Updated local storage

src/layout_store.hpp

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+namespace udpscope {
+
+/// The user-arranged part of a session, persisted per data source in
+/// `~/.config/udpscope/<host>_<port>.toml`: the display window, the plot layout
+/// (rows and which signal each of a row's slots holds) and the per-signal
+/// calibration. Signal names are the stable identity (channel indexes are
+/// renumbered by every enable/disable, see the model's own invariant).
+struct LayoutState {
+  struct Row {
+    /// One entry per slot; an empty string is an empty slot.
+    std::vector<std::string> signals;
+  };
+
+  double window_s = 0.0;  ///< 0 keeps the default window
+  std::vector<Row> rows;
+
+  struct Calibration {
+    std::string name;
+    double gain = 1.0;
+    double offset = 0.0;
+  };
+  std::vector<Calibration> calibration;
+};
+
+/// `~/.config/udpscope/<host>_<port>.toml`, with the directory created.
+/// Characters unsafe in a filename are replaced in the host part.
+std::string layout_path(const std::string& host, std::uint16_t port);
+
+/// Parses the file's TOML subset. Returns false when the file is missing or
+/// malformed; `out` is left usable either way (a malformed file loads as much as
+/// parsed, which beats refusing a hand-edited file over one stray character).
+bool load_layout(const std::string& path, LayoutState& out);
+
+/// Writes `state` as TOML. Atomic in effect: writes a sibling temp file and
+/// renames it over the target.
+bool save_layout(const std::string& path, const LayoutState& state);
+
+}  // namespace udpscope