class Sass::Tree::Visitors::Perform

def self.perform_arguments(callable, args, keywords, splat)
  desc = "#{callable.type.capitalize} #{callable.name}"
  downcase_desc = "#{callable.type} #{callable.name}"
  begin
    unless keywords.empty?
      unknown_args = Sass::Util.array_minus(keywords.keys,
        callable.args.map {|var| var.first.underscored_name})
      if callable.splat && unknown_args.include?(callable.splat.underscored_name)
        raise Sass::SyntaxError.new("Argument $#{callable.splat.name} of #{downcase_desc} cannot be used as a named argument.")
      elsif unknown_args.any?
        description = unknown_args.length > 1 ? 'the following arguments:' : 'an argument named'
        raise Sass::SyntaxError.new("#{desc} doesn't have #{description} #{unknown_args.map {|name| "$#{name}"}.join ', '}.")
      end
    end
  rescue Sass::SyntaxError => keyword_exception
  end
  # If there's no splat, raise the keyword exception immediately. The actual
  # raising happens in the ensure clause at the end of this function.
  return if keyword_exception && !callable.splat
  if args.size > callable.args.size && !callable.splat
    takes = callable.args.size
    passed = args.size
    raise Sass::SyntaxError.new(
      "#{desc} takes #{takes} argument#{'s' unless takes == 1} " +
      "but #{passed} #{passed == 1 ? 'was' : 'were'} passed.")
  end
  splat_sep = :comma
  if splat
    args += splat.to_a
    splat_sep = splat.separator if splat.is_a?(Sass::Script::List)
    # If the splat argument exists, there won't be any keywords passed in
    # manually, so we can safely overwrite rather than merge here.
    keywords = splat.keywords if splat.is_a?(Sass::Script::ArgList)
  end
  keywords = keywords.dup
  env = Sass::Environment.new(callable.environment)
  callable.args.zip(args[0...callable.args.length]) do |(var, default), value|
    if value && keywords.include?(var.underscored_name)
      raise Sass::SyntaxError.new("#{desc} was passed argument $#{var.name} both by position and by name.")
    end
    value ||= keywords.delete(var.underscored_name)
    value ||= default && default.perform(env)
    raise Sass::SyntaxError.new("#{desc} is missing argument #{var.inspect}.") unless value
    env.set_local_var(var.name, value)
  end
  if callable.splat
    rest = args[callable.args.length..-1]
    arg_list = Sass::Script::ArgList.new(rest, keywords.dup, splat_sep)
    arg_list.options = env.options
    env.set_local_var(callable.splat.name, arg_list)
  end
  yield env
rescue Exception => e
ensure
  # If there's a keyword exception, we don't want to throw it immediately,
  # because the invalid keywords may be part of a glob argument that should be
  # passed on to another function. So we only raise it if we reach the end of
  # this function *and* the keywords attached to the argument list glob object
  # haven't been accessed.
  #
  # The keyword exception takes precedence over any Sass errors, but not over
  # non-Sass exceptions.
  if keyword_exception &&
      !(arg_list && arg_list.keywords_accessed) &&
      (e.nil? || e.is_a?(Sass::SyntaxError))
    raise keyword_exception
  elsif e
    raise e
  end
end

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

def handle_import_loop!(node)
  msg = "An @import loop has been found:"
  files = @stack.map {|s| s[:filename]}.compact
  if node.filename == node.imported_file.options[:filename]
    raise Sass::SyntaxError.new("#{msg} #{node.filename} imports itself")
  end
  files << node.filename << node.imported_file.options[:filename]
  msg << "\n" << Sass::Util.enum_cons(files, 2).map do |m1, m2|
    "    #{m1} imports #{m2}"
  end.join("\n")
  raise Sass::SyntaxError.new(msg)
end

def handle_include_loop!(node)
  msg = "An @include loop has been found:"
  content_count = 0
  mixins = @stack.reverse.map {|s| s[:name]}.compact.select do |s|
    if s == '@content'
      content_count += 1
      false
    elsif content_count > 0
      content_count -= 1
      false
    else
      true
    end
  end
  return unless mixins.include?(node.name)
  raise Sass::SyntaxError.new("#{msg} #{node.name} includes itself") if mixins.size == 1
  msg << "\n" << Sass::Util.enum_cons(mixins.reverse + [node.name], 2).map do |m1, m2|
    "    #{m1} includes #{m2}"
  end.join("\n")
  raise Sass::SyntaxError.new(msg)
end

def initialize(env)
  @environment = env
  # Stack trace information, including mixin includes and imports.
  @stack = []
end

def run_interp(text)
  run_interp_no_strip(text).strip
end

def run_interp_no_strip(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
end

def stack_trace
  trace = []
  stack = @stack.map {|e| e.dup}.reverse
  stack.each_cons(2) {|(e1, e2)| e1[:caller] = e2[:name]; [e1, e2]}
  stack.each_with_index do |entry, i|
    msg = "#{i == 0 ? "on" : "from"} line #{entry[:line]}"
    msg << " of #{entry[:filename] || "an unknown file"}"
    msg << ", in `#{entry[:caller]}'" if entry[:caller]
    trace << msg
  end
  trace
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, parent.options) do
    parent.children = super.flatten
    parent
  end
end

def visit_comment(node)
  return [] if node.invisible?
  node.resolved_value = run_interp_no_strip(node.value)
  node.resolved_value.gsub!(/\\([\\#])/, '\1')
  node
end

def visit_content(node)
  return [] unless content = @environment.content
  @stack.push(:filename => node.filename, :line => node.line, :name => '@content')
  trace_node = Sass::Tree::TraceNode.from_node('@content', node)
  with_environment(@environment.caller) {trace_node.children = content.map {|c| visit(c.dup)}.flatten}
  trace_node
rescue Sass::SyntaxError => e
  e.modify_backtrace(:mixin => '@content', :line => node.line)
  e.add_backtrace(:line => node.line)
  raise e
ensure
  @stack.pop if content
end

def visit_cssimport(node)
  node.resolved_uri = run_interp([node.uri])
  if node.query
    parser = Sass::SCSS::StaticParser.new(run_interp(node.query), node.filename, node.line)
    node.resolved_query ||= parser.parse_media_query_list
  end
  yield
end

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

def visit_directive(node)
  node.resolved_value = run_interp(node.value)
  yield
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::StaticParser.new(run_interp(node.selector), node.filename, node.line)
  node.resolved_selector = parser.parse_selector
  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)
  env = Sass::Environment.new(@environment, node.options)
  @environment.set_local_function(node.name,
    Sass::Callable.new(node.name, node.args, node.splat, env, node.children, !:has_content, "function"))
  []
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::CssImportNode.resolved("url(#{path})")
  end
  file = node.imported_file
  handle_import_loop!(node) if @stack.any? {|e| e[:filename] == file.options[:filename]}
  begin
    @stack.push(:filename => node.filename, :line => node.line)
    root = file.to_tree
    Sass::Tree::Visitors::CheckNesting.visit(root)
    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
  end
ensure
  @stack.pop unless path
end

def visit_media(node)
  parser = Sass::SCSS::StaticParser.new(run_interp(node.query), node.filename, node.line)
  node.resolved_query ||= parser.parse_media_query_list
  yield
end

def visit_mixin(node)
  include_loop = true
  handle_include_loop!(node) if @stack.any? {|e| e[:name] == node.name}
  include_loop = false
  @stack.push(:filename => node.filename, :line => node.line, :name => node.name)
  raise Sass::SyntaxError.new("Undefined mixin '#{node.name}'.") unless mixin = @environment.mixin(node.name)
  if node.children.any? && !mixin.has_content
    raise Sass::SyntaxError.new(%Q{Mixin "#{node.name}" does not accept a content block.})
  end
  args = node.args.map {|a| a.perform(@environment)}
  keywords = Sass::Util.map_hash(node.keywords) {|k, v| [k, v.perform(@environment)]}
  splat = node.splat.perform(@environment) if node.splat
  self.class.perform_arguments(mixin, args, keywords, splat) do |env|
    env.caller = Sass::Environment.new(@environment)
    env.content = node.children if node.has_children
    trace_node = Sass::Tree::TraceNode.from_node(node.name, node)
    with_environment(env) {trace_node.children = mixin.tree.map {|c| visit(c)}.flatten}
    trace_node
  end
rescue Sass::SyntaxError => e
  unless include_loop
    e.modify_backtrace(:mixin => node.name, :line => node.line)
    e.add_backtrace(:line => node.line)
  end
  raise e
ensure
  @stack.pop unless include_loop
end

def visit_mixindef(node)
  env = Sass::Environment.new(@environment, node.options)
  @environment.set_local_mixin(node.name,
    Sass::Callable.new(node.name, node.args, node.splat, env, node.children, node.has_content, "mixin"))
  []
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)
  yield
rescue Sass::SyntaxError => e
  e.sass_template ||= node.template
  raise e
end

def visit_rule(node)
  rule = node.rule
  rule = rule.map {|e| e.is_a?(String) && e != ' ' ? e.strip : e} if node.style == :compressed
  parser = Sass::SCSS::StaticParser.new(run_interp(node.rule), node.filename, node.line)
  node.parsed_rules ||= parser.parse_selector
  if node.options[:trace_selectors]
    @stack.push(:filename => node.filename, :line => node.line)
    node.stack_trace = stack_trace
    @stack.pop
  end
  yield
end

def visit_supports(node)
  node.condition = node.condition.deep_copy
  node.condition.perform(@environment)
  yield
end

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

def visit_warn(node)
  @stack.push(: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         "
  msg << stack_trace.join("\n         ") << "\n"
  Sass::Util.sass_warn msg
  []
ensure
  @stack.pop
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