feat(writer): 🎉 Enhance primary key handling and add tests

* Implement checks for existing primary keys before adding new ones.
* Drop auto-generated primary keys if they exist.
* Add tests for primary key existence and column size specifiers.
* Improve type conversion handling for PostgreSQL compatibility.

pkg/writers/pgsql/writer_test.go

@@ -305,3 +305,136 @@ func TestTypeConversion(t *testing.T) {
 		t.Errorf("Output missing 'smallint' type (converted from 'int16')\nFull output:\n%s", output)
 	}
 }
+
+func TestPrimaryKeyExistenceCheck(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+	table := models.InitTable("products", "public")
+
+	idCol := models.InitColumn("id", "products", "public")
+	idCol.Type = "integer"
+	idCol.IsPrimaryKey = true
+	table.Columns["id"] = idCol
+
+	nameCol := models.InitColumn("name", "products", "public")
+	nameCol.Type = "text"
+	table.Columns["name"] = nameCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	options := &writers.WriterOptions{}
+	writer := NewWriter(options)
+	writer.writer = &buf
+
+	err := writer.WriteDatabase(db)
+	if err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	t.Logf("Generated SQL:\n%s", output)
+
+	// Verify our naming convention is used
+	if !strings.Contains(output, "pk_public_products") {
+		t.Errorf("Output missing expected primary key name 'pk_public_products'\nFull output:\n%s", output)
+	}
+
+	// Verify it drops auto-generated primary keys
+	if !strings.Contains(output, "products_pkey") || !strings.Contains(output, "DROP CONSTRAINT") {
+		t.Errorf("Output missing logic to drop auto-generated primary key\nFull output:\n%s", output)
+	}
+
+	// Verify it checks for our specific named constraint before adding it
+	if !strings.Contains(output, "constraint_name = 'pk_public_products'") {
+		t.Errorf("Output missing check for our named primary key constraint\nFull output:\n%s", output)
+	}
+}
+
+func TestColumnSizeSpecifiers(t *testing.T) {
+	db := models.InitDatabase("testdb")
+	schema := models.InitSchema("public")
+	table := models.InitTable("test_sizes", "public")
+
+	// Integer with invalid size specifier - should ignore size
+	integerCol := models.InitColumn("int_col", "test_sizes", "public")
+	integerCol.Type = "integer"
+	integerCol.Length = 32
+	table.Columns["int_col"] = integerCol
+
+	// Bigint with invalid size specifier - should ignore size
+	bigintCol := models.InitColumn("bigint_col", "test_sizes", "public")
+	bigintCol.Type = "bigint"
+	bigintCol.Length = 64
+	table.Columns["bigint_col"] = bigintCol
+
+	// Smallint with invalid size specifier - should ignore size
+	smallintCol := models.InitColumn("smallint_col", "test_sizes", "public")
+	smallintCol.Type = "smallint"
+	smallintCol.Length = 16
+	table.Columns["smallint_col"] = smallintCol
+
+	// Text with length - should convert to varchar
+	textCol := models.InitColumn("text_col", "test_sizes", "public")
+	textCol.Type = "text"
+	textCol.Length = 100
+	table.Columns["text_col"] = textCol
+
+	// Varchar with length - should keep varchar with length
+	varcharCol := models.InitColumn("varchar_col", "test_sizes", "public")
+	varcharCol.Type = "varchar"
+	varcharCol.Length = 50
+	table.Columns["varchar_col"] = varcharCol
+
+	// Decimal with precision and scale - should keep them
+	decimalCol := models.InitColumn("decimal_col", "test_sizes", "public")
+	decimalCol.Type = "decimal"
+	decimalCol.Precision = 19
+	decimalCol.Scale = 4
+	table.Columns["decimal_col"] = decimalCol
+
+	schema.Tables = append(schema.Tables, table)
+	db.Schemas = append(db.Schemas, schema)
+
+	var buf bytes.Buffer
+	options := &writers.WriterOptions{}
+	writer := NewWriter(options)
+	writer.writer = &buf
+
+	err := writer.WriteDatabase(db)
+	if err != nil {
+		t.Fatalf("WriteDatabase failed: %v", err)
+	}
+
+	output := buf.String()
+	t.Logf("Generated SQL:\n%s", output)
+
+	// Verify invalid size specifiers are NOT present
+	invalidPatterns := []string{
+		"integer(32)",
+		"bigint(64)",
+		"smallint(16)",
+		"text(100)",
+	}
+	for _, pattern := range invalidPatterns {
+		if strings.Contains(output, pattern) {
+			t.Errorf("Output contains invalid pattern '%s' - PostgreSQL doesn't support this\nFull output:\n%s", pattern, output)
+		}
+	}
+
+	// Verify valid patterns ARE present
+	validPatterns := []string{
+		"integer",     // without size
+		"bigint",      // without size
+		"smallint",    // without size
+		"varchar(100)", // text converted to varchar with length
+		"varchar(50)",  // varchar with length
+		"decimal(19,4)", // decimal with precision and scale
+	}
+	for _, pattern := range validPatterns {
+		if !strings.Contains(output, pattern) {
+			t.Errorf("Output missing expected pattern '%s'\nFull output:\n%s", pattern, output)
+		}
+	}
+}