package runcmdopt

import (
	"reflect"

	"github.com/mongodb/mongo-go-driver/core/readpref"
	"github.com/mongodb/mongo-go-driver/core/session"
)

var runCmdBundle = new(RunCmdBundle)

// Option represents a RunCommand option.
type Option interface {
	runCmdOption()
}

// RunCmdSession is the session for the runCommand() function
type RunCmdSession interface {
	Option
	ConvertRunCmdSession() *session.Client
}

// optionFunc adds the option to the RunCmd instance.
type optionFunc func(*RunCmd) error

// RunCmd represents a run command.
type RunCmd struct {
	ReadPreference *readpref.ReadPref
}

// RunCmdBundle is a bundle of RunCommand options.
type RunCmdBundle struct {
	option Option
	next   *RunCmdBundle
}

func (*RunCmdBundle) runCmdOption() {}

func (optionFunc) runCmdOption() {}

// BundleRunCmd bundles RunCommand options
func BundleRunCmd(opts ...Option) *RunCmdBundle {
	head := runCmdBundle

	for _, opt := range opts {
		newBundle := RunCmdBundle{
			option: opt,
			next:   head,
		}
		head = &newBundle
	}

	return head
}

// ReadPreference sets the read preference.
func (rcb *RunCmdBundle) ReadPreference(rp *readpref.ReadPref) *RunCmdBundle {
	return &RunCmdBundle{
		option: ReadPreference(rp),
		next:   rcb,
	}
}

// Unbundle unbundles the options, returning a RunCmd instance.
func (rcb *RunCmdBundle) Unbundle() (*RunCmd, *session.Client, error) {
	database := &RunCmd{}
	sess, err := rcb.unbundle(database)
	if err != nil {
		return nil, nil, err
	}

	return database, sess, nil
}

// Helper that recursively unwraps the bundle.
func (rcb *RunCmdBundle) unbundle(database *RunCmd) (*session.Client, error) {
	if rcb == nil {
		return nil, nil
	}

	var sess *session.Client
	for head := rcb; head != nil && head.option != nil; head = head.next {
		var err error
		switch opt := head.option.(type) {
		case *RunCmdBundle:
			s, e := opt.unbundle(database) // add all bundle's options to database
			if s != nil {
				sess = s
			}
			err = e
		case optionFunc:
			err = opt(database) // add option to database
		case RunCmdSession:
			sess = opt.ConvertRunCmdSession()
		default:
			return sess, nil
		}
		if err != nil {
			return sess, err
		}
	}

	return sess, nil
}

// String implements the Stringer interface
func (rcb *RunCmdBundle) String() string {
	if rcb == nil {
		return ""
	}

	str := ""
	for head := rcb; head != nil && head.option != nil; head = head.next {
		switch opt := head.option.(type) {
		case *RunCmdBundle:
			str += opt.String()
		case optionFunc:
			str += reflect.TypeOf(opt).String() + "\n"
		}
	}

	return str
}

// ReadPreference sets the read preference.
func ReadPreference(rp *readpref.ReadPref) Option {
	return optionFunc(
		func(rc *RunCmd) error {
			if rc.ReadPreference == nil {
				rc.ReadPreference = rp
			}
			return nil
		})
}

// RunCmdSessionOpt is a RunCommand session option.
type RunCmdSessionOpt struct{}

func (RunCmdSessionOpt) runCmdOption() {}

// ConvertRunCmdSession implements the RunCmdSession interface.
func (RunCmdSessionOpt) ConvertRunCmdSession() *session.Client {
	return nil
}