1 files changed, 127 insertions, 0 deletions
diff --git a/src/line.cc b/src/line.cc
new file mode 100644
index 0000000..23370fc
--- /dev/null
+++ b/src/line.cc
@@ -0,0 +1,127 @@
+#include "line.hh"
+
+#include "check.hh"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <expected>
+#include <memory>
+#include <string_view>
+#include <utility>
+
+namespace line {
+
+namespace {
+
+const char kLineTerminators[] = "\r\n";
+
+class ReaderImpl : public Reader {
+ public:
+  ReaderImpl(std::unique_ptr<io::Reader> reader, size_t max_len)
+      : reader_(std::move(reader)),
+        max_len_(max_len),
+        buffer_(std::make_unique_for_overwrite<char[]>(
+            check::add(max_len, static_cast<size_t>(2)))),
+        rptr_(buffer_.get()),
+        wptr_(buffer_.get()),
+        search_(rptr_),
+        end_(buffer_.get() + check::add(max_len, static_cast<size_t>(2))) {}
+
+  [[nodiscard]] std::expected<std::string_view, io::ReadError> read() override {
+    while (true) {
+      search_ = std::find_first_of(search_, wptr_, kLineTerminators,
+                                   kLineTerminators + 2);
+      if (search_ < wptr_) {
+        if (std::cmp_greater(search_ - rptr_, max_len_)) {
+          return line(max_len_, 0);
+        }
+
+        size_t tlen;
+        if (*search_ == '\n') {
+          tlen = 1;
+        } else {
+          if (search_ + 1 == wptr_) {
+            make_space_if_needed();
+            auto got = fill();
+            if (!got.has_value()) {
+              if (got.error() == io::ReadError::Eof) {
+                return line(search_ - rptr_, 1);
+              }
+              return std::unexpected(got.error());
+            }
+          }
+          if (search_[1] == '\n') {
+            tlen = 2;
+          } else {
+            tlen = 1;
+          }
+        }
+        return line(search_ - rptr_, tlen);
+      }
+      if (std::cmp_greater_equal(wptr_ - rptr_, max_len_)) {
+        return line(max_len_, 0);
+      }
+
+      make_space_if_needed();
+      auto got = fill();
+      if (!got.has_value()) {
+        if (got.error() == io::ReadError::Eof && rptr_ != wptr_) {
+          return line(wptr_ - rptr_, 0);
+        }
+        return std::unexpected(got.error());
+      }
+    }
+  }
+
+  [[nodiscard]] uint64_t number() const override { return number_; }
+
+ private:
+  std::string_view line(size_t len, size_t terminator_len) {
+    assert(len <= max_len_);
+    auto ret = std::string_view(rptr_, len);
+    rptr_ += len + terminator_len;
+    search_ = rptr_;
+    ++number_;
+    return ret;
+  }
+
+  void make_space_if_needed() {
+    size_t free = rptr_ - buffer_.get();
+    if (free == 0)
+      return;
+    size_t avail = end_ - wptr_;
+    if (avail > 1024)
+      return;
+    memmove(buffer_.get(), rptr_, wptr_ - rptr_);
+    search_ -= free;
+    wptr_ -= free;
+    rptr_ = buffer_.get();
+  }
+
+  std::expected<size_t, io::ReadError> fill() {
+    auto ret = reader_->read(wptr_, end_ - wptr_);
+    if (ret.has_value())
+      wptr_ += ret.value();
+    return ret;
+  }
+
+  std::unique_ptr<io::Reader> reader_;
+  size_t const max_len_;
+  uint64_t number_{0};
+  std::unique_ptr<char[]> buffer_;
+  char* rptr_;
+  char* wptr_;
+  char* search_;
+  char* const end_;
+};
+
+}  // namespace
+
+std::unique_ptr<Reader> open(std::unique_ptr<io::Reader> reader,
+                             size_t max_len) {
+  return std::make_unique<ReaderImpl>(std::move(reader), max_len);
+}
+
+}  // namespace line