"""Per-user usage metering with configurable caps and the at-cap policy.

Skill requirements met here: metering enforced per-user and accurately; the cap is
the plan's effective cap (base × multiplier); the at-cap behavior is the plan's
configurable CapPolicy, not a hardcoded branch.
"""
from __future__ import annotations

from backend.billing import store
from backend.billing.plans import CapPolicy, Feature, Plan
from backend.billing.subscription import effective_plan

# Reset window for the model-call meter. Monthly-ish; a config value, not magic.
MODEL_CALL_WINDOW_SECONDS = 30 * 24 * 3600
MODEL_CALL_METER = "model_calls"


def usage_status(user_id: str) -> dict:
    plan = effective_plan(user_id)
    cap = plan.effective_model_cap
    used, window_start = store.get_usage(user_id, MODEL_CALL_METER, MODEL_CALL_WINDOW_SECONDS)
    remaining = None if cap is None else max(0, cap - used)
    return {
        "plan_id": plan.id,
        "meter": MODEL_CALL_METER,
        "used": used,
        "cap": cap,                      # None = unmetered
        "remaining": remaining,
        "cap_policy": plan.cap_policy.value,
        "window_start": window_start,
        "window_seconds": MODEL_CALL_WINDOW_SECONDS,
    }


def check_and_consume(user_id: str, feature: Feature = Feature.AR_MODEL_GEN) -> dict:
    """Call BEFORE doing metered work. Returns {allowed, reason, status}.
    On allowed=True it has already incremented the counter (reserve-then-do).
    Unmetered plans (cap None) always allow."""
    plan = effective_plan(user_id)
    if not plan.grants(feature):
        return {"allowed": False, "reason": "feature_not_in_plan",
                "status": usage_status(user_id)}
    cap = plan.effective_model_cap
    if cap is None:
        return {"allowed": True, "reason": "unmetered", "status": usage_status(user_id)}
    used, _ = store.get_usage(user_id, MODEL_CALL_METER, MODEL_CALL_WINDOW_SECONDS)
    if used >= cap:
        return {"allowed": False, "reason": f"cap_reached:{plan.cap_policy.value}",
                "status": usage_status(user_id)}
    store.increment_usage(user_id, MODEL_CALL_METER, MODEL_CALL_WINDOW_SECONDS, 1)
    return {"allowed": True, "reason": "ok", "status": usage_status(user_id)}