package com.bitcointxoko.gudariwallet.api

import kotlinx.serialization.ExperimentalSerializationApi
import kotlinx.serialization.KSerializer
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.descriptors.buildClassSerialDescriptor
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.encoding.Encoder
import kotlinx.serialization.json.JsonArray
import kotlinx.serialization.json.JsonDecoder
import kotlinx.serialization.json.JsonNull
import kotlinx.serialization.json.JsonPrimitive
import kotlinx.serialization.json.jsonPrimitive

/**
 * LNbits returns `comment` in PaymentExtra as either:
 *   - a plain string  "Thanks!"
 *   - a JSON array    ["Thanks!"]
 *   - null
 *
 * Mirrors the behavior of the old Gson FlexibleStringAdapter.
 */
object FlexibleStringSerializer : KSerializer<String?> {

    override val descriptor: SerialDescriptor =
        buildClassSerialDescriptor("FlexibleString")

    @OptIn(ExperimentalSerializationApi::class)
    override fun serialize(encoder: Encoder, value: String?) {
        if (value == null) encoder.encodeNull()
        else encoder.encodeString(value)
    }

    override fun deserialize(decoder: Decoder): String? {
        val jsonDecoder = decoder as JsonDecoder
        return when (val element = jsonDecoder.decodeJsonElement()) {
            is JsonNull -> null
            is JsonPrimitive -> element.content                  // plain string → as-is
            is JsonArray -> element                          // array → join elements
                .mapNotNull { if (it is JsonNull) null else it.jsonPrimitive.content }
                .joinToString(", ")
                .ifEmpty { null }
            else             -> null
        }
    }
}