"""python-snap7 S7 server for integration tests.

Reads a JSON profile from argv[1], allocates bytearrays for each declared area
(DB / MB / EB / AB), poke-seeds values at declared offsets, then starts the
snap7 Server on the configured port + blocks until Ctrl+C. Shape intentionally
mirrors the pymodbus `serve.ps1 + *.json` pattern one directory over so
someone familiar with the Modbus fixture can read this without re-learning.

The snap7.server.Server class is the MIT-licensed S7 PLC emulator wrapped by
python-snap7 (https://github.com/gijzelaerr/python-snap7). Its own docstring
admits "protocol compliance testing rather than full industrial-grade
functionality" — good enough for ISO-on-TCP wire-level round-trip but NOT
for S7-1500 Optimized-DB symbolic access, SCL variant-specific behaviour, or
PG/OP/S7-Basic session differentiation.
"""

from __future__ import annotations

import argparse
import ctypes
import json
import signal
import sys
import time
from pathlib import Path

# python-snap7 installs as `snap7` package; Server class lives under `snap7.server`.
import snap7
from snap7.type import SrvArea


# Map JSON area names → SrvArea enum values. PE = inputs (I/E), PA = outputs
# (Q/A), MK = memory (M), DB = data blocks, TM = timers, CT = counters.
AREA_MAP: dict[str, int] = {
    "PE": SrvArea.PE,
    "PA": SrvArea.PA,
    "MK": SrvArea.MK,
    "DB": SrvArea.DB,
    "TM": SrvArea.TM,
    "CT": SrvArea.CT,
}


def seed_buffer(buf: bytearray, seeds: list[dict]) -> None:
    """Poke seed values into the area buffer at declared byte offsets.

    Each seed is {"offset": int, "type": str, "value": int|float|bool|str}
    where type ∈ {u8, i8, u16, i16, u32, i32, f32, bool, ascii}. Endianness is
    big-endian (Siemens wire format).
    """
    for seed in seeds:
        off = int(seed["offset"])
        t = seed["type"]
        v = seed["value"]
        if t == "u8":
            buf[off] = int(v) & 0xFF
        elif t == "i8":
            buf[off] = int(v) & 0xFF
        elif t == "u16":
            buf[off:off + 2] = int(v).to_bytes(2, "big", signed=False)
        elif t == "i16":
            buf[off:off + 2] = int(v).to_bytes(2, "big", signed=True)
        elif t == "u32":
            buf[off:off + 4] = int(v).to_bytes(4, "big", signed=False)
        elif t == "i32":
            buf[off:off + 4] = int(v).to_bytes(4, "big", signed=True)
        elif t == "f32":
            import struct
            buf[off:off + 4] = struct.pack(">f", float(v))
        elif t == "bool":
            bit = int(seed.get("bit", 0))
            if bool(v):
                buf[off] |= (1 << bit)
            else:
                buf[off] &= ~(1 << bit) & 0xFF
        elif t == "ascii":
            # Siemens STRING type: byte 0 = max length, byte 1 = current length,
            # bytes 2+ = payload. Seeds supply the payload text; we fill max/cur.
            payload = str(v).encode("ascii")
            max_len = int(seed.get("max_len", 254))
            buf[off] = max_len
            buf[off + 1] = len(payload)
            buf[off + 2:off + 2 + len(payload)] = payload
        else:
            raise ValueError(f"Unknown seed type '{t}'")


def main() -> int:
    parser = argparse.ArgumentParser(description="python-snap7 S7 server for integration tests")
    parser.add_argument("profile", help="Path to profile JSON")
    parser.add_argument("--port", type=int, default=1102, help="TCP port (default 1102 non-privileged)")
    args = parser.parse_args()

    profile_path = Path(args.profile)
    if not profile_path.is_file():
        print(f"profile not found: {profile_path}", file=sys.stderr)
        return 1

    with profile_path.open() as f:
        profile = json.load(f)

    server = snap7.server.Server()
    # Keep bytearray refs alive for the server's lifetime — snap7 doesn't copy
    # the buffer, it takes a pointer. Letting GC collect would corrupt reads.
    buffers: list[bytearray] = []

    for area_decl in profile.get("areas", []):
        area_name = area_decl["area"]
        if area_name not in AREA_MAP:
            print(f"unknown area '{area_name}' (expected one of {list(AREA_MAP)})", file=sys.stderr)
            return 1
        index = int(area_decl.get("index", 0))  # DB number for DB area, 0 for MK/PE/PA
        size = int(area_decl["size"])
        buf = bytearray(size)
        seed_buffer(buf, area_decl.get("seeds", []))
        buffers.append(buf)
        # register_area takes (area, index, c-array); we wrap the bytearray
        # into a ctypes char array so the native lib can take &buf[0].
        arr_type = ctypes.c_char * size
        arr = arr_type.from_buffer(buf)
        server.register_area(AREA_MAP[area_name], index, arr)
        print(f"  seeded {area_name}{index} size={size} seeds={len(area_decl.get('seeds', []))}")

    port = int(args.port)
    print(f"Starting python-snap7 server on TCP {port}  (Ctrl+C to stop)")
    server.start(tcp_port=port)

    stop = {"sig": False}
    def _handle(*_a):
        stop["sig"] = True
    signal.signal(signal.SIGINT, _handle)
    try:
        signal.signal(signal.SIGTERM, _handle)
    except Exception:
        pass  # SIGTERM not on all platforms

    try:
        while not stop["sig"]:
            time.sleep(0.25)
    finally:
        print("stopping python-snap7 server")
        try:
            server.stop()
        except Exception:
            pass
    return 0


if __name__ == "__main__":
    sys.exit(main())