lakehouse/bot/cost.ts

// Daily cost tracker. Resets at UTC midnight by keying the file by date.
// Hard ceilings are the policy surface — the bot refuses to call the
// cloud once the budget is exhausted for the day.

import { readFile, writeFile, mkdir } from "node:fs/promises";
import { join } from "node:path";
import type { CostState } from "./types.ts";

const COST_DIR = "/home/profit/lakehouse/data/_bot";

export const DAILY_CALLS_BUDGET = 20;
export const DAILY_TOKENS_BUDGET = 8000 * DAILY_CALLS_BUDGET; // 160k tokens/day ceiling

function todayUtc(): string {
  return new Date().toISOString().slice(0, 10);
}

function costFile(date: string): string {
  return join(COST_DIR, `cost-${date}.json`);
}

export async function readCost(): Promise<CostState> {
  const date = todayUtc();
  try {
    const raw = await readFile(costFile(date), "utf8");
    return JSON.parse(raw) as CostState;
  } catch {
    return { date, calls: 0, tokens: 0 };
  }
}

export async function recordCost(calls: number, tokens: number): Promise<CostState> {
  await mkdir(COST_DIR, { recursive: true });
  const current = await readCost();
  const updated: CostState = {
    date: current.date,
    calls: current.calls + calls,
    tokens: current.tokens + tokens,
  };
  await writeFile(costFile(updated.date), JSON.stringify(updated, null, 2));
  return updated;
}

export function budgetCheck(c: CostState): { ok: boolean; reason: string } {
  if (c.calls >= DAILY_CALLS_BUDGET) {
    return { ok: false, reason: `daily call budget exhausted (${c.calls}/${DAILY_CALLS_BUDGET})` };
  }
  if (c.tokens >= DAILY_TOKENS_BUDGET) {
    return { ok: false, reason: `daily token budget exhausted (${c.tokens}/${DAILY_TOKENS_BUDGET})` };
  }
  return { ok: true, reason: `${c.calls}/${DAILY_CALLS_BUDGET} calls, ${c.tokens}/${DAILY_TOKENS_BUDGET} tokens used today` };
}