expr

type AttributeDescriptorFinder interface {
	// GetAttribute finds attribute descriptor in the vocabulary. returns nil if not found.
	GetAttribute(name string) *cfgpb.AttributeManifest_AttributeInfo
}

type Constant struct {
	StrValue string
	Value    interface{}
	Type     dpb.ValueType
}

type Evaluator interface {
	// Eval evaluates given expression using the attribute bag
	Eval(expr string, attrs attribute.Bag) (interface{}, error)

	// Eval evaluates given expression using the attribute bag to a string
	EvalString(expr string, attrs attribute.Bag) (string, error)

	PredicateEvaluator

	TypeChecker
}

type Expression struct {
	// Oneof the following
	Const *Constant
	Var   *Variable
	Fn    *Function
}

type Func interface {
	FuncBase

	// Call performs the function call. It is guaranteed
	// that call will be made with correct arity.
	// may panic.
	Call(attrs attribute.Bag, args []*Expression, fMap map[string]FuncBase) (interface{}, error)
}

type FuncBase interface {
	// Name uniquely identifies the function.
	Name() string

	// ReturnType specifies the return type of this function.
	ReturnType() config.ValueType

	// ArgTypes specifies the argument types in order expected by the function.
	ArgTypes() []config.ValueType
}

type Function struct {
	Name string
	Args []*Expression
}

type PredicateEvaluator interface {
	// EvalPredicate evaluates given predicate using the attribute bag
	EvalPredicate(expr string, attrs attribute.Bag) (bool, error)
}

type TypeChecker interface {
	// EvalType produces the type of an expression or an error if the type cannot be evaluated.
	// TODO: we probably want to use a golang type rather than pb.ValueType (a proto).
	EvalType(expr string, finder AttributeDescriptorFinder) (pb.ValueType, error)

	// AssertType evaluates the type of expr using the attribute set; if the evaluated type is equal to
	// the expected type we return nil, and return an error otherwise.
	AssertType(expr string, finder AttributeDescriptorFinder, expectedType pb.ValueType) error
}

type Variable struct {
	Name string
}