[all hosts] (Common APIs) Add an Office.Slice sample (#2437)

* Add an Office.Slice sample

* Refactor recursion and add process functionality

* Update docs/code-snippets/office-snippets.yaml

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update docs/code-snippets/office-snippets.yaml

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: AlexJerabek

docs/code-snippets/office-snippets.yaml

@@ -4353,6 +4353,81 @@ Office.Settings#saveAsync:member(2):
     function write(message){
         document.getElementById('message').innerText += message; 
     }
+Office.Slice:interface:
+  - |-
+    // This example demonstrates how to read file slices using the Office.Slice interface.
+    // Each slice represents a portion of the document file and includes the data, 
+    // index, and size properties.
+    Office.context.document.getFileAsync(Office.FileType.Compressed, { sliceSize: 65536 }, 
+        function (result) {
+            if (result.status === Office.AsyncResultStatus.Succeeded) {
+                const file = result.value;
+                const sliceCount = file.sliceCount;
+                let slicesReceived = 0;
+                let fileData = [];
+
+                console.log(`File sliced into ${sliceCount} parts.`);
+
+                // Get the first slice.
+                getSliceAsync(file, 0, sliceCount);
+
+                /**
+                 * Recursively retrieves slices from the file.
+                 * @param file - The Office.File object to retrieve slices from.
+                 * @param sliceIndex - The zero-based index of the slice to retrieve.
+                 * @param totalSlices - The total number of slices in the file.
+                 */
+                function getSliceAsync(file, sliceIndex, totalSlices) {
+                    file.getSliceAsync(sliceIndex, function (sliceResult) {
+                        if (sliceResult.status === Office.AsyncResultStatus.Succeeded) {
+                            const slice: Office.Slice = sliceResult.value;
+                            
+                            // Access the properties of the Slice.
+                            console.log(`Processing slice ${slice.index + 1} of ${totalSlices}`);
+                            console.log(`Slice size: ${slice.size} bytes`);
+                            
+                            // Store the slice data.
+                            fileData[slice.index] = slice.data;
+                            slicesReceived++;
+
+                            // Check if we've received all slices.
+                            if (slicesReceived === totalSlices) {
+                                file.closeAsync();
+                                console.log("All slices received. File data complete.");
+                                
+                                // Process the complete file data.
+                                processFileData(fileData);
+                            } else {
+                                // Get the next slice.
+                                getSliceAsync(file, sliceIndex + 1, totalSlices);
+                            }
+                        } else {
+                            file.closeAsync();
+                            console.error(`Error getting slice: ${sliceResult.error.message}`);
+                        }
+                    });
+                }
+
+                /**
+                 * Processes the complete file data by combining all slices.
+                 * @param data - An array of slice data arrays to combine.
+                 */
+                function processFileData(data) {
+                    // Combine all slice data into a complete file.
+                    let combinedData = [];
+                    for (let i = 0; i < data.length; i++) {
+                        combinedData.push(...data[i]);
+                    }
+                    
+                    console.log(`File processing complete. Total bytes: ${combinedData.length}`);
+                    // At this point, combinedData contains the complete file content.
+                    // You can now save it, send it to a server, or process it further.
+                }
+            } else {
+                console.error(`Error getting file: ${result.error.message}`);
+            }
+        }
+    );
 Office.StartupBehavior:enum:
   - |-
     // Configure your add-in to load and start running when the document is opened.