package usecase

import (
	"context"
	"errors"
	"time"
)

// OperationScope owns an optional deadline and its invocation-specific cause.
type OperationScope struct {
	Context context.Context
	cancel  context.CancelFunc
	cause   error
}

// NewOperationScope creates a child only when the selected duration is positive.
func NewOperationScope(parent context.Context, duration time.Duration) *OperationScope {
	scope := &OperationScope{Context: parent, cancel: func() {}}
	if duration > 0 {
		scope.cause = errors.New("operation deadline")
		scope.Context, scope.cancel = context.WithTimeoutCause(parent, duration, scope.cause)
	}
	return scope
}

// Finalize preserves the failure and marks it only when this scope expired.
func (s *OperationScope) Finalize(err error) error {
	if err != nil && s.cause != nil && s.Context.Err() == context.DeadlineExceeded &&
		errors.Is(err, s.Context.Err()) && context.Cause(s.Context) == s.cause {
		return &OperationError{Category: ErrOperationTimeout, Cause: err}
	}
	return err
}

// Close releases the timer and associated child context.
func (s *OperationScope) Close() { s.cancel() }