generate excel worksheets when data is available instead of on-demand

internal/report/snapshots.go

@@ -6,6 +6,8 @@ import (
 	"database/sql"
 	"fmt"
 	"log/slog"
+	"os"
+	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
@@ -637,6 +639,29 @@ func CreateTableReport(logger *slog.Logger, Database db.Database, ctx context.Co
 	return buffer.Bytes(), nil
 }
 
+// SaveTableReport renders a table report and writes it to the destination directory with a .xlsx extension.
+func SaveTableReport(logger *slog.Logger, Database db.Database, ctx context.Context, tableName, destDir string) (string, error) {
+	if err := db.ValidateTableName(tableName); err != nil {
+		return "", err
+	}
+	if strings.TrimSpace(destDir) == "" {
+		return "", fmt.Errorf("destination directory is empty")
+	}
+	if err := os.MkdirAll(destDir, 0o755); err != nil {
+		return "", fmt.Errorf("failed to create reports directory: %w", err)
+	}
+
+	data, err := CreateTableReport(logger, Database, ctx, tableName)
+	if err != nil {
+		return "", err
+	}
+	filename := filepath.Join(destDir, fmt.Sprintf("%s.xlsx", tableName))
+	if err := os.WriteFile(filename, data, 0o644); err != nil {
+		return "", err
+	}
+	return filename, nil
+}
+
 func addTotalsChartSheet(logger *slog.Logger, database db.Database, ctx context.Context, xlsx *excelize.File, tableName string) {
 	if strings.HasPrefix(tableName, "inventory_daily_summary_") {
 		suffix := strings.TrimPrefix(tableName, "inventory_daily_summary_")