import logging
from sqlalchemy import text
from sqlalchemy.ext.asyncio import AsyncSession

logger = logging.getLogger(__name__)

# ── In-memory threshold cache ──────────────────────────────────────────────────
# Loaded from DB on first use; invalidated by settings API after updates.
# Falls back to hard-coded defaults if DB has no rows yet (pre-seed).

_caches: dict[str, list[dict]] = {}
_dirty_sites: set[str] = {"sg-01"}   # start dirty so first request loads from DB


def invalidate_threshold_cache(site_id: str = "sg-01") -> None:
    """Mark a site's cache as stale. Called by settings API after threshold changes."""
    _dirty_sites.add(site_id)


async def _ensure_cache(session: AsyncSession, site_id: str) -> None:
    if site_id not in _dirty_sites and site_id in _caches:
        return

    result = await session.execute(text("""
        SELECT sensor_type, threshold_value, direction, severity, message_template
        FROM alarm_thresholds
        WHERE site_id = :site_id AND enabled = true
        ORDER BY id
    """), {"site_id": site_id})
    rows = result.mappings().all()

    if rows:
        _caches[site_id] = [dict(r) for r in rows]
    else:
        # DB not yet seeded — fall back to hard-coded defaults
        _caches[site_id] = _FALLBACK_RULES

    _dirty_sites.discard(site_id)
    logger.info(f"Loaded {len(_caches[site_id])} threshold rules for {site_id}")


async def check_and_update_alarms(
    session: AsyncSession,
    sensor_id: str,
    sensor_type: str,
    site_id: str,
    room_id: str | None,
    rack_id: str | None,
    value: float,
) -> None:
    await _ensure_cache(session, site_id)

    for rule in _caches.get(site_id, []):
        if rule["sensor_type"] != sensor_type:
            continue

        threshold  = rule["threshold_value"]
        direction  = rule["direction"]
        severity   = rule["severity"]
        msg_tpl    = rule["message_template"]

        breached = (
            (direction == "above" and value > threshold) or
            (direction == "below" and value < threshold)
        )

        if breached:
            existing = await session.execute(text("""
                SELECT id FROM alarms
                WHERE sensor_id = :sid AND severity = :sev AND state = 'active'
                LIMIT 1
            """), {"sid": sensor_id, "sev": severity})

            if not existing.fetchone():
                message = msg_tpl.format(value=value, sensor_id=sensor_id)
                await session.execute(text("""
                    INSERT INTO alarms
                        (sensor_id, site_id, room_id, rack_id, severity, message, state, triggered_at)
                    VALUES
                        (:sensor_id, :site_id, :room_id, :rack_id, :severity, :message, 'active', NOW())
                """), {
                    "sensor_id": sensor_id, "site_id": site_id,
                    "room_id":   room_id,   "rack_id": rack_id,
                    "severity":  severity,  "message": message,
                })
                logger.info(f"Alarm raised [{severity}]: {message}")
        else:
            await session.execute(text("""
                UPDATE alarms
                SET state = 'resolved', resolved_at = NOW()
                WHERE sensor_id = :sid AND severity = :sev AND state = 'active'
            """), {"sid": sensor_id, "sev": severity})


# ── Hard-coded fallback (used before DB seed runs) ─────────────────────────────

_FALLBACK_RULES: list[dict] = [
    {"sensor_type": st, "threshold_value": tv, "direction": d, "severity": s, "message_template": m}
    for st, tv, d, s, m in [
        ("temperature",        28.0, "above", "warning",  "Temperature elevated at {sensor_id}: {value:.1f}°C"),
        ("temperature",        32.0, "above", "critical", "Temperature critical at {sensor_id}: {value:.1f}°C"),
        ("humidity",           65.0, "above", "warning",  "Humidity elevated at {sensor_id}: {value:.0f}%"),
        ("power_kw",            7.5, "above", "warning",  "PDU load elevated at {sensor_id}: {value:.1f} kW"),
        ("power_kw",            9.5, "above", "critical", "PDU load critical at {sensor_id}: {value:.1f} kW"),
        ("ups_charge",         80.0, "below", "warning",  "UPS battery low at {sensor_id}: {value:.0f}%"),
        ("ups_charge",         50.0, "below", "critical", "UPS battery critical at {sensor_id}: {value:.0f}%"),
        ("ups_state",           0.5, "above", "critical", "UPS switched to battery at {sensor_id} — mains power lost"),
        ("ups_state",           1.5, "above", "critical", "UPS overloaded at {sensor_id} — immediate risk of failure"),
        ("ups_load",           85.0, "above", "warning",  "UPS load high at {sensor_id}: {value:.0f}%"),
        ("ups_load",           95.0, "above", "critical", "UPS load critical at {sensor_id}: {value:.0f}% — overload"),
        ("ups_runtime",        15.0, "below", "warning",  "UPS runtime low at {sensor_id}: {value:.0f} min remaining"),
        ("ups_runtime",         5.0, "below", "critical", "UPS runtime critical at {sensor_id}: {value:.0f} min — imminent shutdown"),
        ("leak",                0.5, "above", "critical", "Water leak detected at {sensor_id}!"),
        ("cooling_cap_pct",    90.0, "above", "warning",  "CRAC near capacity limit at {sensor_id}: {value:.1f}%"),
        ("cooling_cop",         1.5, "below", "warning",  "CRAC running inefficiently at {sensor_id}: COP {value:.2f}"),
        ("cooling_comp_load",  95.0, "above", "warning",  "CRAC compressor overloaded at {sensor_id}: {value:.1f}%"),
        ("cooling_high_press", 22.0, "above", "critical", "CRAC high refrigerant pressure at {sensor_id}: {value:.1f} bar"),
        ("cooling_low_press",   3.0, "below", "critical", "CRAC low refrigerant pressure at {sensor_id}: {value:.1f} bar — possible leak"),
        ("cooling_superheat",  16.0, "above", "warning",  "CRAC discharge superheat high at {sensor_id}: {value:.1f}°C"),
        ("cooling_filter_dp",  80.0, "above", "warning",  "CRAC filter requires attention at {sensor_id}: {value:.0f} Pa"),
        ("cooling_filter_dp", 120.0, "above", "critical", "CRAC filter critically blocked at {sensor_id}: {value:.0f} Pa — replace now"),
        ("cooling_return",     36.0, "above", "warning",  "CRAC return air temperature high at {sensor_id}: {value:.1f}°C"),
        ("cooling_return",     42.0, "above", "critical", "CRAC return air temperature critical at {sensor_id}: {value:.1f}°C"),
        ("gen_fuel_pct",       25.0, "below", "warning",  "Generator fuel low at {sensor_id}: {value:.1f}%"),
        ("gen_fuel_pct",       10.0, "below", "critical", "Generator fuel critical at {sensor_id}: {value:.1f}%"),
        ("gen_state",           0.5, "above", "warning",  "Generator running at {sensor_id} — site is on standby power"),
        ("gen_state",          -0.5, "below", "critical", "Generator fault at {sensor_id} — no standby power available"),
        ("gen_load_pct",       85.0, "above", "warning",  "Generator load high at {sensor_id}: {value:.1f}%"),
        ("gen_load_pct",       95.0, "above", "critical", "Generator overloaded at {sensor_id}: {value:.1f}%"),
        ("gen_coolant_c",      95.0, "above", "warning",  "Generator coolant temperature high at {sensor_id}: {value:.1f}°C"),
        ("gen_coolant_c",     105.0, "above", "critical", "Generator coolant critical at {sensor_id}: {value:.1f}°C — risk of shutdown"),
        ("gen_oil_press",       2.0, "below", "critical", "Generator oil pressure low at {sensor_id}: {value:.1f} bar"),
        ("pdu_imbalance",       5.0, "above", "warning",  "PDU phase imbalance at {sensor_id}: {value:.1f}%"),
        ("pdu_imbalance",      15.0, "above", "critical", "PDU phase imbalance critical at {sensor_id}: {value:.1f}%"),
        ("ats_active",          1.5, "above", "warning",  "ATS transferred to generator at {sensor_id} — utility power lost"),
        ("ats_ua_v",           50.0, "below", "critical", "Utility A power failure at {sensor_id} — supply lost"),
        ("chiller_state",       0.5, "below", "critical", "Chiller fault at {sensor_id} — CHW supply lost"),
        ("chiller_cop",         2.5, "below", "warning",  "Chiller running inefficiently at {sensor_id}: COP {value:.2f}"),
        ("vesda_level",         0.5, "above", "warning",  "VESDA smoke detected at {sensor_id}: level elevated"),
        ("vesda_level",         1.5, "above", "warning",  "VESDA action threshold reached at {sensor_id}"),
        ("vesda_level",         2.5, "above", "critical", "VESDA FIRE ALARM at {sensor_id}!"),
        ("vesda_flow",          0.5, "below", "critical", "VESDA aspirator flow fault at {sensor_id} — detector may be compromised"),
        ("vesda_det1",          0.5, "below", "warning",  "VESDA detector 1 fault at {sensor_id}"),
        ("vesda_det2",          0.5, "below", "warning",  "VESDA detector 2 fault at {sensor_id}"),
        ("net_state",           0.5, "above", "warning",  "Network switch degraded at {sensor_id}"),
        ("net_state",           1.5, "above", "critical", "Network switch down at {sensor_id} — connectivity lost"),
        ("net_pkt_loss_pct",    1.0, "above", "warning",  "Packet loss detected at {sensor_id}: {value:.1f}%"),
        ("net_pkt_loss_pct",    5.0, "above", "critical", "High packet loss at {sensor_id}: {value:.1f}%"),
        ("net_temp_c",         65.0, "above", "warning",  "Switch temperature high at {sensor_id}: {value:.1f}°C"),
        ("net_temp_c",         75.0, "above", "critical", "Switch temperature critical at {sensor_id}: {value:.1f}°C"),
    ]
]