From 28d1866cb813d4b21880a154ffaa139c6103667b Mon Sep 17 00:00:00 2001
From: Correl Roush <correl@gmail.com>
Date: Fri, 4 Dec 2015 23:06:38 -0500
Subject: [PATCH] Re-implement group-topo using streams

---
 git-graph-tests.el | 26 +++++++++++++++++++++++---
 git-graph.el       | 32 +++++++++++++++++++++++++++++---
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/git-graph-tests.el b/git-graph-tests.el
index 3141f69..1050328 100644
--- a/git-graph-tests.el
+++ b/git-graph-tests.el
@@ -24,12 +24,13 @@
 ;;; Code:
 
 (require 'ert)
+(require 'stream)
 (require 'git-graph)
 
 ;; 1---2---5---6---7 [master]
 ;;      \     /
 ;;       3---4 [topic]
-(ert-deftest automatically-group-nodes ()
+(ert-deftest automatically-group-nodes-list ()
   (let* ((example-graph
           (git-graph/group-topo
            (list (git-graph/make-node 7 '(6) '((label . master)))
@@ -45,7 +46,26 @@
          (topic-nodes (seq-map #'git-graph/node-id
                                (seq-filter (lambda (node) (eq 4 (git-graph/node-group node)))
                                            example-graph))))
-    (should (equal '(7 6 5 2 1) master-nodes))
-    (should (equal '(4 3) topic-nodes))))
+    (should (equal '(7 6 5 2 1) (seq-into-sequence master-nodes)))
+    (should (equal '(4 3) (seq-into-sequence topic-nodes)))))
+
+(ert-deftest automatically-group-nodes-stream ()
+  (let* ((example-graph
+          (git-graph/group-topo
+           (stream (list (git-graph/make-node 7 '(6) '((label . master)))
+                         (git-graph/make-node 6 '(5 4))
+                         (git-graph/make-node 5 '(2))
+                         (git-graph/make-node 4 '(3) '((label . topic)))
+                         (git-graph/make-node 3 '(2))
+                         (git-graph/make-node 2 '(1))
+                         (git-graph/make-node 1 '())))))
+         (master-nodes (seq-map #'git-graph/node-id
+                                (seq-filter (lambda (node) (eq 7 (git-graph/node-group node)))
+                                            example-graph)))
+         (topic-nodes (seq-map #'git-graph/node-id
+                               (seq-filter (lambda (node) (eq 4 (git-graph/node-group node)))
+                                           example-graph))))
+    (should (equal '(7 6 5 2 1) (seq-into-sequence master-nodes)))
+    (should (equal '(4 3) (seq-into-sequence topic-nodes)))))
 
 ;;; git-graph-tests.el ends here
diff --git a/git-graph.el b/git-graph.el
index 7be0bf0..7d3a90e 100644
--- a/git-graph.el
+++ b/git-graph.el
@@ -115,7 +115,7 @@
 (defun git-graph/group-topo (nodelist)
   (reverse
    (car
-    (-reduce-from
+    (seq-reduce
      (lambda (acc node)
        (let* ((grouped-nodes (car acc))
               (group-stack (cdr acc))
@@ -135,8 +135,34 @@
                                       (label . ,(git-graph/node-label node))))
                      grouped-nodes)
                group-stack)))
-     nil
-     nodelist))))
+     nodelist
+     nil))))
+
+(defun git-graph/group-topo (nodes)
+  (let ((node-stream (if (streamp nodes) nodes
+                       (stream nodes))))
+    (git-graph/group-topo--with-stack node-stream '())))
+
+(defun git-graph/group-topo--with-stack (node-stream group-stack)
+  (unless (stream-empty-p node-stream)
+    (let* ((node (stream-first node-stream))
+           (rest (stream-rest node-stream))
+           (node-id (git-graph/node-id node))
+           (group-from-stack (--if-let (assoc node-id group-stack)
+                                 (cdr it)))
+           (group (or group-from-stack node-id))
+           (parents (git-graph/node-parents node))
+           (first-parent (first parents)))
+      (if group-from-stack
+          (pop group-stack))
+      (if (and first-parent (not (assoc first-parent group-stack)))
+          (push (cons first-parent group) group-stack))
+      (stream-cons
+       (git-graph/make-node node-id
+                            parents
+                            `((group . ,group)
+                              (label . ,(git-graph/node-label node))))
+       (git-graph/group-topo--with-stack rest group-stack)))))
 
 (defun git-graph/git-execute (repo-url command &rest args)
   (with-temp-buffer