Show better errors when loading notifications fails (#3448)

* Show better errors with notification loading fails

The errors are returned as a JSON object, parse it, and show the error
message it contains.

Handle the cases where there might be no error message, or the JSON may be
malformed.

Add tests.

Fixes #3445

* Lint

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationsPagingSource.kt

@@ -20,6 +20,7 @@ package com.keylesspalace.tusky.components.notifications
 import android.util.Log
 import androidx.paging.PagingSource
 import androidx.paging.PagingState
+import com.google.gson.Gson
 import com.keylesspalace.tusky.entity.Notification
 import com.keylesspalace.tusky.network.MastodonApi
 import com.keylesspalace.tusky.util.HttpHeaderLink
@@ -35,6 +36,7 @@ data class Links(val next: String?, val prev: String?)
 /** [PagingSource] for Mastodon Notifications, identified by the Notification ID */
 class NotificationsPagingSource @Inject constructor(
     private val mastodonApi: MastodonApi,
+    private val gson: Gson,
     private val notificationFilter: Set<Notification.Type>
 ) : PagingSource<String, Notification>() {
     override suspend fun load(params: LoadParams<String>): LoadResult<String, Notification> {
@@ -58,7 +60,23 @@ class NotificationsPagingSource @Inject constructor(
             }
 
             if (!response.isSuccessful) {
-                return LoadResult.Error(Throwable(response.errorBody()?.string()))
+                val code = response.code()
+
+                val msg = response.errorBody()?.string()?.let { errorBody ->
+                    if (errorBody.isBlank()) return@let "no reason given"
+
+                    val error = try {
+                        gson.fromJson(errorBody, com.keylesspalace.tusky.entity.Error::class.java)
+                    } catch (e: Exception) {
+                        return@let "$errorBody ($e)"
+                    }
+
+                    when (val desc = error.error_description) {
+                        null -> error.error
+                        else -> "${error.error}: $desc"
+                    }
+                } ?: "no reason given"
+                return LoadResult.Error(Throwable("HTTP $code: $msg"))
             }
 
             val links = getPageLinks(response.headers()["link"])

app/src/main/java/com/keylesspalace/tusky/components/notifications/NotificationsRepository.kt

@@ -23,6 +23,7 @@ import androidx.paging.Pager
 import androidx.paging.PagingConfig
 import androidx.paging.PagingData
 import androidx.paging.PagingSource
+import com.google.gson.Gson
 import com.keylesspalace.tusky.entity.Notification
 import com.keylesspalace.tusky.network.MastodonApi
 import kotlinx.coroutines.flow.Flow
@@ -31,7 +32,8 @@ import retrofit2.Response
 import javax.inject.Inject
 
 class NotificationsRepository @Inject constructor(
-    private val mastodonApi: MastodonApi
+    private val mastodonApi: MastodonApi,
+    private val gson: Gson
 ) {
     private var factory: InvalidatingPagingSourceFactory<String, Notification>? = null
 
@@ -47,7 +49,7 @@ class NotificationsRepository @Inject constructor(
         Log.d(TAG, "getNotificationsStream(), filtering: $filter")
 
         factory = InvalidatingPagingSourceFactory {
-            NotificationsPagingSource(mastodonApi, filter)
+            NotificationsPagingSource(mastodonApi, gson, filter)
         }
 
         return Pager(

app/src/main/java/com/keylesspalace/tusky/entity/Error.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2023 Tusky Contributors
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>.
+ */
+
+package com.keylesspalace.tusky.entity
+
+/** @see [Error](https://docs.joinmastodon.org/entities/Error/) */
+data class Error(
+    val error: String,
+    val error_description: String?
+)