liquid/lib/liquid/variable_lookup.rb

module Liquid
  class VariableLookup
    SQUARE_BRACKETED = /\A\[(.*)\]\z/m
    COMMAND_METHODS = ['size'.freeze, 'first'.freeze, 'last'.freeze]

    attr_reader :name, :lookups

    def self.parse(markup)
      new(markup)
    end

    def initialize(markup)
      @lookups = markup.scan(VariableParser)

      name = @lookups.shift
      if name =~ SQUARE_BRACKETED
        name = Expression.parse($1)
      end
      @name = name

      @command_flags = 0

      @lookups.each_index do |i|
        lookup = @lookups[i]
        if lookup =~ SQUARE_BRACKETED
          @lookups[i] = Expression.parse($1)
        elsif COMMAND_METHODS.include?(lookup)
          @command_flags |= 1 << i
        end
      end
    end

    def evaluate(context)
      name = context.evaluate(@name)
      object = context.find_variable(name)

      @lookups.each_index do |i|
        key = context.evaluate(@lookups[i])

        # If object is a hash- or array-like object we look for the
        # presence of the key and if its available we return it
        if object.respond_to?(:[]) &&
          ((object.respond_to?(:has_key?) && object.has_key?(key)) ||
           (object.respond_to?(:fetch) && key.is_a?(Integer)))

          # if its a proc we will replace the entry with the proc
          res = context.lookup_and_evaluate(object, key)
          object = res.to_liquid

          # Some special cases. If the part wasn't in square brackets and
          # no key with the same name was found we interpret following calls
          # as commands and call them on the current object
        elsif @command_flags & (1 << i) != 0 && object.respond_to?(key)
          object = object.send(key).to_liquid

          # No key was present with the desired value and it wasn't one of the directly supported
          # keywords either. The only thing we got left is to return nil
        else
          return nil
        end

        # If we are dealing with a drop here we have to
        object.context = context if object.respond_to?(:context=)
      end

      object
    end

    def ==(other)
      self.class == other.class && self.state == other.state
    end

    protected

    def state
      [@name, @lookups, @command_flags]
    end
  end
end