feat: add FilenameTemplateParser with placeholder evaluation and validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ExportDXF/Services/FilenameTemplateParser.cs

@@ -0,0 +1,96 @@
+using System;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+
+namespace ExportDXF.Services
+{
+    public static class FilenameTemplateParser
+    {
+        private static readonly Regex PlaceholderPattern = new Regex(
+            @"\{(?<name>\w+)(?::(?<pad>\d+))?\}",
+            RegexOptions.Compiled);
+
+        /// <summary>
+        /// Evaluates a template string for a given item.
+        /// e.g. "4321 A01 PT{item_no:2}" with item_no=3 → "4321 A01 PT03"
+        /// </summary>
+        public static string Evaluate(string template, Item item)
+        {
+            return PlaceholderPattern.Replace(template, match =>
+            {
+                var name = match.Groups["name"].Value.ToLowerInvariant();
+                var padStr = match.Groups["pad"].Value;
+                int pad = string.IsNullOrEmpty(padStr) ? 0 : int.Parse(padStr);
+
+                string value;
+                switch (name)
+                {
+                    case "item_no":
+                        value = item.ItemNo ?? "0";
+                        if (pad > 0)
+                            value = value.PadLeft(pad, '0');
+                        break;
+                    case "part_name":
+                        value = item.PartName ?? "";
+                        break;
+                    case "config":
+                        value = item.Configuration ?? "";
+                        break;
+                    case "material":
+                        value = item.Material ?? "";
+                        break;
+                    default:
+                        value = match.Value;
+                        break;
+                }
+
+                return value;
+            });
+        }
+
+        /// <summary>
+        /// Extracts the literal prefix before the first placeholder.
+        /// Used for naming the xlsx and log files.
+        /// Falls back to documentName if prefix is empty.
+        /// </summary>
+        public static string GetPrefix(string template, string documentName)
+        {
+            var match = PlaceholderPattern.Match(template);
+            if (!match.Success)
+                return template.Trim();
+
+            var prefix = template.Substring(0, match.Index).Trim();
+            if (string.IsNullOrEmpty(prefix))
+                return Path.GetFileNameWithoutExtension(documentName);
+
+            return prefix;
+        }
+
+        /// <summary>
+        /// Validates that the template contains {item_no} to prevent filename collisions.
+        /// </summary>
+        public static bool Validate(string template, out string error)
+        {
+            error = null;
+
+            if (string.IsNullOrWhiteSpace(template))
+            {
+                error = "Template cannot be empty.";
+                return false;
+            }
+
+            var hasItemNo = PlaceholderPattern.Matches(template)
+                .Cast<Match>()
+                .Any(m => m.Groups["name"].Value.Equals("item_no", StringComparison.OrdinalIgnoreCase));
+
+            if (!hasItemNo)
+            {
+                error = "Template must contain {item_no} or {item_no:N} to avoid filename collisions.";
+                return false;
+            }
+
+            return true;
+        }
+    }
+}