package models

import (
	"fmt"
	"io"
)

// A Tag associates a story with other content, like other stories, logs and more.
type Tag struct {
	Kind TagKind `bson:"kind"`
	Name string  `bson:"name"`
}

// Equal returns true if the tags match one another.
func (tag *Tag) Equal(other Tag) bool {
	return tag.Kind == other.Kind && tag.Name == other.Name
}

// IsChangeObject is an interface implementation to identify it as a valid
// ChangeObject in GQL.
func (*Tag) IsChangeObject() {
	panic("this method is a dummy, and so is its caller")
}

// TagKind represents the kind of tags.
type TagKind string

const (
	// TagKindOrganization is a tag kind, see GraphQL documentation.
	TagKindOrganization TagKind = "Organization"

	// TagKindCharacter is a tag kind, see GraphQL documentation.
	TagKindCharacter TagKind = "Character"

	// TagKindLocation is a tag kind, see GraphQL documentation.
	TagKindLocation TagKind = "Location"

	// TagKindEvent is a tag kind, see GraphQL documentation.
	TagKindEvent TagKind = "Event"

	// TagKindSeries is a tag kind, see GraphQL documentation.
	TagKindSeries TagKind = "Series"
)

// UnmarshalGQL unmarshals
func (e *TagKind) UnmarshalGQL(v interface{}) error {
	str, ok := v.(string)
	if !ok {
		return fmt.Errorf("enums must be strings")
	}

	*e = TagKind(str)
	switch *e {
	case TagKindOrganization, TagKindCharacter, TagKindLocation, TagKindEvent, TagKindSeries:
		return nil
	default:
		return fmt.Errorf("%s is not a valid TagKind", str)
	}
}

// MarshalGQL turns it into a JSON string
func (e TagKind) MarshalGQL(w io.Writer) {
	fmt.Fprint(w, "\""+string(e), "\"")
}

// TagFilter is a filter for tag listing.
type TagFilter struct {
	Kind *TagKind `bson:"kind,omitempty"`
}