🚧 WIP

src/opcda_diagnozer/report/jsonl.py

@@ -1,25 +1,77 @@
 """Rotating JSONL reporter — the primary evidence trail (IMPLEMENTATION_PLAN §5.1).
 
-Phase 2 adds: size-based rotation with ``backups`` kept, atomic-ish append,
-and a header line carrying the config digest for provenance.
+One JSON event per line (spec §8), size-based rotation with ``backups`` kept,
+and a header line per file carrying the config digest for provenance — so a
+rotated file can always be traced to the exact thresholds that produced it.
+
+Appends are "atomic-ish": one pre-serialized line + newline, flushed. A hard
+kill can at worst lose the current line, never corrupt earlier ones (event
+lines are a few hundred bytes — single small appends, not torn writes).
 """
 
 from __future__ import annotations
 
+import hashlib
+import json
 from pathlib import Path
 
+from opcda_diagnozer.config import Config
 from opcda_diagnozer.events import DiagEvent
 
 
-class JsonlReporter:
-    """One JSON event per line, rotated by size — implemented in Phase 2."""
+def config_digest(config: Config) -> str:
+    """Stable SHA-256 over the effective config (provenance for log headers)."""
+    payload = json.dumps(config, default=lambda o: getattr(o, "__dict__", str(o)),
+                         sort_keys=True)
+    return hashlib.sha256(payload.encode("utf-8")).hexdigest()
 
-    def __init__(self, directory: str | Path, max_mb: int = 50, backups: int = 10) -> None:
+
+def rotate_file(path: Path, backups: int) -> None:
+    """Size-rotation used by both file reporters: ``p`` -> ``p.1`` … ``p.backups``.
+
+    The oldest copy is dropped; numbering shifts by one so ``p.1`` is always
+    the most recently closed file. Shared so the JSONL and text reporters
+    guarantee identical retention semantics (spec §9.1).
+    """
+    if not path.exists():
+        return
+    for index in range(backups - 1, 0, -1):
+        older = path.with_name(f"{path.name}.{index}")
+        if older.exists():
+            older.replace(path.with_name(f"{path.name}.{index + 1}"))
+    path.replace(path.with_name(f"{path.name}.1"))
+
+
+class JsonlReporter:
+    """One JSON event per line, rotated by size (spec §9)."""
+
+    def __init__(self, directory: str | Path, max_mb: int = 50, backups: int = 10,
+                 digest: str = "") -> None:
         self._directory = Path(directory)
-        self._max_mb = max_mb
+        self._max_bytes = max_mb * 1024 * 1024
         self._backups = backups
+        self._digest = digest
+        self._directory.mkdir(parents=True, exist_ok=True)
+        self._current = self._directory / "events.jsonl"
 
     def emit(self, event: DiagEvent) -> None:
-        raise NotImplementedError(
-            "Phase 2: JSONL reporter (docs/IMPLEMENTATION_PLAN.md §5.1)"
-        )
+        """Append one event; rotate first when the file would exceed the cap."""
+        line = event.to_json()
+        needs_header = not self._current.exists()
+        if self._current.exists() and (
+            self._current.stat().st_size + len(line) + 2 > self._max_bytes
+        ):
+            rotate_file(self._current, self._backups)
+            needs_header = True
+        with self._current.open("a", encoding="utf-8") as stream:
+            if needs_header:
+                header = {
+                    "header": True,
+                    "format": "opcda-diagnozer events v1",
+                    "config_sha256": self._digest,
+                }
+                stream.write(json.dumps(header) + "\n")
+            stream.write(line + "\n")
+
+    def close(self) -> None:
+        """Lifecycle symmetry with the other reporters (nothing to release)."""