# =============================================================================
# wire.py - wire format for server transmission (body JSON + raw-body HMAC signature)
#
# [Why a separate module]
#   The server (php/api/sensor_data.php) verifies, against the received "body bytes as-is",
#   X-Signature = lowercase_hex(HMAC-SHA256(key=API_KEY, msg=raw_body)).
#   Therefore the "signed bytes" and the "actually transmitted bytes" must be 100% identical.
#   We build the body directly as a string, sign those bytes, then POST those same bytes as-is.
#   (Leaving serialization to requests' json= can change float/whitespace/order and break the signature.)
#
# [Byte-level compatibility targets] — output must be identical to the four below.
#   - firmware/common/jsonbody.c::jb_sht30_event   (STM32 body generation)
#   - firmware/common/sig.c::sig_raw_body          (STM32 HMAC signature)
#   - firmware/test/host/reference.py              (verified Python reference)
#   - php/config.php::verify_signature_raw         (server verification part)
#
#   fixed2()             <-> jb_fixed2()      / reference.fixed2()
#   sht30_event_body()   <-> jb_sht30_event() / reference.sht30_event_body()
#   sign_raw()           <-> sig_raw_body()   / reference.sign_raw()
# =============================================================================
from __future__ import annotations

import hashlib
import hmac


def fixed2(v: float) -> str:
    """Fixed 2-decimal format (round-half-up, locale-independent).

    Byte-identical to jb_fixed2() / reference.fixed2().
      24.0   -> "24.00"
      48.5   -> "48.50"
      -3.245 -> "-3.25"
    """
    neg = v < 0
    if neg:
        v = -v
    scaled = int(v * 100.0 + 0.5)          # round half up (C: (long long)(v*100+0.5))
    ip = scaled // 100
    fp = scaled % 100
    sign = "-" if (neg and scaled != 0) else ""
    return f"{sign}{ip}.{fp:02d}"


def _esc(s: str) -> str:
    r"""Escape JSON string value (identical to jb_estr / reference._esc).

    Escapes only '"', '\\', and control characters (<0x20). '/' is left as-is.
    Multibyte UTF-8 (e.g. Korean) is left as-is (server verifies raw bytes).
    """
    out = []
    for ch in s:
        o = ord(ch)
        if ch == '"':
            out.append('\\"')
        elif ch == '\\':
            out.append('\\\\')
        elif o < 0x20:
            out.append('\\u%04x' % o)
        else:
            out.append(ch)
    return "".join(out)


def sht30_event_body(device_id: str, device_location: str, sensor_id: int,
                     sensor_name: str, event_type: str, timestamp: int,
                     temperature_c: float, humidity_percent: float,
                     metric_status: str, app_version: str) -> str:
    """Generate SHT30 event body JSON string.

    Field order is fixed to match firmware jb_sht30_event() (signature compatibility).
    metric_type is always fixed to "sht30". Temperature/humidity serialized to 2 decimals via fixed2.
    """
    return (
        '{'
        f'"device_id":"{_esc(device_id)}",'
        f'"device_location":"{_esc(device_location)}",'
        f'"sensor_id":{int(sensor_id)},'
        f'"sensor_name":"{_esc(sensor_name)}",'
        f'"event_type":"{_esc(event_type)}",'
        f'"timestamp":{int(timestamp)},'
        f'"metric_type":"sht30",'
        f'"temperature_c":{fixed2(temperature_c)},'
        f'"humidity_percent":{fixed2(humidity_percent)},'
        f'"metric_status":"{_esc(metric_status)}",'
        f'"app_version":"{_esc(app_version)}"'
        '}'
    )


def sign_raw(api_key: str, body: str) -> str:
    """raw-body signature: lowercase_hex(HMAC-SHA256(key=api_key, msg=body)).

    Identical to sig_raw_body() / reference.sign_raw() / php verify_signature_raw.
    The body is encoded as UTF-8 then signed (same as transmitted bytes).
    """
    return hmac.new(api_key.encode("utf-8"), body.encode("utf-8"),
                    hashlib.sha256).hexdigest()