Fix Mangabaka dates drifting in negative timezones (#3711)

* Fix Mangabaka dates drifting in negative timezones

This was only partially handled in #3047, but MB returns full datetime
strings with a truncated time component that's always midnight UTC.
So when Mihon then parses the returned dates, it gets the day wrong in
any negative offset timezones.

With this, Mihon now discards the time component and instead takes the
date component + start-of-day in the device timezone.

* Add Changelog

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 ## [Unreleased]
 ### Fixed
 - Fixed app and extension update check running again on configuration change ([@AntsyLich](https://github.com/AntsyLich)) ([#3708](https://github.com/mihonapp/mihon/pull/3708))
+- Fixed MangaBaka user start/finish dates drifting in negative offset timezones ([@MajorTanya](https://github.com/MajorTanya)) ([#3711](https://github.com/mihonapp/mihon/pull/3711))
 
 ## [v0.20.4] - 2026-08-05
 ### Fixed

app/src/main/java/eu/kanade/tachiyomi/data/track/mangabaka/MangaBakaApi.kt

@@ -22,6 +22,9 @@ import eu.kanade.tachiyomi.network.awaitSuccess
 import eu.kanade.tachiyomi.network.parseAs
 import eu.kanade.tachiyomi.util.PkceUtil
 import eu.kanade.tachiyomi.util.lang.toLocalDate
+import kotlinx.datetime.LocalDate
+import kotlinx.datetime.TimeZone
+import kotlinx.datetime.atStartOfDayIn
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.buildJsonObject
 import kotlinx.serialization.json.put
@@ -35,7 +38,6 @@ import java.math.RoundingMode
 import java.security.SecureRandom
 import java.util.Base64
 import java.util.Locale
-import kotlin.time.Instant
 import tachiyomi.domain.track.model.Track as DomainTrack
 
 class MangaBakaApi(
@@ -123,9 +125,8 @@ class MangaBakaApi(
                         title = additionalData.chooseBestTitle()
                         status = userData.getStatus()
                         score = userData.rating?.toDouble() ?: 0.0
-                        started_reading_date = userData.startDate?.let { Instant.parse(it).toEpochMilliseconds() } ?: 0
-                        finished_reading_date =
-                            userData.finishDate?.let { Instant.parse(it).toEpochMilliseconds() } ?: 0
+                        started_reading_date = parseIsoDateAsLocalStartOfDay(userData.startDate) ?: 0
+                        finished_reading_date = parseIsoDateAsLocalStartOfDay(userData.finishDate) ?: 0
                         last_chapter_read = userData.progressChapter ?: 0.0
                         private = userData.isPrivate
                     }
@@ -266,6 +267,16 @@ class MangaBakaApi(
 
     fun verifyOAuthState(state: String): Boolean = state == oauthStateParam
 
+    private fun parseIsoDateAsLocalStartOfDay(isoDate: String?): Long? {
+        // The v1 API returns full ISO 8601 strings with a midnight-UTC-truncated time component, regardless of the
+        // actual time of the change made.
+        return isoDate
+            ?.substringBefore("T")
+            ?.let { LocalDate.parse(it) }
+            ?.atStartOfDayIn(TimeZone.currentSystemDefault())
+            ?.toEpochMilliseconds()
+    }
+
     companion object {
         private const val CLIENT_ID = "zEZYMHXLWsLsafgbvJHXqzGvqQNOdkpo"