class RBS::Resolver::ConstantResolver

def children(module_name)
  module_name = builder.env.normalize_module_name(module_name)
  unless child_constants_cache.key?(module_name)
    load_child_constants(module_name)
  end
  child_constants_cache[module_name] or raise
end

def constants(context)
  unless context_constants_cache.key?(context)
    load_context_constants(context)
  end
  context_constants_cache[context]
end

def constants_from_ancestors(module_name, constants:)
  entry = builder.env.normalized_module_class_entry(module_name) or raise
  if entry.is_a?(Environment::ClassEntry) || entry.is_a?(Environment::ModuleEntry)
    constants.merge!(table.children(BuiltinNames::Object.name) || raise)
    constants.merge!(table.toplevel)
  end
  builder.ancestor_builder.instance_ancestors(entry.name).ancestors.reverse_each do |ancestor|
    if ancestor.is_a?(Definition::Ancestor::Instance)
      case ancestor.source
      when AST::Members::Include, :super, nil
        consts = table.children(ancestor.name) or raise
        if ancestor.name == BuiltinNames::Object.name && entry.is_a?(Environment::ClassEntry)
          # Insert toplevel constants as ::Object's constants
          consts.merge!(table.toplevel)
        end
        constants.merge!(consts)
      end
    end
  end
end

def constants_from_context(context, constants:)
  if context
    parent, last = context
    constants_from_context(parent, constants: constants) or return false
    if last
      consts = table.children(builder.env.normalize_module_name(last)) or return false
      constants.merge!(consts)
    end
  end
  true
end

def constants_itself(context, constants:)
  if context
    _, typename = context
    if typename
      if (ns = typename.namespace).empty?
        constant = table.toplevel[typename.name] or raise
      else
        hash = table.children(ns.to_type_name) or raise
        constant = hash[typename.name]
      end
      constants[typename.name] = constant
    end
  end
end

def initialize(builder:)
  @builder = builder
  @table = Table.new(builder.env)
  @context_constants_cache = {}
  @child_constants_cache = {}
end

def load_child_constants(name)
  # @type var constants: Hash[Symbol, Constant]
  constants = {}
  if table.children(name)
    builder.ancestor_builder.instance_ancestors(name).ancestors.reverse_each do |ancestor|
      if ancestor.is_a?(Definition::Ancestor::Instance)
        if ancestor.name == BuiltinNames::Object.name
          if name != BuiltinNames::Object.name
            next
          end
        end
        case ancestor.source
        when AST::Members::Include, :super, nil
          consts = table.children(ancestor.name) or raise
          constants.merge!(consts)
        end
      end
    end
  end
  child_constants_cache[name] = constants
end

def load_context_constants(context)
  # @type var consts: Hash[Symbol, Constant]
  consts = {}
  if last = context&.[](1)
    constants_from_ancestors(last, constants: consts)
  else
    constants_from_ancestors(BuiltinNames::Object.name, constants: consts)
  end
  constants_from_context(context, constants: consts) or return
  constants_itself(context, constants: consts)
  context_constants_cache[context] = consts
end

def resolve(name, context:)
  cs = constants(context) or raise "Broken context is given"
  cs[name]
end

def resolve_child(module_name, name)
  children(module_name)[name]
end