voltrb/volt

require 'volt/page/bindings/base_binding'

module Volt
  class IfBinding < BaseBinding
    def initialize(volt_app, target, context, binding_name, branches)
      super(volt_app, target, context, binding_name)

      getter, template_name = branches[0]

      @branches  = []
      @listeners = []

      branches.each do |branch|
        getter, template_name = branch

        if getter.present?
          value = getter
        else
          # A nil value means this is an unconditional else branch, it
          # should always be true
          value = true
        end

        @branches << [value, template_name]
      end

      # The promise dependency can be invalidated when we need to rerun the update
      # manually because a promise resolved.
      @promise_dependency = Dependency.new

      @computation = lambda do
        @promise_dependency.depend

        update
      end.watch!
    end

    def update
      # Find the true branch
      true_template = nil
      @branches.each do |branch|
        value, template_name = branch

        if value.is_a?(Proc)
          begin
            current_value = @context.instance_eval(&value)

            if current_value.is_a?(Promise)
              # If we got a promise, use its value if resolved.
              if current_value.resolved?
                # Should call then immediately
                current_value.then do |value|
                  current_value = value
                end
              else
                # if its not, resolve it and try again.
                # TODO: we maybe could cache this so we don't have to run a full update again
                current_value.then do |val|
                  # Run update again
                  @promise_dependency.changed!
                end

                current_value = nil
              end
            end
          rescue => e
            Volt.logger.error("IfBinding:#{object_id} error: #{e.inspect}\n" + `value.toString()`)
            current_value = false
          end
        else
          current_value = value
        end

        if current_value && !current_value.is_a?(Exception)
          # This branch is currently true
          true_template = template_name
          break
        end
      end

      # Change out the template only if the true branch has changed.
      if @last_true_template != true_template
        @last_true_template = true_template

        if @template
          @template.remove
          @template = nil
        end

        if true_template
          @template = TemplateRenderer.new(@volt_app, @target, @context, binding_name, true_template)
        end
      end
    end

    def remove
      @computation.stop if @computation
      @computation = nil

      @template.remove if @template

      super
    end
  end
end