refactor: migrate db and config packages to use struct-based API

Removed global variables in favor of instance variables. This makes the code more maintainable and making it easier to write unit tests without relying on global state.

Marked the old functions with global state as obsolete, redirecting them to use a new API based on struct in order to rewrite the code using these functions gradually.

internal/db/utils.go

@@ -0,0 +1,36 @@
+package db
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"errors"
+
+	"golang.org/x/exp/slices"
+	"modernc.org/sqlite"
+)
+
+func init() {
+	sqlite.MustRegisterScalarFunction("json_array_contains", 2, jsonArrayContains)
+}
+
+// jsonArrayContains is an SQLite function that checks if a JSON array
+// in the database contains a given value
+func jsonArrayContains(ctx *sqlite.FunctionContext, args []driver.Value) (driver.Value, error) {
+	value, ok := args[0].(string)
+	if !ok {
+		return nil, errors.New("both arguments to json_array_contains must be strings")
+	}
+
+	item, ok := args[1].(string)
+	if !ok {
+		return nil, errors.New("both arguments to json_array_contains must be strings")
+	}
+
+	var array []string
+	err := json.Unmarshal([]byte(value), &array)
+	if err != nil {
+		return nil, err
+	}
+
+	return slices.Contains(array, item), nil
+}