class Sass::Tree::Visitors::Perform

def self.visit(root, environment = Sass::Environment.new)
  new(environment).send(:visit, root)
end

def handle_include_loop!(node)
  msg = "An @include loop has been found:"
  mixins = @environment.stack.map {|s| s[:mixin]}.compact
  if mixins.size == 2 && mixins[0] == mixins[1]
    raise Sass::SyntaxError.new("#{msg} #{node.name} includes itself")
  end
  mixins << node.name
  msg << "\n" << Sass::Util.enum_cons(mixins, 2).map do |m1, m2|
    "    #{m1} includes #{m2}"
  end.join("\n")
  raise Sass::SyntaxError.new(msg)
end

def initialize(env)
  @environment = env
end

def run_interp(text)
  text.map do |r|
    next r if r.is_a?(String)
    val = r.perform(@environment)
    # Interpolated strings should never render with quotes
    next val.value if val.is_a?(Sass::Script::String)
    val.to_s
  end.join.strip
end

def visit(node)
  super(node.dup)
rescue Sass::SyntaxError => e
  e.modify_backtrace(:filename => node.filename, :line => node.line)
  raise e
end

def visit_children(parent)
  with_environment Sass::Environment.new(@environment) do
    parent.children = super.flatten
    parent
  end
end

def visit_comment(node)
  return [] if node.invisible?
  if node.evaluated?
    node.value.gsub!(/(^|[^\\])\#\{([^}]*)\}/) do |md|
      $1+Sass::Script.parse($2, node.line, 0, node.options).perform(@environment).to_s
    end
    node.value = run_interp([Sass::Script::String.new(node.value)])
  end
  node
end

def visit_debug(node)
  res = node.expr.perform(@environment)
  res = res.value if res.is_a?(Sass::Script::String)
  if node.filename
    $stderr.puts "#{node.filename}:#{node.line} DEBUG: #{res}"
  else
    $stderr.puts "Line #{node.line} DEBUG: #{res}"
  end
  []
end

def visit_directive(node)
  if node.value['#{']
    node.value = run_interp(Sass::Engine.parse_interp(node.value, node.line, 0, node.options))
  end
  yield
  node
end

def visit_each(node)
  list = node.list.perform(@environment)
  with_environment Sass::Environment.new(@environment) do
    list.to_a.map do |v|
      @environment.set_local_var(node.var, v)
      node.children.map {|c| visit(c)}
    end.flatten
  end
end

def visit_extend(node)
  parser = Sass::SCSS::CssParser.new(run_interp(node.selector), node.line)
  node.resolved_selector = parser.parse_selector(node.filename)
  node
end

def visit_for(node)
  from = node.from.perform(@environment)
  to = node.to.perform(@environment)
  from.assert_int!
  to.assert_int!
  to = to.coerce(from.numerator_units, from.denominator_units)
  range = Range.new(from.to_i, to.to_i, node.exclusive)
  with_environment Sass::Environment.new(@environment) do
    range.map do |i|
      @environment.set_local_var(node.var,
        Sass::Script::Number.new(i, from.numerator_units, from.denominator_units))
      node.children.map {|c| visit(c)}
    end.flatten
  end
end

def visit_function(node)
  @environment.set_function(node.name,
    Sass::Callable.new(node.name, node.args, @environment, node.children))
  []
end

def visit_if(node)
  if node.expr.nil? || node.expr.perform(@environment).to_bool
    yield
    node.children
  elsif node.else
    visit(node.else)
  else
    []
  end
end

def visit_import(node)
  if path = node.css_import?
    return Sass::Tree::DirectiveNode.new("@import url(#{path})")
  end
  @environment.push_frame(:filename => node.filename, :line => node.line)
  root = node.imported_file.to_tree
  node.children = root.children.map {|c| visit(c)}.flatten
  node
rescue Sass::SyntaxError => e
  e.modify_backtrace(:filename => node.imported_file.options[:filename])
  e.add_backtrace(:filename => node.filename, :line => node.line)
  raise e
ensure
  @environment.pop_frame
end

def visit_mixin(node)
  handle_include_loop!(node) if @environment.mixins_in_use.include?(node.name)
  original_env = @environment
  original_env.push_frame(:filename => node.filename, :line => node.line)
  original_env.prepare_frame(:mixin => node.name)
  raise Sass::SyntaxError.new("Undefined mixin '#{node.name}'.") unless mixin = @environment.mixin(node.name)
  passed_args = node.args.dup
  passed_keywords = node.keywords.dup
  raise Sass::SyntaxError.new(<<END.gsub("\n", "")) if mixin.args.size < passed_args.size
xin #{node.name} takes #{mixin.args.size} argument#{'s' if mixin.args.size != 1}
ut #{node.args.size} #{node.args.size == 1 ? 'was' : 'were'} passed.
D
  passed_keywords.each do |name, value|
    # TODO: Make this fast
    unless mixin.args.find {|(var, default)| var.underscored_name == name}
      raise Sass::SyntaxError.new("Mixin #{node.name} doesn't have an argument named $#{name}")
    end
  end
  environment = mixin.args.zip(passed_args).
    inject(Sass::Environment.new(mixin.environment)) do |env, ((var, default), value)|
    env.set_local_var(var.name,
      if value
        value.perform(@environment)
      elsif kv = passed_keywords[var.underscored_name]
        kv.perform(@environment)
      elsif default
        default.perform(env)
      end)
    raise Sass::SyntaxError.new("Mixin #{node.name} is missing parameter #{var.inspect}.") unless env.var(var.name)
    env
  end
  with_environment(environment) {node.children = mixin.tree.map {|c| visit(c)}.flatten}
  node
rescue Sass::SyntaxError => e
  if original_env # Don't add backtrace info if this is an @include loop
    e.modify_backtrace(:mixin => node.name, :line => node.line)
    e.add_backtrace(:line => node.line)
  end
  raise e
ensure
  original_env.pop_frame if original_env
end

def visit_mixindef(node)
  @environment.set_mixin(node.name,
    Sass::Callable.new(node.name, node.args, @environment, node.children))
  []
end

def visit_prop(node)
  node.resolved_name = run_interp(node.name)
  val = node.value.perform(@environment)
  node.resolved_value = val.to_s
  yield
end

def visit_return(node)
  throw :_sass_return, node.expr.perform(@environment)
end

def visit_root(node)
  @environment.options = node.options if @environment.options.nil? || @environment.options.empty?
  yield
rescue Sass::SyntaxError => e
  e.sass_template ||= node.template
  raise e
end

def visit_rule(node)
  parser = Sass::SCSS::StaticParser.new(run_interp(node.rule), node.line)
  node.parsed_rules ||= parser.parse_selector(node.filename)
  yield
end

def visit_variable(node)
  return [] if node.guarded && !@environment.var(node.name).nil?
  val = node.expr.perform(@environment)
  @environment.set_var(node.name, val)
  []
end

def visit_warn(node)
  @environment.push_frame(:filename => node.filename, :line => node.line)
  res = node.expr.perform(@environment)
  res = res.value if res.is_a?(Sass::Script::String)
  msg = "WARNING: #{res}\n"
  @environment.stack.reverse.each_with_index do |entry, i|
    msg << "        #{i == 0 ? "on" : "from"} line #{entry[:line]}" <<
      " of #{entry[:filename] || "an unknown file"}"
    msg << ", in `#{entry[:mixin]}'" if entry[:mixin]
    msg << "\n"
  end
  Sass::Util.sass_warn msg
  []
ensure
  @environment.pop_frame
end

def visit_while(node)
  children = []
  with_environment Sass::Environment.new(@environment) do
    children += node.children.map {|c| visit(c)} while node.expr.perform(@environment).to_bool
  end
  children.flatten
end

def with_environment(env)
  old_env, @environment = @environment, env
  yield
ensure
  @environment = old_env
end