diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 55f5bf2..d5956c3 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -30,6 +30,7 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_17
         targetCompatibility = JavaVersion.VERSION_17
+        isCoreLibraryDesugaringEnabled = true
     }
     kotlinOptions {
         jvmTarget = "17"
@@ -51,6 +52,7 @@ android {
 }
 
 dependencies {
+    coreLibraryDesugaring("com.android.tools:desugar_jdk_libs:2.0.4")
     implementation("androidx.core:core-ktx:1.12.0")
     implementation("com.google.android.material:material:1.11.0")
     implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.7.0")
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/CalendarRepository.kt b/app/src/main/java/com/scarriffle/calendarr/data/CalendarRepository.kt
new file mode 100644
index 0000000..2b3b18c
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/CalendarRepository.kt
@@ -0,0 +1,348 @@
+package com.scarriffle.calendarr.data
+
+import com.scarriffle.calendarr.data.remote.ApiException
+import com.scarriffle.calendarr.data.remote.ApiProvider
+import com.scarriffle.calendarr.data.remote.TwoFactorRequiredException
+import com.scarriffle.calendarr.data.remote.UnauthorizedException
+import com.scarriffle.calendarr.data.remote.ensureSuccess
+import com.scarriffle.calendarr.data.remote.errorDetail
+import com.scarriffle.calendarr.data.remote.jsonBody
+import com.scarriffle.calendarr.domain.model.AppSettings
+import com.scarriffle.calendarr.domain.model.CalDAVAccount
+import com.scarriffle.calendarr.domain.model.CalEvent
+import com.scarriffle.calendarr.domain.model.GoogleAccount
+import com.scarriffle.calendarr.domain.model.HomeAssistantAccount
+import com.scarriffle.calendarr.domain.model.ICalSubscription
+import com.scarriffle.calendarr.domain.model.LocalCalendar
+import com.scarriffle.calendarr.domain.model.UserProfile
+import com.scarriffle.calendarr.domain.model.WritableCalendar
+import com.scarriffle.calendarr.util.Dates
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import org.json.JSONObject
+import retrofit2.HttpException
+import java.time.Instant
+import javax.inject.Inject
+import javax.inject.Singleton
+
+data class LoginResult(val token: String, val username: String, val isAdmin: Boolean)
+
+data class TotpSetup(val secret: String, val qrUrl: String)
+
+/**
+ * Single entry point for all server interaction. Wraps [com.scarriffle.calendarr.data.remote.CalendarrApi],
+ * converts HTTP failures into [ApiException]s carrying the server's `detail`
+ * message, and parses the mixed-type event payloads with org.json.
+ */
+@Singleton
+class CalendarRepository @Inject constructor(
+    private val apiProvider: ApiProvider,
+    private val credentialStore: CredentialStore,
+    private val settingsStore: SettingsStore,
+) {
+    private val api get() = apiProvider.api()
+
+    private suspend fun <T> guarded(block: suspend () -> T): T = withContext(Dispatchers.IO) {
+        try {
+            block()
+        } catch (e: HttpException) {
+            if (e.code() == 401) throw UnauthorizedException()
+            throw ApiException(errorDetail(e.response()?.errorBody(), e.code()))
+        }
+    }
+
+    // ---- Auth ----
+
+    suspend fun setupRequired(baseUrl: String): Boolean = withContext(Dispatchers.IO) {
+        val resp = apiProvider.apiFor(baseUrl).setupRequired()
+        if (!resp.isSuccessful) return@withContext false
+        val raw = resp.body()?.string() ?: return@withContext false
+        runCatching { JSONObject(raw).optBoolean("required", false) }.getOrDefault(false)
+    }
+
+    suspend fun login(
+        baseUrl: String,
+        username: String,
+        password: String,
+        totpCode: String?,
+        rememberMe: Boolean,
+    ): LoginResult = withContext(Dispatchers.IO) {
+        val body = jsonBody(
+            "username" to username,
+            "password" to password,
+            "remember_me" to rememberMe,
+            "totp_code" to totpCode,
+        )
+        val resp = apiProvider.apiFor(baseUrl).login(body)
+        if (resp.code() == 401) {
+            val detail = runCatching {
+                JSONObject(resp.errorBody()?.string() ?: "").optString("detail")
+            }.getOrNull()
+            if (detail == "2fa_required") throw TwoFactorRequiredException()
+            throw UnauthorizedException()
+        }
+        if (!resp.isSuccessful) throw ApiException(errorDetail(resp.errorBody(), resp.code()))
+
+        val json = JSONObject(resp.body()?.string() ?: throw ApiException("Leere Antwort"))
+        val token = json.optString("access_token").takeIf { it.isNotBlank() }
+            ?: throw ApiException("Antwort konnte nicht verarbeitet werden")
+        val user = json.optJSONObject("user")
+        val uname = user?.optString("username") ?: username
+        val isAdmin = user?.optBoolean("is_admin", false) ?: false
+
+        credentialStore.serverUrl = ApiProvider.normalize(baseUrl)
+        credentialStore.saveLogin(token, uname, isAdmin)
+        apiProvider.invalidate()
+        LoginResult(token, uname, isAdmin)
+    }
+
+    // ---- Settings / profile ----
+
+    suspend fun getSettings(): AppSettings = guarded { api.getSettings() }
+
+    suspend fun updateSettings(s: AppSettings) = guarded {
+        api.updateSettings(
+            jsonBody(
+                "default_view" to s.defaultView,
+                "week_start_day" to s.weekStartDay,
+                "primary_color" to s.primaryColor,
+                "accent_color" to s.accentColor,
+                "today_color" to s.todayColor,
+                "dim_past_events" to s.dimPastEvents,
+                "text_contrast" to s.textContrast,
+                "line_contrast" to s.lineContrast,
+                "hour_height" to s.hourHeight,
+                "language" to s.language,
+                "month_divider_color" to s.monthDividerColor,
+                "month_label_color" to s.monthLabelColor,
+            )
+        ).ensureSuccess()
+    }
+
+    suspend fun getProfile(): UserProfile = guarded { api.getProfile() }
+
+    suspend fun updateEmail(email: String) = guarded {
+        api.updateEmail(jsonBody("email" to email)).ensureSuccess()
+    }
+
+    suspend fun changePassword(current: String, new: String) = guarded {
+        api.changePassword(
+            jsonBody("current_password" to current, "new_password" to new)
+        ).ensureSuccess()
+    }
+
+    suspend fun setup2fa(): TotpSetup = guarded {
+        val resp = api.setup2fa()
+        resp.ensureSuccess()
+        val json = JSONObject(resp.body()?.string() ?: "{}")
+        TotpSetup(json.optString("secret"), json.optString("qr_url"))
+    }
+
+    suspend fun enable2fa(code: String) = guarded {
+        api.enable2fa(jsonBody("code" to code)).ensureSuccess()
+    }
+
+    suspend fun disable2fa(password: String) = guarded {
+        api.disable2fa(jsonBody("password" to password)).ensureSuccess()
+    }
+
+    // ---- Accounts ----
+
+    suspend fun getCalDAVAccounts(): List<CalDAVAccount> = guarded { api.getCalDAVAccounts() }
+
+    suspend fun addCalDAVAccount(name: String, url: String, username: String, password: String, color: String) =
+        guarded {
+            api.addCalDAVAccount(
+                jsonBody(
+                    "name" to name, "url" to url, "username" to username,
+                    "password" to password, "color" to color,
+                )
+            )
+        }
+
+    suspend fun deleteCalDAVAccount(id: Int) = guarded { api.deleteCalDAVAccount(id).ensureSuccess() }
+
+    suspend fun getLocalCalendars(): List<LocalCalendar> = guarded { api.getLocalCalendars() }
+
+    suspend fun addLocalCalendar(name: String, color: String) =
+        guarded { api.addLocalCalendar(jsonBody("name" to name, "color" to color)) }
+
+    suspend fun deleteLocalCalendar(id: Int) = guarded { api.deleteLocalCalendar(id).ensureSuccess() }
+
+    suspend fun getICalSubscriptions(): List<ICalSubscription> = guarded { api.getICalSubscriptions() }
+
+    suspend fun addICalSubscription(name: String, url: String, color: String, refreshMinutes: Int) =
+        guarded {
+            api.addICalSubscription(
+                jsonBody(
+                    "name" to name, "url" to url, "color" to color,
+                    "refresh_minutes" to refreshMinutes,
+                )
+            )
+        }
+
+    suspend fun deleteICalSubscription(id: Int) = guarded { api.deleteICalSubscription(id).ensureSuccess() }
+
+    suspend fun getGoogleAccounts(): List<GoogleAccount> = guarded { api.getGoogleAccounts() }
+
+    suspend fun deleteGoogleAccount(id: Int) = guarded { api.deleteGoogleAccount(id).ensureSuccess() }
+
+    suspend fun getHomeAssistantAccounts(): List<HomeAssistantAccount> =
+        guarded { api.getHomeAssistantAccounts() }
+
+    suspend fun addHomeAssistantAccount(name: String, url: String, token: String) =
+        guarded {
+            api.addHomeAssistantAccount(
+                jsonBody("name" to name, "url" to url, "token" to token, "auth_method" to "token")
+            )
+        }
+
+    suspend fun deleteHomeAssistantAccount(id: Int) =
+        guarded { api.deleteHomeAssistantAccount(id).ensureSuccess() }
+
+    /** Toggle a calendar's server-side visibility (caldav/google/homeassistant only). */
+    suspend fun setCalendarSidebarHidden(source: String, calendarId: Int, hidden: Boolean) = guarded {
+        val body = jsonBody("enabled" to !hidden, "sidebar_hidden" to hidden)
+        when (source) {
+            "caldav" -> api.updateCalDAVCalendar(calendarId, body).ensureSuccess()
+            "google" -> api.updateGoogleCalendar(calendarId, body).ensureSuccess()
+            "homeassistant" -> api.updateHACalendar(calendarId, body).ensureSuccess()
+            else -> Unit
+        }
+    }
+
+    /** Resolve all calendars the user can create events in. */
+    suspend fun getWritableCalendars(): List<WritableCalendar> = withContext(Dispatchers.IO) {
+        val result = mutableListOf<WritableCalendar>()
+        runCatching { api.getLocalCalendars() }.getOrDefault(emptyList()).forEach { cal ->
+            result += WritableCalendar("local-${cal.id}", cal.name, cal.color, "local", cal.id)
+        }
+        runCatching { api.getCalDAVAccounts() }.getOrDefault(emptyList())
+            .filter { it.enabled }
+            .forEach { acc ->
+                acc.calendars.orEmpty().filter { it.enabled }.forEach { cal ->
+                    result += WritableCalendar(
+                        "caldav-${cal.id}", "${acc.name} – ${cal.name}",
+                        cal.color ?: acc.color, "caldav", cal.id,
+                    )
+                }
+            }
+        runCatching { api.getGoogleAccounts() }.getOrDefault(emptyList()).forEach { acc ->
+            acc.calendars.orEmpty().filter { it.enabled }.forEach { cal ->
+                result += WritableCalendar(
+                    "google-${cal.id}", "${acc.email} – ${cal.name}",
+                    cal.color ?: "#4285f4", "google", cal.id,
+                )
+            }
+        }
+        runCatching { api.getHomeAssistantAccounts() }.getOrDefault(emptyList()).forEach { acc ->
+            acc.calendars.orEmpty().filter { it.enabled }.forEach { cal ->
+                result += WritableCalendar(
+                    "ha-${cal.id}", "${acc.name} – ${cal.name}",
+                    cal.color ?: "#46bdc6", "homeassistant", cal.id,
+                )
+            }
+        }
+        result
+    }
+
+    // ---- Events ----
+
+    suspend fun fetchEvents(start: Instant, end: Instant): List<CalEvent> = withContext(Dispatchers.IO) {
+        val resp = api.fetchEvents(Dates.isoUtc(start), Dates.isoUtc(end))
+        resp.ensureSuccess()
+        val raw = resp.body()?.string() ?: return@withContext emptyList()
+        val root = JSONObject(raw)
+        val arr = root.optJSONArray("events") ?: return@withContext emptyList()
+        buildList {
+            for (i in 0 until arr.length()) {
+                val obj = arr.optJSONObject(i) ?: continue
+                CalEvent.fromJson(obj)?.let { add(it) }
+            }
+        }
+    }
+
+    suspend fun createLocalEvent(
+        calendarId: Int, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String, color: String?,
+    ) = guarded {
+        api.createLocalEvent(eventBody(calendarId, title, start, end, isAllDay, location, description, color))
+            .ensureSuccess()
+    }
+
+    suspend fun updateLocalEvent(
+        uid: String, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String, color: String?,
+    ) = guarded {
+        api.updateLocalEvent(uid, eventBody(null, title, start, end, isAllDay, location, description, color))
+            .ensureSuccess()
+    }
+
+    suspend fun deleteLocalEvent(uid: String) = guarded { api.deleteLocalEvent(uid).ensureSuccess() }
+
+    suspend fun createCalDAVEvent(
+        calendarId: Int, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String, color: String?,
+    ) = guarded {
+        api.createCalDAVEvent(eventBody(calendarId, title, start, end, isAllDay, location, description, color))
+            .ensureSuccess()
+    }
+
+    suspend fun updateCalDAVEvent(
+        uid: String, url: String, calendarId: Int?, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String, color: String?,
+    ) = guarded {
+        api.updateCalDAVEvent(
+            uid, url, calendarId,
+            eventBody(null, title, start, end, isAllDay, location, description, color),
+        ).ensureSuccess()
+    }
+
+    suspend fun deleteCalDAVEvent(uid: String, url: String, calendarId: Int?) =
+        guarded { api.deleteCalDAVEvent(uid, url, calendarId).ensureSuccess() }
+
+    suspend fun createGoogleEvent(
+        calendarDbId: Int, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String,
+    ) = guarded {
+        api.createGoogleEvent(
+            jsonBody(
+                "calendar_db_id" to calendarDbId, "title" to title,
+                "start" to Dates.format(start, isAllDay), "end" to Dates.format(end, isAllDay),
+                "allDay" to isAllDay, "location" to location, "description" to description,
+            )
+        ).ensureSuccess()
+    }
+
+    suspend fun createHAEvent(
+        calendarId: Int, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String,
+    ) = guarded {
+        api.createHAEvent(
+            jsonBody(
+                "calendar_id" to calendarId, "title" to title,
+                "start" to Dates.format(start, isAllDay), "end" to Dates.format(end, isAllDay),
+                "allDay" to isAllDay, "location" to location, "description" to description,
+            )
+        ).ensureSuccess()
+    }
+
+    suspend fun deleteHAEvent(calendarId: Int, uid: String) =
+        guarded { api.deleteHAEvent(calendarId, uid).ensureSuccess() }
+
+    private fun eventBody(
+        calendarId: Int?, title: String, start: Instant, end: Instant,
+        isAllDay: Boolean, location: String, description: String, color: String?,
+    ) = jsonBody(
+        buildMap {
+            calendarId?.let { put("calendar_id", it) }
+            put("title", title)
+            put("start", Dates.format(start, isAllDay))
+            put("end", Dates.format(end, isAllDay))
+            put("allDay", isAllDay)
+            put("location", location)
+            put("description", description)
+            if (!color.isNullOrBlank()) put("color", color)
+        }
+    )
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/CredentialStore.kt b/app/src/main/java/com/scarriffle/calendarr/data/CredentialStore.kt
new file mode 100644
index 0000000..d9c5ab6
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/CredentialStore.kt
@@ -0,0 +1,83 @@
+package com.scarriffle.calendarr.data
+
+import android.content.Context
+import android.content.SharedPreferences
+import androidx.security.crypto.EncryptedSharedPreferences
+import androidx.security.crypto.MasterKey
+import dagger.hilt.android.qualifiers.ApplicationContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Securely stores the server URL and auth token in EncryptedSharedPreferences
+ * (Android's equivalent of the iOS Keychain). The iOS app keeps these in
+ * UserDefaults; on Android we encrypt them at rest.
+ */
+@Singleton
+class CredentialStore @Inject constructor(
+    @ApplicationContext context: Context,
+) {
+    private val prefs: SharedPreferences = run {
+        val masterKey = MasterKey.Builder(context)
+            .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
+            .build()
+        EncryptedSharedPreferences.create(
+            context,
+            "calendarr_secure_prefs",
+            masterKey,
+            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
+            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM,
+        )
+    }
+
+    var serverUrl: String?
+        get() = prefs.getString(KEY_SERVER_URL, null)
+        set(value) = prefs.edit().putString(KEY_SERVER_URL, value).apply()
+
+    var token: String?
+        get() = prefs.getString(KEY_TOKEN, null)
+        set(value) = prefs.edit().putString(KEY_TOKEN, value).apply()
+
+    var username: String?
+        get() = prefs.getString(KEY_USERNAME, null)
+        set(value) = prefs.edit().putString(KEY_USERNAME, value).apply()
+
+    var isAdmin: Boolean
+        get() = prefs.getBoolean(KEY_IS_ADMIN, false)
+        set(value) = prefs.edit().putBoolean(KEY_IS_ADMIN, value).apply()
+
+    /** True once a server URL has been entered (setup step complete). */
+    val isConfigured: Boolean get() = !serverUrl.isNullOrBlank()
+
+    /** True once we hold an auth token (logged in). */
+    val isLoggedIn: Boolean get() = !token.isNullOrBlank()
+
+    fun saveLogin(token: String, username: String, isAdmin: Boolean) {
+        prefs.edit()
+            .putString(KEY_TOKEN, token)
+            .putString(KEY_USERNAME, username)
+            .putBoolean(KEY_IS_ADMIN, isAdmin)
+            .apply()
+    }
+
+    /** Clear the token (logout) but keep the server URL. */
+    fun clearToken() {
+        prefs.edit()
+            .remove(KEY_TOKEN)
+            .remove(KEY_USERNAME)
+            .remove(KEY_IS_ADMIN)
+            .apply()
+    }
+
+    /** Full reset, including the server URL ("switch server"). */
+    fun clearAll() {
+        prefs.edit().clear().apply()
+    }
+
+    private companion object {
+        const val KEY_SERVER_URL = "server_url"
+        const val KEY_TOKEN = "auth_token"
+        const val KEY_USERNAME = "username"
+        const val KEY_IS_ADMIN = "is_admin"
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/SettingsStore.kt b/app/src/main/java/com/scarriffle/calendarr/data/SettingsStore.kt
new file mode 100644
index 0000000..cf7ab91
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/SettingsStore.kt
@@ -0,0 +1,90 @@
+package com.scarriffle.calendarr.data
+
+import android.content.Context
+import android.content.SharedPreferences
+import com.scarriffle.calendarr.domain.model.AppSettings
+import dagger.hilt.android.qualifiers.ApplicationContext
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Local persistence for cached appearance settings and the per-device
+ * calendar visibility sets (hidden / banished). Mirrors the UserDefaults
+ * usage in the iOS `CalendarStore`.
+ */
+@Singleton
+class SettingsStore @Inject constructor(
+    @ApplicationContext context: Context,
+) {
+    private val prefs: SharedPreferences =
+        context.getSharedPreferences("calendarr_prefs", Context.MODE_PRIVATE)
+
+    // --- Appearance settings cache (mirror of the server) ---
+
+    fun loadSettings(): AppSettings = AppSettings(
+        defaultView = prefs.getString(K_DEFAULT_VIEW, null) ?: "month",
+        weekStartDay = prefs.getString(K_WEEK_START, null) ?: "monday",
+        primaryColor = prefs.getString(K_PRIMARY, null) ?: "#4285f4",
+        accentColor = prefs.getString(K_ACCENT, null) ?: "#ea4335",
+        todayColor = prefs.getString(K_TODAY, null) ?: "#4285f4",
+        dimPastEvents = prefs.getBoolean(K_DIM_PAST, false),
+        textContrast = prefs.getInt(K_TEXT_CONTRAST, 3),
+        lineContrast = prefs.getInt(K_LINE_CONTRAST, 3),
+        hourHeight = prefs.getInt(K_HOUR_HEIGHT, 60),
+        language = prefs.getString(K_LANGUAGE, null) ?: "de",
+        monthDividerColor = prefs.getString(K_DIVIDER, null) ?: "#7090c0",
+        monthLabelColor = prefs.getString(K_LABEL, null) ?: "#7090c0",
+    )
+
+    fun saveSettings(s: AppSettings) {
+        prefs.edit()
+            .putString(K_DEFAULT_VIEW, s.defaultView)
+            .putString(K_WEEK_START, s.weekStartDay)
+            .putString(K_PRIMARY, s.primaryColor)
+            .putString(K_ACCENT, s.accentColor)
+            .putString(K_TODAY, s.todayColor)
+            .putBoolean(K_DIM_PAST, s.dimPastEvents)
+            .putInt(K_TEXT_CONTRAST, s.textContrast)
+            .putInt(K_LINE_CONTRAST, s.lineContrast)
+            .putInt(K_HOUR_HEIGHT, s.hourHeight)
+            .putString(K_LANGUAGE, s.language)
+            .putString(K_DIVIDER, s.monthDividerColor)
+            .putString(K_LABEL, s.monthLabelColor)
+            .apply()
+    }
+
+    /** Device-local cache range in months around today (default 3). */
+    var cacheMonths: Int
+        get() = prefs.getInt(K_CACHE_MONTHS, 3)
+        set(value) = prefs.edit().putInt(K_CACHE_MONTHS, value).apply()
+
+    // --- Hidden calendars ("source:id") ---
+
+    var hiddenCalendarKeys: Set<String>
+        get() = prefs.getStringSet(K_HIDDEN, emptySet())?.toSet() ?: emptySet()
+        set(value) = prefs.edit().putStringSet(K_HIDDEN, value).apply()
+
+    // --- Banished calendars ("source:id") ---
+
+    var banishedCalendarKeys: Set<String>
+        get() = prefs.getStringSet(K_BANISHED, emptySet())?.toSet() ?: emptySet()
+        set(value) = prefs.edit().putStringSet(K_BANISHED, value).apply()
+
+    private companion object {
+        const val K_DEFAULT_VIEW = "default_view"
+        const val K_WEEK_START = "week_start_day"
+        const val K_PRIMARY = "primary_color"
+        const val K_ACCENT = "accent_color"
+        const val K_TODAY = "today_color"
+        const val K_DIM_PAST = "dim_past_events"
+        const val K_TEXT_CONTRAST = "text_contrast"
+        const val K_LINE_CONTRAST = "line_contrast"
+        const val K_HOUR_HEIGHT = "hour_height"
+        const val K_LANGUAGE = "language"
+        const val K_DIVIDER = "month_divider_color"
+        const val K_LABEL = "month_label_color"
+        const val K_CACHE_MONTHS = "cache_months"
+        const val K_HIDDEN = "hidden_calendar_keys"
+        const val K_BANISHED = "banished_calendar_keys"
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiException.kt b/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiException.kt
new file mode 100644
index 0000000..526e52b
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiException.kt
@@ -0,0 +1,34 @@
+package com.scarriffle.calendarr.data.remote
+
+import okhttp3.ResponseBody
+import org.json.JSONObject
+import retrofit2.Response
+
+/** Generic server error carrying the `detail` message when available. */
+open class ApiException(message: String) : Exception(message)
+
+/** Credentials rejected (HTTP 401, not a 2FA prompt). */
+class UnauthorizedException : ApiException("Benutzername oder Passwort falsch")
+
+/** Server requires a TOTP code to finish login (HTTP 401, detail "2fa_required"). */
+class TwoFactorRequiredException : ApiException("2FA-Code erforderlich")
+
+/** Extract the `detail` field from an error response body, with a fallback. */
+fun errorDetail(errorBody: ResponseBody?, status: Int): String {
+    val raw = runCatching { errorBody?.string() }.getOrNull()
+    if (!raw.isNullOrBlank()) {
+        runCatching {
+            val detail = JSONObject(raw).optString("detail")
+            if (detail.isNotBlank()) return detail
+        }
+    }
+    return "Fehler $status"
+}
+
+/** Throw an [ApiException] if the response is unsuccessful. */
+fun Response<*>.ensureSuccess() {
+    if (!isSuccessful) {
+        if (code() == 401) throw UnauthorizedException()
+        throw ApiException(errorDetail(errorBody(), code()))
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiProvider.kt b/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiProvider.kt
new file mode 100644
index 0000000..f7c7979
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/remote/ApiProvider.kt
@@ -0,0 +1,71 @@
+package com.scarriffle.calendarr.data.remote
+
+import com.scarriffle.calendarr.data.CredentialStore
+import com.squareup.moshi.Moshi
+import okhttp3.OkHttpClient
+import okhttp3.logging.HttpLoggingInterceptor
+import retrofit2.Retrofit
+import retrofit2.converter.moshi.MoshiConverterFactory
+import java.util.concurrent.TimeUnit
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Builds [CalendarrApi] instances. The base URL is dynamic (the user's server),
+ * so the cached instance is rebuilt whenever the stored server URL changes.
+ */
+@Singleton
+class ApiProvider @Inject constructor(
+    private val credentialStore: CredentialStore,
+    private val moshi: Moshi,
+    private val authInterceptor: AuthInterceptor,
+) {
+    private val client: OkHttpClient by lazy {
+        OkHttpClient.Builder()
+            .addInterceptor(authInterceptor)
+            .addInterceptor(
+                HttpLoggingInterceptor().apply { level = HttpLoggingInterceptor.Level.BASIC }
+            )
+            .connectTimeout(30, TimeUnit.SECONDS)
+            .readTimeout(60, TimeUnit.SECONDS)
+            .build()
+    }
+
+    @Volatile private var cached: Pair<String, CalendarrApi>? = null
+
+    /** API bound to the currently stored server URL. Requires a configured server. */
+    fun api(): CalendarrApi {
+        val base = normalize(credentialStore.serverUrl ?: error("No server URL configured"))
+        cached?.let { (url, api) -> if (url == base) return api }
+        val api = build(base)
+        cached = base to api
+        return api
+    }
+
+    /** API for an explicit base URL (used during server setup / login). */
+    fun apiFor(baseUrl: String): CalendarrApi = build(normalize(baseUrl))
+
+    /** Force the cached instance to be rebuilt (e.g. after switching servers). */
+    fun invalidate() { cached = null }
+
+    private fun build(baseUrl: String): CalendarrApi =
+        Retrofit.Builder()
+            .baseUrl(baseUrl)
+            .client(client)
+            .addConverterFactory(MoshiConverterFactory.create(moshi))
+            .build()
+            .create(CalendarrApi::class.java)
+
+    companion object {
+        /** Ensure https:// prefix, strip trailing slashes, then add exactly one. */
+        fun normalize(raw: String): String {
+            var url = raw.trim()
+            if (url.isEmpty()) return url
+            if (!url.startsWith("http://") && !url.startsWith("https://")) {
+                url = "https://$url"
+            }
+            url = url.trimEnd('/')
+            return "$url/"
+        }
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/remote/AuthInterceptor.kt b/app/src/main/java/com/scarriffle/calendarr/data/remote/AuthInterceptor.kt
new file mode 100644
index 0000000..ab34832
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/remote/AuthInterceptor.kt
@@ -0,0 +1,27 @@
+package com.scarriffle.calendarr.data.remote
+
+import com.scarriffle.calendarr.data.CredentialStore
+import okhttp3.Interceptor
+import okhttp3.Response
+import javax.inject.Inject
+
+/**
+ * Attaches the current bearer token (read dynamically from the
+ * [CredentialStore]) to every request. Requests made before login simply
+ * carry no Authorization header.
+ */
+class AuthInterceptor @Inject constructor(
+    private val credentialStore: CredentialStore,
+) : Interceptor {
+    override fun intercept(chain: Interceptor.Chain): Response {
+        val token = credentialStore.token
+        val request = if (!token.isNullOrBlank()) {
+            chain.request().newBuilder()
+                .header("Authorization", "Bearer $token")
+                .build()
+        } else {
+            chain.request()
+        }
+        return chain.proceed(request)
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/remote/CalendarrApi.kt b/app/src/main/java/com/scarriffle/calendarr/data/remote/CalendarrApi.kt
new file mode 100644
index 0000000..65cb42a
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/remote/CalendarrApi.kt
@@ -0,0 +1,181 @@
+package com.scarriffle.calendarr.data.remote
+
+import com.scarriffle.calendarr.domain.model.AppSettings
+import com.scarriffle.calendarr.domain.model.CalDAVAccount
+import com.scarriffle.calendarr.domain.model.GoogleAccount
+import com.scarriffle.calendarr.domain.model.HomeAssistantAccount
+import com.scarriffle.calendarr.domain.model.ICalSubscription
+import com.scarriffle.calendarr.domain.model.LocalCalendar
+import com.scarriffle.calendarr.domain.model.UserProfile
+import okhttp3.RequestBody
+import okhttp3.ResponseBody
+import retrofit2.Response
+import retrofit2.http.Body
+import retrofit2.http.DELETE
+import retrofit2.http.GET
+import retrofit2.http.HTTP
+import retrofit2.http.PATCH
+import retrofit2.http.POST
+import retrofit2.http.PUT
+import retrofit2.http.Path
+import retrofit2.http.Query
+
+/**
+ * Retrofit definition of the Calendarr server HTTP API.
+ *
+ * Endpoints whose responses contain mixed-type fields (event `id` /
+ * `calendar_id` arrive as either String or Int) return a raw [ResponseBody]
+ * and are parsed manually with org.json, mirroring the iOS client.
+ */
+interface CalendarrApi {
+
+    // ---- Auth ----
+
+    @GET("api/auth/setup-required")
+    suspend fun setupRequired(): Response<ResponseBody>
+
+    @POST("api/auth/login")
+    suspend fun login(@Body body: RequestBody): Response<ResponseBody>
+
+    @GET("api/auth/me")
+    suspend fun getProfile(): UserProfile
+
+    // ---- Settings ----
+
+    @GET("api/settings/")
+    suspend fun getSettings(): AppSettings
+
+    @PUT("api/settings/")
+    suspend fun updateSettings(@Body body: RequestBody): Response<ResponseBody>
+
+    // ---- Profile ----
+
+    @PATCH("api/profile/")
+    suspend fun updateEmail(@Body body: RequestBody): Response<ResponseBody>
+
+    @POST("api/profile/password")
+    suspend fun changePassword(@Body body: RequestBody): Response<ResponseBody>
+
+    @POST("api/profile/2fa/setup")
+    suspend fun setup2fa(): Response<ResponseBody>
+
+    @POST("api/profile/2fa/enable")
+    suspend fun enable2fa(@Body body: RequestBody): Response<ResponseBody>
+
+    @POST("api/profile/2fa/disable")
+    suspend fun disable2fa(@Body body: RequestBody): Response<ResponseBody>
+
+    // ---- CalDAV ----
+
+    @GET("api/caldav/accounts")
+    suspend fun getCalDAVAccounts(): List<CalDAVAccount>
+
+    @POST("api/caldav/accounts")
+    suspend fun addCalDAVAccount(@Body body: RequestBody): CalDAVAccount
+
+    @DELETE("api/caldav/accounts/{id}")
+    suspend fun deleteCalDAVAccount(@Path("id") id: Int): Response<ResponseBody>
+
+    @POST("api/caldav/accounts/{id}/sync")
+    suspend fun syncCalDAVAccount(@Path("id") id: Int): Response<ResponseBody>
+
+    @PUT("api/caldav/calendars/{id}")
+    suspend fun updateCalDAVCalendar(@Path("id") id: Int, @Body body: RequestBody): Response<ResponseBody>
+
+    // ---- Local ----
+
+    @GET("api/local/calendars")
+    suspend fun getLocalCalendars(): List<LocalCalendar>
+
+    @POST("api/local/calendars")
+    suspend fun addLocalCalendar(@Body body: RequestBody): LocalCalendar
+
+    @DELETE("api/local/calendars/{id}")
+    suspend fun deleteLocalCalendar(@Path("id") id: Int): Response<ResponseBody>
+
+    // ---- iCal subscriptions ----
+
+    @GET("api/ical/subscriptions")
+    suspend fun getICalSubscriptions(): List<ICalSubscription>
+
+    @POST("api/ical/subscriptions")
+    suspend fun addICalSubscription(@Body body: RequestBody): ICalSubscription
+
+    @DELETE("api/ical/subscriptions/{id}")
+    suspend fun deleteICalSubscription(@Path("id") id: Int): Response<ResponseBody>
+
+    @POST("api/ical/subscriptions/{id}/refresh")
+    suspend fun refreshICalSubscription(@Path("id") id: Int): Response<ResponseBody>
+
+    // ---- Google ----
+
+    @GET("api/google/accounts")
+    suspend fun getGoogleAccounts(): List<GoogleAccount>
+
+    @DELETE("api/google/accounts/{id}")
+    suspend fun deleteGoogleAccount(@Path("id") id: Int): Response<ResponseBody>
+
+    @PUT("api/google/calendars/{id}")
+    suspend fun updateGoogleCalendar(@Path("id") id: Int, @Body body: RequestBody): Response<ResponseBody>
+
+    // ---- Home Assistant ----
+
+    @GET("api/homeassistant/accounts")
+    suspend fun getHomeAssistantAccounts(): List<HomeAssistantAccount>
+
+    @POST("api/homeassistant/accounts")
+    suspend fun addHomeAssistantAccount(@Body body: RequestBody): HomeAssistantAccount
+
+    @DELETE("api/homeassistant/accounts/{id}")
+    suspend fun deleteHomeAssistantAccount(@Path("id") id: Int): Response<ResponseBody>
+
+    @PUT("api/homeassistant/calendars/{id}")
+    suspend fun updateHACalendar(@Path("id") id: Int, @Body body: RequestBody): Response<ResponseBody>
+
+    // ---- Events ----
+
+    @GET("api/caldav/events")
+    suspend fun fetchEvents(
+        @Query("start") start: String,
+        @Query("end") end: String,
+    ): Response<ResponseBody>
+
+    @POST("api/local/events")
+    suspend fun createLocalEvent(@Body body: RequestBody): Response<ResponseBody>
+
+    @PUT("api/local/events/{uid}")
+    suspend fun updateLocalEvent(@Path("uid") uid: String, @Body body: RequestBody): Response<ResponseBody>
+
+    @DELETE("api/local/events/{uid}")
+    suspend fun deleteLocalEvent(@Path("uid") uid: String): Response<ResponseBody>
+
+    @POST("api/caldav/events")
+    suspend fun createCalDAVEvent(@Body body: RequestBody): Response<ResponseBody>
+
+    @PUT("api/caldav/events/{uid}")
+    suspend fun updateCalDAVEvent(
+        @Path("uid") uid: String,
+        @Query("event_url") eventUrl: String,
+        @Query("calendar_id") calendarId: Int?,
+        @Body body: RequestBody,
+    ): Response<ResponseBody>
+
+    @HTTP(method = "DELETE", path = "api/caldav/events/{uid}", hasBody = false)
+    suspend fun deleteCalDAVEvent(
+        @Path("uid") uid: String,
+        @Query("event_url") eventUrl: String,
+        @Query("calendar_id") calendarId: Int?,
+    ): Response<ResponseBody>
+
+    @POST("api/google/events")
+    suspend fun createGoogleEvent(@Body body: RequestBody): Response<ResponseBody>
+
+    @POST("api/homeassistant/events")
+    suspend fun createHAEvent(@Body body: RequestBody): Response<ResponseBody>
+
+    @DELETE("api/homeassistant/events/{calendarId}/{uid}")
+    suspend fun deleteHAEvent(
+        @Path("calendarId") calendarId: Int,
+        @Path("uid") uid: String,
+    ): Response<ResponseBody>
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/data/remote/JsonBody.kt b/app/src/main/java/com/scarriffle/calendarr/data/remote/JsonBody.kt
new file mode 100644
index 0000000..b6d08d5
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/data/remote/JsonBody.kt
@@ -0,0 +1,26 @@
+package com.scarriffle.calendarr.data.remote
+
+import okhttp3.MediaType.Companion.toMediaType
+import okhttp3.RequestBody
+import okhttp3.RequestBody.Companion.toRequestBody
+import org.json.JSONObject
+
+private val JSON = "application/json; charset=utf-8".toMediaType()
+
+/** Build a JSON request body from key/value pairs, dropping null values. */
+fun jsonBody(vararg pairs: Pair<String, Any?>): RequestBody {
+    val obj = JSONObject()
+    for ((k, v) in pairs) {
+        if (v != null) obj.put(k, v)
+    }
+    return obj.toString().toRequestBody(JSON)
+}
+
+/** Build a JSON request body from a map, dropping null values. */
+fun jsonBody(map: Map<String, Any?>): RequestBody {
+    val obj = JSONObject()
+    for ((k, v) in map) {
+        if (v != null) obj.put(k, v)
+    }
+    return obj.toString().toRequestBody(JSON)
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/di/AppModule.kt b/app/src/main/java/com/scarriffle/calendarr/di/AppModule.kt
new file mode 100644
index 0000000..95ba7a7
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/di/AppModule.kt
@@ -0,0 +1,21 @@
+package com.scarriffle.calendarr.di
+
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
+import dagger.Module
+import dagger.Provides
+import dagger.hilt.InstallIn
+import dagger.hilt.components.SingletonComponent
+import javax.inject.Singleton
+
+@Module
+@InstallIn(SingletonComponent::class)
+object AppModule {
+
+    @Provides
+    @Singleton
+    fun provideMoshi(): Moshi =
+        Moshi.Builder()
+            .add(KotlinJsonAdapterFactory())
+            .build()
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/domain/model/Accounts.kt b/app/src/main/java/com/scarriffle/calendarr/domain/model/Accounts.kt
new file mode 100644
index 0000000..aa41878
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/domain/model/Accounts.kt
@@ -0,0 +1,97 @@
+package com.scarriffle.calendarr.domain.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+@JsonClass(generateAdapter = false)
+data class CalDAVAccount(
+    val id: Int,
+    val name: String = "",
+    val url: String = "",
+    val username: String = "",
+    val color: String = "#4285f4",
+    val enabled: Boolean = true,
+    val calendars: List<CalDAVCalendar>? = null,
+)
+
+@JsonClass(generateAdapter = false)
+data class CalDAVCalendar(
+    val id: Int,
+    val name: String = "",
+    val color: String? = null,
+    val enabled: Boolean = true,
+    @Json(name = "sidebar_hidden") val sidebarHidden: Boolean = false,
+)
+
+@JsonClass(generateAdapter = false)
+data class LocalCalendar(
+    val id: Int,
+    val name: String = "",
+    val color: String = "#34a853",
+    val enabled: Boolean = true,
+)
+
+@JsonClass(generateAdapter = false)
+data class ICalSubscription(
+    val id: Int,
+    val name: String = "",
+    val url: String = "",
+    val color: String = "#46bdc6",
+    val enabled: Boolean = true,
+    @Json(name = "refresh_minutes") val refreshMinutes: Int = 60,
+    @Json(name = "last_fetched") val lastFetched: String? = null,
+)
+
+@JsonClass(generateAdapter = false)
+data class GoogleAccount(
+    val id: Int,
+    val email: String = "",
+    val calendars: List<GoogleCalendar>? = null,
+)
+
+@JsonClass(generateAdapter = false)
+data class GoogleCalendar(
+    val id: Int,
+    val name: String = "",
+    val color: String? = null,
+    val enabled: Boolean = true,
+    @Json(name = "sidebar_hidden") val sidebarHidden: Boolean = false,
+)
+
+@JsonClass(generateAdapter = false)
+data class HomeAssistantAccount(
+    val id: Int,
+    val name: String = "",
+    val url: String = "",
+    @Json(name = "auth_method") val authMethod: String = "token",
+    val calendars: List<HACalendar>? = null,
+)
+
+@JsonClass(generateAdapter = false)
+data class HACalendar(
+    val id: Int,
+    val name: String = "",
+    @Json(name = "entity_id") val entityId: String = "",
+    val color: String? = null,
+    val enabled: Boolean = true,
+    @Json(name = "sidebar_hidden") val sidebarHidden: Boolean = false,
+)
+
+@JsonClass(generateAdapter = false)
+data class UserProfile(
+    val id: Int,
+    val username: String = "",
+    val email: String? = null,
+    @Json(name = "is_admin") val isAdmin: Boolean = false,
+    @Json(name = "has_avatar") val hasAvatar: Boolean = false,
+    @Json(name = "totp_enabled") val totpEnabled: Boolean = false,
+)
+
+/** A calendar the user can create events in (resolved from all writable sources). */
+data class WritableCalendar(
+    val id: String,
+    val name: String,
+    val color: String,
+    val source: String,
+    val numericId: Int,
+)
diff --git a/app/src/main/java/com/scarriffle/calendarr/domain/model/AppSettings.kt b/app/src/main/java/com/scarriffle/calendarr/domain/model/AppSettings.kt
new file mode 100644
index 0000000..2e5f5d0
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/domain/model/AppSettings.kt
@@ -0,0 +1,27 @@
+package com.scarriffle.calendarr.domain.model
+
+import com.squareup.moshi.Json
+import com.squareup.moshi.JsonClass
+
+/**
+ * User appearance / behaviour settings, synced with the server.
+ * Mirrors iOS `AppSettings`. Missing keys fall back to the defaults below
+ * (the server only persists a subset).
+ */
+@JsonClass(generateAdapter = false)
+data class AppSettings(
+    @Json(name = "default_view") val defaultView: String = "month",
+    @Json(name = "week_start_day") val weekStartDay: String = "monday",
+    @Json(name = "primary_color") val primaryColor: String = "#4285f4",
+    @Json(name = "accent_color") val accentColor: String = "#ea4335",
+    @Json(name = "today_color") val todayColor: String = "#4285f4",
+    @Json(name = "dim_past_events") val dimPastEvents: Boolean = false,
+    @Json(name = "text_contrast") val textContrast: Int = 3,
+    @Json(name = "line_contrast") val lineContrast: Int = 3,
+    @Json(name = "hour_height") val hourHeight: Int = 60,
+    @Json(name = "language") val language: String = "de",
+    @Json(name = "month_divider_color") val monthDividerColor: String = "#7090c0",
+    @Json(name = "month_label_color") val monthLabelColor: String = "#7090c0",
+) {
+    val weekStartsOnMonday: Boolean get() = weekStartDay != "sunday"
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/domain/model/CalEvent.kt b/app/src/main/java/com/scarriffle/calendarr/domain/model/CalEvent.kt
new file mode 100644
index 0000000..a67ff6a
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/domain/model/CalEvent.kt
@@ -0,0 +1,71 @@
+package com.scarriffle.calendarr.domain.model
+
+import com.scarriffle.calendarr.util.Dates
+import org.json.JSONObject
+import java.time.Instant
+
+/**
+ * A unified calendar event, blended from all server sources
+ * (local, caldav, google, ical, homeassistant). Mirrors iOS `CalEvent`.
+ */
+data class CalEvent(
+    val id: String,
+    val url: String,
+    val title: String,
+    val startDate: Instant,
+    val endDate: Instant,
+    val isAllDay: Boolean,
+    val location: String,
+    val notes: String,
+    val color: String?,
+    val calendarId: String,
+    val calendarName: String,
+    val calendarColor: String,
+    val source: String,
+) {
+    /** Per-event override colour, falling back to the calendar's colour. */
+    val effectiveColor: String get() = color?.takeIf { it.isNotBlank() } ?: calendarColor
+
+    companion object {
+        /** Parse one event object from the `/api/caldav/events` aggregate response. */
+        fun fromJson(json: JSONObject): CalEvent? {
+            val title = json.optString("title").takeIf { json.has("title") } ?: return null
+            val startStr = json.optString("start").takeIf { json.has("start") } ?: return null
+            val endStr = json.optString("end").takeIf { json.has("end") } ?: return null
+
+            // id may be a String (local UUID) or an Int (CalDAV numeric)
+            val id: String = when (val raw = json.opt("id")) {
+                is String -> raw
+                is Number -> raw.toString()
+                else -> return null
+            }
+
+            val isAllDay = json.optBoolean("allDay", false)
+            val start = Dates.parse(startStr, isAllDay) ?: return null
+            val end = Dates.parse(endStr, isAllDay) ?: return null
+
+            // calendar_id arrives as raw numeric (caldav) or "<source>-<id>" string
+            val calendarId = when (val raw = json.opt("calendar_id")) {
+                null, JSONObject.NULL -> ""
+                else -> raw.toString()
+            }
+
+            val colorRaw = json.optString("color", "")
+            return CalEvent(
+                id = id,
+                url = json.optString("url", ""),
+                title = title,
+                startDate = start,
+                endDate = end,
+                isAllDay = isAllDay,
+                location = json.optString("location", ""),
+                notes = json.optString("description", ""),
+                color = colorRaw.takeIf { it.isNotBlank() },
+                calendarId = calendarId,
+                calendarName = json.optString("calendar_name", ""),
+                calendarColor = json.optString("calendarColor", "#4285f4"),
+                source = json.optString("source", "local"),
+            )
+        }
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/domain/model/CalViewType.kt b/app/src/main/java/com/scarriffle/calendarr/domain/model/CalViewType.kt
new file mode 100644
index 0000000..cb67305
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/domain/model/CalViewType.kt
@@ -0,0 +1,31 @@
+package com.scarriffle.calendarr.domain.model
+
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.CalendarMonth
+import androidx.compose.material.icons.filled.CalendarViewWeek
+import androidx.compose.material.icons.filled.DateRange
+import androidx.compose.material.icons.filled.ViewList
+import androidx.compose.material.icons.filled.WbSunny
+import androidx.compose.ui.graphics.vector.ImageVector
+
+enum class CalViewType(val key: String) {
+    MONTH("month"),
+    WEEK("week"),
+    DAY("day"),
+    QUARTER("quarter"),
+    AGENDA("agenda");
+
+    val icon: ImageVector
+        get() = when (this) {
+            MONTH -> Icons.Filled.CalendarMonth
+            WEEK -> Icons.Filled.CalendarViewWeek
+            DAY -> Icons.Filled.WbSunny
+            QUARTER -> Icons.Filled.DateRange
+            AGENDA -> Icons.Filled.ViewList
+        }
+
+    companion object {
+        fun fromKey(key: String?): CalViewType =
+            entries.firstOrNull { it.key == key } ?: MONTH
+    }
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/ui/L10n.kt b/app/src/main/java/com/scarriffle/calendarr/ui/L10n.kt
new file mode 100644
index 0000000..5170248
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/ui/L10n.kt
@@ -0,0 +1,220 @@
+package com.scarriffle.calendarr.ui
+
+import java.util.Locale
+
+/**
+ * In-app localization mirroring the iOS `L10n`. The stored language may be
+ * "de", "en" or "system" (resolve to device language).
+ */
+object L10n {
+
+    fun resolved(stored: String): String {
+        if (stored == "de" || stored == "en") return stored
+        val pref = Locale.getDefault().language.lowercase()
+        return if (pref.startsWith("de")) "de" else "en"
+    }
+
+    fun locale(stored: String): Locale = Locale(resolved(stored))
+
+    fun t(key: String, stored: String): String {
+        val lang = resolved(stored)
+        return strings[lang]?.get(key) ?: strings["en"]?.get(key) ?: key
+    }
+
+    fun t(key: String, stored: String, vararg args: Any): String {
+        val template = t(key, stored)
+        // Support both %@ (iOS) and %s / %d (Java) placeholders.
+        val javaTemplate = template.replace("%@", "%s")
+        return runCatching { String.format(locale(stored), javaTemplate, *args) }
+            .getOrDefault(template)
+    }
+
+    private val strings: Map<String, Map<String, String>> = mapOf(
+        "de" to mapOf(
+            "nav.today" to "Heute", "nav.menu" to "Menü", "nav.done" to "Fertig",
+            "view.month" to "Monat", "view.week" to "Woche", "view.day" to "Tag",
+            "view.quarter" to "Quartal", "view.agenda" to "Termine", "view.change" to "Ansicht",
+            "cal.cw" to "KW", "cal.allday" to "Ganztägig",
+            "cal.no_events_title" to "Keine Termine",
+            "cal.no_events_body" to "In den nächsten 90 Tagen sind keine Termine vorhanden.",
+            "cal.loading_more" to "Lade weitere Wochen…", "cal.new_event" to "Neues Ereignis",
+            "menu.section.settings" to "Einstellungen", "menu.profile" to "Profil",
+            "menu.appearance" to "Darstellung", "menu.accounts" to "Konten & Kalender",
+            "menu.server" to "Server", "menu.logout" to "Abmelden", "menu.admin" to "Admin",
+            "menu.sync" to "Mit Server synchronisieren", "menu.sync.section" to "Synchronisierung",
+            "settings.title" to "Darstellung", "settings.loading" to "Lade Einstellungen…",
+            "settings.save" to "Speichern", "settings.saved" to "Gespeichert",
+            "settings.cache.title" to "Vorladen", "settings.cache.range" to "Zeitraum",
+            "settings.cache.1m" to "±1 Monat", "settings.cache.3m" to "±3 Monate",
+            "settings.cache.6m" to "±6 Monate", "settings.cache.1y" to "±1 Jahr",
+            "settings.language" to "Sprache", "lang.system" to "Systemstandard",
+            "lang.german" to "Deutsch", "lang.english" to "English",
+            "settings.colors" to "Farben", "settings.color.primary" to "Primärfarbe",
+            "settings.color.accent" to "Akzentfarbe", "settings.color.today" to "Heutige-Tag-Farbe",
+            "settings.color.divider" to "Monatswechsel-Linie", "settings.color.label" to "Monatskürzel",
+            "settings.textcontrast" to "Schriftkontrast", "settings.linecontrast" to "Linienkontrast",
+            "settings.calview" to "Kalenderansicht", "settings.defaultview" to "Standardansicht",
+            "settings.firstweekday" to "Erster Wochentag", "settings.monday" to "Montag",
+            "settings.sunday" to "Sonntag", "settings.dimpast" to "Vergangene Termine ausgrauen",
+            "settings.hourheight" to "Stundenhöhe",
+            "common.cancel" to "Abbrechen", "common.close" to "Schliessen",
+            "common.ok" to "OK", "common.error" to "Fehler", "common.delete" to "Löschen",
+            "common.save" to "Sichern", "common.retry" to "Erneut versuchen",
+            "server.title" to "Server", "server.connected" to "Verbundener Server",
+            "server.switch" to "Server wechseln", "server.logout_title" to "Abmelden",
+            "server.version" to "Version",
+            "profile.title" to "Profil", "profile.loading" to "Lade Profil…",
+            "profile.account" to "Konto", "profile.username" to "Benutzername",
+            "profile.role" to "Rolle", "profile.role.admin" to "Administrator",
+            "profile.role.user" to "Benutzer", "profile.email" to "E-Mail",
+            "profile.no_email" to "Keine E-Mail", "profile.save_email" to "E-Mail speichern",
+            "profile.email_saved" to "E-Mail gespeichert", "profile.change_password" to "Passwort ändern",
+            "profile.current_password" to "Aktuelles Passwort", "profile.new_password" to "Neues Passwort",
+            "profile.new_password_repeat" to "Neues Passwort wiederholen",
+            "profile.password_mismatch" to "Passwörter stimmen nicht überein",
+            "profile.password_changed" to "Passwort geändert",
+            "profile.twofa" to "Zwei-Faktor-Authentifizierung",
+            "profile.twofa.active" to "2FA ist aktiviert", "profile.twofa.inactive" to "2FA ist deaktiviert",
+            "profile.twofa.enable" to "2FA einrichten", "profile.twofa.disable" to "2FA deaktivieren",
+            "twofa.setup_title" to "2FA einrichten",
+            "twofa.scan_hint" to "Scanne den QR-Code mit deiner Authenticator-App.",
+            "twofa.code_placeholder" to "6-stelliger Code", "twofa.activate" to "Aktivieren",
+            "twofa.disable_title" to "2FA deaktivieren", "twofa.password_placeholder" to "Passwort",
+            "twofa.disable" to "Deaktivieren",
+            "event.title_placeholder" to "Titel", "event.allday" to "Ganztägig",
+            "event.start" to "Start", "event.end" to "Ende", "event.location" to "Ort",
+            "event.description" to "Beschreibung", "event.calendar_section" to "Kalender",
+            "event.no_writable" to "Keine beschreibbaren Kalender vorhanden",
+            "event.calendar_picker" to "Kalender", "event.color_section" to "Farbe",
+            "event.color" to "Terminfarbe", "event.reset_color" to "Zurücksetzen",
+            "event.edit_title" to "Termin bearbeiten", "event.new_title" to "Neuer Termin",
+            "event.save" to "Sichern", "event.add" to "Hinzufügen",
+            "event.delete_confirm" to "Diesen Termin löschen?",
+            "accounts.title" to "Konten", "accounts.loading" to "Lade Konten…",
+            "accounts.caldav.header" to "CalDAV-Konten", "accounts.caldav.empty" to "Keine CalDAV-Konten",
+            "accounts.caldav.add" to "CalDAV hinzufügen", "accounts.local.header" to "Lokale Kalender",
+            "accounts.local.empty" to "Keine lokalen Kalender", "accounts.local.add" to "Lokalen Kalender erstellen",
+            "accounts.ical.header" to "iCal-Abonnements", "accounts.ical.empty" to "Keine Abonnements",
+            "accounts.ical.add" to "iCal-URL abonnieren", "accounts.google.header" to "Google-Konten",
+            "accounts.google.empty" to "Keine Google-Konten",
+            "accounts.google.hint" to "Google-Konten werden über den Browser verknüpft",
+            "accounts.ha.header" to "Home Assistant", "accounts.ha.empty" to "Keine Home Assistant-Konten",
+            "accounts.ha.add" to "Home Assistant hinzufügen",
+            "filter.title" to "Kalender", "filter.empty" to "Keine Kalender vorhanden",
+            "filter.show_all" to "Alle anzeigen", "filter.hide_all" to "Alle ausblenden",
+            "filter.button" to "Kalender ein-/ausblenden",
+            "caldav.display_name" to "Anzeigename", "caldav.url" to "CalDAV-URL",
+            "caldav.username" to "Benutzername", "caldav.password" to "Passwort",
+            "caldav.color" to "Farbe", "caldav.connect" to "Verbinden", "caldav.title" to "CalDAV-Konto",
+            "local.title" to "Lokaler Kalender", "local.name" to "Name", "local.color" to "Farbe",
+            "local.create" to "Erstellen",
+            "ical.title" to "iCal abonnieren", "ical.name" to "Name", "ical.url" to "iCal-URL",
+            "ical.color" to "Farbe", "ical.interval" to "Intervall", "ical.subscribe" to "Abonnieren",
+            "ical.refresh.15m" to "Alle 15 Min.", "ical.refresh.30m" to "Alle 30 Min.",
+            "ical.refresh.1h" to "Stündlich", "ical.refresh.6h" to "Alle 6 Std.", "ical.refresh.1d" to "Täglich",
+            "ha.display_name" to "Anzeigename", "ha.url_placeholder" to "URL (z.B. http://homeassistant.local:8123)",
+            "ha.token" to "Long-Lived Access Token", "ha.connect" to "Verbinden",
+            // Auth screens
+            "auth.server_title" to "Server verbinden", "auth.server_url" to "Server-URL",
+            "auth.server_hint" to "Gib die Adresse deines Calendarr-Servers ein.",
+            "auth.continue" to "Weiter", "auth.checking" to "Verbinde…",
+            "auth.login_title" to "Anmelden", "auth.username" to "Benutzername",
+            "auth.password" to "Passwort", "auth.login" to "Anmelden",
+            "auth.totp" to "2FA-Code", "auth.remember" to "Angemeldet bleiben",
+            "auth.back" to "Zurück",
+        ),
+        "en" to mapOf(
+            "nav.today" to "Today", "nav.menu" to "Menu", "nav.done" to "Done",
+            "view.month" to "Month", "view.week" to "Week", "view.day" to "Day",
+            "view.quarter" to "Quarter", "view.agenda" to "Agenda", "view.change" to "View",
+            "cal.cw" to "W", "cal.allday" to "All-day",
+            "cal.no_events_title" to "No events",
+            "cal.no_events_body" to "No events in the next 90 days.",
+            "cal.loading_more" to "Loading more weeks…", "cal.new_event" to "New event",
+            "menu.section.settings" to "Settings", "menu.profile" to "Profile",
+            "menu.appearance" to "Appearance", "menu.accounts" to "Accounts & Calendars",
+            "menu.server" to "Server", "menu.logout" to "Sign out", "menu.admin" to "Admin",
+            "menu.sync" to "Sync with server", "menu.sync.section" to "Synchronization",
+            "settings.title" to "Appearance", "settings.loading" to "Loading settings…",
+            "settings.save" to "Save", "settings.saved" to "Saved",
+            "settings.cache.title" to "Preloading", "settings.cache.range" to "Range",
+            "settings.cache.1m" to "±1 month", "settings.cache.3m" to "±3 months",
+            "settings.cache.6m" to "±6 months", "settings.cache.1y" to "±1 year",
+            "settings.language" to "Language", "lang.system" to "System default",
+            "lang.german" to "Deutsch", "lang.english" to "English",
+            "settings.colors" to "Colors", "settings.color.primary" to "Primary color",
+            "settings.color.accent" to "Accent color", "settings.color.today" to "Today color",
+            "settings.color.divider" to "Month divider line", "settings.color.label" to "Month abbreviation",
+            "settings.textcontrast" to "Text contrast", "settings.linecontrast" to "Line contrast",
+            "settings.calview" to "Calendar view", "settings.defaultview" to "Default view",
+            "settings.firstweekday" to "First day of week", "settings.monday" to "Monday",
+            "settings.sunday" to "Sunday", "settings.dimpast" to "Dim past events",
+            "settings.hourheight" to "Hour height",
+            "common.cancel" to "Cancel", "common.close" to "Close",
+            "common.ok" to "OK", "common.error" to "Error", "common.delete" to "Delete",
+            "common.save" to "Save", "common.retry" to "Retry",
+            "server.title" to "Server", "server.connected" to "Connected server",
+            "server.switch" to "Switch server", "server.logout_title" to "Sign out",
+            "server.version" to "Version",
+            "profile.title" to "Profile", "profile.loading" to "Loading profile…",
+            "profile.account" to "Account", "profile.username" to "Username",
+            "profile.role" to "Role", "profile.role.admin" to "Administrator",
+            "profile.role.user" to "User", "profile.email" to "Email",
+            "profile.no_email" to "No email", "profile.save_email" to "Save email",
+            "profile.email_saved" to "Email saved", "profile.change_password" to "Change password",
+            "profile.current_password" to "Current password", "profile.new_password" to "New password",
+            "profile.new_password_repeat" to "Repeat new password",
+            "profile.password_mismatch" to "Passwords don't match",
+            "profile.password_changed" to "Password changed",
+            "profile.twofa" to "Two-factor authentication",
+            "profile.twofa.active" to "2FA is enabled", "profile.twofa.inactive" to "2FA is disabled",
+            "profile.twofa.enable" to "Set up 2FA", "profile.twofa.disable" to "Disable 2FA",
+            "twofa.setup_title" to "Set up 2FA",
+            "twofa.scan_hint" to "Scan the QR code with your authenticator app.",
+            "twofa.code_placeholder" to "6-digit code", "twofa.activate" to "Activate",
+            "twofa.disable_title" to "Disable 2FA", "twofa.password_placeholder" to "Password",
+            "twofa.disable" to "Disable",
+            "event.title_placeholder" to "Title", "event.allday" to "All-day",
+            "event.start" to "Start", "event.end" to "End", "event.location" to "Location",
+            "event.description" to "Description", "event.calendar_section" to "Calendar",
+            "event.no_writable" to "No writable calendars available",
+            "event.calendar_picker" to "Calendar", "event.color_section" to "Color",
+            "event.color" to "Event color", "event.reset_color" to "Reset",
+            "event.edit_title" to "Edit event", "event.new_title" to "New event",
+            "event.save" to "Save", "event.add" to "Add",
+            "event.delete_confirm" to "Delete this event?",
+            "accounts.title" to "Accounts", "accounts.loading" to "Loading accounts…",
+            "accounts.caldav.header" to "CalDAV accounts", "accounts.caldav.empty" to "No CalDAV accounts",
+            "accounts.caldav.add" to "Add CalDAV", "accounts.local.header" to "Local calendars",
+            "accounts.local.empty" to "No local calendars", "accounts.local.add" to "Create local calendar",
+            "accounts.ical.header" to "iCal subscriptions", "accounts.ical.empty" to "No subscriptions",
+            "accounts.ical.add" to "Subscribe to iCal URL", "accounts.google.header" to "Google accounts",
+            "accounts.google.empty" to "No Google accounts",
+            "accounts.google.hint" to "Google accounts are linked via the browser",
+            "accounts.ha.header" to "Home Assistant", "accounts.ha.empty" to "No Home Assistant accounts",
+            "accounts.ha.add" to "Add Home Assistant",
+            "filter.title" to "Calendars", "filter.empty" to "No calendars available",
+            "filter.show_all" to "Show all", "filter.hide_all" to "Hide all",
+            "filter.button" to "Show/hide calendars",
+            "caldav.display_name" to "Display name", "caldav.url" to "CalDAV URL",
+            "caldav.username" to "Username", "caldav.password" to "Password",
+            "caldav.color" to "Color", "caldav.connect" to "Connect", "caldav.title" to "CalDAV account",
+            "local.title" to "Local calendar", "local.name" to "Name", "local.color" to "Color",
+            "local.create" to "Create",
+            "ical.title" to "Subscribe to iCal", "ical.name" to "Name", "ical.url" to "iCal URL",
+            "ical.color" to "Color", "ical.interval" to "Interval", "ical.subscribe" to "Subscribe",
+            "ical.refresh.15m" to "Every 15 min", "ical.refresh.30m" to "Every 30 min",
+            "ical.refresh.1h" to "Hourly", "ical.refresh.6h" to "Every 6 hours", "ical.refresh.1d" to "Daily",
+            "ha.display_name" to "Display name", "ha.url_placeholder" to "URL (e.g. http://homeassistant.local:8123)",
+            "ha.token" to "Long-Lived Access Token", "ha.connect" to "Connect",
+            // Auth screens
+            "auth.server_title" to "Connect server", "auth.server_url" to "Server URL",
+            "auth.server_hint" to "Enter the address of your Calendarr server.",
+            "auth.continue" to "Continue", "auth.checking" to "Connecting…",
+            "auth.login_title" to "Sign in", "auth.username" to "Username",
+            "auth.password" to "Password", "auth.login" to "Sign in",
+            "auth.totp" to "2FA code", "auth.remember" to "Stay signed in",
+            "auth.back" to "Back",
+        ),
+    )
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/util/ColorUtil.kt b/app/src/main/java/com/scarriffle/calendarr/util/ColorUtil.kt
new file mode 100644
index 0000000..3220474
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/util/ColorUtil.kt
@@ -0,0 +1,44 @@
+package com.scarriffle.calendarr.util
+
+import androidx.compose.ui.graphics.Color
+
+/** Parse a "#RRGGBB" (or "RRGGBB") hex string into a Compose [Color]. */
+fun colorFromHex(hex: String?, fallback: Color = Color(0xFF4285F4)): Color {
+    if (hex.isNullOrBlank()) return fallback
+    val clean = hex.trim().removePrefix("#")
+    return when (clean.length) {
+        6 -> runCatching {
+            val v = clean.toLong(16)
+            Color(
+                red = ((v shr 16) and 0xFF) / 255f,
+                green = ((v shr 8) and 0xFF) / 255f,
+                blue = (v and 0xFF) / 255f,
+                alpha = 1f,
+            )
+        }.getOrDefault(fallback)
+        8 -> runCatching {
+            val v = clean.toLong(16)
+            Color(
+                alpha = ((v shr 24) and 0xFF) / 255f,
+                red = ((v shr 16) and 0xFF) / 255f,
+                green = ((v shr 8) and 0xFF) / 255f,
+                blue = (v and 0xFF) / 255f,
+            )
+        }.getOrDefault(fallback)
+        else -> fallback
+    }
+}
+
+/** Convert a Compose [Color] back to a "#RRGGBB" string. */
+fun Color.toHex(): String {
+    val r = (red * 255).toInt().coerceIn(0, 255)
+    val g = (green * 255).toInt().coerceIn(0, 255)
+    val b = (blue * 255).toInt().coerceIn(0, 255)
+    return String.format("#%02X%02X%02X", r, g, b)
+}
+
+/** Pick black or white text for legibility on a given background color. */
+fun Color.contrastingTextColor(): Color {
+    val luminance = 0.299 * red + 0.587 * green + 0.114 * blue
+    return if (luminance > 0.6) Color.Black else Color.White
+}
diff --git a/app/src/main/java/com/scarriffle/calendarr/util/Dates.kt b/app/src/main/java/com/scarriffle/calendarr/util/Dates.kt
new file mode 100644
index 0000000..1f42f10
--- /dev/null
+++ b/app/src/main/java/com/scarriffle/calendarr/util/Dates.kt
@@ -0,0 +1,77 @@
+package com.scarriffle.calendarr.util
+
+import java.time.Instant
+import java.time.LocalDate
+import java.time.LocalDateTime
+import java.time.OffsetDateTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.format.DateTimeFormatter
+
+/**
+ * Date parsing/formatting that mirrors the iOS client (CalEvent.swift).
+ *
+ * The backend may produce any of these forms:
+ *   "2026-05-17"                    (all-day, date only)
+ *   "2026-05-17T10:00:00Z"
+ *   "2026-05-17T10:00:00+02:00"
+ *   "2026-05-17T10:00:00.000Z"
+ *   "2026-05-17T10:00:00"           (no timezone -> treat as UTC)
+ *   "2026-05-17 10:00:00+00:00"     (Python isoformat, space separator)
+ */
+object Dates {
+
+    private val zone: ZoneId get() = ZoneId.systemDefault()
+
+    private val spaceSep: DateTimeFormatter =
+        DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ssXXX")
+    private val noTz: DateTimeFormatter =
+        DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss")
+
+    /** Parse a server date string into an [Instant]. Returns null if unparseable. */
+    fun parse(raw: String, allDay: Boolean): Instant? {
+        val s = raw.trim()
+        if (s.isEmpty()) return null
+
+        if (allDay || (s.length == 10 && !s.contains('T'))) {
+            return runCatching {
+                LocalDate.parse(s.take(10)).atStartOfDay(zone).toInstant()
+            }.getOrNull()
+        }
+        // ISO with offset / Z
+        runCatching { return OffsetDateTime.parse(s).toInstant() }
+        runCatching { return Instant.parse(s) }
+        // Python isoformat with a space
+        runCatching { return OffsetDateTime.parse(s, spaceSep).toInstant() }
+        // No timezone -> UTC
+        runCatching {
+            return LocalDateTime.parse(s.take(19), noTz).toInstant(ZoneOffset.UTC)
+        }
+        // Last resort: just the date part
+        return runCatching {
+            LocalDate.parse(s.take(10)).atStartOfDay(zone).toInstant()
+        }.getOrNull()
+    }
+
+    /** Format an [Instant] for sending to the server. */
+    fun format(instant: Instant, allDay: Boolean): String {
+        return if (allDay) {
+            LocalDate.ofInstant(instant, zone).toString() // yyyy-MM-dd
+        } else {
+            // ISO8601 with Z, no fractional seconds (matches iOS isoBasic)
+            DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'")
+                .withZone(ZoneOffset.UTC)
+                .format(instant)
+        }
+    }
+
+    /** ISO8601 UTC string used for the events query range (`?start=&end=`). */
+    fun isoUtc(instant: Instant): String =
+        DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'")
+            .withZone(ZoneOffset.UTC)
+            .format(instant)
+
+    fun localDate(instant: Instant): LocalDate = LocalDate.ofInstant(instant, zone)
+
+    fun startOfDay(date: LocalDate): Instant = date.atStartOfDay(zone).toInstant()
+}