Add initial implementation of a comparison method

ace-am/src/main/java/edu/umiacs/ace/rest/CompareController.java

+package edu.umiacs.ace.rest;
+
+import com.google.common.collect.ImmutableList;
+import edu.umiacs.ace.monitor.core.Collection;
+import edu.umiacs.ace.monitor.core.MonitoredItem;
+import edu.umiacs.ace.rest.models.CompareFile;
+import edu.umiacs.ace.rest.models.CompareRequest;
+import edu.umiacs.ace.rest.models.CompareResponse;
+import edu.umiacs.ace.util.PersistUtil;
+
+import javax.persistence.EntityManager;
+import javax.persistence.TypedQuery;
+import javax.ws.rs.Consumes;
+import javax.ws.rs.POST;
+import javax.ws.rs.Path;
+import javax.ws.rs.PathParam;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.MediaType;
+import java.util.Objects;
+
+/**
+ * Compare files to what ACE knows about a collection
+ *
+ * Created by shake on 3/9/17.
+ */
+@Path("/")
+public class CompareController {
+
+    /**
+     * API method for comparing files and their digests to a given collection
+     *
+     * todo: It would be nice to not have "compare/id" and instead be more along the lines of "collection/id/compare"
+     * todo: BadRequest if a collection == null?
+     *
+     * @param id the id of the collection
+     * @param request the request containing the comparisons
+     * @return the result of the comparison
+     */
+    @POST
+    @Path("compare/{id}")
+    @Consumes(MediaType.APPLICATION_JSON)
+    @Produces(MediaType.APPLICATION_JSON)
+    public CompareResponse compare(@PathParam("id") Long id, CompareRequest request) {
+        if (request == null) {
+            request = new CompareRequest();
+            request.setComparisons(ImmutableList.<CompareFile>of());
+        }
+
+        EntityManager em = PersistUtil.getEntityManager();
+        CompareResponse response = new CompareResponse();
+        Collection collection = em.find(Collection.class, id); // can this throw an exception?
+        for (CompareFile file : request.getComparisons()) {
+            TypedQuery<MonitoredItem> query = em.createNamedQuery("MonitoredItem.getItemByPath", MonitoredItem.class);
+            query.setParameter("path", file.getPath());
+            query.setParameter("coll", collection);
+            try {
+                MonitoredItem result = query.getSingleResult();
+                if (Objects.equals(result.getFileDigest(), file.getDigest())) {
+                    response.addMatch(file.getPath());
+                } else {
+                    response.addDiff(file.getPath());
+                }
+            } catch (Exception e) {
+                response.addNotFound(file.getPath());
+            }
+        }
+
+        return response;
+    }
+
+}