From 17901a10325e6c70d9b92ac1d86d3bc99b043299 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Sat, 15 Feb 2020 09:28:44 -0800
Subject: [PATCH] oker

---
 quad/quadwriter/query.rkt | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/quad/quadwriter/query.rkt b/quad/quadwriter/query.rkt
index c0f6df28..82362034 100644
--- a/quad/quadwriter/query.rkt
+++ b/quad/quadwriter/query.rkt
@@ -39,12 +39,12 @@
       ;; if lidx is bigger, search backward
       [(> start-arg end-arg) (values start-arg (sub1 end-arg) -1)]
       [else (values start-arg (add1 end-arg) 1)]))
-  (for/fold ([start-adjusted (- start step)]) ; remove step for reason below
+  (for/fold ([adjusted-start (- start step)]) ; remove step for reason below
             ([seen (in-range count)]
-             #:break (not start-adjusted))
+             #:break (not adjusted-start))
     ;; add step so we find next matcher
     ;; and won't re-find the last one immediately
-    (for/first ([idx (in-range (+ start-adjusted step) end step)]
+    (for/first ([idx (in-range (+ adjusted-start step) end step)]
                 #:when (pred (vector-ref vec idx)))
       idx)))
 
@@ -57,21 +57,28 @@
              #:result (and vidx (vector-ref vec vidx)))
             ([query-piece (in-list (parse-query query-str))]
              #:break (not vidx))
-    (match-define (cons pred count) query-piece)
+    (match-define (cons pred subscript) query-piece)
+    (define (find start end count) (find-inclusive vec pred start end count))
     (define res-idx
-      (match count
-        [(== 'this eq?) ; start at querying quad, then search backward
-         (find-inclusive vec pred (vector-memq starting-q vec) 0)]
-        [(== 'last eq?) ; search backward from end
-         (find-inclusive vec pred maxidx 0)]
-        [(== 'prev eq?) (find-inclusive vec pred (vector-memq starting-q vec) 0 2)]
-        [(== 'next eq?) (find-inclusive vec pred ((if (pred starting-q) add1 values) (vector-memq starting-q vec)) maxidx)]
-        [count (find-inclusive vec pred vidx maxidx count)]))
+      (let loop ([subscript subscript])
+        (match subscript
+          [(== 'this eq?) ; start at querying quad, then search 1 back
+           (find (vector-memq starting-q vec) 0 1)]
+          [(== 'last eq?) (loop -1)]
+          [(== 'prev eq?) ; search 2 back. same algo if starting-q is pred or not.
+           (find (vector-memq starting-q vec) 0 2)]
+          [(== 'next eq?) ; search 1 ahead, but if starting-q is also pred, search 2 ahead
+           (find (vector-memq starting-q vec) maxidx (if (pred starting-q) 2 1))]
+          [(? negative? count) ; search backward from end
+           (find maxidx vidx (abs count))]
+          [(? positive? count) ; seach forward
+           (find vidx maxidx count)]
+          [_ #false])))
     (define next-maxidx
       (cond
         [(not res-idx) maxidx]
         ;; try searching for next occurence after this one, up to max.
-        [(find-inclusive vec pred (add1 res-idx) maxidx)]
+        [(find (add1 res-idx) maxidx 1)]
         [else maxidx]))
     (values res-idx next-maxidx)))
           
@@ -112,5 +119,8 @@
                 (count (query doc "page[1]")))
   (check-equal? (count (query doc "page[next]" (query doc "page[2]:line[1]")))
                 (count (query doc "page[3]")))
+
+  (check-equal? (count (query doc "page[next]" (query doc "page[2]:line[1]")))
+                (count (query doc "page[3]")))
   
   )
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