"""SSD discovery, mount state and the on-disk session layout.

Layout (date, then time, then file format):

    /mnt/microscope/2026-10-30/21-33-05/raw/frame_000001.raw
    /mnt/microscope/2026-10-30/21-33-05/index.jsonl
    /mnt/microscope/2026-10-30/21-33-05/session.json
    /mnt/microscope/2026-10-30/21-40-12/raw/still_0001.dng
    /mnt/microscope/2026-10-30/21-40-12/tiff/still_0001.tiff
    /mnt/microscope/2026-10-30/21-40-12/jpeg/still_0001.jpg
"""

import datetime as _dt
import logging
import os
import re
import shutil
import subprocess
import time
from pathlib import Path

log = logging.getLogger("storage")

UUID_BY_PATH = "/dev/disk/by-uuid"
MOUNT_HELPER = "/usr/local/sbin/microscope-ssd"


class Storage:
    def __init__(self, cfg):
        self.cfg = cfg
        self.mount_point = Path(cfg.get("mount_point", "/mnt/microscope"))
        self.uuid = cfg.get("fs_uuid", "")
        self._last_session_key = None
        self._last_session_dir = None

    # ------------------------------------------------------------------ state
    @property
    def device_node(self):
        if not self.uuid:
            return None
        node = Path(UUID_BY_PATH) / self.uuid
        return node if node.exists() else None

    def device_present(self) -> bool:
        """True when the SSD is plugged in and the partition node exists."""
        return self.device_node is not None

    def mount_source(self):
        """Device backing the mount point, or None when it is a plain directory."""
        target = os.fspath(self.mount_point)
        try:
            with open("/proc/self/mounts", "r", encoding="utf-8") as handle:
                for line in handle:
                    parts = line.split()
                    if len(parts) >= 2 and parts[1] == target:
                        return parts[0]
        except OSError:
            log.debug("could not read /proc/self/mounts", exc_info=True)
        return None

    def is_mounted(self) -> bool:
        """True only when the SSD is really mounted *and* still present.

        Yanking a USB drive leaves a stale entry in /proc/mounts that still
        reports as a mount point, so the backing device is checked too.
        """
        source = self.mount_source()
        if source is None:
            return False
        try:
            os.statvfs(self.mount_point)
        except OSError:
            return False
        if self.uuid:
            return (Path(UUID_BY_PATH) / self.uuid).exists()
        return os.path.exists(source)

    def free_mb(self) -> int:
        if not self.is_mounted():
            return 0
        try:
            usage = shutil.disk_usage(self.mount_point)
            return int(usage.free // (1024 * 1024))
        except OSError:
            return 0

    def state(self) -> str:
        """One of: 'ready', 'unmounted', 'absent'."""
        if self.is_mounted():
            return "ready"
        if self.device_present():
            return "unmounted"
        return "absent"

    # ------------------------------------------------------------- mount ops
    def _run_helper(self, action: str, timeout: float = 20.0):
        if not os.access(MOUNT_HELPER, os.X_OK):
            return False, f"{MOUNT_HELPER} not installed"
        try:
            proc = subprocess.run(
                ["sudo", "-n", MOUNT_HELPER, action],
                capture_output=True, text=True, timeout=timeout,
            )
        except subprocess.TimeoutExpired:
            return False, "mount helper timed out"
        except OSError as exc:
            return False, str(exc)
        out = (proc.stdout + proc.stderr).strip()
        return proc.returncode == 0, out

    def mount(self):
        if self.is_mounted():
            return True, "already mounted"
        return self._run_helper("mount")

    def unmount(self):
        if not self.is_mounted():
            return True, "not mounted"
        return self._run_helper("umount")

    # --------------------------------------------------------- session paths
    def new_session(self, kind: str) -> Path:
        """Create (or reuse) the date/time session directory for a capture.

        Two captures in the same second share a directory and continue the
        frame/still numbering, which keeps rapid photo bursts tidy.
        """
        now = _dt.datetime.now()
        date_part = now.strftime("%Y-%m-%d")
        time_part = now.strftime("%H-%M-%S")
        key = f"{date_part}/{time_part}"
        session = self.mount_point / date_part / time_part

        if key == self._last_session_key and session.is_dir():
            return session

        session.mkdir(parents=True, exist_ok=True)
        self._last_session_key = key
        self._last_session_dir = session
        log.info("new %s session: %s", kind, session)
        return session

    @staticmethod
    def format_dir(session: Path, fmt: str) -> Path:
        path = session / fmt
        path.mkdir(exist_ok=True)
        return path

    @staticmethod
    def next_serial(directory: Path, prefix: str) -> int:
        """Highest existing ``prefix_NNNN`` number in *directory*, plus one."""
        highest = 0
        pattern = re.compile(rf"^{re.escape(prefix)}_(\d+)\.[A-Za-z0-9]+$")
        if directory.is_dir():
            for entry in directory.iterdir():
                match = pattern.match(entry.name)
                if match:
                    highest = max(highest, int(match.group(1)))
        return highest + 1

    def relative(self, path: Path) -> str:
        try:
            return str(Path(path).relative_to(self.mount_point))
        except ValueError:
            return str(path)

    def wait_mounted(self, timeout: float = 15.0) -> bool:
        deadline = time.monotonic() + timeout
        while time.monotonic() < deadline:
            if self.is_mounted():
                return True
            time.sleep(0.25)
        return self.is_mounted()