Source Browser

class SourceBrowser
  class NotAllowed < StandardError; end

  class << self
    def list(relative_dir = "")
      validate_path!(relative_dir) if relative_dir.present?

      allowed = whitelisted_files
      prefix = relative_dir.present? ? "#{relative_dir}/" : ""

      entries = Set.new
      allowed.each do |file|
        next unless file.start_with?(prefix)

        remainder = file.delete_prefix(prefix)
        top = remainder.split("/").first
        full = prefix + top
        is_dir = remainder.include?("/")

        entries << { name: top, path: full, directory: is_dir }
      end

      entries.sort_by { |e| [e[:directory] ? 0 : 1, e[:name]] }
    end

    def read(relative_path)
      validate_path!(relative_path)

      unless whitelisted_files.include?(relative_path)
        raise NotAllowed, "File not in whitelist"
      end

      full_path = Rails.root.join(relative_path)
      raise NotAllowed, "File not found" unless File.file?(full_path)

      File.read(full_path)
    end

    def file?(relative_path)
      whitelisted_files.include?(relative_path)
    end

    def language_for(path)
      case File.extname(path)
      when ".rb"   then "ruby"
      when ".erb"  then "erb"
      when ".yml", ".yaml" then "yaml"
      when ".js"   then "javascript"
      when ".css"  then "css"
      else "plaintext"
      end
    end

    private

    def validate_path!(path)
      raise NotAllowed, "Invalid path" if path.nil?
      raise NotAllowed, "Null bytes not allowed" if path.include?("\0")
      raise NotAllowed, "Invalid path" if path.include?("..")

      expanded = File.expand_path(path, Rails.root)
      root = Rails.root.to_s

      unless expanded.start_with?("#{root}/")
        raise NotAllowed, "Path traversal detected"
      end
    end

    def whitelisted_files
      @whitelisted_files ||= compute_whitelist
    end

    def compute_whitelist
      globs = Rails.application.config.source_browser_whitelist
      root = Rails.root.to_s

      files = Set.new
      globs.each do |glob|
        Dir[Rails.root.join(glob)].each do |full_path|
          next unless File.file?(full_path)
          files << full_path.delete_prefix("#{root}/")
        end
      end
      files
    end
  end

  # Reload whitelist cache in development
  def self.reload!
    @whitelisted_files = nil
  end
end