feat(data): implement global fixture data seeding

- Implements the `seedGlobalFixtureData` method in `DatabaseSeedingService` to populate the database with initial categories, sources, countries, and headlines from the shared fixtures.
- Uses `ON CONFLICT DO NOTHING` to make the seeding process idempotent.
- Fixes the `createTables` method by replacing the problematic `.transaction()` helper with a manual `BEGIN`/`COMMIT`/`ROLLBACK` block for compatibility and robustness.

Author: fulleni

lib/src/services/database_seeding_service.dart

@@ -28,9 +28,14 @@ class DatabaseSeedingService {
   Future<void> createTables() async {
     _log.info('Starting database schema creation...');
     try {
-      await _connection.transaction((ctx) async {
+      // Manually handle the transaction with BEGIN/COMMIT/ROLLBACK.
+      await _connection.execute('BEGIN');
+
+      try {
         _log.fine('Creating "users" table...');
-        await ctx.execute('''
+        // All statements are executed on the main connection within the
+        // manual transaction.
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS users (
             id TEXT PRIMARY KEY,
             email TEXT UNIQUE,
@@ -41,7 +46,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "app_config" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS app_config (
             id TEXT PRIMARY KEY,
             user_preference_limits JSONB NOT NULL,
@@ -51,7 +56,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "categories" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS categories (
             id TEXT PRIMARY KEY,
             name TEXT NOT NULL UNIQUE,
@@ -61,7 +66,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "sources" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS sources (
             id TEXT PRIMARY KEY,
             name TEXT NOT NULL UNIQUE,
@@ -71,7 +76,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "countries" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS countries (
             id TEXT PRIMARY KEY,
             name TEXT NOT NULL UNIQUE,
@@ -82,7 +87,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "headlines" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS headlines (
             id TEXT PRIMARY KEY,
             title TEXT NOT NULL,
@@ -99,7 +104,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "user_app_settings" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS user_app_settings (
             id TEXT PRIMARY KEY,
             user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
@@ -111,7 +116,7 @@ class DatabaseSeedingService {
         ''');
 
         _log.fine('Creating "user_content_preferences" table...');
-        await ctx.execute('''
+        await _connection.execute('''
           CREATE TABLE IF NOT EXISTS user_content_preferences (
             id TEXT PRIMARY KEY,
             user_id TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
@@ -123,7 +128,13 @@ class DatabaseSeedingService {
             updated_at TIMESTAMPTZ
           );
         ''');
-      });
+
+        await _connection.execute('COMMIT');
+      } catch (e) {
+        // If any query inside the transaction fails, roll back.
+        await _connection.execute('ROLLBACK');
+        rethrow; // Re-throw the original error
+      }
       _log.info('Database schema creation completed successfully.');
     } on Object catch (e, st) {
       _log.severe(
@@ -137,4 +148,86 @@ class DatabaseSeedingService {
       );
     }
   }
+
+  /// Seeds the database with global fixture data (categories, sources, etc.).
+  ///
+  /// This method is idempotent, using `ON CONFLICT DO NOTHING` to prevent
+  /// errors if the data already exists. It runs within a single transaction.
+  Future<void> seedGlobalFixtureData() async {
+    _log.info('Seeding global fixture data...');
+    try {
+      await _connection.execute('BEGIN');
+      try {
+        // Seed Categories
+        _log.fine('Seeding categories...');
+        for (final data in categoriesFixturesData) {
+          final category = Category.fromJson(data);
+          await _connection.execute(
+            Sql.named(
+              'INSERT INTO categories (id, name) VALUES (@id, @name) '
+              'ON CONFLICT (id) DO NOTHING',
+            ),
+            parameters: category.toJson(),
+          );
+        }
+
+        // Seed Sources
+        _log.fine('Seeding sources...');
+        for (final data in sourcesFixturesData) {
+          final source = Source.fromJson(data);
+          await _connection.execute(
+            Sql.named(
+              'INSERT INTO sources (id, name) VALUES (@id, @name) '
+              'ON CONFLICT (id) DO NOTHING',
+            ),
+            parameters: source.toJson(),
+          );
+        }
+
+        // Seed Countries
+        _log.fine('Seeding countries...');
+        for (final data in countriesFixturesData) {
+          final country = Country.fromJson(data);
+          await _connection.execute(
+            Sql.named(
+              'INSERT INTO countries (id, name, code) '
+              'VALUES (@id, @name, @code) ON CONFLICT (id) DO NOTHING',
+            ),
+            parameters: country.toJson(),
+          );
+        }
+
+        // Seed Headlines
+        _log.fine('Seeding headlines...');
+        for (final data in headlinesFixturesData) {
+          final headline = Headline.fromJson(data);
+          await _connection.execute(
+            Sql.named(
+              'INSERT INTO headlines (id, title, source_id, category_id, '
+              'image_url, url, published_at, description, content) '
+              'VALUES (@id, @title, @sourceId, @categoryId, @imageUrl, @url, '
+              '@publishedAt, @description, @content) '
+              'ON CONFLICT (id) DO NOTHING',
+            ),
+            parameters: headline.toJson(),
+          );
+        }
+
+        await _connection.execute('COMMIT');
+        _log.info('Global fixture data seeding completed successfully.');
+      } catch (e) {
+        await _connection.execute('ROLLBACK');
+        rethrow;
+      }
+    } on Object catch (e, st) {
+      _log.severe(
+        'An error occurred during global fixture data seeding.',
+        e,
+        st,
+      );
+      throw OperationFailedException(
+        'Failed to seed global fixture data: $e',
+      );
+    }
+  }
 }