/**
 * @fileoverview Per-tenant usage metering counters.
 * @module store/usage
 */

import { getStore, persist } from './db.js';
import { getTenant, resolveLimits } from './tenants.js';
import { createDebugger } from '../debug/logger.js';

const log = createDebugger('billing');

/**
 * @returns {string} YYYY-MM period key
 */
function currentPeriod() {
  const d = new Date();
  return `${d.getUTCFullYear()}-${String(d.getUTCMonth() + 1).padStart(2, '0')}`;
}

/**
 * @param {string} tenantId
 * @returns {{ period: string, timestamps: number, verifications: number, statusChecks: number, batchTimestamps: number, overage: object }}
 */
function emptyUsage(tenantId) {
  return {
    tenantId,
    period: currentPeriod(),
    timestamps: 0,
    verifications: 0,
    statusChecks: 0,
    batchTimestamps: 0,
    overage: { timestamps: 0, verifications: 0 },
  };
}

/**
 * Get usage for tenant, rolling period if month changed.
 * @param {string} tenantId
 * @returns {ReturnType<typeof emptyUsage>}
 */
export function getUsage(tenantId) {
  const store = getStore();
  let usage = store.usage[tenantId];
  const period = currentPeriod();

  if (!usage || usage.period !== period) {
    usage = emptyUsage(tenantId);
    store.usage[tenantId] = usage;
  }

  return usage;
}

/**
 * Public summary for /auth/me.
 * @param {string} tenantId
 * @returns {object}
 */
export function getUsageSummary(tenantId) {
  const usage = getUsage(tenantId);
  const tenant = getTenant(tenantId);
  const limits = tenant ? resolveLimits(tenant) : null;

  return {
    period: usage.period,
    timestamps: usage.timestamps,
    verifications: usage.verifications,
    statusChecks: usage.statusChecks,
    batchTimestamps: usage.batchTimestamps,
    limits: limits
      ? {
          timestamps: limits.timestamps,
          verifications: limits.verifications,
          batch: limits.batch,
          batchMaxItems: limits.batchMaxItems,
        }
      : null,
  };
}

/**
 * Increment a usage metric.
 *
 * @param {string} tenantId
 * @param {string} metric - e.g. `timestamps`, `verifications`, `statusChecks`, `batchTimestamps`, `overage.timestamps`
 * @param {number} [amount=1]
 * @returns {void}
 */
export function incrementUsage(tenantId, metric, amount = 1) {
  const usage = getUsage(tenantId);

  if (metric.startsWith('overage.')) {
    const key = metric.slice('overage.'.length);
    usage.overage[key] = (usage.overage[key] ?? 0) + amount;
  } else {
    usage[metric] = (usage[metric] ?? 0) + amount;
  }

  getStore().usage[tenantId] = usage;
  persist();
  log.debug('usage incremented', { tenantId, metric, amount, value: usage[metric] ?? usage.overage });
}