"""The cutoffs a host's readings are graded by, as Settings → Thresholds sets
them: amber past `warn`, red past `crit`."""
from __future__ import annotations

from steward.core.settings import DEFAULTS, get_all_settings, set_setting, to_thresholds_cfg
from steward.mcp._context import mcp_app
from steward.models.users import UserRole

from ._audit import audit_mcp
from ._shape import db_session

# Each graded reading, its unit, and what it measures.
READINGS = {
    "cpu": ("%", "CPU use"),
    "mem": ("%", "memory used"),
    "disk": ("%", "fullest mount's space used"),
    "load": ("%", "1-minute load per core"),
    "temp": ("°C", "hottest real thermometer"),
}


def _view(settings: dict) -> dict:
    cfg = to_thresholds_cfg(settings)
    return {kind: {"warn": cfg[kind]["warn"], "crit": cfg[kind]["crit"], "unit": unit, "measures": what,
                   "default": {"warn": DEFAULTS[f"thresholds.{kind}_warn"],
                               "crit": DEFAULTS[f"thresholds.{kind}_crit"]}}
            for kind, (unit, what) in READINGS.items()}


async def get_thresholds() -> dict:
    """The cutoffs host readings are graded by, as Settings → Thresholds
    sets them: per reading (cpu, mem, disk, load, temp), `warn` (amber past
    it) and `crit` (red past it) in `unit`, with Steward's default for each.
    The host pages, the Overview and get_overview grade by these. Alert
    rules have their own cutoffs (list_alert_rules); these don't fire
    anything. set_thresholds (admin) changes them.
    """
    async with db_session() as db:
        return _view(await get_all_settings(db))


async def set_thresholds(cutoffs: dict[str, dict[str, float]]) -> dict:
    """Change the cutoffs host readings are graded by, as Settings →
    Thresholds does. Takes effect on the next page load; audited.

    cutoffs: {reading: {"warn": n, "crit": n}} for any of get_thresholds'
    readings, e.g. {"temp": {"crit": 90}}. Either of warn and crit may be
    left out and keeps its value; warn must stay below crit. A reading not
    named is left as it is. Returns the cutoffs as they now stand.
    """
    unknown = sorted(set(cutoffs or {}) - set(READINGS))
    if unknown:
        raise ValueError(f"No reading named {', '.join(unknown)}; they are {', '.join(READINGS)}.")
    if not cutoffs:
        raise ValueError("Nothing to change: pass cutoffs, e.g. {\"temp\": {\"crit\": 90}}.")
    async with db_session() as db:
        current = _view(await get_all_settings(db))
    changes: dict = {}
    for kind, given in cutoffs.items():
        extra = sorted(set(given or {}) - {"warn", "crit"})
        if extra or not given:
            raise ValueError(f"{kind} takes warn and/or crit, not {', '.join(extra) or 'nothing'}.")
        new = {}
        for edge in ("warn", "crit"):
            if edge not in given:
                new[edge] = current[kind][edge]
                continue
            try:
                value = float(given[edge])
            except (TypeError, ValueError):
                raise ValueError(f"{kind} {edge} must be a number.") from None
            if not value > 0:
                raise ValueError(f"{kind} {edge} must be more than 0.")
            new[edge] = int(value) if value.is_integer() else value
            changes[f"thresholds.{kind}_{edge}"] = new[edge]
        if new["warn"] >= new["crit"]:
            raise ValueError(f"{kind} warn ({new['warn']}) must be below its crit ({new['crit']}).")
    app = mcp_app()
    async with db_session() as db:
        async with db.begin():
            before = await get_all_settings(db)
            for key, value in changes.items():
                await set_setting(db, key, value)
        fresh = await get_all_settings(db)
    app.config["THRESHOLDS"] = to_thresholds_cfg(fresh)
    await audit_mcp("settings.saved", "settings", "thresholds",
                    {"section": "thresholds",
                     "changes": {k: {"from": before.get(k), "to": v} for k, v in changes.items()}})
    return _view(fresh)


def register(register_tool) -> None:
    register_tool(get_thresholds, role=UserRole.viewer, read_only=True)
    register_tool(set_thresholds, role=UserRole.admin, read_only=False)