initial runs

src/merge_sorter.cpp

@@ -0,0 +1,46 @@
+#include "../include/merge_sorter.hpp"
+
+size_t MergeSorter::create_initial_runs(const std::string& input_file)
+{
+    FileReader reader(input_file);
+    std::span<Record> chunk(buffer_);
+    size_t run_count = 0;
+
+    for (run_count = 0;; run_count++) {
+        size_t records_read = reader.read_chunk(chunk);
+        if (records_read == 0) {
+            break;
+        }
+
+        std::sort(chunk.begin(), chunk.begin() + records_read);
+
+        std::string run_file = tmp_dir_ + "pass0/run_" + std::to_string(run_count) + ".dat";
+        FileWriter writer(run_file);
+        auto output = std::span<const Record>(chunk.data(), records_read);
+        writer.write_chunk(output);
+
+        disk_reads_ += reader.total_reads() - disk_reads_;
+        disk_writes_ += writer.total_writes() - disk_writes_;
+    }
+
+    return run_count;
+}
+MergeSorter::MergeSorter(size_t buffer_rows, size_t buffer_cols, const std::string& tmp_dir)
+    : buffer_(buffer_rows * buffer_cols)
+    , tmp_dir_(tmp_dir)
+    , buffer_rows(buffer_rows)
+    , disk_reads_(0)
+    , disk_writes_(0)
+    , phases_(0)
+{
+    if (buffer_rows < 3) {
+        throw std::invalid_argument("Buffer must have at least 3 rows for merging");
+    }
+}
+
+bool MergeSorter::sort_file(const std::string& input_file, const std::string& output_file)
+{
+    create_initial_runs(input_file);
+    std::cout << output_file << '\n';
+    return true;
+}