package normalorder

import (
	"git.maximhutz.com/max/lambda/pkg/emitter"
	"git.maximhutz.com/max/lambda/pkg/lambda"
	"git.maximhutz.com/max/lambda/pkg/repr"
	"git.maximhutz.com/max/lambda/pkg/runtime"
)

// NormalOrderReducer implements normal order (leftmost-outermost) reduction
// for lambda calculus expressions.
type Runtime struct {
	emitter.BaseEmitter[runtime.Event]
	expression lambda.Expression
}

// NewNormalOrderReducer creates a new normal order reducer.
func NewRuntime(expression lambda.Expression) *Runtime {
	return &Runtime{
		BaseEmitter: *emitter.New[runtime.Event](),
		expression:  expression,
	}
}

// Expression returns the current expression state.
func (r *Runtime) Expression() repr.Repr {
	return r.expression
}

func (r *Runtime) Step() bool {
	result, done := ReduceOnce(r.expression)
	r.expression = result
	return !done
}

// Reduce performs normal order reduction on a lambda expression.
// The expression must be a lambda.Expression; other types are returned unchanged.
func (r *Runtime) Run() {
	r.Emit(runtime.StartEvent)

	for !r.Step() {
		r.Emit(runtime.StepEvent)
	}

	r.Emit(runtime.StopEvent)
}