package debian

import (
	"errors"
	"fmt"

	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/reflect/protoreflect"

	"go.wit.com/lib/config"
)

func SetDebInfoString(pb proto.Message, varname string, varvalue string) error {
	// 1. Get the reflection interface for the top-level message (e.g., Package).
	msg := pb.ProtoReflect()
	descriptor := msg.Descriptor()

	// 2. Find the FieldDescriptor for the nested message field (named "debInfo").
	//    This is the corrected line: call .Fields().ByName().
	debInfoFieldDescriptor := descriptor.Fields().ByName("debInfo")
	if debInfoFieldDescriptor == nil {
		return fmt.Errorf("field 'debInfo' not found in message %s", descriptor.FullName())
	}

	// 3. From the field descriptor, get the MessageDescriptor for the DebInfo type.
	//    This gives us the "schema" for the DebInfo message.
	debInfoMsgDescriptor := debInfoFieldDescriptor.Message()
	if debInfoMsgDescriptor == nil {
		// This would happen if the 'debInfo' field was not a message type.
		// return ErrFieldNotMessage
		return errors.New("debInfo failed to turn into a message?")
	}

	// 4. Now, find the FieldDescriptor for the target string field (varname)
	//    WITHIN the DebInfo message's schema.
	fieldName := protoreflect.Name(varname)
	fieldDescriptor := debInfoMsgDescriptor.Fields().ByName(fieldName)
	if fieldDescriptor == nil {
		return fmt.Errorf("field '%s' not found in nested message 'debInfo'", varname)
	}

	// 5. Validate that the target field is a string.
	if fieldDescriptor.Kind() != protoreflect.StringKind {
		return config.ErrProtoVarNotString
	}

	// 6. CRITICAL STEP: Get a mutable reference to the actual nested DebInfo message.
	//    msg.Mutable() is perfect for this. It will:
	//    a) Get the existing DebInfo message if it's already been set.
	//    b) Create a NEW, empty DebInfo message if it's currently nil.
	//    Then, we get the reflection interface for that nested message.
	debInfoMsg := msg.Mutable(debInfoFieldDescriptor).Message()

	// 7. Prepare the value and SET it on the nested message.
	valueToSet := protoreflect.ValueOfString(varvalue)
	debInfoMsg.Set(fieldDescriptor, valueToSet)

	return nil
}