parse Subsonic dates with java.time via core library desugaring

app/src/main/kotlin/com/subtracks/data/source/subsonic/SubsonicXml.kt

@@ -7,6 +7,10 @@ import com.subtracks.data.model.PlaylistSong
 import com.subtracks.data.model.Song
 import org.w3c.dom.Document
 import org.w3c.dom.Element
+import java.time.LocalDate
+import java.time.OffsetDateTime
+import java.time.ZoneOffset
+import java.time.format.DateTimeParseException
 
 object SubsonicXml {
     fun artists(
@@ -128,46 +132,19 @@ private fun Element.longAttr(name: String): Long? = getAttribute(name).takeIf {
 private fun Element.dateAttr(name: String): Long? = getAttribute(name).takeIf { it.isNotEmpty() }?.let(IsoDate::parse)
 
 internal object IsoDate {
-    private val pattern =
-        Regex(
-            "^(\\d{4})-(\\d{2})-(\\d{2})(?:[T ](\\d{2}):(\\d{2}):(\\d{2})(?:\\.\\d+)?\\s*(Z|[+-]\\d{2}:?\\d{2})?)?$",
-        )
+    private val timezone = Regex("(Z|[+-]\\d{2}:?\\d{2})$", RegexOption.IGNORE_CASE)
 
     fun parse(value: String): Long? {
-        val match = pattern.matchEntire(value.trim()) ?: return null
-        val year = match.groupValues[1].toIntOrNull() ?: return null
-        val month = match.groupValues[2].toIntOrNull() ?: return null
-        val day = match.groupValues[3].toIntOrNull() ?: return null
-        val hour = match.groupValues[4].toIntOrNull() ?: 0
-        val minute = match.groupValues[5].toIntOrNull() ?: 0
-        val second = match.groupValues[6].toIntOrNull() ?: 0
-        if (month !in 1..12 || day !in 1..31 || hour !in 0..23 || minute !in 0..59 || second !in 0..59) {
-            return null
+        val text = value.trim()
+        return try {
+            val zoned = if (timezone.containsMatchIn(text)) text else text + "Z"
+            OffsetDateTime.parse(zoned).toEpochSecond()
+        } catch (_: DateTimeParseException) {
+            try {
+                LocalDate.parse(text).atStartOfDay(ZoneOffset.UTC).toEpochSecond()
+            } catch (_: DateTimeParseException) {
+                null
+            }
         }
-        val days = daysFromCivil(year, month, day)
-        return days * 86400L + hour * 3600L + minute * 60L + second - offsetSeconds(match.groupValues[7])
-    }
-
-    private fun offsetSeconds(zone: String): Long {
-        if (zone.isEmpty() || zone.equals("Z", ignoreCase = true)) return 0
-        val digits = zone.drop(1).replace(":", "")
-        if (digits.length != 4) return 0
-        val hours = digits.take(2).toLongOrNull() ?: return 0
-        val minutes = digits.drop(2).toLongOrNull() ?: return 0
-        val sign = if (zone[0] == '-') -1L else 1L
-        return sign * (hours * 3600 + minutes * 60)
-    }
-
-    private fun daysFromCivil(
-        year: Int,
-        month: Int,
-        day: Int,
-    ): Long {
-        val y = if (month <= 2) year - 1 else year
-        val era = (if (y >= 0) y else y - 399) / 400
-        val yearOfEra = y - era * 400
-        val dayOfYear = (153 * (if (month > 2) month - 3 else month + 9) + 2) / 5 + day - 1
-        val dayOfEra = yearOfEra * 365 + yearOfEra / 4 - yearOfEra / 100 + dayOfYear
-        return era * 146097L + dayOfEra - 719468L
     }
 }