class Steep::Interface::Substitution

def self.build(vars, types = nil, instance_type: nil, module_type: nil, self_type: nil)
  types ||= vars.map {|var| AST::Types::Var.fresh(var) }
  raise InvalidSubstitutionError.new(vars_size: vars.size, types_size: types.size) unless vars.size == types.size
  dic = vars.zip(types).each.with_object({}) do |(var, type), d| #$ Hash[Symbol, AST::Types::t]
    type or raise
    d[var] = type
  end
  new(dictionary: dic, instance_type: instance_type, module_type: module_type, self_type: self_type)
end

def self.empty
  new(dictionary: {},
      instance_type: AST::Types::Instance.instance,
      module_type: AST::Types::Class.instance,
      self_type: AST::Types::Self.instance)
end

def [](key)
  dictionary[key] or raise "Unknown variable: #{key}"
end

def add!(v, ty)
  merge!(Substitution.new(dictionary: { v => ty }, instance_type: instance_type, module_type: module_type, self_type: self_type))
end

def apply?(type)
  case type
  when AST::Types::Var
    key?(type.name)
  when AST::Types::Self
    !self_type.is_a?(AST::Types::Self)
  when AST::Types::Instance
    !instance_type.is_a?(AST::Types::Instance)
  when AST::Types::Class
    !module_type.is_a?(AST::Types::Class)
  when AST::Types::Name::Applying
    type.args.any? {|ty| apply?(ty) }
  else
    type.each_child.any? {|t| apply?(t) }
  end
end

def domain
  set = Set.new
  set.merge(dictionary.keys)
  set << AST::Types::Self.instance if self_type
  set << AST::Types::Class.instance if module_type
  set << AST::Types::Instance.instance if instance_type
  set
end

def empty?
  dictionary.empty? &&
    instance_type.is_a?(AST::Types::Instance) &&
    module_type.is_a?(AST::Types::Class) &&
    self_type.is_a?(AST::Types::Self)
end

def except(vars)
  self.class.new(
    dictionary: dictionary.dup,
    instance_type: instance_type,
    module_type: module_type,
    self_type: self_type
  ).except!(vars)
end

def except!(vars)
  vars.each do |var|
    dictionary.delete(var)
  end
  self
end

def initialize(dictionary:, instance_type:, module_type:, self_type:)
  @dictionary = dictionary
  @instance_type = instance_type
  @module_type = module_type
  @self_type = self_type
end

def key?(var)
  dictionary.key?(var)
end

def merge(s)
  Substitution.new(dictionary: dictionary.dup,
                   instance_type: instance_type,
                   module_type: module_type,
                   self_type: self_type).merge!(s)
end

def merge!(s, overwrite: false)
  dictionary.transform_values! {|ty| ty.subst(s) }
  dictionary.merge!(s.dictionary) do |key, a, b|
    if a == b
      a
    else
      if overwrite
        b
      else
        raise "Duplicated key on merge!: #{key}, #{a}, #{b} (#{self})"
      end
    end
  end
  @instance_type = instance_type.subst(s) if instance_type
  @module_type = module_type.subst(s) if module_type
  @self_type = self_type.subst(s) if self_type
  self
end

def to_s
  a = [] #: Array[String]
  dictionary.each do |x, ty|
    a << "#{x} -> #{ty}"
  end
  a << "[instance_type] -> #{instance_type}"
  a << "[module_type] -> #{module_type}"
  a << "[self_type] -> #{self_type}"
  "{ #{a.join(", ")} }"
end

def update(self_type: self_type(), instance_type: instance_type(), module_type: module_type())
  Substitution.new(dictionary: dictionary.dup, instance_type: instance_type, self_type: self_type, module_type: module_type)
end