feature: Change state management from global variables to object passing

This restructures dbcore (now the db package) and jwtcore (now the jwt
package) to use a single struct. There is now a state package, which
contains a struct with the full application state.

After this, instead of initializing the API routes directly in the main
function, the state object gets passed, and the API routes get
initialized with their accompanying code.

One fix done to reduce memory usage and increase speed is that the
validator object is now persistent across requests, instead of
recreating it each time. This should speed things up slightly, and
improve memory usage.

One additional chore done is that the database models have been moved to
be a seperate file from the DB initialization itself.

backend/api/db/db.go

@@ -0,0 +1,77 @@
+package db
+
+import (
+	"fmt"
+	"os"
+
+	"gorm.io/driver/postgres"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+type DB struct {
+	DB *gorm.DB
+}
+
+func New(backend, params string) (*DB, error) {
+	var err error
+
+	dialector, err := initDialector(backend, params)
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to initialize physical database: %s", err)
+	}
+
+	database, err := gorm.Open(dialector)
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database: %s", err)
+	}
+
+	return &DB{DB: database}, nil
+}
+
+func (db *DB) DoMigrations() error {
+	if err := db.DB.AutoMigrate(&Proxy{}); err != nil {
+		return err
+	}
+
+	if err := db.DB.AutoMigrate(&Backend{}); err != nil {
+		return err
+	}
+
+	if err := db.DB.AutoMigrate(&Permission{}); err != nil {
+		return err
+	}
+
+	if err := db.DB.AutoMigrate(&Token{}); err != nil {
+		return err
+	}
+
+	if err := db.DB.AutoMigrate(&User{}); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func initDialector(backend, params string) (gorm.Dialector, error) {
+	switch backend {
+	case "sqlite":
+		if params == "" {
+			return nil, fmt.Errorf("sqlite database file not specified")
+		}
+
+		return sqlite.Open(params), nil
+	case "postgresql":
+		if params == "" {
+			return nil, fmt.Errorf("postgres DSN not specified")
+		}
+
+		return postgres.Open(params), nil
+	case "":
+		return nil, fmt.Errorf("no database backend specified in environment variables")
+	default:
+		return nil, fmt.Errorf("unknown database backend specified: %s", os.Getenv(backend))
+	}
+}