inverting the relationship between root scanner and function such that the function takes a parameter which is the scanner expression

Author: Greenwood

json-path/src/main/java/com/jayway/jsonpath/internal/path/CompiledPath.java

@@ -19,9 +19,13 @@
 import com.jayway.jsonpath.internal.EvaluationContext;
 import com.jayway.jsonpath.internal.Path;
 import com.jayway.jsonpath.internal.PathRef;
+import com.jayway.jsonpath.internal.function.ParamType;
+import com.jayway.jsonpath.internal.function.Parameter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.Arrays;
+
 public class CompiledPath implements Path {
 
     private static final Logger logger = LoggerFactory.getLogger(CompiledPath.class);
@@ -32,7 +36,7 @@ public class CompiledPath implements Path {
 
 
     public CompiledPath(RootPathToken root, boolean isRootPath) {
-        this.root = root;
+        this.root = invertScannerFunctionRelationship(root);
         this.isRootPath = isRootPath;
     }
 
@@ -41,6 +45,48 @@ public boolean isRootPath() {
         return isRootPath;
     }
 
+
+
+    /**
+     * In the event the writer of the path referenced a function at the tail end of a scanner, augment the query such
+     * that the root node is the function and the parameter to the function is the scanner.   This way we maintain
+     * relative sanity in the path expression, functions either evaluate scalar values or arrays, they're
+     * not re-entrant nor should they maintain state, they do however take parameters.
+     *
+     * @param path
+     *      this is our old root path which will become a parameter (assuming there's a scanner terminated by a function
+     *
+     * @return
+     *      A function with the scanner as input, or if this situation doesn't exist just the input path
+     */
+    private RootPathToken invertScannerFunctionRelationship(final RootPathToken path) {
+        if (path.isFunctionPath() && path.next() instanceof ScanPathToken) {
+            PathToken token = path;
+            PathToken prior = null;
+            while (null != (token = token.next()) && !(token instanceof FunctionPathToken)) {
+                prior = token;
+            }
+            // Invert the relationship $..path.function() to $.function($..path)
+            if (token instanceof FunctionPathToken) {
+                prior.setNext(null);
+                path.setTail(prior);
+
+                // Now generate a new parameter from our path
+                Parameter parameter = new Parameter();
+                parameter.setPath(new CompiledPath(path, true));
+                parameter.setType(ParamType.PATH);
+                ((FunctionPathToken)token).setParameters(Arrays.asList(parameter));
+                RootPathToken functionRoot = new RootPathToken('$');
+                functionRoot.setTail(token);
+                functionRoot.setNext(token);
+
+                // Define the function as the root
+                return functionRoot;
+            }
+        }
+        return path;
+    }
+
     @Override
     public EvaluationContext evaluate(Object document, Object rootDocument, Configuration configuration, boolean forUpdate) {
         if (logger.isDebugEnabled()) {

json-path/src/main/java/com/jayway/jsonpath/internal/path/FunctionPathToken.java

@@ -20,7 +20,7 @@ public class FunctionPathToken extends PathToken {
 
     private final String functionName;
     private final String pathFragment;
-    private final List<Parameter> functionParams;
+    private List<Parameter> functionParams;
 
     public FunctionPathToken(String pathFragment, List<Parameter> parameters) {
         this.pathFragment = pathFragment + ((parameters != null && parameters.size() > 0) ? "(...)" : "()");
@@ -81,4 +81,7 @@ public String getPathFragment() {
     }
 
 
+    public void setParameters(List<Parameter> parameters) {
+        this.functionParams = parameters;
+    }
 }

json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java

@@ -215,4 +215,7 @@ public void invoke(PathFunction pathFunction, String currentPath, PathRef parent
 
     protected abstract String getPathFragment();
 
+    public void setNext(final PathToken next) {
+        this.next = next;
+    }
 }

json-path/src/main/java/com/jayway/jsonpath/internal/path/RootPathToken.java

@@ -76,4 +76,8 @@ public boolean isTokenDefinite() {
     public boolean isFunctionPath() {
         return (tail instanceof FunctionPathToken);
     }
+
+    public void setTail(PathToken token) {
+        this.tail = token;
+    }
 }

json-path/src/test/java/com/jayway/jsonpath/internal/function/Issue191.java

@@ -27,6 +27,14 @@ public void testResultSetNumericComputation() {
                 Long.valueOf(35679716813L), value);
     }
 
+    @Test
+    public void testResultSetNumericComputationTail() {
+        InputStream stream = ClassLoader.getSystemResourceAsStream("issue_191.json");
+        Long value = JsonPath.parse(stream).read("$..timestamp.sum()", Long.class);
+        assertEquals("Expected the max function to consume the aggregation parameters and calculate the max over the result set",
+                Long.valueOf(35679716813L), value);
+    }
+
     @Test
     public void testMultipleResultSetSums() {
         InputStream stream = ClassLoader.getSystemResourceAsStream("issue_191.json");