"""
sfm/waveform_store.py — On-disk store for Blastware-format event files.

Layout (flat per-serial):

    <root>/<serial>/<filename>            ← event file (Blastware-readable binary)
    <root>/<serial>/<filename>.a5.pkl     ← pickled list of A5 S3Frame dicts

`<filename>` is whatever `minimateplus.blastware_file.blastware_filename`
produces for the event.  The extension is NOT a fixed type tag — it encodes
the event timestamp (`AB0T` format: 2-char base-36 of `total_seconds %
1296`, literal `0`, then `W`=Full Waveform / `H`=Full Histogram for ACH
downloads, or 3-char `AB0` for direct/manual downloads).  Every event's
filename therefore contains its own timestamp + record-type fingerprint and
collisions across the same physical event don't occur.

The `.a5.pkl` sidecar lets the event file be regenerated later if the
encoder changes — captures the raw 5A frame stream as serializable dicts so
the schema isn't tied to the `S3Frame` dataclass layout.
"""

from __future__ import annotations

import logging
import pickle
from pathlib import Path
from typing import Optional

from minimateplus.blastware_file import blastware_filename, write_blastware_file
from minimateplus.framing import S3Frame
from minimateplus.models import Event

log = logging.getLogger("sfm.waveform_store")

A5_PICKLE_VERSION = 1


def _frame_to_dict(f: S3Frame) -> dict:
    return {
        "sub": f.sub,
        "page_hi": f.page_hi,
        "page_lo": f.page_lo,
        "data": bytes(f.data),
        "chk_byte": f.chk_byte,
        "checksum_valid": f.checksum_valid,
    }


def _dict_to_frame(d: dict) -> S3Frame:
    return S3Frame(
        sub=d["sub"],
        page_hi=d["page_hi"],
        page_lo=d["page_lo"],
        data=bytes(d["data"]),
        checksum_valid=d.get("checksum_valid", True),
        chk_byte=d.get("chk_byte", 0),
    )


class WaveformStore:
    """
    Persistent store for Blastware-format waveform files + their A5 source frames.

    Thread safety: write_blastware_file is single-shot; concurrent saves of the
    *same* filename would race, but the filename encodes second-resolution
    timestamps + serial, so collisions across threads/processes are vanishingly
    unlikely in practice.
    """

    def __init__(self, root: str | Path) -> None:
        self.root = Path(root)
        self.root.mkdir(parents=True, exist_ok=True)
        log.info("WaveformStore root=%s", self.root)

    # ── path helpers ────────────────────────────────────────────────────────────

    def _serial_dir(self, serial: str) -> Path:
        d = self.root / serial
        d.mkdir(parents=True, exist_ok=True)
        return d

    def paths_for(self, serial: str, filename: str) -> tuple[Path, Path]:
        """Return (blastware_path, a5_pickle_path) for a given serial+filename."""
        d = self._serial_dir(serial)
        return d / filename, d / f"{filename}.a5.pkl"

    def open_blastware(self, serial: str, filename: str) -> Optional[Path]:
        """Return absolute path to an existing event file or None."""
        bw_path, _ = self.paths_for(serial, filename)
        return bw_path if bw_path.exists() else None

    # ── save / load ─────────────────────────────────────────────────────────────

    def save(
        self,
        ev: Event,
        serial: str,
        a5_frames: list[S3Frame],
    ) -> dict:
        """
        Write the event file and its .a5.pkl sidecar for one event.

        Returns a record dict suitable for persisting alongside the DB row:

            {
              "filename":           "M529LKIQ.7M0W",
              "filesize":           8708,
              "a5_pickle_filename": "M529LKIQ.7M0W.a5.pkl",
            }

        The exact extension is timestamp-encoded per event (see
        `minimateplus.blastware_file.blastware_filename`).

        Idempotent: if the event file already exists, it is overwritten with
        the freshly-encoded version (same bytes for the same a5_frames).
        """
        if not a5_frames:
            raise ValueError("WaveformStore.save: a5_frames is empty")
        if not serial:
            raise ValueError("WaveformStore.save: serial is required")

        filename = blastware_filename(ev, serial)
        bw_path, a5_path = self.paths_for(serial, filename)

        # 1. encode the event file
        # Delete any stale file at this path so partial writes never leak
        # trailing bytes from a previous larger file (matches the live
        # endpoint's defensive unlink).
        try:
            bw_path.unlink()
        except FileNotFoundError:
            pass
        write_blastware_file(ev, a5_frames, bw_path)
        filesize = bw_path.stat().st_size

        # 2. write the .a5.pkl sidecar
        try:
            a5_path.unlink()
        except FileNotFoundError:
            pass
        payload = {
            "version": A5_PICKLE_VERSION,
            "frames": [_frame_to_dict(f) for f in a5_frames],
        }
        with a5_path.open("wb") as fp:
            pickle.dump(payload, fp, protocol=pickle.HIGHEST_PROTOCOL)

        log.info(
            "WaveformStore.save serial=%s filename=%s filesize=%d frames=%d",
            serial, filename, filesize, len(a5_frames),
        )
        return {
            "filename":            filename,
            "filesize":            filesize,
            "a5_pickle_filename":  a5_path.name,
        }

    def load_a5(self, serial: str, filename: str) -> Optional[list[S3Frame]]:
        """
        Re-hydrate the pickled A5 frame stream for a stored event.
        Returns None if the sidecar is missing.
        """
        _, a5_path = self.paths_for(serial, filename)
        if not a5_path.exists():
            return None
        with a5_path.open("rb") as fp:
            payload = pickle.load(fp)
        if not isinstance(payload, dict) or "frames" not in payload:
            log.warning("WaveformStore.load_a5: malformed sidecar at %s", a5_path)
            return None
        return [_dict_to_frame(d) for d in payload["frames"]]