [check|correct|forward]"
end