import "server-only";
import { prisma } from "@/lib/db";
import { periodKey } from "@/lib/utils";
import type { UsageMetric } from "@/lib/billing/plans";

const METRICS: UsageMetric[] = ["script", "audio", "art", "repurpose"];

export interface UsageHistoryPoint {
  /** Monthly bucket key, e.g. "2026-06". */
  period: string;
  script: number;
  audio: number;
  art: number;
  repurpose: number;
}

/**
 * Read-only usage history for a billing subject: the last `months` monthly
 * buckets (oldest → newest), with per-metric counts. Missing buckets are zero
 * so the series is always dense (handy for a usage chart). `ownerId` is a
 * user.id or organization.id (the billing subject).
 */
export async function getUsageHistory(
  ownerId: string,
  months = 6,
  now = new Date()
): Promise<UsageHistoryPoint[]> {
  const n = Math.max(1, Math.min(36, months));

  // Build the ordered list of period keys we care about (oldest first).
  const periods: string[] = [];
  for (let i = n - 1; i >= 0; i--) {
    const d = new Date(Date.UTC(now.getUTCFullYear(), now.getUTCMonth() - i, 1));
    periods.push(periodKey(d));
  }

  const rows = await prisma.usageRecord.findMany({
    where: { ownerId, periodKey: { in: periods } },
    select: { periodKey: true, metric: true, count: true },
  });

  const byPeriod = new Map<string, UsageHistoryPoint>();
  for (const period of periods) {
    byPeriod.set(period, { period, script: 0, audio: 0, art: 0, repurpose: 0 });
  }
  for (const row of rows) {
    const point = byPeriod.get(row.periodKey);
    if (point && (METRICS as string[]).includes(row.metric)) {
      point[row.metric as UsageMetric] = row.count;
    }
  }

  return periods.map((p) => byPeriod.get(p)!);
}