Unmarshalling JSON structs containing interfaces in Go

.go

package main

import (
	"encoding/json"
	"fmt"
	"time"
)

type Playable interface {
	Play() error
}

type Movie struct {
	Title  string `json:"title"`
	Length int    `json:"length"`
}

func (m *Movie) Play() error {
	time.Sleep(time.Duration(m.Length) * time.Minute)
	return nil
}

type Playables []Playable

type TVGuide struct {
	Company string    `json:"company"`
	Notices string    `json:"notices"`
	ID      string    `json:"id"`
	Library Playables `json:"library"`
}

func (p *Playables) UnmarshalJSON(b []byte) error {
	var LibraryFields map[string]*json.RawMessage
	if err := json.Unmarshal(b, &LibraryFields); err != nil {
		return err
	}
	for LFKey, LFValue := range LibraryFields {
		if LFKey == "movies" {
			var LibraryMovies []*json.RawMessage
			if err := json.Unmarshal(*LFValue, &LibraryMovies); err != nil {
				return err
			}
			for _, LibraryMovie := range LibraryMovies {
				var movie Movie
				if err := json.Unmarshal(*LibraryMovie, &movie); err != nil {
					return err
				}
				*p = append(*p, &movie)
			}
		}
	}
	return nil
}

func main() {
	myjson := []byte(`{"company":"0rkaTV","notices":"NO RUNNING WITH SCISSORS","id":"0x1337H4X0R","library":{"movies":[{"title":"Titanic","length":194},{"title":"Matrix","length":150}]}}`)
	var OrkaTVGuide TVGuide
	if err := json.Unmarshal(myjson, &OrkaTVGuide); err != nil {
		fmt.Println(err)
	}
	fmt.Println(OrkaTVGuide)
	fmt.Println("Hello, playground")
}