require 'set'

module Sass
  # The lexical environment for SassScript.
  # This keeps track of variable, mixin, and function definitions.
  #
  # A new environment is created for each level of Sass nesting.
  # This allows variables to be lexically scoped.
  # The new environment refers to the environment in the upper scope,
  # so it has access to variables defined in enclosing scopes,
  # but new variables are defined locally.
  #
  # Environment also keeps track of the {Engine} options
  # so that they can be made available to {Sass::Script::Functions}.
  class Environment
    # The enclosing environment,
    # or nil if this is the global environment.
    #
    # @return [Environment]
    attr_reader :parent
    attr_reader :options
    attr_writer :caller
    attr_writer :content

    # @param options [{Symbol => Object}] The options hash. See
    #   {file:SASS_REFERENCE.md#sass_options the Sass options documentation}.
    # @param parent [Environment] See \{#parent}
    def initialize(parent = nil, options = nil)
      @parent = parent
      @options = options || (parent && parent.options) || {}
    end

    # The environment of the caller of this environment's mixin or function.
    # @return {Environment?}
    def caller
      @caller || (@parent && @parent.caller)
    end

    # The content passed to this environmnet. This is naturally only set
    # for mixin body environments with content passed in.
    # @return {Environment?}
    def content
      @content || (@parent && @parent.content)
    end

    def global_env
      @global_env ||= parent.nil? ? self : parent.global_env
    end

    private

    class << self
      private
      UNDERSCORE, DASH = '_', '-'

      # Note: when updating this,
      # update sass/yard/inherited_hash.rb as well.
      def inherited_hash(name)
        class_eval <<RUBY, __FILE__, __LINE__ + 1
          def #{name}(name)
            _#{name}(name.tr(UNDERSCORE, DASH))
          end

          def _#{name}(name)
            (@#{name}s && @#{name}s[name]) || @parent && @parent._#{name}(name)
          end
          protected :_#{name}

          def set_#{name}(name, value)
            name = name.tr(UNDERSCORE, DASH)
            @#{name}s[name] = value unless try_set_#{name}(name, value)
          end

          def try_set_#{name}(name, value)
            @#{name}s ||= {}
            if @#{name}s.include?(name)
              @#{name}s[name] = value
              true
            elsif @parent
              @parent.try_set_#{name}(name, value)
            else
              false
            end
          end
          protected :try_set_#{name}

          def set_local_#{name}(name, value)
            @#{name}s ||= {}
            @#{name}s[name.tr(UNDERSCORE, DASH)] = value
          end
RUBY
      end
    end

    # variable
    # Script::Value
    inherited_hash :var
    # mixin
    # Sass::Callable
    inherited_hash :mixin
    # function
    # Sass::Callable
    inherited_hash :function
  end
end