feat: add PostgreSQL persistence layer with Neon DB support

internal/app/server.go

@@ -1,9 +1,11 @@
 package app
 
 import (
+	"log"
 	"net/http"
 
 	"tutor/internal/config"
+	"tutor/internal/db"
 	"tutor/internal/httpapi"
 	"tutor/internal/interview"
 	"tutor/internal/learnermemory"
@@ -15,12 +17,38 @@ import (
 
 func NewServer(cfg config.Config) *http.Server {
 	runner := workflows.NewStubRunner()
-	store := interview.NewMemoryStore()
-	memory := learnermemory.NewService(learnermemory.NewMemoryStore())
+
+	var interviewStore interview.Store
+	var memoryStore learnermemory.Store
+	var ontologyStore ontology.Store
+	var assetsStore teachingassets.Store
+
+	if cfg.DatabaseURL != "" {
+		pool, err := db.Open(cfg.DatabaseURL)
+		if err != nil {
+			log.Fatalf("open database: %v", err)
+		}
+		if err := db.Migrate(pool); err != nil {
+			log.Fatalf("migrate database: %v", err)
+		}
+		interviewStore = interview.NewPostgresStore(pool)
+		memoryStore = learnermemory.NewPostgresStore(pool)
+		ontologyStore = ontology.NewPostgresStore(pool)
+		assetsStore = teachingassets.NewPostgresStore(pool)
+		log.Println("using postgres persistence")
+	} else {
+		interviewStore = interview.NewMemoryStore()
+		memoryStore = learnermemory.NewMemoryStore()
+		ontologyStore = ontology.NewMemoryStore()
+		assetsStore = teachingassets.NewMemoryStore()
+		log.Println("using in-memory persistence")
+	}
+
+	memory := learnermemory.NewService(memoryStore)
 	progress := progression.NewService(memory)
-	onto := ontology.NewService(ontology.NewMemoryStore())
-	assets := teachingassets.NewService(teachingassets.NewMemoryStore(), onto, cfg.ImageModelKey)
-	service := interview.NewService(store, runner, memory)
+	onto := ontology.NewService(ontologyStore)
+	assets := teachingassets.NewService(assetsStore, onto, cfg.ImageModelKey)
+	service := interview.NewService(interviewStore, runner, memory)
 	handler := httpapi.NewHandler(cfg, service, memory, progress, onto, assets)
 
 	return &http.Server{