Added ValueBuffer implementation and simple recording

ValueBuffer is now the default buffer object for storing data for
recording and processing purposes, a simple recording implementation has
been done, core.py example starts recording as soon as the core has
started then on exit it saves the output as a csv file through the
ValueBuffer export_csv method

.gitignore

@@ -8,3 +8,7 @@ wheels/
 
 # Virtual environments
 .venv
+
+# Output files
+*.csv
+*.dlpak

src/dynalab_core/__init__.py

@@ -6,11 +6,11 @@ import logging
 from queue import Empty, Queue
 import threading
 from threading import Lock, Thread
-from time import monotonic, monotonic_ns, sleep
 from typing import Literal
 from uuid import UUID
 
 
+from dynalab_core.buffer import ValueBuffer
 from dynalab_core.config import CoreConfig
 from dynalab_core.constants import CORE_VERSION
 from dynalab_core.errors import CoreStateMismatchError
@@ -33,10 +33,10 @@ class Core:
             "unintid"
         )
         self._recording = threading.Event()
+        self._recording_buffer = ValueBuffer()
         self._core_version: VersionDescriptor = CORE_VERSION
         self._stop_event: threading.Event = threading.Event()
         self._core_config: CoreConfig = config
-        # TODO: Implement live values dict
         self._live_values: dict[UUID, Value] = {}
         self._live_values_lock = Lock()
 
@@ -105,10 +105,12 @@ class Core:
         )
 
     def start_recording(self) -> None:
+        self._recording_buffer.clear()
         self._recording.set()
 
     def stop_recording(self) -> None:
         self._recording.clear()
+        self._recording_buffer.export_csv("output.csv")
 
     def get_signal_descriptor(self, signal_id: UUID) -> SignalDescriptor | None:
         return self._connector_registry.get_signal_descriptor(signal_id)
@@ -155,3 +157,7 @@ class Core:
                         self._live_values[message.signal_id] = live_value
 
                 live_value.update(message.value, message.timestamp)
+                if self._recording.is_set():
+                    self._recording_buffer.append(
+                        message.timestamp, message.signal_id, message.value
+                    )

src/dynalab_core/buffer.py

@@ -0,0 +1,60 @@
+# Copyright (C) 2026 Hector van der Aa <hector@h3cx.dev>
+# Copyright (C) 2026 Association Exergie <association.exergie@gmail.com>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from collections import defaultdict
+import csv
+from pathlib import Path
+from threading import Lock
+from uuid import UUID
+
+
+class ValueBuffer:
+    def __init__(self) -> None:
+        self._samples: list[tuple[int, UUID, float]] = []
+        self._lock = Lock()
+
+    def append(self, timestamp: int, uuid: UUID, value: float) -> None:
+        with self._lock:
+            self._samples.append((timestamp, uuid, value))
+
+    def clear(self) -> None:
+        with self._lock:
+            self._samples.clear()
+
+    def __len__(self) -> int:
+        with self._lock:
+            return len(self._samples)
+
+    def export_csv(self, path: str | Path) -> None:
+        with self._lock:
+            samples = list(self._samples)
+
+        rows: dict[int, dict[UUID, float]] = defaultdict(dict)
+        signal_ids: set[UUID] = set()
+
+        for timestamp_ns, signal_id, value in samples:
+            rows[timestamp_ns][signal_id] = value
+            signal_ids.add(signal_id)
+
+        ordered_signal_ids = sorted(signal_ids, key=str)
+
+        with Path(path).open(mode="w", newline="", encoding="utf-8") as file:
+            writer = csv.writer(file)
+
+            writer.writerow(
+                ["timestamp_ns", *(str(signal_id) for signal_id in ordered_signal_ids)]
+            )
+
+            for timestamp_ns in sorted(rows):
+                timestamp_values = rows[timestamp_ns]
+
+                writer.writerow(
+                    [
+                        timestamp_ns,
+                        *(
+                            timestamp_values.get(signal_id, "")
+                            for signal_id in ordered_signal_ids
+                        ),
+                    ]
+                )

test/manual/core.py

@@ -19,6 +19,7 @@ config = CoreConfig(port=8765)
 log.info("Configured manual core on %s", config.bind_str())
 dl_core = Core(config)
 dl_core.start()
+dl_core.start_recording()
 
 try:
     while True:
@@ -27,4 +28,5 @@ try:
         log.debug(f"Core values: {values}")
 except KeyboardInterrupt:
     log.info("Received keyboard interrupt")
+    dl_core.stop_recording()
     dl_core.stop()

test/manual/peer.py

@@ -116,24 +116,12 @@ def value_sender_thread(
 
                 next_send_time += period
 
-            value = ValueDescriptor(
-                signal_id=signal_id, value=2.0, timestamp=monotonic_ns()
-            )
-
-            message = ValueBatch(
-                values=[
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                    value,
-                ]
-            )
+            message = ValueBatch(values=[])
+            for i in range(10):
+                value = ValueDescriptor(
+                    signal_id=signal_id, value=2.0, timestamp=monotonic_ns()
+                )
+                message.values.append(value)
 
             future = asyncio.run_coroutine_threadsafe(
                 send_message(