Add playlist classes

src/main/kotlin/com/github/warriorzz/ktify/model/Playlist.kt

@@ -1 +1,71 @@
 package com.github.warriorzz.ktify.model
+
+import com.github.warriorzz.ktify.model.external.ExternalUrl
+import com.github.warriorzz.ktify.model.util.Image
+import com.github.warriorzz.ktify.model.util.ObjectType
+import kotlinx.serialization.DeserializationStrategy
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonContentPolymorphicSerializer
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.jsonObject
+
+@Serializable
+data class Playlist(
+    val collaborative: Boolean,
+    val description: String? = null,
+    @SerialName("external_urls")
+    val externalUrl: ExternalUrl,
+    val followers: Followers,
+    val href: String,
+    val id: String,
+    val images: List<Image>,
+    val name: String,
+    val owner: PublicUser,
+    val public: Boolean? = null,
+    @SerialName("snapshot_id")
+    val snapshotId: String,
+    val tracks: List<PlaylistTrackObject>? = null,
+    override val type: ObjectType = ObjectType.PLAYLIST,
+    val uri: String,
+) : KtifyObject()
+
+@Serializable
+data class PlaylistTrack(
+    @SerialName("added_at")
+    val addedAt: String? = null,
+    @SerialName("added_by")
+    val addedBy: PublicUser? = null,
+    @SerialName("is_local")
+    val isLocal: Boolean,
+    val track: KtifyObject,
+) : PlaylistTrackObject()
+
+@Serializable
+data class PlaylistTrackRef(
+    val href: String,
+    val total: Int
+) : PlaylistTrackObject()
+
+@Serializable(with = PlaylistTrackObjectSerializer::class)
+sealed class PlaylistTrackObject {
+
+    /**
+     *  Get the instance as a PlaylistTrack object
+     *  @return Null if the instance is an PlaylistTrackRef
+     */
+    fun asPlaylistTrack() : PlaylistTrack? = if (this is PlaylistTrack) this else null
+
+    /**
+     *  Get the instance as a PlaylistTrackRef object
+     *  @return Null if the instance is an PlaylistTrack
+     */
+    fun asPlaylistTrackRef() : PlaylistTrackRef? = if (this is PlaylistTrackRef) this else null
+
+}
+
+object PlaylistTrackObjectSerializer: JsonContentPolymorphicSerializer<PlaylistTrackObject>(PlaylistTrackObject::class) {
+    override fun selectDeserializer(element: JsonElement): DeserializationStrategy<out PlaylistTrackObject> {
+        return if (element.jsonObject["track"] != null) PlaylistTrack.serializer() else PlaylistTrackRef.serializer()
+    }
+}