Add library sync functionality

.gitignore

@@ -1,3 +1,4 @@
 /.direnv/
 /sheetless-server
+/src/sheetless-server
 /sheetless.db

src/main.go

@@ -4,6 +4,8 @@ import (
 	"log"
 	"sheetless-server/database"
 	"sheetless-server/routes"
+	"sheetless-server/sync"
+	"time"
 
 	"github.com/gin-gonic/gin"
 )
@@ -11,6 +13,20 @@ import (
 func main() {
 	database.InitDatabase()
 
+	// Start sync runner
+	go func() {
+		ticker := time.NewTicker(1 * time.Minute)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				if err := sync.SyncSheets(); err != nil {
+					log.Printf("Sync error: %v", err)
+				}
+			}
+		}
+	}()
+
 	r := gin.Default()
 
 	routes.SetupRoutes(r)

src/sync/sync.go

@@ -0,0 +1,102 @@
+package sync
+
+import (
+	"log"
+	"os"
+	"path/filepath"
+	"sheetless-server/database"
+	"sheetless-server/handlers"
+	"sheetless-server/models"
+	"sheetless-server/utils"
+	"time"
+)
+
+const uploadDir = "./uploads"
+
+func SyncSheets() error {
+	// Get all sheets
+	var sheets []models.Sheet
+	if err := database.DB.Find(&sheets).Error; err != nil {
+		return err
+	}
+
+	// Maps
+	pathsInDb := make(map[string]*models.Sheet)
+	hashToSheets := make(map[uint64][]*models.Sheet)
+	for i := range sheets {
+		sheet := &sheets[i]
+		pathsInDb[sheet.FilePath] = sheet
+		hashToSheets[sheet.FileHash] = append(hashToSheets[sheet.FileHash], sheet)
+	}
+
+	// Walk uploads dir
+	files, err := os.ReadDir(uploadDir)
+	if err != nil {
+		return err
+	}
+
+	for _, file := range files {
+		if file.IsDir() {
+			continue
+		}
+		filePath := filepath.Join(uploadDir, file.Name())
+		hash, err := utils.FileHash(filePath)
+		if err != nil {
+			log.Printf("Error hashing file %s: %v", filePath, err)
+			continue
+		}
+		info, err := file.Info()
+		if err != nil {
+			log.Printf("Error getting file info %s: %v", filePath, err)
+			continue
+		}
+
+		existingSheet, exists := pathsInDb[filePath]
+		if exists {
+			if existingSheet.FileHash != hash {
+				// Case 1: File has been altered -> update hash
+				existingSheet.FileHash = hash
+				existingSheet.UpdatedAt = time.Now()
+				if err := database.DB.Save(existingSheet).Error; err != nil {
+					log.Printf("Error updating sheet hash for %s: %v", filePath, err)
+				}
+			}
+		} else {
+			sheetsWithHash, hasHash := hashToSheets[hash]
+			if hasHash {
+				for _, s := range sheetsWithHash {
+					if _, err := os.Stat(s.FilePath); os.IsNotExist(err) {
+						// Case 2: File has been renamed or moved -> update path
+						s.FilePath = filePath
+						s.UpdatedAt = time.Now()
+						if err := database.DB.Save(s).Error; err != nil {
+							log.Printf("Error updating sheet path for %s: %v", filePath, err)
+						}
+						break
+					}
+				}
+			} else {
+				// Case 3: New sheets file -> Add to database
+				uuid, err := handlers.GenerateNonexistentSheetUuid()
+				if err != nil {
+					log.Printf("Error generating uuid: %v", err)
+					continue
+				}
+				newSheet := models.Sheet{
+					Uuid:      *uuid,
+					Title:     file.Name(), // use filename as title
+					FilePath:  filePath,
+					FileSize:  info.Size(),
+					FileHash:  hash,
+					CreatedAt: time.Now(),
+					UpdatedAt: time.Now(),
+				}
+				if err := database.DB.Create(&newSheet).Error; err != nil {
+					log.Printf("Error creating new sheet for %s: %v", filePath, err)
+				}
+			}
+		}
+	}
+
+	return nil
+}