liquid/lib/liquid/context.rb

module Liquid

  # Context keeps the variable stack and resolves variables, as well as keywords
  #
  #   context['variable'] = 'testing'
  #   context['variable'] #=> 'testing'
  #   context['true']     #=> true
  #   context['10.2232']  #=> 10.2232
  #
  #   context.stack do
  #      context['bob'] = 'bobsen'
  #   end
  #
  #   context['bob']  #=> nil  class Context
  class Context
    attr_reader :scopes
    attr_reader :errors, :registers

    def initialize(assigns = {}, registers = {}, rethrow_errors = false)
      @scopes     = [(assigns || {})]
      @registers  = registers
      @errors     = []
      @rethrow_errors = rethrow_errors
    end

    def strainer
      @strainer ||= Strainer.create(self)
    end

    # adds filters to this context.
    # this does not register the filters with the main Template object. see <tt>Template.register_filter</tt>
    # for that
    def add_filters(filters)
      filters = [filters].flatten.compact

      filters.each do |f|
        raise ArgumentError, "Expected module but got: #{f.class}" unless f.is_a?(Module)
        strainer.extend(f)
      end
    end

    def handle_error(e)
      errors.push(e)
      raise if @rethrow_errors

      case e
      when SyntaxError
        "Liquid syntax error: #{e.message}"
      else
        "Liquid error: #{e.message}"
      end
    end


    def invoke(method, *args)
      if strainer.respond_to?(method)
        strainer.__send__(method, *args)
      else
        args.first
      end
    end

    # push new local scope on the stack. use <tt>Context#stack</tt> instead
    def push
      raise StackLevelError, "Nesting too deep" if @scopes.length > 100
      @scopes.unshift({})
    end

    # merge a hash of variables in the current local scope
    def merge(new_scopes)
      @scopes[0].merge!(new_scopes)
    end

    # pop from the stack. use <tt>Context#stack</tt> instead
    def pop
      raise ContextError if @scopes.size == 1
      @scopes.shift
    end

    # pushes a new local scope on the stack, pops it at the end of the block
    #
    # Example:
    #
    #   context.stack do
    #      context['var'] = 'hi'
    #   end
    #   context['var]  #=> nil
    #
    def stack(&block)
      result = nil
      push
      begin
        result = yield
      ensure
        pop
      end
      result
    end

    # Only allow String, Numeric, Hash, Array, Proc, Boolean or <tt>Liquid::Drop</tt>
    def []=(key, value)
      @scopes[0][key] = value
    end

    def [](key)
      resolve(key)
    end

    def has_key?(key)
      resolve(key) != nil
    end

    private

    # Look up variable, either resolve directly after considering the name. We can directly handle
    # Strings, digits, floats and booleans (true,false). If no match is made we lookup the variable in the current scope and
    # later move up to the parent blocks to see if we can resolve the variable somewhere up the tree.
    # Some special keywords return symbols. Those symbols are to be called on the rhs object in expressions
    #
    # Example:
    #
    #   products == empty #=> products.empty?
    #
    def resolve(key)
      case key
      when nil, 'nil', 'null', ''
        nil
      when 'true'
        true
      when 'false'
        false
      when 'blank'
        :blank?
      when 'empty'
        :empty?
      # Single quoted strings
      when /^'(.*)'$/
        $1.to_s
      # Double quoted strings
      when /^"(.*)"$/
        $1.to_s
      # Integer and floats
      when /^(\d+)$/
        $1.to_i
      # Ranges
      when /^\((\S+)\.\.(\S+)\)$/
        (resolve($1).to_i..resolve($2).to_i)
      # Floats
      when /^(\d[\d\.]+)$/
        $1.to_f
      else
        variable(key)
      end
    end

    # fetches an object starting at the local scope and then moving up
    # the hierachy
    def find_variable(key)
      @scopes.each do |scope|
        if scope.has_key?(key)
          variable = scope[key]
          variable = scope[key] = variable.call(self) if variable.is_a?(Proc)
          variable = variable.to_liquid
          variable.context = self if variable.respond_to?(:context=)
          return variable
        end
      end
      nil
    end

    # resolves namespaced queries gracefully.
    #
    # Example
    #
    #  @context['hash'] = {"name" => 'tobi'}
    #  assert_equal 'tobi', @context['hash.name']
    #  assert_equal 'tobi', @context['hash["name"]']
    #
    def variable(markup)
      parts = markup.scan(VariableParser)
      square_bracketed = /^\[(.*)\]$/

      first_part = parts.shift
      if first_part =~ square_bracketed
        first_part = resolve($1)
      end

      if object = find_variable(first_part)

        parts.each do |part|

          # If object is a hash we look for the presence of the key and if its available
          # we return it

          if part =~ square_bracketed
            part = resolve($1)

            object[pos] = object[part].call(self) if object[part].is_a?(Proc) and object.respond_to?(:[]=)
            object      = object[part].to_liquid

          else

            # Hash
            if object.respond_to?(:has_key?) and object.has_key?(part)

              # if its a proc we will replace the entry in the hash table with the proc
              res = object[part]
              res = object[part] = res.call(self) if res.is_a?(Proc) and object.respond_to?(:[]=)
              object = res.to_liquid

            # Array
            elsif object.respond_to?(:fetch) and part =~ /^\d+$/
              pos = part.to_i

              object[pos] = object[pos].call(self) if object[pos].is_a?(Proc) and object.respond_to?(:[]=)
              object = object[pos].to_liquid

            # Some special cases. If no key with the same name was found we interpret following calls
            # as commands and call them on the current object
            elsif object.respond_to?(part) and ['size', 'first', 'last'].include?(part)

              object = object.send(part.intern).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
          end

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

      object
    end

    private

    def execute_proc(proc)
      proc.call(self)
    end
  end
end