"""Author: Sandeep Belgavi. Deterministic admission; units are synthetic, not money."""
from dataclasses import dataclass
import json


@dataclass(frozen=True)
class Route:
    name: str
    capability: int
    reserve_units: int


class Router:
    """Single-process sequential ledger, with no model implementation."""
    def __init__(self, budget=7, max_inflight=1):
        if budget < 0 or max_inflight < 1:
            raise ValueError('Invalid limits')
        self.remaining, self.limit, self.active, self.used = budget, max_inflight, {}, set()
        self.routes = (Route('fast', 1, 2), Route('deep', 2, 5))

    def admit(self, request_id, capability, deadline_ms):
        if not request_id or capability not in (1, 2):
            raise ValueError('Invalid request')
        if request_id in self.used:
            raise ValueError('Request identifier already used')
        if deadline_ms <= 0:
            return 'expired'
        if len(self.active) >= self.limit:
            return 'overloaded'
        eligible = [r for r in self.routes if r.capability >= capability and r.reserve_units <= self.remaining]
        if not eligible:
            return 'budget_denied'
        route = min(eligible, key=lambda r: r.reserve_units)
        self.remaining -= route.reserve_units
        self.active[request_id] = route
        self.used.add(request_id)
        return route.name

    def settle(self, request_id, actual_units):
        route = self.active[request_id]
        if not isinstance(actual_units, int) or isinstance(actual_units, bool) or not 0 <= actual_units <= route.reserve_units:
            raise ValueError('Invalid charge; retain reservation for review')
        self.remaining += route.reserve_units - actual_units
        del self.active[request_id]


def main():
    router = Router()
    first = router.admit('incident-a', 2, 1000)
    pressure = router.admit('incident-b', 1, 1000)
    router.settle('incident-a', 4)
    second = router.admit('incident-b', 1, 1000)
    router.settle('incident-b', 2)
    denied = router.admit('incident-c', 2, 1000)
    print(json.dumps(dict(first=first, pressure=pressure, second=second, denied=denied, remaining=router.remaining), sort_keys=True))


if __name__ == '__main__': main()