class Opal::Nodes::MassAssignNode

def compile
  with_temp do |array|
    if rhs.type == :array
      push "#{array} = ", expr(rhs)
      rhs_len = rhs.children.any? { |c| c.type == :splat } ? nil : rhs.children.size
      compile_masgn(lhs.children, array, rhs_len)
      push ", #{array}" # a mass assignment evaluates to the RHS
    else
      helper :to_ary
      with_temp do |retval|
        push "#{retval} = ", expr(rhs)
        push ", #{array} = $to_ary(#{retval})"
        compile_masgn(lhs.children, array)
        push ", #{retval}"
      end
    end
  end
end

def compile_assignment(child, array, idx, len = nil)
  assign =
    if !len || idx >= len
      s(:js_tmp, "(#{array}[#{idx}] == null ? nil : #{array}[#{idx}])")
    else
      s(:js_tmp, "#{array}[#{idx}]")
    end
  part = child.updated
  if SIMPLE_ASSIGNMENT.include?(child.type)
    part = part.updated(nil, part.children + [assign])
  elsif child.type == :send
    part = part.updated(nil, part.children + [assign])
  elsif child.type == :attrasgn
    part.last << assign
  elsif child.type == :mlhs
    helper :to_ary
    # nested destructuring
    tmp = scope.new_temp
    push ", (#{tmp} = $to_ary(#{assign.children[0]})"
    compile_masgn(child.children, tmp)
    push ')'
    scope.queue_temp(tmp)
    return
  else
    raise "Bad child node in masgn LHS: #{child}. LHS: #{lhs}"
  end
  push ', '
  push expr(part)
end

def compile_masgn(lhs_items, array, len = nil)
  pre_splat  = lhs_items.take_while { |child| child.type != :splat }
  post_splat = lhs_items.drop(pre_splat.size)
  pre_splat.each_with_index do |child, idx|
    compile_assignment(child, array, idx, len)
  end
  unless post_splat.empty?
    splat = post_splat.shift
    if post_splat.empty? # trailing splat
      if part = splat.children[0]
        helper :slice
        part = part.dup << s(:js_tmp, "$slice(#{array}, #{pre_splat.size})")
        push ', '
        push expr(part)
      end
    else
      tmp = scope.new_temp # end index for items consumed by splat
      push ", #{tmp} = #{array}.length - #{post_splat.size}"
      push ", #{tmp} = (#{tmp} < #{pre_splat.size}) ? #{pre_splat.size} : #{tmp}"
      if part = splat.children[0]
        helper :slice
        part = part.dup << s(:js_tmp, "$slice(#{array}, #{pre_splat.size}, #{tmp})")
        push ', '
        push expr(part)
      end
      post_splat.each_with_index do |child, idx|
        if idx == 0
          compile_assignment(child, array, tmp)
        else
          compile_assignment(child, array, "#{tmp} + #{idx}")
        end
      end
      scope.queue_temp(tmp)
    end
  end
end