From a070922c2c2e6ab767b3bea30d7228a16648a7f1 Mon Sep 17 00:00:00 2001
From: Theodor Diaconu <diaconu.theodor@gmail.com>
Date: Tue, 23 Oct 2018 10:35:12 +0300
Subject: [PATCH] Fixed #303 - Reducer inter-dependency computational rules

---
 lib/query/nodes/reducerNode.js           |  1 +
 lib/query/reducers/lib/applyReducers.js  | 35 ++++++++++++++++++++----
 lib/query/reducers/lib/createReducers.js | 17 ++++++------
 3 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/lib/query/nodes/reducerNode.js b/lib/query/nodes/reducerNode.js
index f0d2f26..3ecd5fd 100644
--- a/lib/query/nodes/reducerNode.js
+++ b/lib/query/nodes/reducerNode.js
@@ -3,6 +3,7 @@ export default class ReducerNode {
         this.name = name;
         this.body = body;
         this.reduceFunction = reduce;
+        this.dependencies = []; // This is a list of the reducer this reducer uses.
     }
 
     /**
diff --git a/lib/query/reducers/lib/applyReducers.js b/lib/query/reducers/lib/applyReducers.js
index 980692b..9398b85 100644
--- a/lib/query/reducers/lib/applyReducers.js
+++ b/lib/query/reducers/lib/applyReducers.js
@@ -3,9 +3,32 @@ export default function applyReducers(root, params) {
         applyReducers(node, params);
     });
 
-    _.each(root.reducerNodes, reducerNode => {
-        root.results.forEach(result => {
-            reducerNode.compute(result, params);
-        });
-    });
-}
\ No newline at end of file
+    const processedReducers = [];
+    let reducersQueue = [...root.reducerNodes];
+
+    // TODO: find out if there's an infinite reducer inter-deendency
+
+    while (reducersQueue.length) {
+        const reducerNode = reducersQueue.shift();
+
+        // If this reducer depends on other reducers
+        if (reducerNode.dependencies.length) {
+            // If there is an unprocessed reducer, move it at the end of the queue
+            const allDependenciesComputed = _.all(reducerNode.dependencies, dep => processedReducers.includes(dep));
+            if (allDependenciesComputed) {
+                root.results.forEach(result => {
+                    reducerNode.compute(result, params);
+                });
+                processedReducers.push(reducerNode.name);
+            } else {
+                // Move it at the end of the queue
+                reducersQueue.push(reducerNode);
+            }
+        } else {
+            root.results.forEach(result => {
+                reducerNode.compute(result, params);
+            });
+            processedReducers.push(reducerNode.name);
+        }
+    }
+}
diff --git a/lib/query/reducers/lib/createReducers.js b/lib/query/reducers/lib/createReducers.js
index 9d72e9d..0522451 100644
--- a/lib/query/reducers/lib/createReducers.js
+++ b/lib/query/reducers/lib/createReducers.js
@@ -9,7 +9,7 @@ export default function addReducers(root) {
     // we add reducers last, after we have added all the fields.
     root.reducerNodes.forEach(reducer => {
         _.each(reducer.body, (body, fieldName) => {
-            handleAddElement(root, fieldName, body);
+            handleAddElement(reducer, root, fieldName, body);
         })
     });
 }
@@ -19,7 +19,7 @@ export default function addReducers(root) {
  * @param fieldName
  * @param body
  */
-export function handleAddElement(root, fieldName, body) {
+export function handleAddElement(reducerNode, root, fieldName, body) {
     // if it's a link
     const collection = root.collection;
     const linker = collection.getLinker(fieldName);
@@ -29,6 +29,7 @@ export function handleAddElement(root, fieldName, body) {
 
     const reducer = collection.getReducer(fieldName);
     if (reducer) {
+        reducerNode.dependencies.push(fieldName);
         return handleAddReducer(fieldName, reducer, root);
     }
 
@@ -41,14 +42,14 @@ export function handleAddElement(root, fieldName, body) {
  * @param reducer
  * @param root
  */
-export function handleAddReducer(fieldName, reducer, root) {
+export function handleAddReducer(fieldName, {body, reduce}, root) {
     if (!root.hasReducerNode(fieldName)) {
-        let reducerNode = new ReducerNode(fieldName, reducer);
-        root.add(reducerNode);
-        reducerNode.scheduledForDeletion = true;
+        let childReducerNode = new ReducerNode(fieldName, {body, reduce});
+        root.add(childReducerNode);
+        childReducerNode.scheduledForDeletion = true;
 
-        _.each(reducer.body, (body, fieldName) => {
-            handleAddElement(root, fieldName, body);
+        _.each(childReducerNode.body, (body, fieldName) => {
+            handleAddElement(childReducerNode, root, fieldName, body);
         })
     }
 }