Add a line content iterator.

src/vase/line_iter.cc

@@ -0,0 +1,98 @@
+#include "vase/line_iter.h"
+
+LineIterator::LineIterator(Shard *r, uint32_t start_line) : root(r) {
+  if (!root)
+    return;
+  Shard::retain(root);
+  seek_line(start_line);
+}
+
+LineIterator::~LineIterator() {
+  Shard::release(root);
+}
+
+void LineIterator::descend(Shard *s) {
+  while (s->kind == Shard::ShardKind::Branch) {
+    auto *b = static_cast<Branch *>(s);
+    stack.push_back(b);
+    s = b->left;
+  }
+  petal = static_cast<Petal *>(s);
+  petal_offset = 0;
+}
+
+bool LineIterator::advance_petal() {
+  while (!stack.empty()) {
+    Branch *top = stack.back();
+    stack.pop_back();
+    descend(top->right);
+    if (petal->length > 0)
+      return true;
+  }
+  petal = nullptr;
+  return false;
+}
+
+void LineIterator::seek_line(uint32_t line_index) {
+  stack.clear();
+  if (line_index == 0) {
+    descend(root);
+    return;
+  }
+  uint32_t nth = line_index; // we want the position right after the nth '\n' (1-indexed)
+  Shard *s = root;
+  while (s->kind == Shard::ShardKind::Branch) {
+    auto *b = static_cast<Branch *>(s);
+    if (nth <= b->left->lines) {
+      stack.push_back(b); // still need to visit b->right later
+      s = b->left;
+    } else {
+      nth -= b->left->lines; // left fully skipped, don't revisit it
+      s = b->right;
+    }
+  }
+  petal = static_cast<Petal *>(s);
+  uint32_t nl_pos = petal->source->nth_newline(petal->pos, nth);
+  petal_offset = (nl_pos - petal->pos) + 1;
+  if (petal_offset >= petal->length)
+    advance_petal();
+}
+
+bool LineIterator::next(std::string &line) {
+  line.clear();
+  if (!petal)
+    return false;
+
+  bool produced = false;
+  while (petal) {
+    produced = true;
+    uint32_t abs_pos = petal->pos + petal_offset;
+    uint32_t petal_end = petal->pos + petal->length;
+
+    uint32_t nl = petal->source->next_newline(abs_pos);
+    uint32_t stop = (nl != UINT32_MAX && nl < petal_end) ? nl : petal_end;
+
+    uint32_t remaining = stop - abs_pos;
+    uint32_t cur = abs_pos;
+    while (remaining) {
+      uint32_t got;
+      const char *data = petal->source->read(cur, &got);
+      uint32_t take = std::min(got, remaining);
+      line.append(data, take);
+      cur += take;
+      remaining -= take;
+    }
+    petal_offset = cur - petal->pos;
+
+    if (stop == nl) {
+      petal_offset += 1;
+      if (petal_offset >= petal->length)
+        advance_petal();
+      return true;
+    }
+
+    if (!advance_petal())
+      break;
+  }
+  return produced;
+}