"""Cost ledger for cloud model usage and a budget guard.

.env: BUDGET_LIMIT_USD (default 45), BUDGET_CYCLE_START (YYYY-MM-DD, default 2026-10-02).
Prices are DeepSeek V4.1 Flash list prices without cache discount (upper bound).
"""
import json
import os
import time

ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
LEDGER = os.path.join(ROOT, "runs", "ledger.jsonl")
PRICE_IN, PRICE_OUT = 0.30 / 1e6, 1.20 / 1e6


class BudgetExceeded(Exception):
    pass


def add_usage(model, usage, kind, ref=""):
    if ":cloud" not in model:
        return
    pin, pout = usage.get("prompt_tokens", 0), usage.get("completion_tokens", 0)
    os.makedirs(os.path.dirname(LEDGER), exist_ok=True)
    with open(LEDGER, "a") as f:
        f.write(json.dumps({"t": time.time(), "day": time.strftime("%Y-%m-%d"), "model": model, "kind": kind,
                            "ref": ref, "in": pin, "out": pout,
                            "usd": round(pin * PRICE_IN + pout * PRICE_OUT, 5)}) + "\n")


def spent(since=None):
    since = since or os.environ.get("BUDGET_CYCLE_START", "2026-10-02")
    if not os.path.exists(LEDGER):
        return 0.0
    return round(sum(json.loads(l)["usd"] for l in open(LEDGER) if json.loads(l)["day"] >= since), 4)


def check_budget():
    limit = float(os.environ.get("BUDGET_LIMIT_USD", "45"))
    s = spent()
    if s >= limit:
        raise BudgetExceeded(f"cycle spend {s} USD >= limit {limit} USD")
    return s