interpreter

type Activation interface {
	// ResolveName returns a value from the activation by qualified name, or false if the name
	// could not be found.
	ResolveName(name string) (interface{}, bool)

	// Parent returns the parent of the current activation, may be nil.
	// If non-nil, the parent will be searched during resolve calls.
	Parent() Activation
}

type Attribute interface {
	Qualifier

	// AddQualifier adds a qualifier on the Attribute or error if the qualification is not a valid
	// qualifier type.
	AddQualifier(Qualifier) (Attribute, error)

	// Resolve returns the value of the Attribute given the current Activation.
	Resolve(Activation) (interface{}, error)
}

type AttributeFactory interface {
	// AbsoluteAttribute creates an attribute that refers to a top-level variable name.
	//
	// Only type-checked expressions generate absolute attributes.
	AbsoluteAttribute(id int64, name string) Attribute

	// ConditionalAttribute creates an attribute with two Attribute branches, where the Attribute
	// that is resolved depends on the boolean evaluation of the input 'expr'.
	ConditionalAttribute(id int64, expr Interpretable, t, f Attribute) Attribute

	// MaybeAttribute creates an attribute that refers to either a field selection or a namespaced
	// variable name.
	//
	// Only expressions which have not been type-checked may generate oneof attributes.
	MaybeAttribute(id int64, name string) Attribute

	// RelativeAttribute creates an attribute whose value is a qualification of a dynamic
	// computation rather than a static variable reference.
	RelativeAttribute(id int64, operand Interpretable) Attribute

	// NewQualifier creates a qualifier on the target object with a given value.
	//
	// The 'val' may be an Attribute or any proto-supported map key type: bool, int, string, uint.
	//
	// The qualifier may consider the object type being qualified, if present. If absent, the
	// qualification should be considered dynamic and the qualification should still work, though
	// it may be sub-optimal.
	NewQualifier(objType *exprpb.Type, qualID int64, val interface{}) (Qualifier, error)
}

type Dispatcher interface {
	// Add one or more overloads, returning an error if any Overload has the same Overload#Name.
	Add(overloads ...*functions.Overload) error

	// FindOverload returns an Overload definition matching the provided name.
	FindOverload(overload string) (*functions.Overload, bool)

	// OverloadIds returns the set of all overload identifiers configured for dispatch.
	OverloadIds() []string
}

type EvalState interface {
	// IDs returns the list of ids with recorded values.
	IDs() []int64

	// Value returns the observed value of the given expression id if found, and a nil false
	// result if not.
	Value(int64) (ref.Val, bool)

	// SetValue sets the observed value of the expression id.
	SetValue(int64, ref.Val)

	// Reset clears the previously recorded expression values.
	Reset()
}

type Interpretable interface {
	// ID value corresponding to the expression node.
	ID() int64

	// Eval an Activation to produce an output.
	Eval(activation Activation) ref.Val
}

type InterpretableDecorator func(Interpretable) (Interpretable, error)

type Interpreter interface {
	// NewInterpretable creates an Interpretable from a checked expression and an
	// optional list of InterpretableDecorator values.
	NewInterpretable(checked *exprpb.CheckedExpr,
		decorators ...InterpretableDecorator) (Interpretable, error)

	// NewUncheckedInterpretable returns an Interpretable from a parsed expression
	// and an optional list of InterpretableDecorator values.
	NewUncheckedInterpretable(expr *exprpb.Expr,
		decorators ...InterpretableDecorator) (Interpretable, error)
}

type Qualifier interface {
	// ID where the qualifier appears within an expression.
	ID() int64

	// Qualify performs a qualification, e.g. field selection, on the input object and returns
	// the value or error that results.
	Qualify(vars Activation, obj interface{}) (interface{}, error)
}