feat: Implement basic DiskBackend struct with constructor (for now it isn't implementing Backend interface)

internal/backends/disk/backend.go

@@ -0,0 +1,70 @@
+package disk
+
+import (
+	"fmt"
+	"regexp"
+	"sync"
+
+	"github.com/HouzuoGuo/tiedot/db"
+)
+
+const (
+	DatabasePath       = "signaller.db" // TODO: make changing the path of database
+	UsersColName       = "users"
+	RoomsColName       = "rooms"
+	EventsColName      = "events"
+	RoomAliasesColName = "roomAliases"
+)
+
+func createCollections(database *db.DB) {
+	if err := database.Create(UsersColName); err != nil {
+		panic(err)
+	}
+	if err := database.Create(RoomsColName); err != nil {
+		panic(err)
+	}
+	if err := database.Create(EventsColName); err != nil {
+		panic(err)
+	}
+	if err := database.Create(RoomAliasesColName); err != nil {
+		panic(err)
+	}
+}
+
+func defaultValidationUsernameFunc(userName string) error {
+	const re = `^\w{5,}$`
+
+	if !regexp.MustCompile(re).MatchString(userName) {
+		return fmt.Errorf("username does not match %s", re)
+	}
+
+	return nil
+}
+
+type DiskBackend struct {
+	currentDatabase      *db.DB
+	users                *db.Col
+	rooms                *db.Col
+	events               *db.Col
+	roomAliases          *db.Col
+	hostname             string
+	validateUsernameFunc func(string) error // TODO: create ability to redefine validation func
+	mutex                sync.RWMutex
+}
+
+func NewDiskBackend(hostname string) *DiskBackend {
+	database, err := db.OpenDB(DatabasePath)
+	if err != nil {
+		panic(err)
+	}
+	createCollections(database)
+
+	return &DiskBackend{
+		currentDatabase:      database,
+		users:                database.Use(UsersColName),
+		rooms:                database.Use(RoomsColName),
+		events:               database.Use(EventsColName),
+		roomAliases:          database.Use(RoomAliasesColName),
+		hostname:             hostname,
+		validateUsernameFunc: defaultValidationUsernameFunc}
+}