module Steep
  module TypeInference
    class BlockParams
      class Param
        attr_reader :var
        attr_reader :type
        attr_reader :value
        attr_reader :node

        def initialize(var:, type:, value:, node:)
          @var = var
          @type = type
          @value = value
          @node = node
        end

        def ==(other)
          other.is_a?(self.class) && other.var == var && other.type == type && other.value == value && other.node == node
        end

        alias eql? ==

        def hash
          self.class.hash ^ var.hash ^ type.hash ^ value.hash ^ node.hash
        end

        def each_param(&block)
          if block
            yield self
          else
            enum_for :each_param
          end
        end
      end

      class MultipleParam
        attr_reader :node

        attr_reader :params

        def initialize(node:, params:)
          @params = params
          @node = node
        end

        def ==(other)
          other.is_a?(self.class) &&
            other.node == node &&
            other.params == params
        end

        alias eql? ==

        def hash
          self.class.hash ^ node.hash ^ params.hash
        end

        def variable_types
          each_param.with_object({}) do |param, hash| #$ Hash[Symbol, AST::Types::t?]
            var_name = param.var || next
            hash[var_name] = param.type
          end
        end

        def each_param(&block)
          if block
            params.each do |param|
              case param
              when Param
                yield param
              when MultipleParam
                param.each_param(&block)
              end
            end
          else
            enum_for :each_param
          end
        end

        def type
          types = params.map do |param|
            param.type or return
          end

          AST::Types::Tuple.new(types: types)
        end
      end

      attr_reader :leading_params
      attr_reader :optional_params
      attr_reader :rest_param
      attr_reader :trailing_params
      attr_reader :block_param

      def initialize(leading_params:, optional_params:, rest_param:, trailing_params:, block_param:)
        @leading_params = leading_params
        @optional_params = optional_params
        @rest_param = rest_param
        @trailing_params = trailing_params
        @block_param = block_param
      end

      def params
        [].tap do |params|
          params.push(*leading_params)
          params.push(*optional_params)
          params.push rest_param if rest_param
          params.push(*trailing_params)
          params.push(block_param) if block_param
        end
      end

      def self.from_node(node, annotations:)
        # @type var leading_params: Array[Param | MultipleParam]
        leading_params = []
        # @type var optional_params: Array[Param]
        optional_params = []
        # @type var rest_param: Param?
        rest_param = nil
        # @type var trailing_params: Array[Param | MultipleParam]
        trailing_params = []
        # @type var block_param: Param?
        block_param = nil

        default_params = leading_params

        node.children.each do |arg|
          case
          when arg.type == :mlhs
            default_params << from_multiple(arg, annotations)
          when arg.type == :procarg0 && arg.children.size > 1
            default_params << from_multiple(arg, annotations)
          else
            var = arg.children[0]
            type = annotations.var_type(lvar: var)
            case arg.type
            when :arg
              default_params << Param.new(var: var, type: type, value: nil, node: arg)
            when :procarg0
              var = arg.children[0]
              if var.is_a?(Symbol)
                default_params << Param.new(var: var, type: type, value: nil, node: arg)
              else
                var = var.children[0]
                default_params << Param.new(var: var, type: type, value: nil, node: arg)
              end
            when :optarg
              default_params = trailing_params
              optional_params << Param.new(var: var, type: type, value: arg.children.last, node: arg)
            when :restarg
              default_params = trailing_params
              rest_param = Param.new(var: var, type: type, value: nil, node: arg)
            when :blockarg
              block_param = Param.new(var: var, type: type, value: nil, node: arg)
              break
            end
          end
        end

        new(
          leading_params: leading_params,
          optional_params: optional_params,
          rest_param: rest_param,
          trailing_params: trailing_params,
          block_param: block_param
        )
      end

      def params_type(hint: nil)
        params_type0(hint: hint) or params_type0(hint: nil)
      end

      def params_type0(hint:)
        # @type var leadings: Array[AST::Types::t]
        # @type var optionals: Array[AST::Types::t]

        if hint
          case
          when leading_params.size == hint.required.size
            leadings = leading_params.map.with_index do |param, index|
              param.type || hint.required[index]
            end
          when !hint.rest && hint.optional.empty? && leading_params.size > hint.required.size
            leadings = leading_params.take(hint.required.size).map.with_index do |param, index|
              param.type || hint.required[index]
            end
          when !hint.rest && hint.optional.empty? && leading_params.size < hint.required.size
            leadings = leading_params.map.with_index do |param, index|
              param.type || hint.required[index]
            end + hint.required.drop(leading_params.size)
          else
            return nil
          end

          case
          when optional_params.size == hint.optional.size
            optionals = optional_params.map.with_index do |param, index|
              param.type || hint.optional[index]
            end
          when !hint.rest && optional_params.size > hint.optional.size
            optionals = optional_params.take(hint.optional.size).map.with_index do |param, index|
              param.type || hint.optional[index]
            end
          when !hint.rest && optional_params.size < hint.optional.size
            optionals = optional_params.map.with_index do |param, index|
              param.type || hint.optional[index]
            end + hint.optional.drop(optional_params.size)
          else
            return nil
          end

          if rest_param
            if hint.rest
              if rest_type = rest_param.type
                if AST::Builtin::Array.instance_type?(rest_type)
                  rest_type.is_a?(AST::Types::Name::Instance) or raise
                  rest = rest_type.args.first or raise
                end
              end

              rest ||= hint.rest
            end
          end
        else
          leadings = leading_params.map {|param| param.type || AST::Types::Any.instance }
          optionals = optional_params.map {|param| param.type || AST::Types::Any.instance }

          if rest_param
            if rest_type = rest_param.type
              if array = AST::Builtin::Array.instance_type?(rest_type)
                rest = array.args.first or raise
              end
            end
            rest ||= AST::Types::Any.instance
          end
        end

        Interface::Function::Params.build(
          required: leadings,
          optional: optionals,
          rest: rest
        )
      end

      def zip(params_type, block, factory:)
        if trailing_params.any?
          Steep.logger.error "Block definition with trailing required parameters are not supported yet"
        end

        # @type var zip: Array[[Param | MultipleParam, AST::Types::t]]
        zip = []

        if params_type.nil? || untyped_args?(params_type)
          params.each do |param|
            if param == rest_param
              zip << [param, AST::Builtin::Array.instance_type(fill_untyped: true)]
            else
              zip << [param, AST::Builtin.any_type]
            end
          end
          return zip
        end

        if expandable? && (type = expandable_params?(params_type, factory))
          case
          when AST::Builtin::Array.instance_type?(type)
            type.is_a?(AST::Types::Name::Instance) or raise

            type_arg = type.args.fetch(0)
            params.each do |param|
              unless param == rest_param
                zip << [param, AST::Types::Union.build(types: [type_arg, AST::Builtin.nil_type])]
              else
                zip << [param, AST::Builtin::Array.instance_type(type_arg)]
              end
            end
          when type.is_a?(AST::Types::Tuple)
            types = type.types.dup
            (leading_params + optional_params).each do |param|
              ty = types.shift
              if ty
                zip << [param, ty]
              else
                zip << [param, AST::Types::Nil.instance]
              end
            end

            if rest_param
              if types.any?
                union = AST::Types::Union.build(types: types)
                zip << [rest_param, AST::Builtin::Array.instance_type(union)]
              else
                zip << [rest_param, AST::Types::Nil.instance]
              end
            end
          end
        else
          types = params_type.flat_unnamed_params

          (leading_params + optional_params).each do |param|
            typ = types.shift&.last || params_type.rest

            if typ
              zip << [param, typ]
            else
              zip << [param, AST::Builtin.nil_type]
            end
          end

          if rest_param
            if types.empty?
              array = AST::Builtin::Array.instance_type(params_type.rest || AST::Builtin.any_type)
              zip << [rest_param, array]
            else
              union_members = types.map(&:last)
              union_members << params_type.rest if params_type.rest
              union = AST::Types::Union.build(types: union_members)
              array = AST::Builtin::Array.instance_type(union)
              zip << [rest_param, array]
            end
          end
        end

        if block_param
          if block
            proc_type = AST::Types::Proc.new(type: block.type, block: nil, self_type: block.self_type)
            if block.optional?
              proc_type = AST::Types::Union.build(types: [proc_type, AST::Builtin.nil_type])
            end

            zip << [block_param, proc_type]
          else
            zip << [block_param, AST::Builtin.nil_type]
          end
        end

        zip
      end

      def expandable_params?(params_type, factory)
        if params_type.flat_unnamed_params.size == 1
          type = params_type.required.first or raise
          type = factory.deep_expand_alias(type) || type

          case type
          when AST::Types::Tuple
            type
          when AST::Types::Name::Base
            if AST::Builtin::Array.instance_type?(type)
              type
            end
          end
        end
      end

      def expandable?
        case
        when leading_params.size + trailing_params.size > 1
          true
        when (leading_params.any? || trailing_params.any?) && rest_param
          true
        when params.size == 1 && params.fetch(0).node.type == :arg
          true
        else
          false
        end
      end

      def each(&block)
        if block
          params.each(&block)
        else
          enum_for :each
        end
      end

      def each_single_param()
        each do |param|
          case param
          when Param
            yield param
          when MultipleParam
            param.each_param do |p|
              yield p
            end
          end
        end
      end

      def self.from_multiple(node, annotations)
        # @type var params: Array[Param | MultipleParam]
        params = []

        node.children.each do |child|
          if child.type == :mlhs
            params << from_multiple(child, annotations)
          else
            var = child.children.first

            raise unless var.is_a?(Symbol)
            type = annotations.var_type(lvar: var)

            params << Param.new(var: var, node: child, value: nil, type: type)
          end
        end

        MultipleParam.new(node: node, params: params)
      end

      def untyped_args?(params)
        flat = params.flat_unnamed_params
        flat.size == 1 && flat.dig(0, 1)&.is_a?(AST::Types::Any)
      end
    end
  end
end