Refactoring to extract GpsCategoryModel and ensure single-responsibility-principle is maintained in CategoryApi.

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

@@ -0,0 +1,101 @@
+package fr.free.nrw.commons.mwapi;
+
+import com.google.gson.Gson;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+
+import javax.inject.Inject;
+import javax.inject.Named;
+
+import fr.free.nrw.commons.mwapi.model.ApiResponse;
+import fr.free.nrw.commons.mwapi.model.Page;
+import fr.free.nrw.commons.mwapi.model.PageCategory;
+import io.reactivex.Single;
+import okhttp3.HttpUrl;
+import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.Response;
+import okhttp3.ResponseBody;
+import timber.log.Timber;
+
+/**
+ * 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.
+ */
+public class CategoryApi {
+
+    private final OkHttpClient okHttpClient;
+    private final HttpUrl mwUrl;
+    private final Gson gson;
+
+    @Inject
+    public CategoryApi(OkHttpClient okHttpClient, Gson gson,
+                       @Named("commons_mediawiki_url") HttpUrl mwUrl) {
+        this.okHttpClient = okHttpClient;
+        this.mwUrl = mwUrl;
+        this.gson = gson;
+    }
+
+    public Single<List<String>> request(String coords) {
+        return Single.fromCallable(() -> {
+            HttpUrl apiUrl = buildUrl(coords);
+            Timber.d("URL: %s", apiUrl.toString());
+
+            Request request = new Request.Builder().get().url(apiUrl).build();
+            Response response = okHttpClient.newCall(request).execute();
+            ResponseBody body = response.body();
+            if (body == null) {
+                return Collections.emptyList();
+            }
+
+            ApiResponse apiResponse = gson.fromJson(body.charStream(), ApiResponse.class);
+            Set<String> categories = new LinkedHashSet<>();
+            if (apiResponse != null && apiResponse.hasPages()) {
+                for (Page page : apiResponse.query.pages) {
+                    for (PageCategory category : page.getCategories()) {
+                        categories.add(category.withoutPrefix());
+                    }
+                }
+            }
+            return new ArrayList<>(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 HttpUrl buildUrl(String coords) {
+        return mwUrl.newBuilder()
+                .addPathSegment("w")
+                .addPathSegment("api.php")
+                .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();
+    }
+
+}
+
+
+

app/src/main/java/fr/free/nrw/commons/mwapi/model/ApiResponse.java

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+package fr.free.nrw.commons.mwapi.model;
+
+public class ApiResponse {
+    public Query query;
+
+    public ApiResponse() {
+    }
+
+    public boolean hasPages() {
+        return query != null && query.pages != null;
+    }
+}

app/src/main/java/fr/free/nrw/commons/mwapi/model/Page.java

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+package fr.free.nrw.commons.mwapi.model;
+
+import android.support.annotation.NonNull;
+
+public class Page {
+    public String title;
+    public PageCategory[] categories;
+    public PageCategory category;
+
+    public Page() {
+    }
+
+    @NonNull
+    public PageCategory[] getCategories() {
+        return categories != null ? categories : new PageCategory[0];
+    }
+}

app/src/main/java/fr/free/nrw/commons/mwapi/model/PageCategory.java

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+package fr.free.nrw.commons.mwapi.model;
+
+public class PageCategory {
+    public String title;
+
+    public PageCategory() {
+    }
+
+    public String withoutPrefix() {
+        return title != null ? title.replace("Category:", "") : "";
+    }
+}

app/src/main/java/fr/free/nrw/commons/mwapi/model/Query.java

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+package fr.free.nrw.commons.mwapi.model;
+
+public class Query {
+    public Page[] pages;
+
+    public Query() {
+        pages = new Page[0];
+    }
+
+}