Rewrite project, add daily update of services list

The project was rewritten from Elixir to Go, primarily because:

- I don't write Elixir anymore and don't want to maintain a project in a
  language I no longer write
- I already write Go for other projects, including my day job, so it's
  a safer bet for a project that I want to maintain long term
- Go allows me to build portable executables that will make it easier
  for others to run farside on their own machines

The Go version of Farsside also has a built in task to fetch the latest
services{-full}.json file from the repo and ingest it, which makes
running a farside server a lot simpler.

It also automatically fetches the latest instance state from
https://farside.link unless configured as a primary farside node, which
will allow others to use farside without increasing traffic to all
instances that are queried by farside (just to the farside node itself).

1 files changed, 150 insertions, 0 deletions

diff --git a/db/db.go b/db/db.go
new file mode 100644
index 0000000..efdf145
--- /dev/null
+++ b/db/db.go
@@ -0,0 +1,150 @@
+package db
+
+import (
+	"encoding/json"
+	"errors"
+	"log"
+	"math/rand"
+	"os"
+	"slices"
+	"time"
+
+	"github.com/benbusby/farside/services"
+	"github.com/dgraph-io/badger/v4"
+)
+
+var (
+	badgerDB     *badger.DB
+	selectionMap map[string]string
+
+	cachedServiceList []services.Service
+	cacheUpdated      time.Time
+)
+
+func InitializeDB() error {
+	var err error
+
+	dbDir := os.Getenv("FARSIDE_DB_DIR")
+	if len(dbDir) == 0 {
+		dbDir = "./badger-db"
+	}
+
+	badgerDB, err = badger.Open(badger.DefaultOptions(dbDir))
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func SetInstances(service string, instances []string) error {
+	instancesBytes, err := json.Marshal(instances)
+	if err != nil {
+		return err
+	}
+
+	err = badgerDB.Update(func(txn *badger.Txn) error {
+		err := txn.Set([]byte(service), instancesBytes)
+		return err
+	})
+
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func GetInstance(service string) (string, error) {
+	instances, err := GetAllInstances(service)
+	if err != nil || len(instances) == 0 {
+		if err != nil {
+			log.Println("DB err:", err)
+		}
+
+		link, ok := services.FallbackMap[service]
+		if !ok {
+			return "", errors.New("invalid service")
+		}
+
+		return link, nil
+	}
+
+	previous, ok := selectionMap[service]
+	if ok && len(instances) > 2 {
+		instances = slices.DeleteFunc(instances, func(i string) bool {
+			return i == previous
+		})
+	}
+
+	index := rand.Intn(len(instances))
+	value := instances[index]
+	selectionMap[service] = value
+	return value, nil
+}
+
+func GetAllInstances(service string) ([]string, error) {
+	var instances []string
+	err := badgerDB.View(func(txn *badger.Txn) error {
+		item, err := txn.Get([]byte(service))
+		if err != nil {
+			return err
+		}
+
+		err = item.Value(func(val []byte) error {
+			err := json.Unmarshal(val, &instances)
+			return err
+		})
+
+		return err
+	})
+
+	return instances, err
+}
+
+func GetServiceList() []services.Service {
+	if cacheUpdated.Add(5 * time.Minute).After(time.Now().UTC()) {
+		return cachedServiceList
+	}
+
+	canCache := true
+
+	var serviceList []services.Service
+	for _, service := range services.ServiceList {
+		instances, err := GetAllInstances(service.Type)
+		if err != nil {
+			canCache = false
+			instances = []string{service.Fallback}
+		}
+
+		storedService := services.Service{
+			Type:      service.Type,
+			Instances: instances,
+		}
+
+		serviceList = append(serviceList, storedService)
+	}
+
+	if canCache {
+		cachedServiceList = serviceList
+		cacheUpdated = time.Now().UTC()
+	}
+
+	return serviceList
+}
+
+func CloseDB() error {
+	log.Println("Closing database...")
+	err := badgerDB.Close()
+	if err != nil {
+		log.Println("Error closing database", err)
+		return err
+	}
+
+	log.Println("Database closed!")
+	return nil
+}
+
+func init() {
+	selectionMap = make(map[string]string)
+}