Upload session logger

session_logger.py

@@ -0,0 +1,64 @@
+"""
+session_logger.py
+Phase 1: logs the live gaze stream to a per session file.
+
+Writes one line of JSON per frame to:
+    sessions/live/gaze_log.jsonl
+
+Fields per line:
+    t       wall clock seconds (time.time()). Same epoch the browser uses
+            via Date.now()/1000, so gaze and DOM logs align by time.
+    sx, sy  gaze in calibration screen space (SCREEN_W x SCREEN_H)
+    fx, fy  gaze as a fraction of the screen (0..1). Phase 4 multiplies
+            these by the browser viewport size to land on a real element.
+
+The file is truncated on each run, so one tracker run equals one clean session.
+"""
+
+import os
+import json
+import time
+
+
+class GazeLogger:
+    def __init__(self, screen_w, screen_h, session_dir=os.path.join("sessions", "live")):
+        self.screen_w = float(screen_w)
+        self.screen_h = float(screen_h)
+
+        os.makedirs(session_dir, exist_ok=True)
+        self.session_dir = session_dir
+        self.gaze_path = os.path.join(session_dir, "gaze_log.jsonl")
+
+        # "w" truncates: each run starts a fresh gaze log
+        self._f = open(self.gaze_path, "w", buffering=1)
+
+        meta = {
+            "type": "meta",
+            "screen_w": screen_w,
+            "screen_h": screen_h,
+            "t": round(time.time(), 4),
+        }
+        self._f.write(json.dumps(meta) + "\n")
+        print(f"[GazeLogger] writing gaze stream to {self.gaze_path}")
+
+    def log(self, sx, sy, t=None):
+        if t is None:
+            t = time.time()
+        fx = sx / self.screen_w if self.screen_w else 0.0
+        fy = sy / self.screen_h if self.screen_h else 0.0
+        rec = {
+            "type": "gaze",
+            "t": round(t, 4),
+            "sx": round(float(sx), 2),
+            "sy": round(float(sy), 2),
+            "fx": round(float(fx), 5),
+            "fy": round(float(fy), 5),
+        }
+        self._f.write(json.dumps(rec) + "\n")
+
+    def close(self):
+        try:
+            self._f.close()
+            print(f"[GazeLogger] gaze log closed: {self.gaze_path}")
+        except Exception:
+            pass