require 'active_support/current_attributes'

module MultiTenant
  class Current < ::ActiveSupport::CurrentAttributes
    attribute :tenant
  end

  def self.tenant_klass_defined?(tenant_name, options = {})
    class_name = if options[:class_name].present?
                   options[:class_name]
                 else
                   tenant_name.to_s.classify
                 end
    !!class_name.safe_constantize
  end

  def self.partition_key(tenant_name)
    "#{tenant_name}_id"
  end

  # rubocop:disable Style/ClassVars
  # In some cases we only have an ID - if defined we'll return the default tenant class in such cases
  def self.default_tenant_class=(tenant_class)
    @@default_tenant_class = tenant_class
  end

  def self.default_tenant_class
    @@default_tenant_class ||= nil
  end

  # Write-only Mode - this only adds the tenant_id to new records, but doesn't
  # require its presence for SELECTs/UPDATEs/DELETEs
  def self.enable_write_only_mode
    @@enable_write_only_mode = true
  end

  def self.with_write_only_mode_enabled?
    @@enable_write_only_mode ||= false
  end

  # Registry that maps table names to models (used by the query rewriter)
  def self.register_multi_tenant_model(model_klass)
    @@multi_tenant_models ||= []
    @@multi_tenant_models.push(model_klass)

    remove_class_variable(:@@multi_tenant_model_table_names) if defined?(@@multi_tenant_model_table_names)
  end

  def self.multi_tenant_model_for_table(table_name)
    @@multi_tenant_models ||= []

    unless defined?(@@multi_tenant_model_table_names)
      @@multi_tenant_model_table_names = @@multi_tenant_models.map do |model|
        [model.table_name, model] if model.table_name
      end.compact.to_h
    end

    @@multi_tenant_model_table_names[table_name.to_s]
    # rubocop:enable Style/ClassVars
  end

  def self.multi_tenant_model_for_arel(arel)
    return nil unless arel.respond_to?(:ast)

    if arel.ast.relation.is_a? Arel::Nodes::JoinSource
      MultiTenant.multi_tenant_model_for_table(TableNode.table_name(arel.ast.relation.left))
    else
      MultiTenant.multi_tenant_model_for_table(TableNode.table_name(arel.ast.relation))
    end
  end

  def self.current_tenant=(tenant)
    Current.tenant = tenant
  end

  def self.current_tenant
    Current.tenant
  end

  def self.current_tenant_id
    current_tenant_is_id? ? current_tenant : current_tenant.try(:id)
  end

  def self.current_tenant_is_id?
    current_tenant.is_a?(String) || current_tenant.is_a?(Integer)
  end

  def self.current_tenant_class
    if current_tenant_is_id?
      MultiTenant.default_tenant_class || raise('Only have tenant id, and no default tenant class set')
    elsif current_tenant
      MultiTenant.current_tenant.class.name
    end
  end

  def self.load_current_tenant!
    return MultiTenant.current_tenant if MultiTenant.current_tenant && !current_tenant_is_id?
    raise 'MultiTenant.current_tenant must be set to load' if MultiTenant.current_tenant.nil?

    klass = MultiTenant.default_tenant_class || raise('Only have tenant id, and no default tenant class set')
    self.current_tenant = klass.find(MultiTenant.current_tenant_id)
  end

  def self.with(tenant, &block)
    return block.call if current_tenant == tenant

    old_tenant = current_tenant
    begin
      self.current_tenant = tenant
      block.call
    ensure
      self.current_tenant = old_tenant
    end
  end

  def self.without(&block)
    return block.call if current_tenant.nil?

    old_tenant = current_tenant
    begin
      self.current_tenant = nil
      block.call
    ensure
      self.current_tenant = old_tenant
    end
  end

  # Wrap calls to any of `method_names` on an instance Class `klass` with MultiTenant.with
  # when `'owner'` (evaluated in context of the klass instance) is a ActiveRecord model instance that is multi-tenant
  # Instruments the methods provided with previously set Multitenant parameters
  # In Ruby 2 using splat (*) operator with `&block` is not supported, so we need to use `method(...)` syntax
  # TODO: Could not understand the use of owner here. Need to check
  if Gem::Version.create(RUBY_VERSION) < Gem::Version.new('3.0.0')
    def self.wrap_methods(klass, owner, *method_names)
      method_names.each do |method_name|
        original_method_name = :"_mt_original_#{method_name}"
        klass.class_eval <<-CODE, __FILE__, __LINE__ + 1
          alias_method :#{original_method_name}, :#{method_name}
          def #{method_name}(*args, &block)
            if MultiTenant.multi_tenant_model_for_table(#{owner}.class.table_name).present? && #{owner}.persisted? && MultiTenant.current_tenant_id.nil? && #{owner}.class.respond_to?(:partition_key) && #{owner}.attributes.include?(#{owner}.class.partition_key)
              MultiTenant.with(#{owner}.public_send(#{owner}.class.partition_key)) { #{original_method_name}(*args, &block) }
            else
              #{original_method_name}(*args, &block)
            end
          end
        CODE
      end
    end
  else
    def self.wrap_methods(klass, owner, *method_names)
      method_names.each do |method_name|
        original_method_name = :"_mt_original_#{method_name}"
        klass.class_eval <<-CODE, __FILE__, __LINE__ + 1
        alias_method :#{original_method_name}, :#{method_name}
        def #{method_name}(...)
          if MultiTenant.multi_tenant_model_for_table(#{owner}.class.table_name).present? && #{owner}.persisted? && MultiTenant.current_tenant_id.nil? && #{owner}.class.respond_to?(:partition_key) && #{owner}.attributes.include?(#{owner}.class.partition_key)
            MultiTenant.with(#{owner}.public_send(#{owner}.class.partition_key)) { #{original_method_name}(...) }
          else
            #{original_method_name}(...)
          end
        end
        CODE
      end
    end
  end

  # Preserve backward compatibility for people using .with_id
  singleton_class.send(:alias_method, :with_id, :with)

  # This exception is raised when a there is an attempt to change tenant
  class TenantIsImmutable < StandardError
  end

  class MissingTenantError < StandardError
  end
end