From 5f3fea525ded153e2ceb244b14b41bbf2afd5bc5 Mon Sep 17 00:00:00 2001
From: Ekaitz Zarraga <ekaitz@elenq.tech>
Date: Thu, 18 Jan 2024 14:46:22 +0100
Subject: par: piece-table: add substring and rewrite ->string

Now ->string is rewritten in terms of substring, but later we'll need to
rewrite this in a more generic way
---
 par/piece-table.scm   | 20 ++++++++++++--------
 par/piece-table.sld   |  1 +
 tests/piece-table.scm |  9 +++++++++
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/par/piece-table.scm b/par/piece-table.scm
index a9b61f1..2892578 100644
--- a/par/piece-table.scm
+++ b/par/piece-table.scm
@@ -262,16 +262,20 @@
 ;; From/to string
 (define string->piece-table make-piece-table)
 
-(define (piece-table->string piece-table)
-  (let ((out-string (make-string (piece-table-text-length piece-table))))
+(define (piece-table-substring piece-table from to)
+  (let ((out-string (make-string (- to from))))
     (let loop ((pieces (piece-table-pieces piece-table))
                (acc    0))
-      (if (null? pieces)
+      (if (or (null? pieces) (>= acc to))
         out-string
         (let ((piece (car pieces)))
-          (string-copy! out-string
-                        acc
-                        (buffer->string (piece-buffer piece))
-                        (piece-start piece)
-                        (+ (piece-start piece) (piece-length piece)))
+          (string-copy!
+            out-string
+            (max (- acc from) 0)
+            (buffer->string (piece-buffer piece))
+            (+ (piece-start piece) (max (- from acc) 0))
+            (+ (piece-start piece) (min (- to acc) (piece-length piece))))
           (loop (cdr pieces) (+ acc (piece-length piece))))))))
+
+(define (piece-table->string piece-table)
+  (piece-table-substring piece-table 0 (piece-table-text-length piece-table)))
diff --git a/par/piece-table.sld b/par/piece-table.sld
index 420175f..4650cb7 100644
--- a/par/piece-table.sld
+++ b/par/piece-table.sld
@@ -7,6 +7,7 @@
           piece-table-insert!
           piece-table-delete!
           piece-table->string
+          piece-table-substring
           string->piece-table
           add-buffer-length)
   (include "piece-table.scm"))
diff --git a/tests/piece-table.scm b/tests/piece-table.scm
index d6c1105..317286c 100644
--- a/tests/piece-table.scm
+++ b/tests/piece-table.scm
@@ -21,6 +21,15 @@
   (test-equal "HOLA910" (piece-table->string table))
 (test-end "insert")
 
+(test-begin "substring")
+  (parameterize ((add-buffer-length 10))
+    (define table (make-piece-table "1234567890"))
+    (test-equal  "1234567890" (piece-table-substring table 0 10))
+    (test-equal  "67890" (piece-table-substring table 5 10))
+    (piece-table-insert! table 6 "X" 'normal)
+    (test-equal  "6X78" (piece-table-substring table 5 9)))
+(test-end "substring")
+
 (test-begin "delete")
   (define table (make-piece-table "HOLA SOY EKAITZ"))
   (piece-table-delete! table 4 1)
-- 
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