Fix bug in split and add line->byte lookup.

include/vase/vase.h

@@ -105,4 +105,6 @@ struct Vase {
       flatten(b->right, out);
     }
   }
+
+  uint32_t offset_of(uint32_t line_number, uint32_t col);
 };

src/main.cc

@@ -26,10 +26,12 @@ int main() {
   vase.type(7, '3');
   vase.type(8, '4');
 
-  vase.erase(9, -2);
+  vase.erase(vase.offset_of(7, 3), -3);
 
   print_shard(vase.root);
 
+  std::cout << (int)vase.offset_of(6, 0) << "\n\n";
+
   LineIterator it(vase.root, 3);
   std::string line;
   while (it.next(line))

src/vase/shard.cc

@@ -125,13 +125,13 @@ std::pair<Shard *, Shard *> split_shard(Shard *n, uint32_t offset) {
     Petal *p = (Petal *)n;
     auto left = new Petal(
       offset,
-      p->source->count_lines(0, offset),
+      p->source->count_lines(p->pos, offset),
       p->source,
       p->pos
     );
     auto right = new Petal(
       p->length - offset,
-      p->source->count_lines(offset, p->length),
+      p->source->count_lines(p->pos + offset, p->length - offset),
       p->source,
       p->pos + offset
     );

src/vase/vase.cc

@@ -0,0 +1,26 @@
+#include "vase/vase.h"
+
+uint32_t Vase::offset_of(uint32_t line_number, uint32_t col) {
+  if (line_number == 0)
+    return col;
+
+  Shard *s = root;
+  uint32_t nth = line_number;
+  uint32_t base_offset = 0;
+
+  while (s->kind == Shard::ShardKind::Branch) {
+    auto *b = static_cast<Branch *>(s);
+    if (nth <= b->left->lines) {
+      s = b->left;
+    } else {
+      nth -= b->left->lines;
+      base_offset += b->left->length;
+      s = b->right;
+    }
+  }
+
+  auto *petal = static_cast<Petal *>(s);
+  uint32_t nl_pos = petal->source->nth_newline(petal->pos, nth);
+  uint32_t offset_in_petal = (nl_pos - petal->pos) + 1;
+  return base_offset + offset_in_petal + col;
+}