Report maths (#448)

* Rename file

* Expand conditional example

* Add documentation for using media variables

docs/report/helpers.md

@@ -1,14 +1,8 @@
 ---
-title: Using media files
+title: Helper Functions
 ---
 
-## Media Files
-
-*Media files* are any files uploaded to the InvenTree server by the user. These are stored under the `/media/` directory and can be accessed for use in custom reports or labels.
-
-**Load Report Functions**
-
-To load images into the reports/labels the report helper functions must first be loaded in the template:
+Some common functions are provided for use in custom report and label templates. To include these, load the `report` functions at the start of the template:
 
 ```html
 {% raw %}
@@ -17,6 +11,40 @@ To load images into the reports/labels the report helper functions must first be
 {% endraw %}
 ```
 
+## Maths Operations
+
+Simple mathematical operators are available, as demonstrated in the example template below:
+
+```html
+{% raw %}
+<!-- Load the report helper functions -->
+{% load report %}
+
+{% add 1 3 %} <!-- Add two numbers together -->
+{% subtract 4 3 %} <!-- Subtract 3 from 4 -->
+{% multiply 1.2 3.4 %} <!-- Multiply two numbers -->
+{% divide 10 2 %} <!-- Divide 10 by 2 -->
+
+{% endraw %}
+```
+
+These operators can also be used with variables:
+
+```html
+{% raw %}
+{% load report %}
+
+{% for line in order.lines %}
+Total: {% multiply line.purchase_price line.quantity %}<br>
+{% endfor %}
+
+{% endraw %}
+```
+
+## Media Files
+
+*Media files* are any files uploaded to the InvenTree server by the user. These are stored under the `/media/` directory and can be accessed for use in custom reports or labels.
+
 ### Uploaded Images
 
 You can access an uploaded image file if you know the *path* of the image, relative to the top-level `/media/` directory. To load the image into a report, use the `{% raw %}{% uploaded_image ... %}{% endraw %}` tag:

docs/report/labels.md

@@ -106,7 +106,7 @@ Refer to the [barcode documentation](./barcodes.md).
 
 ### Using media files 
 
-Refer to the [media files documentation](./media.md).
+Refer to the [media files documentation](./helpers.md#media-files).
 
 ### Conditional Formatting
 

docs/report/report.md

@@ -60,6 +60,10 @@ The django template system allows for conditional rendering, providing condition
 {% raw %}
 {% if <condition> %}
 {% do_something %}
+{% elif <other_condition> %}
+<!-- something else -->
+{% else %}
+<!-- finally -->
 {% endif %}
 {% endraw %}
 ```

mkdocs.yml

@@ -118,7 +118,7 @@ nav:
       - Sales Order: report/sales_order.md
       - BOM: report/bom.md
     - Labels: report/labels.md
-    - Media Files: report/media.md
+    - Helper Functions: report/helpers.md
     - Barcodes: report/barcodes.md
     - Context Variables: report/context_variables.md
   - Admin: