added backend with DELETE and PUT routes

Author: Bradley

backend/src/main/java/merhoo/backend/App.java

@@ -81,5 +81,40 @@ public static void main(String[] args) {
                 return gson.toJson(new StructuredResponse("ok", "" + newId, null));
             }
         });
+
+        // PUT route for updating a row in the DataStore.  This is almost
+        // exactly the same as POST
+        Spark.put("/messages/:id", (request, response) -> {
+            // If we can't get an ID or can't parse the JSON, Spark will send
+            // a status 500
+            int idx = Integer.parseInt(request.params("id"));
+            SimpleRequest req = gson.fromJson(request.body(), SimpleRequest.class);
+            // ensure status 200 OK, with a MIME type of JSON
+            response.status(200);
+            response.type("application/json");
+            DataRow result = dataStore.updateOne(idx, req.mTitle, req.mMessage);
+            if (result == null) {
+                return gson.toJson(new StructuredResponse("error", "unable to update row " + idx, null));
+            } else {
+                return gson.toJson(new StructuredResponse("ok", null, result));
+            }
+        });
+
+        // DELETE route for removing a row from the DataStore
+        Spark.delete("/messages/:id", (request, response) -> {
+            // If we can't get an ID, Spark will send a status 500
+            int idx = Integer.parseInt(request.params("id"));
+            // ensure status 200 OK, with a MIME type of JSON
+            response.status(200);
+            response.type("application/json");
+            // NB: we won't concern ourselves too much with the quality of the
+            //     message sent on a successful delete
+            boolean result = dataStore.deleteOne(idx);
+            if (!result) {
+                return gson.toJson(new StructuredResponse("error", "unable to delete row " + idx, null));
+            } else {
+                return gson.toJson(new StructuredResponse("ok", null, null));
+            }
+        });
     }
 }

backend/src/main/java/merhoo/backend/DataStore.java

@@ -83,4 +83,47 @@ public synchronized ArrayList<DataRowLite> readAll() {
         }
         return data;
     }
+
+    /**
+     * Update the title and content of a row in the DataStore
+     *
+     * @param id The Id of the row to update
+     * @param title The new title for the row
+     * @param content The new content for the row
+     * @return a copy of the data in the row, if it exists, or null otherwise
+     */
+    public synchronized DataRow updateOne(int id, String title, String content) {
+        // Do not update if we don't have valid data
+        if (title == null || content == null)
+            return null;
+        // Only update if the current entry is valid (not null)
+        if (id >= mRows.size())
+            return null;
+        DataRow data = mRows.get(id);
+        if (data == null)
+            return null;
+        // Update and then return a copy of the data, as a DataRow
+        data.mTitle = title;
+        data.mContent = content;
+        return new DataRow(data);
+    }
+
+    /**
+     * Delete a row from the DataStore
+     *
+     * @param id The Id of the row to delete
+     * @return true if the row was deleted, false otherwise
+     */
+    public synchronized boolean deleteOne(int id) {
+        // Deletion fails for an invalid Id or an Id that has already been
+        // deleted
+        if (id >= mRows.size())
+            return false;
+        if (mRows.get(id) == null)
+            return false;
+        // Delete by setting to null, so that any Ids used by other clients
+        // still refer to the same positions in the ArrayList.
+        mRows.set(id, null);
+        return true;
+    }
 }