import { BillingType, Customer } from './auth';
import { TierConfig } from './pricing';
import { UsageEntry } from './usage';

export interface BillingRow {
  customerId: string;
  name: string;
  billingType: BillingType;
  calls: number;
  totalCents: number;
  creditCents: number;
  billableCents: number;
}

/**
 * Per-customer billing aggregation. Range is inclusive `from`, exclusive `to`;
 * omit both for all time. Every customer matching the filters appears, even
 * with zero usage.
 */
export function billingRows(args: {
  entries: UsageEntry[];
  customers: Customer[];
  tiers: TierConfig[];
  from?: Date;
  to?: Date;
  customerId?: string;
  billingType?: BillingType;
}): BillingRow[] {
  const { entries, customers, tiers, from, to, customerId, billingType } = args;
  const inRange = entries.filter(
    (e) => (!from || e.timestamp >= from) && (!to || e.timestamp < to),
  );
  return customers
    .filter((c) => (customerId ? c.id === customerId : true))
    .filter((c) => (billingType ? (c.billingType ?? 'stripe') === billingType : true))
    .map((c) => {
      const mine = inRange.filter((e) => e.customerId === c.id);
      const totalCents = mine.reduce((sum, e) => sum + e.cents, 0);
      const tier = tiers.find((t) => t.id === c.tierId);
      const creditCents = Math.min(totalCents, tier?.monthlyCreditCents ?? 0);
      return {
        customerId: c.id,
        name: c.name,
        billingType: c.billingType ?? 'stripe',
        calls: mine.length,
        totalCents,
        creditCents,
        billableCents: totalCents - creditCents,
      };
    });
}

export interface TrendPoint {
  /** Day bucket: YYYY-MM-DD. Week bucket: the Monday (UTC) of that week, YYYY-MM-DD. */
  bucket: string;
  calls: number;
  cents: number;
}

export function usageTrend(entries: UsageEntry[], bucket: 'day' | 'week'): TrendPoint[] {
  const key = (d: Date): string => {
    const day = new Date(d);
    day.setUTCHours(0, 0, 0, 0);
    if (bucket === 'week') {
      // Shift back to Monday (ISO weeks start Monday; getUTCDay: Sun=0).
      const dow = (day.getUTCDay() + 6) % 7;
      day.setUTCDate(day.getUTCDate() - dow);
    }
    return day.toISOString().slice(0, 10);
  };
  const buckets = new Map<string, TrendPoint>();
  for (const e of entries) {
    const k = key(e.timestamp);
    const point = buckets.get(k) ?? { bucket: k, calls: 0, cents: 0 };
    point.calls += 1;
    point.cents += e.cents;
    buckets.set(k, point);
  }
  return [...buckets.values()].sort((a, b) => a.bucket.localeCompare(b.bucket));
}

export interface CsvColumn {
  key: string;
  label: string;
}

/** RFC 4180 CSV with a header row. Values containing , " or newlines are quoted. */
export function toCsv<T extends object>(rows: T[], columns: CsvColumn[]): string {
  const cell = (v: unknown): string => {
    const s = String(v ?? '');
    return /[",\n\r]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
  };
  const lines = [columns.map((c) => cell(c.label)).join(',')];
  for (const row of rows) {
    lines.push(columns.map((c) => cell((row as Record<string, unknown>)[c.key])).join(','));
  }
  return lines.join('\n');
}