refactor: extract shared CardStore into internal/store to eliminate duplication

FindCardDirectory, FindOrCreateCardDirectory, GenerateCardID and the
ScanWords helper previously existed in both internal/utils.go (as
standalone functions) and were partially duplicated in
internal/gui/card_service.go (readWordFromDir, ScanExistingWords).

Introduce internal/store.CardStore as the single source of truth for
all on-disk card-directory operations. Both internal/processor and
internal/gui now hold a *store.CardStore field and delegate to it,
removing the last copy of the directory-scanning loop from
card_service.go. internal/utils.go keeps thin forwarding wrappers for
callers that import the root internal package.

Also adds table-driven unit tests for the new package covering
FindCardDirectory (including legacy _word.txt fallback),
FindOrCreateCardDirectory, and CardStore.ScanWords.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 10 insertions, 63 deletions

diff --git a/internal/utils.go b/internal/utils.go
index b83d46a..e16e10e 100644
--- a/internal/utils.go
+++ b/internal/utils.go
@@ -1,85 +1,32 @@
 package internal
 
 import (
-	"crypto/md5"
-	"encoding/hex"
-	"fmt"
-	"os"
-	"path/filepath"
 	"strings"
-	"time"
+
+	"codeberg.org/snonux/totalrecall/internal/store"
 )
 
-// GenerateCardID creates a unique ID for a card based on timestamp and Bulgarian word
+// GenerateCardID creates a unique ID for a card based on timestamp and Bulgarian word.
+// Delegates to store.GenerateCardID which is the single source of truth.
 // Format: epochMillis_md5(word)[:8]
 func GenerateCardID(bulgarianWord string) string {
-	// Get current timestamp in milliseconds
-	now := time.Now()
-	epochMillis := now.UnixNano() / 1000000
-
-	// Calculate MD5 hash of the word
-	hash := md5.Sum([]byte(bulgarianWord))
-	hashStr := hex.EncodeToString(hash[:])[:8] // Use first 8 chars of MD5
-
-	// Combine timestamp and hash
-	return fmt.Sprintf("%d_%s", epochMillis, hashStr)
+	return store.GenerateCardID(bulgarianWord)
 }
 
 // FindCardDirectory searches outputDir for a subdirectory whose word.txt
 // (or legacy _word.txt) matches the given word. Returns the directory path
 // or an empty string if not found.
+// Delegates to store.FindCardDirectory which is the single source of truth.
 func FindCardDirectory(outputDir, word string) string {
-	entries, err := os.ReadDir(outputDir)
-	if err != nil {
-		return ""
-	}
-
-	for _, entry := range entries {
-		if !entry.IsDir() || strings.HasPrefix(entry.Name(), ".") {
-			continue
-		}
-
-		dirPath := filepath.Join(outputDir, entry.Name())
-		wordFile := filepath.Join(dirPath, "word.txt")
-
-		if data, err := os.ReadFile(wordFile); err == nil {
-			if strings.TrimSpace(string(data)) == word {
-				return dirPath
-			}
-		} else {
-			// Backward-compatible fallback: old format used _word.txt
-			wordFile = filepath.Join(dirPath, "_word.txt")
-			if data, err := os.ReadFile(wordFile); err == nil {
-				if strings.TrimSpace(string(data)) == word {
-					return dirPath
-				}
-			}
-		}
-	}
-
-	return ""
+	return store.FindCardDirectory(outputDir, word)
 }
 
 // FindOrCreateCardDirectory returns the existing card directory for word inside
 // outputDir, or creates a new one with a generated card ID. It also writes
 // word.txt so subsequent calls can find the directory.
+// Delegates to store.FindOrCreateCardDirectory which is the single source of truth.
 func FindOrCreateCardDirectory(outputDir, word string) string {
-	if dir := FindCardDirectory(outputDir, word); dir != "" {
-		return dir
-	}
-
-	cardID := GenerateCardID(word)
-	wordDir := filepath.Join(outputDir, cardID)
-	if err := os.MkdirAll(wordDir, 0755); err != nil {
-		fmt.Printf("Warning: failed to create word directory: %v\n", err)
-		return outputDir
-	}
-
-	if err := os.WriteFile(filepath.Join(wordDir, "word.txt"), []byte(word), 0644); err != nil {
-		fmt.Printf("Warning: failed to save word metadata: %v\n", err)
-	}
-
-	return wordDir
+	return store.FindOrCreateCardDirectory(outputDir, word)
 }
 
 // SanitizeFilename creates a safe filename from a string.
@@ -97,7 +44,7 @@ func SanitizeFilename(s string) string {
 	return b.String()
 }
 
-// isAlphaNumeric checks if a rune is alphanumeric
+// isAlphaNumeric checks if a rune is alphanumeric (Latin or Cyrillic).
 func isAlphaNumeric(r rune) bool {
 	return (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') ||
 		(r >= '0' && r <= '9') || (r >= 'а' && r <= 'я') ||