feature: Integrate Room DB to store and fetch the LabResponse

app/build.gradle

@@ -1,4 +1,6 @@
 apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
+apply plugin: 'kotlin-kapt'
 apply plugin: 'com.google.firebase.crashlytics'
 apply plugin: 'androidx.navigation.safeargs'
 
@@ -39,6 +41,9 @@ dependencies {
     implementation "androidx.navigation:navigation-fragment-ktx:$versions.navigation"
     implementation "androidx.navigation:navigation-ui-ktx:$versions.navigation"
 
+    implementation "androidx.room:room-runtime:$versions.room"
+    kapt "androidx.room:room-compiler:$versions.room"
+
     // https://mvnrepository.com/artifact/com.fasterxml.jackson.module/jackson-module-kotlin
     implementation "com.fasterxml.jackson.module:jackson-module-kotlin:$versions.jackson_module_kotlin"
 

app/src/main/java/com/nagpal/shivam/vtucslab/VTUCSLabApplication.kt

@@ -1,19 +1,42 @@
 package com.nagpal.shivam.vtucslab
 
 import androidx.multidex.MultiDexApplication
+import androidx.room.Room
 import com.google.firebase.crashlytics.FirebaseCrashlytics
+import com.nagpal.shivam.vtucslab.data.local.AppDatabase
 import com.nagpal.shivam.vtucslab.repositories.VtuCsLabRepository
 import com.nagpal.shivam.vtucslab.repositories.VtuCsLabRepositoryImpl
 import com.nagpal.shivam.vtucslab.services.VtuCsLabService
+import com.nagpal.shivam.vtucslab.utilities.Constants.VTU_CS_LAB
+import com.nagpal.shivam.vtucslab.utilities.StaticMethods
 
 class VTUCSLabApplication : MultiDexApplication() {
-    val vtuCsLabRepository: VtuCsLabRepository =
-        VtuCsLabRepositoryImpl(this, VtuCsLabService.instance)
+    private lateinit var _db: AppDatabase
+    val db: AppDatabase
+        get() = _db
+
+    private lateinit var _vtuCsLabRepository: VtuCsLabRepository
+    val vtuCsLabRepository: VtuCsLabRepository
+        get() = _vtuCsLabRepository
 
     override fun onCreate() {
         super.onCreate()
         if (BuildConfig.DEBUG) {
             FirebaseCrashlytics.getInstance().setCrashlyticsCollectionEnabled(false)
         }
+
+        _db = Room.databaseBuilder(
+            applicationContext,
+            AppDatabase::class.java,
+            VTU_CS_LAB
+        ).build()
+
+        val vtuCsLabService = VtuCsLabService.instance
+        _vtuCsLabRepository = VtuCsLabRepositoryImpl(
+            this,
+            vtuCsLabService,
+            _db.labResponseDao(),
+            StaticMethods.jsonMapper
+        )
     }
 }

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/AppDatabase.kt

@@ -0,0 +1,11 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+import androidx.room.Database
+import androidx.room.RoomDatabase
+import androidx.room.TypeConverters
+
+@Database(entities = [LabResponse::class], version = 1)
+@TypeConverters(Converters::class)
+abstract class AppDatabase : RoomDatabase() {
+    abstract fun labResponseDao(): LabResponseDao
+}

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/Converters.kt

@@ -0,0 +1,16 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+import androidx.room.TypeConverter
+import java.util.*
+
+class Converters {
+    @TypeConverter
+    fun dateFromTimestamp(value: Long?): Date? {
+        return value?.let { Date(it) }
+    }
+
+    @TypeConverter
+    fun dateToTimestamp(date: Date?): Long? {
+        return date?.time
+    }
+}

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/DBConstants.kt

@@ -0,0 +1,12 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+object Tables {
+    const val LAB_RESPONSE = "lab_response"
+}
+
+object LabResponseAttributes {
+    const val URL = "url"
+    const val RESPONSE = "response"
+    const val RESPONSE_TYPE = "response_type"
+    const val FETCHED_AT = "fetched_at"
+}

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/LabResponse.kt

@@ -0,0 +1,19 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+import androidx.room.ColumnInfo
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+import com.nagpal.shivam.vtucslab.data.local.LabResponseAttributes.FETCHED_AT
+import com.nagpal.shivam.vtucslab.data.local.LabResponseAttributes.RESPONSE
+import com.nagpal.shivam.vtucslab.data.local.LabResponseAttributes.RESPONSE_TYPE
+import com.nagpal.shivam.vtucslab.data.local.LabResponseAttributes.URL
+import com.nagpal.shivam.vtucslab.data.local.Tables.LAB_RESPONSE
+import java.util.*
+
+@Entity(LAB_RESPONSE)
+data class LabResponse(
+    @PrimaryKey @ColumnInfo(name = URL) val url: String,
+    @ColumnInfo(name = RESPONSE) val response: String,
+    @ColumnInfo(name = RESPONSE_TYPE) val responseType: LabResponseType,
+    @ColumnInfo(name = FETCHED_AT) val fetchedAt: Date,
+)

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/LabResponseDao.kt

@@ -0,0 +1,16 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+import androidx.room.Dao
+import androidx.room.Query
+import androidx.room.Upsert
+import com.nagpal.shivam.vtucslab.data.local.LabResponseAttributes.URL
+import com.nagpal.shivam.vtucslab.data.local.Tables.LAB_RESPONSE
+
+@Dao
+interface LabResponseDao {
+    @Upsert
+    fun upsert(labResponse: LabResponse)
+
+    @Query("SELECT * FROM $LAB_RESPONSE where $URL = :url")
+    fun findByUrl(url: String): LabResponse?
+}

app/src/main/java/com/nagpal/shivam/vtucslab/data/local/LabResponseType.kt

@@ -0,0 +1,7 @@
+package com.nagpal.shivam.vtucslab.data.local
+
+enum class LabResponseType {
+    LABORATORY,
+    EXPERIMENT,
+    CONTENT,
+}

app/src/main/java/com/nagpal/shivam/vtucslab/repositories/VtuCsLabRepositoryImpl.kt

@@ -1,65 +1,150 @@
 package com.nagpal.shivam.vtucslab.repositories
 
 import android.app.Application
+import com.fasterxml.jackson.core.JsonParseException
+import com.fasterxml.jackson.databind.json.JsonMapper
 import com.nagpal.shivam.vtucslab.core.ErrorType
 import com.nagpal.shivam.vtucslab.core.Resource
+import com.nagpal.shivam.vtucslab.data.local.LabResponse
+import com.nagpal.shivam.vtucslab.data.local.LabResponseDao
+import com.nagpal.shivam.vtucslab.data.local.LabResponseType
 import com.nagpal.shivam.vtucslab.models.LaboratoryExperimentResponse
 import com.nagpal.shivam.vtucslab.models.LaboratoryResponse
 import com.nagpal.shivam.vtucslab.retrofit.ApiResult
 import com.nagpal.shivam.vtucslab.services.VtuCsLabService
+import com.nagpal.shivam.vtucslab.utilities.Configurations
 import com.nagpal.shivam.vtucslab.utilities.NetworkUtils
 import com.nagpal.shivam.vtucslab.utilities.StaticMethods
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.FlowCollector
 import kotlinx.coroutines.flow.flow
+import java.util.Date
 
 private val LOG_TAG: String = VtuCsLabRepositoryImpl::class.java.name
 
 class VtuCsLabRepositoryImpl(
     private val application: Application,
-    private val vtuCsLabService: VtuCsLabService
+    private val vtuCsLabService: VtuCsLabService,
+    private val labResponseDao: LabResponseDao,
+    private val jsonMapper: JsonMapper,
 ) : VtuCsLabRepository {
     override fun fetchLaboratories(url: String): Flow<Resource<LaboratoryResponse, ErrorType>> =
         flow {
-            fetch(url) {
-                vtuCsLabService.getLaboratoryResponse(it)
+            fetch(
+                flow = this,
+                url,
+                LabResponseType.LABORATORY,
+                vtuCsLabService::getLaboratoryResponse,
+                { data -> jsonMapper.writeValueAsString(data) }
+            ) { stringContent ->
+                jsonMapper.readValue(
+                    stringContent,
+                    LaboratoryResponse::class.java
+                )
             }
         }
 
     override fun fetchExperiments(url: String): Flow<Resource<LaboratoryExperimentResponse, ErrorType>> =
         flow {
-            fetch(url) {
-                vtuCsLabService.getLaboratoryExperimentsResponse(it)
+            fetch(
+                flow = this,
+                url,
+                LabResponseType.EXPERIMENT,
+                vtuCsLabService::getLaboratoryExperimentsResponse,
+                { data -> jsonMapper.writeValueAsString(data) }
+            ) { stringContent ->
+                jsonMapper.readValue(
+                    stringContent,
+                    LaboratoryExperimentResponse::class.java
+                )
             }
         }
 
     override fun fetchContent(url: String): Flow<Resource<String, ErrorType>> = flow {
-        fetch(url) {
-            vtuCsLabService.fetchRawResponse(it)
-        }
+        fetch(
+            flow = this,
+            url,
+            LabResponseType.CONTENT,
+            vtuCsLabService::fetchRawResponse,
+            { stringContent -> stringContent }
+        ) { stringContent -> stringContent }
     }
 
-    private suspend fun <D : Any> FlowCollector<Resource<D, ErrorType>>.fetch(
+    private suspend fun <D : Any> fetch(
+        flow: FlowCollector<Resource<D, ErrorType>>,
         url: String,
-        executable: suspend (String) -> ApiResult<D>
+        labResponseType: LabResponseType,
+        fetchFromNetwork: suspend (String) -> ApiResult<D>,
+        encodeToString: (D) -> String,
+        decodeFromString: (String) -> D,
     ) {
-        emit(Resource.Loading())
+        flow.emit(Resource.Loading())
+
+        val labResponse = labResponseDao.findByUrl(url)
+        var foundInDB = false
+        labResponse?.let {
+            try {
+                flow.emit(Resource.Success(decodeFromString.invoke(it.response)))
+                foundInDB = true
+                if (it.fetchedAt.after(
+                        StaticMethods.getCurrentDateMinusSeconds(Configurations.RESPONSE_FRESHNESS_TIME)
+                    )
+                ) {
+                    return
+                }
+            } catch (_: JsonParseException) {
+            }
+        }
+
         if (!NetworkUtils.isNetworkConnected(application)) {
-            emit(Resource.Error(ErrorType.NoActiveInternetConnection))
+            emitNetworkErrors(
+                flow,
+                foundInDB,
+                Resource.Error(ErrorType.NoActiveInternetConnection),
+            )
             return
         }
-        when (val apiResult = executable.invoke(url)) {
+        when (val apiResult = fetchFromNetwork.invoke(url)) {
             is ApiResult.ApiSuccess -> {
-                emit(Resource.Success(apiResult.data))
+                val data = apiResult.data
+                labResponseDao.upsert(
+                    LabResponse(
+                        url,
+                        encodeToString(data),
+                        labResponseType,
+                        Date(),
+                    )
+                )
+                flow.emit(Resource.Success(data))
             }
+
             is ApiResult.ApiError -> {
                 StaticMethods.logNetworkResultError(LOG_TAG, url, apiResult.code, apiResult.message)
-                emit(Resource.Error(ErrorType.SomeErrorOccurred))
+                emitNetworkErrors(
+                    flow,
+                    foundInDB,
+                    Resource.Error(ErrorType.SomeErrorOccurred),
+                )
             }
+
             is ApiResult.ApiException -> {
                 StaticMethods.logNetworkResultException(LOG_TAG, url, apiResult.throwable)
-                emit(Resource.Error(ErrorType.SomeErrorOccurred))
+                emitNetworkErrors(
+                    flow,
+                    foundInDB,
+                    Resource.Error(ErrorType.SomeErrorOccurred),
+                )
             }
         }
     }
+
+    private suspend fun <D : Any> emitNetworkErrors(
+        flow: FlowCollector<Resource<D, ErrorType>>,
+        foundInDB: Boolean,
+        errorResource: Resource.Error<D, ErrorType>
+    ) {
+        if (!foundInDB) {
+            flow.emit(errorResource)
+        }
+    }
 }

app/src/main/java/com/nagpal/shivam/vtucslab/utilities/Configurations.kt

@@ -0,0 +1,5 @@
+package com.nagpal.shivam.vtucslab.utilities
+
+object Configurations {
+    const val RESPONSE_FRESHNESS_TIME = 3 * 60 * 60
+}

app/src/main/java/com/nagpal/shivam/vtucslab/utilities/Constants.kt

@@ -8,4 +8,5 @@ object Constants {
         "https://raw.githubusercontent.com/vtucs/Index_v3/master/Index_v3.json"
     const val LABEL_CODE = "Code"
     const val GITHUB_RAW_CONTENT = "github_raw_content"
+    const val VTU_CS_LAB = "vtu_cs_lab"
 }

app/src/main/java/com/nagpal/shivam/vtucslab/utilities/StaticMethods.kt

@@ -5,6 +5,7 @@ import com.fasterxml.jackson.databind.DeserializationFeature
 import com.fasterxml.jackson.databind.json.JsonMapper
 import com.nagpal.shivam.vtucslab.models.LaboratoryExperimentResponse
 import com.nagpal.shivam.vtucslab.models.LaboratoryResponse
+import java.util.*
 
 object StaticMethods {
 
@@ -49,4 +50,10 @@ object StaticMethods {
             throwable
         )
     }
+
+    fun getCurrentDateMinusSeconds(seconds: Int): Date {
+        val calendar = Calendar.getInstance()
+        calendar.add(Calendar.SECOND, -seconds)
+        return calendar.time
+    }
 }

app/src/main/res/layout/fragment_display.xml

@@ -38,9 +38,7 @@
 
     <TextView
         android:id="@+id/empty_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:visibility="gone"
+        style="@style/ErrorMessageTextView"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"

app/src/main/res/layout/fragment_program.xml

@@ -17,9 +17,7 @@
 
     <TextView
         android:id="@+id/empty_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:visibility="gone"
+        style="@style/ErrorMessageTextView"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"

app/src/main/res/layout/fragment_repository.xml

@@ -18,9 +18,7 @@
 
     <TextView
         android:id="@+id/empty_text_view"
-        android:layout_width="wrap_content"
-        android:layout_height="wrap_content"
-        android:visibility="gone"
+        style="@style/ErrorMessageTextView"
         app:layout_constraintBottom_toBottomOf="parent"
         app:layout_constraintLeft_toLeftOf="parent"
         app:layout_constraintRight_toRightOf="parent"

app/src/main/res/values/strings.xml

@@ -1,7 +1,7 @@
 <resources>
     <string name="app_name">VTU CS Lab</string>
     <string name="app_name_new">VTU CS Lab New Version</string>
-    <string name="no_internet_connection">No Internet Connection.</string>
+    <string name="no_internet_connection">No Internet Connection.\n\nThis content is not available offline yet, Kindly connect to the internet to sync this content locally.</string>
     <string name="error_occurred">Some Error Occurred.</string>
     <string name="copy">Copy</string>
     <string name="git_repository">Git Repository</string>