"""CsvTelemetryLogger — writes telemetry snapshots to a CSV file with throttling.

Design decisions:
- Does NOT use the logging module — writes directly via csv.writer so the file
  is readable independently of the text log level.
- Flushes after every row so the file is intact even on crash or force-quit.
- Throttle: only one row per TELEMETRY_CSV_INTERVAL_S seconds, even if
  metrics_updated fires every 500 ms.  This keeps the file manageable for
  long sessions (8 h @ 5 s interval = 5 760 rows).
"""

from __future__ import annotations

import csv
import time
from datetime import datetime
from pathlib import Path

from app.config import TELEMETRY_CSV_INTERVAL_S
from app.telemetry.telemetry_collector import TelemetrySnapshot

_CSV_HEADER = [
    "timestamp",
    "fps_got",
    "fps_req",
    "frame_time_ms",
    "dropped_frames",
    "cpu_sys_pct",
    "cpu_core_pct",
    "mem_mb",
]


class CsvTelemetryLogger:
    """
    Receives TelemetrySnapshot objects and writes throttled rows to a CSV file.

    Usage:
        logger = CsvTelemetryLogger(path)
        telemetry_collector.metrics_updated.connect(logger.on_metrics_updated)
        # call logger.close() on application exit
    """

    def __init__(
        self,
        path: Path,
        interval_s: float = TELEMETRY_CSV_INTERVAL_S,
    ) -> None:
        self._interval_s = interval_s
        self._last_write_time: float = 0.0
        self._rows_written: int = 0

        path.parent.mkdir(parents=True, exist_ok=True)
        self._file = path.open("w", newline="", encoding="utf-8")
        self._writer = csv.writer(self._file)
        self._writer.writerow(_CSV_HEADER)
        self._file.flush()

    # ------------------------------------------------------------------
    # Slot — connect to TelemetryCollector.metrics_updated
    # ------------------------------------------------------------------

    def on_metrics_updated(self, snapshot: TelemetrySnapshot) -> None:
        """Write a row if the throttle interval has elapsed."""
        now = time.monotonic()
        if now - self._last_write_time < self._interval_s:
            return
        self._last_write_time = now
        self._write_row(snapshot)

    # ------------------------------------------------------------------
    # Lifecycle
    # ------------------------------------------------------------------

    def close(self) -> None:
        """Flush and close the CSV file. Call on application shutdown."""
        try:
            self._file.flush()
            self._file.close()
        except OSError:
            pass

    @property
    def rows_written(self) -> int:
        return self._rows_written

    # ------------------------------------------------------------------
    # Private
    # ------------------------------------------------------------------

    def _write_row(self, snap: TelemetrySnapshot) -> None:
        ts = datetime.now().strftime("%H:%M:%S.%f")[:-3]  # HH:MM:SS.mmm
        self._writer.writerow([
            ts,
            f"{snap.fps:.1f}",
            f"{snap.target_fps:.1f}" if snap.target_fps is not None else "",
            f"{snap.frame_time_ms:.2f}",
            snap.dropped_frames,
            f"{snap.cpu_percent_sys:.1f}",
            f"{snap.cpu_percent_core:.1f}",
            f"{snap.memory_mb:.1f}" if snap.memory_mb is not None else "",
        ])
        self._file.flush()
        self._rows_written += 1