Make basic (unbalanced) insertion work.

include/vase/buffer/append.h

@@ -21,8 +21,8 @@ struct AppendBuffer : Buffer {
 
   ~AppendBuffer();
 
-  inline void key(char c);
-  void append(const char *text, uint32_t length);
+  inline uint32_t key(char c);
+  uint32_t append(const char *text, uint32_t length, uint32_t *line_count);
 
   const char *read(uint32_t pos, uint32_t *out_len);
   uint32_t count_lines(uint32_t pos, uint32_t length);
@@ -33,5 +33,5 @@ private:
 
   inline uint32_t find_newline(uint32_t target, uint32_t low, uint32_t high);
 
-  inline void _append(const char *text, uint32_t length);
+  inline uint32_t _append(const char *text, uint32_t length);
 };

include/vase/shard.h

@@ -66,6 +66,7 @@ struct Petal : Shard {
       : Shard(ShardKind::Petal, length, lines), source(source), pos(pos) {};
 };
 
-std::pair<ShardPtr, ShardPtr> split(Shard *n, uint32_t offset);
+std::pair<ShardPtr, ShardPtr> split_shard(Shard *n, uint32_t offset);
+ShardPtr concat_shard(ShardPtr left, ShardPtr right);
 
 void print_shard(const Shard *shard, int depth = 0);

include/vase/vase.h

@@ -25,4 +25,18 @@ struct Vase {
       0
     );
   }
+
+  void insert(uint32_t offset, const char *data, uint32_t len) {
+    uint32_t lines = 0;
+    uint32_t pos = append.append(data, len, &lines);
+
+    ShardPtr inserted = new Petal(len, lines, &append, pos);
+
+    auto [left, right] = split_shard(root.ptr, offset);
+
+    root = concat_shard(
+      concat_shard(left, inserted),
+      right
+    );
+  }
 };