"""Event model: DiagEvent, Severity, EventKind (SPECIFICATION §8).

Every anomaly report is one :class:`DiagEvent`. ``time_utc`` is always the
**local client receive time** (wall clock), so events stay comparable even when
the remote host clock is wrong; device timestamps travel inside ``detail``,
clearly labeled (SPECIFICATION §8).
"""

from __future__ import annotations

import json
from dataclasses import asdict, dataclass, field
from datetime import datetime, timezone
from enum import Enum
from typing import Any


def utc_now() -> datetime:
    """Timezone-aware current UTC time (the local receive clock)."""
    return datetime.now(timezone.utc)


class Severity(str, Enum):
    INFO = "INFO"
    WARN = "WARN"
    CRITICAL = "CRITICAL"


class EventKind(str, Enum):
    """Event kinds — one per detection rule D1–D15 (SPECIFICATION §6)."""

    CONNECTED = "CONNECTED"
    DISCONNECTED = "DISCONNECTED"                     # D1
    RECONNECTED = "RECONNECTED"                       # D2
    RECONNECT_FLAPPING = "RECONNECT_FLAPPING"         # D3
    SLOW_POLL = "SLOW_POLL"                           # D4
    SLOW_POLL_STREAK = "SLOW_POLL_STREAK"             # D5
    LATENCY_TREND = "LATENCY_TREND"                   # D6
    POLL_HANG = "POLL_HANG"                           # D7
    QUALITY_BAD = "QUALITY_BAD"                       # D8
    QUALITY_UNCERTAIN = "QUALITY_UNCERTAIN"           # D9
    QUALITY_BAD_PERSISTENT = "QUALITY_BAD_PERSISTENT"  # D10
    QUALITY_FLAPPING = "QUALITY_FLAPPING"             # D11
    STALE_TIMESTAMP = "STALE_TIMESTAMP"               # D12
    FROZEN_VALUE = "FROZEN_VALUE"                     # D13
    CONTROL_LINK_DEGRADED = "CONTROL_LINK_DEGRADED"   # D14
    HEARTBEAT = "HEARTBEAT"                           # D15
    DEVICE_LINK_DOWN = "DEVICE_LINK_DOWN"             # D16
    DEVICE_LINK_UP = "DEVICE_LINK_UP"                 # D16 recovery


@dataclass(frozen=True)
class EventContext:
    """Snapshot counters attached to every event (SPECIFICATION §8)."""

    uptime_s: float
    reconnects_total: int
    rtt_p95_ms: float | None = None
    tags_bad: int = 0
    tags_total: int = 0


@dataclass(frozen=True)
class DiagEvent:
    """One structured diagnostic record — JSONL-ready via :meth:`to_json`."""

    time_utc: datetime
    kind: EventKind
    severity: Severity
    detail: dict[str, Any] = field(default_factory=dict)
    context: EventContext | None = None

    def to_json(self) -> str:
        """Serialize as one JSON line (SPECIFICATION §8, JSONL append-safe)."""
        if self.time_utc.tzinfo is None:
            raise ValueError("time_utc must be timezone-aware (use events.utc_now())")
        payload: dict[str, Any] = {
            "time_utc": _utc_z(self.time_utc),
            "kind": self.kind.value,
            "severity": self.severity.value,
            "detail": self.detail,
            "context": asdict(self.context) if self.context is not None else None,
        }
        return json.dumps(payload, ensure_ascii=False)


def _utc_z(dt: datetime) -> str:
    """ISO-8601 UTC with millisecond precision and a Z suffix."""
    return dt.astimezone(timezone.utc).isoformat(timespec="milliseconds").replace("+00:00", "Z")