feat: add originalPath support with split functionality

- Add extractOriginalPath function with delimiter-based splitting
- Support cross-platform path normalization (Windows \ to /)
- Enable directory-based photo grouping and path component extraction
- Add comprehensive tests for path splitting and stacking scenarios
- Update documentation with originalPath examples and usage guide

This allows users to group photos by directory structure and extract
specific path components using the same split syntax as originalFileName.

Author: Majorfi

docs/features/custom-criteria.md

@@ -36,6 +36,7 @@ You can use any of these keys in your criteria:
 | Key                | Description                    |
 | ------------------ | ------------------------------ |
 | `originalFileName` | Original filename of the asset |
+| `originalPath`     | Original path of the asset     |
 | `localDateTime`    | Local capture time             |
 | `fileCreatedAt`    | File creation time             |
 | `fileModifiedAt`   | File modification time         |
@@ -60,6 +61,25 @@ For example, with a file named `IMG_1234~edit.jpg`:
 1. Split on `~` and `.` gives `["IMG_1234", "edit", "jpg"]`
 2. Using `index: 0` selects `"IMG_1234"`
 
+For paths, you can split by directory separators:
+
+```json
+{
+  "key": "originalPath",
+  "split": {
+    "delimiters": ["/"],
+    "index": 2
+  }
+}
+```
+
+For a path like `photos/2023/vacation/IMG_001.jpg`:
+
+1. Split on `/` gives `["photos", "2023", "vacation", "IMG_001.jpg"]`
+2. Using `index: 2` selects `"vacation"`
+
+Note: The `originalPath` splitter automatically normalizes Windows-style backslashes (`\`) to forward slashes (`/`).
+
 ## Delta Configuration
 
 The `delta` configuration allows for flexible time matching:
@@ -109,32 +129,44 @@ This is useful for:
 ]
 ```
 
-### Combined Criteria
+### Directory-Based Grouping
 
 ```json
 [
   {
-    "key": "originalFileName",
+    "key": "originalPath",
     "split": {
-      "delimiters": ["~", "."],
-      "index": 0
+      "delimiters": ["/"],
+      "index": 2
     }
-  },
+  }
+]
+```
+
+This will group photos by their directory name (e.g., all photos in the "vacation" directory will be grouped together).
+
+### Combined Path and Time Criteria
+
+```json
+[
   {
-    "key": "localDateTime",
-    "delta": {
-      "milliseconds": 1000
+    "key": "originalPath",
+    "split": {
+      "delimiters": ["/"],
+      "index": 2
     }
   },
   {
-    "key": "fileCreatedAt",
+    "key": "localDateTime",
     "delta": {
-      "milliseconds": 5000
+      "milliseconds": 1000
     }
   }
 ]
 ```
 
+This will group photos that are both in the same directory and taken within 1 second of each other.
+
 ## Best Practices
 
 1. **Start Simple:**

pkg/stacker/criteria.go

@@ -112,7 +112,7 @@ func applyCriteria(asset utils.TAsset, criteria []utils.TCriteria) ([]string, er
 			return extractTimeWithDelta(a.LocalDateTime, c.Delta)
 		},
 		"originalFileName": extractOriginalFileName,
-		"originalPath":     func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.OriginalPath, nil },
+		"originalPath":     extractOriginalPath,
 		"ownerId":          func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.OwnerID, nil },
 		"type":             func(a utils.TAsset, _ utils.TCriteria) (string, error) { return a.Type, nil },
 		"updatedAt": func(a utils.TAsset, c utils.TCriteria) (string, error) {
@@ -177,6 +177,40 @@ func extractOriginalFileName(asset utils.TAsset, c utils.TCriteria) (string, err
 	return baseName, nil
 }
 
+/**************************************************************************************************
+** extractOriginalPath extracts and processes the original path from an asset according
+** to the provided criteria. If the criteria include split parameters (delimiters and an
+** index), the path is split by those delimiters, and the part at the specified index
+** is returned. The function handles both forward slashes and backslashes as path
+** separators by always normalizing them to forward slashes.
+**
+** @param asset - The utils.TAsset from which to extract the original path.
+** @param c - The utils.TCriteria containing potential split parameters.
+** @return string - The processed original path (potentially split).
+** @return error - An error if the split index is out of range for the resulting parts,
+**                 or nil otherwise.
+**************************************************************************************************/
+func extractOriginalPath(asset utils.TAsset, c utils.TCriteria) (string, error) {
+	// Always normalize path separators to forward slashes
+	path := strings.ReplaceAll(asset.OriginalPath, "\\", "/")
+
+	if c.Split != nil && len(c.Split.Delimiters) > 0 {
+		parts := []string{path}
+		for _, delim := range c.Split.Delimiters {
+			temp := []string{}
+			for _, part := range parts {
+				temp = append(temp, strings.Split(part, delim)...)
+			}
+			parts = temp
+		}
+		if c.Split.Index < 0 || c.Split.Index >= len(parts) {
+			return "", fmt.Errorf("split index %d out of range for %q", c.Split.Index, path)
+		}
+		path = parts[c.Split.Index]
+	}
+	return path, nil
+}
+
 /**************************************************************************************************
 ** boolToString converts a boolean value to its string representation. It returns "true"
 ** for a true input and "false" for a false input.