"""
USBRead.py
──────────
Reads raw lines from a serial USB device (e.g. Arduino) at the configured
baud rate, parses numeric sensor values, and stores everything in a shared
thread-safe ring-buffer.

Callers import `start_reader()` to launch the background thread, then read
from `get_snapshot()` at any time.
"""

import threading
import time
from collections import deque
from datetime import datetime
from typing import Any

import serial

# ── Populated once by init() ──────────────────────────────────────────────────
_cfg: dict[str, Any] = {}
_lock = threading.Lock()
_buffer: deque = deque()

status: dict[str, Any] = {
    "connected": False,
    "port": "",
    "baud": 0,
    "last_received": None,
    "total_lines": 0,
    "errors": 0,
}

# Callbacks: list of callables(entry) invoked after every parsed entry
_callbacks: list = []


# ── Public API ────────────────────────────────────────────────────────────────

def init(usb_cfg: dict[str, Any]) -> None:
    """Must be called once before start_reader()."""
    global _buffer, _cfg
    _cfg = usb_cfg
    _buffer = deque(maxlen=usb_cfg.get("buffer_size", 200))
    status["port"] = usb_cfg["port"]
    status["baud"] = usb_cfg["baud_rate"]


def register_callback(fn) -> None:
    """Register a function(entry) that is called for each new parsed line."""
    _callbacks.append(fn)


def get_snapshot() -> dict[str, Any]:
    """Return a thread-safe snapshot of the current buffer and status."""
    with _lock:
        return {
            "status": dict(status),
            "entries": list(_buffer),
        }


def start_reader() -> threading.Thread:
    """Start the background serial-reader thread (daemon)."""
    t = threading.Thread(target=_reader_loop, daemon=True, name="usb-reader")
    t.start()
    return t


# ── Parsing helpers ───────────────────────────────────────────────────────────

def parse_line(raw: str) -> dict[str, Any]:
    """
    Parse a raw serial line into a structured entry dict.

    Supported Arduino output formats (auto-detected):
      • Space / comma / semicolon separated numbers:
            "23.5 67.1 4.92"   →  values: [23.5, 67.1, 4.92]
      • Key=value pairs:
            "temp=23.5,hum=67.1"  →  values: [23.5, 67.1],
                                       labels: ["temp", "hum"]
      • JSON (if Arduino outputs JSON):
            '{"temp":23.5,"hum":67.1}'  →  values: [23.5, 67.1],
                                            labels: ["temp", "hum"]
    """
    ts = datetime.now().isoformat(timespec="milliseconds")
    entry: dict[str, Any] = {"ts": ts, "raw": raw, "values": [], "labels": []}

    # Try JSON first
    if raw.startswith("{"):
        try:
            import json
            obj = json.loads(raw)
            for k, v in obj.items():
                try:
                    entry["values"].append(float(v))
                    entry["labels"].append(str(k))
                except (TypeError, ValueError):
                    pass
            return entry
        except Exception:
            pass

    # Try key=value pairs  (e.g. "temp=23.5,hum=67")
    if "=" in raw:
        for token in raw.replace(",", " ").replace(";", " ").split():
            if "=" in token:
                k, _, v = token.partition("=")
                try:
                    entry["values"].append(float(v))
                    entry["labels"].append(k.strip())
                except ValueError:
                    pass
        if entry["values"]:
            return entry

    # Fallback: space / comma / semicolon delimited numbers
    for token in raw.replace(",", " ").replace(";", " ").split():
        try:
            entry["values"].append(float(token))
            entry["labels"].append(f"ch{len(entry['values'])}")
        except ValueError:
            pass

    return entry


# ── Internal reader loop ──────────────────────────────────────────────────────

def _reader_loop() -> None:
    port = _cfg["port"]
    baud = _cfg["baud_rate"]
    reconnect_delay = _cfg.get("reconnect_delay_s", 3)

    while True:
        try:
            with serial.Serial(port, baud, timeout=1) as ser:
                with _lock:
                    status["connected"] = True
                print(f"[USBRead] Connected → {port} @ {baud} baud")

                while True:
                    raw_bytes = ser.readline()
                    if not raw_bytes:
                        continue

                    raw_str = raw_bytes.decode("utf-8", errors="replace").strip()
                    if not raw_str:
                        continue

                    entry = parse_line(raw_str)

                    with _lock:
                        _buffer.append(entry)
                        status["last_received"] = entry["ts"]
                        status["total_lines"] += 1

                    # Fire registered callbacks outside the lock
                    for cb in _callbacks:
                        try:
                            cb(entry)
                        except Exception as exc:
                            print(f"[USBRead] Callback error: {exc}")

        except serial.SerialException as exc:
            with _lock:
                status["connected"] = False
                status["errors"] += 1
            print(f"[USBRead] SerialException: {exc} – retry in {reconnect_delay}s")
            time.sleep(reconnect_delay)

        except Exception as exc:
            with _lock:
                status["connected"] = False
                status["errors"] += 1
            print(f"[USBRead] Unexpected error: {exc} – retry in {reconnect_delay}s")
            time.sleep(reconnect_delay)