Merge pull request #5

Refine conversation screen

Author: tobiasvonderheidt

app/build.gradle.kts

@@ -2,6 +2,7 @@ plugins {
     alias(libs.plugins.android.application)
     alias(libs.plugins.kotlin.android)
     alias(libs.plugins.kotlin.compose)
+    alias(libs.plugins.ksp)
 }
 
 android {
@@ -67,6 +68,9 @@ dependencies {
     implementation(libs.androidx.material3)
     implementation(libs.androidx.navigation.compose)
     implementation(libs.androidx.material.icons.extended)
+    implementation(libs.androidx.room.runtime)
+    ksp(libs.androidx.room.compiler)
+    implementation(libs.androidx.room.ktx)
     implementation(libs.androidx.datastore.preferences)
     testImplementation(libs.junit)
     androidTestImplementation(libs.androidx.junit)

app/src/main/java/org/vonderheidt/hips/MainActivity.kt

@@ -10,6 +10,7 @@ import androidx.compose.ui.Modifier
 import androidx.lifecycle.lifecycleScope
 import kotlinx.coroutines.launch
 import org.vonderheidt.hips.data.HiPSDataStore
+import org.vonderheidt.hips.data.HiPSDatabase
 import org.vonderheidt.hips.navigation.SetupNavGraph
 import org.vonderheidt.hips.ui.theme.HiPSTheme
 
@@ -36,6 +37,10 @@ class MainActivity : ComponentActivity() {
             }
         }
 
+        // Instantiate Room database on app startup
+        // Application context isn't directly available on conversation screen
+        HiPSDatabase.startInstance(applicationContext)
+
         // Instantiate DataStore on app startup and read stored settings
         // Writes default settings to DataStore if app was just installed
         HiPSDataStore.startInstance(applicationContext)

app/src/main/java/org/vonderheidt/hips/data/HiPSDatabase.kt

@@ -0,0 +1,67 @@
+package org.vonderheidt.hips.data
+
+import android.content.Context
+import androidx.room.Database
+import androidx.room.Room
+import androidx.room.RoomDatabase
+
+/**
+ * Class that represents the Room database.
+ */
+@Database(
+    entities = [User::class, Message::class],
+    version = 1
+)
+abstract class HiPSDatabase : RoomDatabase() {
+    // Data access objects to access tables
+    abstract val userDao: UserDao
+    abstract val messageDao: MessageDao
+
+    // Companion object to ensure database is a singleton as abstract class can't be instantiated
+    companion object {
+        // Annotate reference to the database instance as volatile so that r/w to it is atomic and immediately visible to all threads
+        // Avoids race conditions, i.e. multiple threads trying to r/w to the database simultaneously
+        @Volatile
+        private var dbInstance: HiPSDatabase? = null
+
+        /**
+         * Function to check if the database is running.
+         *
+         * @return Boolean that is true if the database is running, false otherwise.
+         */
+        private fun isRunning(): Boolean {
+            return dbInstance != null
+        }
+
+        /**
+         * Function to start the database in a thread-safe manner.
+         *
+         * @param context The application context.
+         */
+        fun startInstance(context: Context) {
+            // If the database is already running, there is nothing to do
+            if (isRunning()) {
+                return
+            }
+
+            // Otherwise, start the database
+            // Synchronized allows only one thread to execute the code inside {...}, so other threads can't start the database simultaneously
+            synchronized(lock = this) {
+                if (!isRunning()) {
+                    // Database builder specifically requires the application context
+                    dbInstance = Room.databaseBuilder(context.applicationContext, HiPSDatabase::class.java, "hips.db").build()
+                }
+            }
+        }
+
+        /**
+         * Function to get the currently running database instance.
+         *
+         * @return The database instance.
+         */
+        fun getInstance(): HiPSDatabase {
+            // Database can be assumed to be running as startInstance is called on app startup in MainActivity
+            return dbInstance!!
+        }
+    }
+}

app/src/main/java/org/vonderheidt/hips/data/Message.kt

@@ -1,18 +1,35 @@
 package org.vonderheidt.hips.data
 
+import androidx.room.ColumnInfo
+import androidx.room.Entity
+import androidx.room.ForeignKey
+import androidx.room.ForeignKey.Companion.CASCADE
+
 /**
  * Class that represents a chat message in a conversation.
+ *
+ * @param senderID User ID of the message's sender.
+ * @param receiverID User ID of the message's receiver.
+ * @param timestamp Time the message was sent at (milliseconds since Unix epoch, i.e. 1970-01-01 00:00).
+ * @param content Content of the message.
  */
+@Entity(
+    primaryKeys = ["sender_id", "receiver_id", "timestamp"],
+    foreignKeys = [
+        ForeignKey(entity = User::class, parentColumns = ["id"], childColumns = ["sender_id"], onDelete = CASCADE, onUpdate = CASCADE),
+        ForeignKey(entity = User::class, parentColumns = ["id"], childColumns = ["receiver_id"], onDelete = CASCADE, onUpdate = CASCADE)
+    ]
+)
 data class Message (
-    val senderID: Int,
-    val receiverID: Int,
+    @ColumnInfo(name = "sender_id") val senderID: Int,
+    @ColumnInfo(name = "receiver_id") val receiverID: Int,
     val timestamp: Long,
     val content: String
 ) {
-    /**
-     * Some sample messages for the conversation screen.
-     */
     companion object {
+        /**
+         * Some sample messages for the conversation screen.
+         */
         val Samples = listOf(
             Message(1, 0, System.currentTimeMillis() - 5982341, "Oi, Lionel! What a match today! I honestly thought we were done for at halftime being 2-0 down, but that second half was brilliant! We really pulled it together, didn’t we?"),
             Message(0, 1, System.currentTimeMillis() - 4553793, "Absolutely, Cristiano! That comeback was mental! Your goal really got everyone buzzing. And that assist I had? Proper chuffed to finally chip in like that! But can we talk about the ref? What a wanker!"),

app/src/main/java/org/vonderheidt/hips/data/MessageDao.kt

@@ -0,0 +1,40 @@
+package org.vonderheidt.hips.data
+
+import androidx.room.Dao
+import androidx.room.Delete
+import androidx.room.Query
+import androidx.room.Upsert
+
+/**
+ * Interface to implement the data access object (DAO) for the Message data class.
+ */
+@Dao
+interface MessageDao {
+    // Covers all CRUD operations
+
+    /**
+     * Function to upsert (update or insert) a message into the database.
+     *
+     * @param message A message.
+     */
+    @Upsert
+    suspend fun upsertMessage(message: Message)
+
+    /**
+     * Function to get all messages between two users from the database.
+     *
+     * @param userID1 A user ID.
+     * @param userID2 Another user ID.
+     * @return List of all messages between the two users.
+     */
+    @Query("SELECT * FROM message WHERE (sender_id = :userID1 AND receiver_id = :userID2) OR (sender_id = :userID2 AND receiver_id = :userID1) ORDER BY timestamp;")
+    suspend fun getConversation(userID1: Int, userID2: Int): List<Message>
+
+    /**
+     * Function to delete a message from the database.
+     *
+     * @param message The message.
+     */
+    @Delete
+    suspend fun deleteMessage(message: Message)
+}

app/src/main/java/org/vonderheidt/hips/data/User.kt

@@ -0,0 +1,16 @@
+package org.vonderheidt.hips.data
+
+import androidx.room.Entity
+import androidx.room.PrimaryKey
+
+/**
+ * Class that represents a user.
+ *
+ * @param id The user ID.
+ * @param name A user name.
+ */
+@Entity
+data class User(
+    @PrimaryKey val id: Int,
+    val name: String
+)

app/src/main/java/org/vonderheidt/hips/data/UserDao.kt

@@ -0,0 +1,18 @@
+package org.vonderheidt.hips.data
+
+import androidx.room.Dao
+import androidx.room.Upsert
+
+/**
+ * Interface to implement the data access object (DAO) for the User data class.
+ */
+@Dao
+interface UserDao {
+    /**
+     * Function to upsert (update or insert) a user into the database.
+     *
+     * @param user A user.
+     */
+    @Upsert
+    suspend fun upsertUser(user: User)
+}