From 1b0cc0a100a3c6d19a36c1927bc3b64697700b25 Mon Sep 17 00:00:00 2001
From: Tommi Reiman <tommi@iki.fi>
Date: Mon, 27 Apr 2020 08:38:27 +0300
Subject: [PATCH] Faster path conflict resolution, O(n2) -> O(n)

---
 modules/reitit-core/src/reitit/impl.cljc      | 17 ++++++++-------
 modules/reitit-core/src/reitit/trie.cljc      | 21 ++++++++++---------
 .../clj/reitit/router_creation_perf_test.clj  |  2 ++
 3 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/modules/reitit-core/src/reitit/impl.cljc b/modules/reitit-core/src/reitit/impl.cljc
index 3e58e48b..cc902295 100644
--- a/modules/reitit-core/src/reitit/impl.cljc
+++ b/modules/reitit-core/src/reitit/impl.cljc
@@ -74,14 +74,15 @@
            coerce (into [] (keep #(coerce % opts)))))
 
 (defn path-conflicting-routes [routes opts]
-  (-> (into {}
-            (comp (map-indexed (fn [index route]
-                                 [route (into #{}
-                                              (filter #(trie/conflicting-paths? (first route) (first %) opts))
-                                              (subvec routes (inc index)))]))
-                  (filter (comp seq second)))
-            routes)
-      (not-empty)))
+  (let [parts-and-routes (mapv (fn [[s :as r]] [(trie/split-path s opts) r]) routes)]
+    (-> (into {} (comp (map-indexed (fn [index [p r]]
+                                      [r (reduce
+                                           (fn [acc [p' r']]
+                                             (if (trie/conflicting-parts? p p')
+                                               (conj acc r') acc))
+                                           #{} (subvec parts-and-routes (inc index)))]))
+                       (filter (comp seq second))) parts-and-routes)
+        (not-empty))))
 
 (defn unresolved-conflicts [path-conflicting]
   (-> (into {}
diff --git a/modules/reitit-core/src/reitit/trie.cljc b/modules/reitit-core/src/reitit/trie.cljc
index c4622b53..bbd1aded 100644
--- a/modules/reitit-core/src/reitit/trie.cljc
+++ b/modules/reitit-core/src/reitit/trie.cljc
@@ -132,17 +132,18 @@
       (concat [(subs x i)] xs)
       xs)))
 
+(defn conflicting-parts? [parts1 parts2]
+  (let [[[s1 & ss1] [s2 & ss2]] (-slice-start parts1 parts2)]
+    (cond
+      (= s1 s2 nil) true
+      (or (nil? s1) (nil? s2)) false
+      (or (catch-all? s1) (catch-all? s2)) true
+      (or (wild? s1) (wild? s2)) (recur (-slice-end s1 ss1) (-slice-end s2 ss2))
+      (not= s1 s2) false
+      :else (recur ss1 ss2))))
+
 (defn conflicting-paths? [path1 path2 opts]
-  (loop [parts1 (split-path path1 opts)
-         parts2 (split-path path2 opts)]
-    (let [[[s1 & ss1] [s2 & ss2]] (-slice-start parts1 parts2)]
-      (cond
-        (= s1 s2 nil) true
-        (or (nil? s1) (nil? s2)) false
-        (or (catch-all? s1) (catch-all? s2)) true
-        (or (wild? s1) (wild? s2)) (recur (-slice-end s1 ss1) (-slice-end s2 ss2))
-        (not= s1 s2) false
-        :else (recur ss1 ss2)))))
+  (conflicting-parts? (split-path path1 opts) (split-path path2 opts)))
 
 ;;
 ;; Creating Tries
diff --git a/perf-test/clj/reitit/router_creation_perf_test.clj b/perf-test/clj/reitit/router_creation_perf_test.clj
index 9349d128..4f812575 100644
--- a/perf-test/clj/reitit/router_creation_perf_test.clj
+++ b/perf-test/clj/reitit/router_creation_perf_test.clj
@@ -40,6 +40,7 @@
   (suite "non-conflicting")
 
   ;; 104ms
+  ;;  11ms (reuse parts in conflict resolution)
   (bench! "default" (r/router hundred-routes))
 
   ;; 7ms
@@ -50,6 +51,7 @@
 
     ;; 205ms
     ;; 105ms (cache path-conflicts)
+    ;;  13ms (reuse parts in conflict resolution)
     (bench! "default" (r/router routes {:conflicts nil}))))
 
 (comment