init

Femto.Database/Migrator.cs

@@ -0,0 +1,122 @@
+using Npgsql;
+
+namespace Femto.Database;
+
+internal class Migrator(string migrationDirectory, NpgsqlDataSource dataSource) : IAsyncDisposable
+{
+    private record MigrationScript(string Id, string Script);
+    
+    public async Task Migrate()
+    {
+        var migrations = await LoadMigrationScripts();
+        
+        await this.EnsureMigrationsTableExists();
+        var executedMigrations = await GetExecutedMigrations();
+
+        EnsureConsistentMigrationHistory(migrations, executedMigrations);
+
+        if (executedMigrations.Count == migrations.Count)
+        {
+            Console.WriteLine("up to date");
+            return;
+        }
+
+        
+        await DoMigrations(migrations.Skip(executedMigrations.Count));
+    }
+
+    private async Task<IList<MigrationScript>> LoadMigrationScripts()
+    {
+        if (!Directory.Exists(migrationDirectory))
+            throw new DirectoryNotFoundException($"Migration directory not found: {migrationDirectory}");
+    
+        var scriptFiles = Directory.EnumerateFiles(migrationDirectory, "*.sql")
+                                    .OrderBy(Path.GetFileName)
+                                    .ToList();
+    
+        if (!scriptFiles.Any())
+            throw new Exception("No migration scripts found in the specified directory.");
+    
+        var migrationScripts = new List<MigrationScript>();
+    
+        foreach (var file in scriptFiles)
+        {
+            var scriptContent = await File.ReadAllTextAsync(file);
+            var scriptId = Path.GetFileName(file);
+    
+            migrationScripts.Add(new MigrationScript(scriptId, scriptContent));
+        }
+    
+        return migrationScripts;
+    }
+
+    private async Task EnsureMigrationsTableExists()
+    {
+        await using var createSchemaCommand = dataSource.CreateCommand(
+            """CREATE SCHEMA IF NOT EXISTS __migrations;"""
+        );
+
+        await createSchemaCommand.ExecuteNonQueryAsync();
+
+        await using var createTableCommand = dataSource.CreateCommand(
+            """
+            CREATE TABLE IF NOT EXISTS __migrations.__migration_history ( migration VARCHAR(127) PRIMARY KEY );
+            """
+        );
+
+        await createTableCommand.ExecuteNonQueryAsync();
+    }
+
+    private async Task<IList<string>> GetExecutedMigrations()
+    {
+        await using var command = dataSource.CreateCommand(
+            """SELECT migration FROM __migrations.__migration_history"""
+        );
+        var reader = await command.ExecuteReaderAsync();
+        var migrations = new List<string>();
+        while (await reader.ReadAsync())
+        {
+            migrations.Add(reader.GetString(0));
+        }
+        return migrations;
+    }
+
+    private void EnsureConsistentMigrationHistory(
+        IList<MigrationScript> migrationScripts,
+        IList<string> executedMigrationIds
+    )
+    {
+        if (executedMigrationIds.Count > migrationScripts.Count)
+            throw new Exception("inconsistent migration history");
+
+        for (var i = 0; i < executedMigrationIds.Count; i++)
+        {
+            var migration = migrationScripts[i];
+            var executedMigrationId = executedMigrationIds[i];
+
+            if (migration.Id != executedMigrationId)
+                throw new Exception($"unexpected migration in history {executedMigrationId}");
+        }
+    }
+
+    private async Task DoMigrations(IEnumerable<MigrationScript> migrationScripts)
+    {
+        foreach (var migration in migrationScripts)
+        {
+            Console.WriteLine($"applying migration {migration.Id}");
+            await using var command = dataSource.CreateCommand(migration.Script);
+            await command.ExecuteNonQueryAsync();
+        
+            await using var addToHistoryCommand = dataSource.CreateCommand(
+                """INSERT INTO __migrations.__migration_history (migration) VALUES (@migration)"""
+            );
+            addToHistoryCommand.Parameters.AddWithValue("@migration", migration.Id);
+            await addToHistoryCommand.ExecuteNonQueryAsync();
+        }
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        return dataSource.DisposeAsync();
+    }
+}