class ActiveRecord::Relation::WhereClause

def self.empty
  @empty ||= new([]).freeze
end

def +(other)
  WhereClause.new(predicates + other.predicates)
end

def -(other)
  WhereClause.new(predicates - other.predicates)
end

def ==(other)
  other.is_a?(WhereClause) &&
    predicates == other.predicates
end

def ast
  predicates = predicates_with_wrapped_sql_literals
  predicates.one? ? predicates.first : Arel::Nodes::And.new(predicates)
end

def contradiction?
  predicates.any? do |x|
    case x
    when Arel::Nodes::In
      Array === x.right && x.right.empty?
    when Arel::Nodes::Equality
      x.right.respond_to?(:unboundable?) && x.right.unboundable?
    end
  end
end

def each_attributes
  predicates.each do |node|
    attr = extract_attribute(node) || begin
      node.left if equality_node?(node) && node.left.is_a?(Arel::Predications)
    end
    yield attr, node if attr
  end
end

def equalities(predicates, equality_only)
  equalities = []
  predicates.each do |node|
    if equality_only ? Arel::Nodes::Equality === node : equality_node?(node)
      equalities << node
    elsif node.is_a?(Arel::Nodes::And)
      equalities.concat equalities(node.children, equality_only)
    end
  end
  equalities
end

def equality_node?(node)
  !node.is_a?(String) && node.equality?
end

def except(*columns)
  WhereClause.new(except_predicates(columns))
end

def except_predicates(columns)
  attrs = columns.extract! { |node| node.is_a?(Arel::Attribute) }
  non_attrs = columns.extract! { |node| node.is_a?(Arel::Predications) }
  predicates.reject do |node|
    if !non_attrs.empty? && node.equality? && node.left.is_a?(Arel::Predications)
      non_attrs.include?(node.left)
    end || Arel.fetch_attribute(node) do |attr|
      attrs.include?(attr) || columns.include?(attr.name.to_s)
    end
  end
end

def extract_attribute(node)
  attr_node = nil
  Arel.fetch_attribute(node) do |attr|
    return if attr_node&.!= attr # all attr nodes should be the same
    attr_node = attr
  end
  attr_node
end

def extract_attributes
  attrs = []
  each_attributes { |attr, _| attrs << attr }
  attrs
end

def extract_node_value(node)
  if node.respond_to?(:value_before_type_cast)
    node.value_before_type_cast
  elsif Array === node
    node.map { |v| extract_node_value(v) }
  end
end

def hash
  [self.class, predicates].hash
end

def initialize(predicates)
  @predicates = predicates
end

def invert
  if predicates.size == 1
    inverted_predicates = [ invert_predicate(predicates.first) ]
  else
    inverted_predicates = [ Arel::Nodes::Not.new(ast) ]
  end
  WhereClause.new(inverted_predicates)
end

def invert_predicate(node)
  case node
  when NilClass
    raise ArgumentError, "Invalid argument for .where.not(), got nil."
  when String
    Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
  else
    node.invert
  end
end

def merge(other)
  predicates = except_predicates(other.extract_attributes)
  WhereClause.new(predicates | other.predicates)
end

def non_empty_predicates
  predicates - ARRAY_WITH_EMPTY_STRING
end

def or(other)
  left = self - other
  common = self - left
  right = other - common
  if left.empty? || right.empty?
    common
  else
    left = left.ast
    left = left.expr if left.is_a?(Arel::Nodes::Grouping)
    right = right.ast
    right = right.expr if right.is_a?(Arel::Nodes::Grouping)
    or_clause = if left.is_a?(Arel::Nodes::Or)
      Arel::Nodes::Or.new(left.children + [right])
    else
      Arel::Nodes::Or.new([left, right])
    end
    common.predicates << Arel::Nodes::Grouping.new(or_clause)
    common
  end
end

def predicates_with_wrapped_sql_literals
  non_empty_predicates.map do |node|
    case node
    when Arel::Nodes::SqlLiteral, ::String
      wrap_sql_literal(node)
    else node
    end
  end
end

def referenced_columns
  hash = {}
  each_attributes { |attr, node| hash[attr] = node }
  hash
end

def to_h(table_name = nil, equality_only: false)
  equalities(predicates, equality_only).each_with_object({}) do |node, hash|
    next if table_name&.!= node.left.relation.name
    name = node.left.name.to_s
    value = extract_node_value(node.right)
    hash[name] = value
  end
end

def wrap_sql_literal(node)
  if ::String === node
    node = Arel.sql(node)
  end
  Arel::Nodes::Grouping.new(node)
end

def |(other)
  WhereClause.new(predicates | other.predicates)
end