```ruby
class CreateExtension
  def initialize(params, user)
    @params = params
    @tags = params[:tag_tokens]
    @compatible_platforms = params[:compatible_platforms]
    @user = user
    @github = @user.octokit
  end

  def process!
    Extension.new(@params).tap do |extension|
      extension.owner = @user

      if extension.valid? and repo_valid?(extension)
        extension.save

        CollectExtensionMetadataWorker.perform_async(extension.id, @compatible_platforms.select { |p| !p.strip.blank? })
        SetupExtensionWebHooksWorker.perform_async(extension.id)
        NotifyModeratorsOfNewExtension.perform_async(extension.id)
      end
    end
  end

  private

  def repo_valid?(extension)
    begin
      result = @github.collaborator?(extension.github_repo, @user.github_account.username)
    rescue ArgumentError, Octokit::Unauthorized, Octokit::Forbidden
      result = false
    end

    if !result then extension.errors[:github_url] = I18n.t("extension.github_url_format_error") end

    result
  end
end
```

Handle re-adding a disabled/removed extension
user
```ruby
class CreateExtension
  def initialize(params, user)
    @params = params
    @tags = params[:tag_tokens]
    @compatible_platforms = params[:compatible_platforms]
    @user = user
    @github = @user.octokit
  end

  def process!
    Extension.new(@params).tap do |extension|
      extension.owner = @user

      if extension.valid? and repo_valid?(extension)
        extension.save

        CollectExtensionMetadataWorker.perform_async(extension.id, @compatible_platforms.select { |p| !p.strip.blank? })
        SetupExtensionWebHooksWorker.perform_async(extension.id)
        NotifyModeratorsOfNewExtension.perform_async(extension.id)
      else if existing = Extension.where(enabled: false, github_url: extension.github_url)
        existing.update_attribute(:enabled, true)
        return existing
      end
    end
  end

  private

  def repo_valid?(extension)
    begin
      result = @github.collaborator?(extension.github_repo, @user.github_account.username)
    rescue ArgumentError, Octokit::Unauthorized, Octokit::Forbidden
      result = false
    end

    if !result then extension.errors[:github_url] = I18n.t("extension.github_url_format_error") end

    result
  end
end
```
assistant