Create MerchantViewModel and MerchantRepository, the first to hold the merchants data and deliver it to the MerchantsFragment and the second to serve as a single source to fetch the Merchants list. When it gets a request for the merchants it retrieves and serves the list from the database and meanwhile refreshes the list from the WebService.

app/src/main/java/cy/agorise/bitsybitshareswallet/database/daos/MerchantDao.kt

@@ -1,8 +1,10 @@
 package cy.agorise.bitsybitshareswallet.database.daos
 
+import androidx.lifecycle.LiveData
 import androidx.room.Dao
 import androidx.room.Insert
 import androidx.room.OnConflictStrategy
+import androidx.room.Query
 import cy.agorise.bitsybitshareswallet.database.entities.Merchant
 
 @Dao
@@ -12,4 +14,7 @@ interface MerchantDao {
 
     @Insert(onConflict = OnConflictStrategy.REPLACE)
     fun insertAll(merchants: List<Merchant>)
+
+    @Query("SELECT * FROM merchants")
+    fun getAll(): LiveData<List<Merchant>>
 }

app/src/main/java/cy/agorise/bitsybitshareswallet/fragments/MerchantsFragment.kt

@@ -12,17 +12,12 @@ import android.view.ViewGroup
 import com.google.android.gms.maps.GoogleMap
 import com.google.android.gms.maps.OnMapReadyCallback
 import com.google.android.gms.maps.SupportMapFragment
-import com.google.gson.GsonBuilder
 
 import cy.agorise.bitsybitshareswallet.R
-import cy.agorise.bitsybitshareswallet.network.MerchantsWebservice
-import cy.agorise.bitsybitshareswallet.network.FeathersResponse
-import retrofit2.Call
-import retrofit2.Response
-import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
 import android.preference.PreferenceManager
 import androidx.core.content.ContextCompat
+import androidx.lifecycle.Observer
+import androidx.lifecycle.ViewModelProviders
 import com.google.android.gms.maps.CameraUpdateFactory
 import com.google.android.gms.maps.model.*
 import com.google.maps.android.clustering.Cluster
@@ -31,10 +26,11 @@ import cy.agorise.bitsybitshareswallet.database.entities.Merchant
 import cy.agorise.bitsybitshareswallet.utils.Constants
 import cy.agorise.bitsybitshareswallet.utils.MerchantMarkerRenderer
 import cy.agorise.bitsybitshareswallet.utils.toast
+import cy.agorise.bitsybitshareswallet.viewmodels.MerchantViewModel
 import java.lang.Exception
 
 
-class MerchantsFragment : Fragment(), OnMapReadyCallback, retrofit2.Callback<FeathersResponse<Merchant>>,
+class MerchantsFragment : Fragment(), OnMapReadyCallback,
             ClusterManager.OnClusterClickListener<Merchant>,
             ClusterManager.OnClusterItemClickListener<Merchant>,
             ClusterManager.OnClusterItemInfoWindowClickListener<Merchant>{
@@ -48,6 +44,8 @@ class MerchantsFragment : Fragment(), OnMapReadyCallback, retrofit2.Callback<Fea
 
     private lateinit var mMap: GoogleMap
 
+    private lateinit var mMerchantViewModel: MerchantViewModel
+
     private var mClusterManager: ClusterManager<Merchant>? = null
 
     override fun onCreateView(
@@ -63,6 +61,8 @@ class MerchantsFragment : Fragment(), OnMapReadyCallback, retrofit2.Callback<Fea
         // Obtain the SupportMapFragment and get notified when the map is ready to be used.
         val mapFragment = childFragmentManager.findFragmentById(R.id.map) as SupportMapFragment
         mapFragment.getMapAsync(this)
+
+        mMerchantViewModel = ViewModelProviders.of(this).get(MerchantViewModel::class.java)
     }
 
     private fun verifyLocationPermission() {
@@ -123,17 +123,11 @@ class MerchantsFragment : Fragment(), OnMapReadyCallback, retrofit2.Callback<Fea
         mClusterManager?.setOnClusterItemClickListener(this)
         mClusterManager?.setOnClusterItemInfoWindowClickListener(this)
 
-        val gson = GsonBuilder()
-            .setLenient()
-            .create()
-        val retrofit = Retrofit.Builder()
-            .baseUrl(Constants.MERCHANTS_WEBSERVICE_URL)
-            .addConverterFactory(GsonConverterFactory.create(gson))
-            .build()
-
-        val ambassadorService = retrofit.create<MerchantsWebservice>(MerchantsWebservice::class.java)
-        val call = ambassadorService.getMerchants(0)
-        call.enqueue(this)
+        mMerchantViewModel.getAllMerchants().observe(this, Observer<List<Merchant>> {merchants ->
+            mClusterManager?.clearItems()
+            mClusterManager?.addItems(merchants)
+            mClusterManager?.cluster()
+        })
     }
 
     private fun applyMapTheme() {
@@ -155,19 +149,6 @@ class MerchantsFragment : Fragment(), OnMapReadyCallback, retrofit2.Callback<Fea
         }
     }
 
-    override fun onResponse(call: Call<FeathersResponse<Merchant>>, response: Response<FeathersResponse<Merchant>>) {
-        if (response.isSuccessful) {
-            val res: FeathersResponse<Merchant>? = response.body()
-            val merchants = res?.data ?: return
-            mClusterManager?.addItems(merchants)
-            mClusterManager?.cluster()
-        } else {
-            Log.e("error_bitsy", response.errorBody()?.string())
-        }
-    }
-
-    override fun onFailure(call: Call<FeathersResponse<Merchant>>, t: Throwable) { /* Do nothing */ }
-
     /**
      * Animates the camera update to focus on an area that shows all the items from the cluster that was tapped.
      */

app/src/main/java/cy/agorise/bitsybitshareswallet/network/MerchantsWebservice.kt

@@ -9,7 +9,9 @@ import retrofit2.http.Query
 interface MerchantsWebservice {
 
     @GET("/api/v1/merchants")
-    fun getMerchants(@Query(value = "\$skip") skip: Int): Call<FeathersResponse<Merchant>>
+    fun getMerchants(@Query(value = "\$skip") skip: Int,
+                     @Query(value = "\$limit") limit: Int = 50):
+            Call<FeathersResponse<Merchant>>
 
     @GET("api/v2/tellers")
     fun getTellers(@Query(value = "\$skip") skip: Int): Call<FeathersResponse<Teller>>

app/src/main/java/cy/agorise/bitsybitshareswallet/repositories/MerchantRepository.kt

@@ -0,0 +1,64 @@
+package cy.agorise.bitsybitshareswallet.repositories
+
+import android.content.Context
+import android.os.AsyncTask
+import androidx.lifecycle.LiveData
+import cy.agorise.bitsybitshareswallet.database.BitsyDatabase
+import cy.agorise.bitsybitshareswallet.database.daos.MerchantDao
+import cy.agorise.bitsybitshareswallet.database.entities.Merchant
+import cy.agorise.bitsybitshareswallet.network.FeathersResponse
+import cy.agorise.bitsybitshareswallet.network.MerchantsWebservice
+import cy.agorise.bitsybitshareswallet.utils.Constants
+import retrofit2.Call
+import retrofit2.Response
+import retrofit2.Retrofit
+import retrofit2.converter.gson.GsonConverterFactory
+
+class MerchantRepository internal constructor(context: Context) : retrofit2.Callback<FeathersResponse<Merchant>> {
+
+    private val mMerchantDao: MerchantDao
+
+    init {
+        val db = BitsyDatabase.getDatabase(context)
+        mMerchantDao = db!!.merchantDao()
+    }
+
+    /**
+     * Returns a LiveData object directly from the database while the response from the WebService is obtained.
+     */
+    fun getAll(): LiveData<List<Merchant>> {
+        refreshMerchants()
+        return mMerchantDao.getAll()
+    }
+
+    private fun refreshMerchants() {
+        val retrofit = Retrofit.Builder()
+            .baseUrl(Constants.MERCHANTS_WEBSERVICE_URL)
+            .addConverterFactory(GsonConverterFactory.create())
+            .build()
+
+        val ambassadorService = retrofit.create<MerchantsWebservice>(MerchantsWebservice::class.java)
+        val call = ambassadorService.getMerchants(0)
+        call.enqueue(this)
+    }
+
+    override fun onResponse(call: Call<FeathersResponse<Merchant>>, response: Response<FeathersResponse<Merchant>>) {
+        if (response.isSuccessful) {
+            val res: FeathersResponse<Merchant>? = response.body()
+            val merchants = res?.data ?: return
+            insertAllAsyncTask(mMerchantDao).execute(merchants)
+        }
+    }
+
+    override fun onFailure(call: Call<FeathersResponse<Merchant>>, t: Throwable) { /* Do nothing */ }
+
+    private class insertAllAsyncTask internal constructor(private val mAsyncTaskDao: MerchantDao) :
+        AsyncTask<List<Merchant>, Void, Void>() {
+
+        override fun doInBackground(vararg merchants: List<Merchant>): Void? {
+            // TODO Delete all first
+            mAsyncTaskDao.insertAll(merchants[0])
+            return null
+        }
+    }
+}

app/src/main/java/cy/agorise/bitsybitshareswallet/viewmodels/MerchantViewModel.kt

@@ -0,0 +1,15 @@
+package cy.agorise.bitsybitshareswallet.viewmodels
+
+import android.app.Application
+import androidx.lifecycle.AndroidViewModel
+import androidx.lifecycle.LiveData
+import cy.agorise.bitsybitshareswallet.database.entities.Merchant
+import cy.agorise.bitsybitshareswallet.repositories.MerchantRepository
+
+class MerchantViewModel(application: Application) : AndroidViewModel(application) {
+    private var mMerchantRepository = MerchantRepository(application)
+
+    internal fun getAllMerchants(): LiveData<List<Merchant>> {
+        return mMerchantRepository.getAll()
+    }
+}