Convert mwapi/wikidata to kotlin (part 1) (commons-app#5991)

* Convert OkHttpJsonApiClient and CategoryApi to kotlin

* Convert GsonUtil to kotlin

* Convert WikidataConstants to kotlin

* Convert WikidataEditListener to kotlin

* Convert WikidataEditService to kotlin

* work in progress

* Convert RequiredFieldsCheckOnReadTypeAdapterFactory to kotlin

* Converted type adapters

* Convert WikiSiteTypeAdapter to kotlin

* Fixed nullability

Author: psh

app/src/main/java/fr/free/nrw/commons/campaigns/CampaignsPresenter.kt

@@ -52,12 +52,12 @@ class CampaignsPresenter @Inject constructor(
                 return
             }
 
-            okHttpJsonApiClient.campaigns
+            okHttpJsonApiClient.getCampaigns()
                 .observeOn(mainThreadScheduler)
                 .subscribeOn(ioScheduler)
                 .doOnSubscribe { disposable = it }
                 .subscribe({ campaignResponseDTO ->
-                    val campaigns = campaignResponseDTO.campaigns?.toMutableList()
+                    val campaigns = campaignResponseDTO?.campaigns?.toMutableList()
                     if (campaigns.isNullOrEmpty()) {
                         Timber.e("The campaigns list is empty")
                         view!!.showCampaigns(null)

app/src/main/java/fr/free/nrw/commons/di/NetworkingModule.kt

@@ -170,14 +170,13 @@ class NetworkingModule {
     @Named(NAMED_WIKI_DATA_WIKI_SITE)
     fun provideWikidataWikiSite(): WikiSite = WikiSite(BuildConfig.WIKIDATA_URL)
 
-
     /**
      * Gson objects are very heavy. The app should ideally be using just one instance of it instead of creating new instances everywhere.
      * @return returns a singleton Gson instance
      */
     @Provides
     @Singleton
-    fun provideGson(): Gson = GsonUtil.getDefaultGson()
+    fun provideGson(): Gson = GsonUtil.defaultGson
 
     @Provides
     @Singleton

app/src/main/java/fr/free/nrw/commons/mwapi/CategoryApi.java

@@ -0,0 +1,83 @@
+package fr.free.nrw.commons.mwapi
+
+import com.google.gson.Gson
+import fr.free.nrw.commons.BuildConfig
+import fr.free.nrw.commons.category.CATEGORY_PREFIX
+import fr.free.nrw.commons.category.CategoryItem
+import fr.free.nrw.commons.wikidata.mwapi.MwQueryResponse
+import io.reactivex.Single
+import okhttp3.HttpUrl
+import okhttp3.HttpUrl.Companion.toHttpUrlOrNull
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import timber.log.Timber
+import javax.inject.Inject
+
+/**
+ * Uses the OkHttp library to implement calls to the Commons MediaWiki API to match GPS coordinates
+ * with nearby Commons categories. Parses the results using GSON to obtain a list of relevant
+ * categories.  Note: that caller is responsible for executing the request() method on a background
+ * thread.
+ */
+class CategoryApi @Inject constructor(
+    private val okHttpClient: OkHttpClient,
+    private val gson: Gson
+) {
+    private val apiUrl : HttpUrl by lazy { BuildConfig.WIKIMEDIA_API_HOST.toHttpUrlOrNull()!! }
+
+    fun request(coords: String): Single<List<CategoryItem>> = Single.fromCallable {
+        val apiUrl = buildUrl(coords)
+        Timber.d("URL: %s", apiUrl.toString())
+
+        val request: Request = Request.Builder().get().url(apiUrl).build()
+        val response = okHttpClient.newCall(request).execute()
+        val body = response.body ?: return@fromCallable emptyList<CategoryItem>()
+
+        val apiResponse = gson.fromJson(body.charStream(), MwQueryResponse::class.java)
+        val categories: MutableSet<CategoryItem> = mutableSetOf()
+        if (apiResponse?.query() != null && apiResponse.query()!!.pages() != null) {
+            for (page in apiResponse.query()!!.pages()!!) {
+                if (page.categories() != null) {
+                    for (category in page.categories()!!) {
+                        categories.add(
+                            CategoryItem(
+                                name = category.title().replace(CATEGORY_PREFIX, ""),
+                                description = "",
+                                thumbnail = "",
+                                isSelected = false
+                            )
+                        )
+                    }
+                }
+            }
+        }
+        ArrayList<CategoryItem>(categories)
+    }
+
+    /**
+     * Builds URL with image coords for MediaWiki API calls
+     * Example URL: https://commons.wikimedia.org/w/api.php?action=query&prop=categories|coordinates|pageprops&format=json&clshow=!hidden&coprop=type|name|dim|country|region|globe&codistancefrompoint=38.11386944444445|13.356263888888888&generator=geosearch&redirects=&ggscoord=38.11386944444445|1.356263888888888&ggsradius=100&ggslimit=10&ggsnamespace=6&ggsprop=type|name|dim|country|region|globe&ggsprimary=all&formatversion=2
+     *
+     * @param coords Coordinates to build query with
+     * @return URL for API query
+     */
+    private fun buildUrl(coords: String): HttpUrl = apiUrl.newBuilder()
+        .addQueryParameter("action", "query")
+        .addQueryParameter("prop", "categories|coordinates|pageprops")
+        .addQueryParameter("format", "json")
+        .addQueryParameter("clshow", "!hidden")
+        .addQueryParameter("coprop", "type|name|dim|country|region|globe")
+        .addQueryParameter("codistancefrompoint", coords)
+        .addQueryParameter("generator", "geosearch")
+        .addQueryParameter("ggscoord", coords)
+        .addQueryParameter("ggsradius", "10000")
+        .addQueryParameter("ggslimit", "10")
+        .addQueryParameter("ggsnamespace", "6")
+        .addQueryParameter("ggsprop", "type|name|dim|country|region|globe")
+        .addQueryParameter("ggsprimary", "all")
+        .addQueryParameter("formatversion", "2")
+        .build()
+}
+
+
+