import type { FastifyReply } from 'fastify';

export const ATTRIBUTION = 'Data © RareIndex.io and its sources; valuations are estimates, listing prices are not confirmed transactions. See https://www.rareindex.io/data for methodology and terms.';

export interface Meta {
  count: number;
  cursor?: string | null;
  as_of: string;
  attribution: string;
  [k: string]: unknown;
}

export function envelope<T>(data: T, meta: Partial<Meta> & { count?: number } = {}) {
  const count = meta.count ?? (Array.isArray(data) ? data.length : 1);
  return { data, meta: { count, cursor: meta.cursor ?? null, as_of: new Date().toISOString(), attribution: ATTRIBUTION, ...meta } };
}

export class ApiProblem extends Error {
  constructor(
    public status: number,
    public title: string,
    detail?: string,
    public type = 'about:blank',
  ) {
    super(detail ?? title);
  }
}

export function problem(reply: FastifyReply, status: number, title: string, detail?: string, extra: Record<string, unknown> = {}) {
  return reply
    .code(status)
    .type('application/problem+json')
    .send({ type: 'https://www.rareindex.io/api-docs#errors', title, status, detail: detail ?? title, instance: reply.request.url, request_id: reply.request.id, ...extra });
}

/** Opaque offset cursor. */
export function encodeCursor(offset: number): string {
  return Buffer.from(String(offset), 'utf8').toString('base64url');
}
export function decodeCursor(cursor: string | undefined | null): number {
  if (!cursor) return 0;
  const n = Number(Buffer.from(cursor, 'base64url').toString('utf8'));
  return Number.isFinite(n) && n >= 0 ? Math.floor(n) : 0;
}

/** Minimal CSV export for flat row arrays. */
export function toCsv(rows: Array<Record<string, unknown>>): string {
  if (rows.length === 0) return '';
  const cols = [...new Set(rows.flatMap((r) => Object.keys(r)))];
  const esc = (v: unknown) => {
    if (v === null || v === undefined) return '';
    const s = v instanceof Date ? v.toISOString() : typeof v === 'object' ? JSON.stringify(v) : String(v);
    return /[",\n\r]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
  };
  return [cols.join(','), ...rows.map((r) => cols.map((c) => esc(r[c])).join(','))].join('\n') + '\n';
}

export function wantsCsv(query: Record<string, unknown>): boolean {
  return String(query.format ?? '').toLowerCase() === 'csv';
}

export function sendList(reply: FastifyReply, rows: Array<Record<string, unknown>>, meta: Partial<Meta> = {}, query: Record<string, unknown> = {}) {
  if (wantsCsv(query)) return reply.type('text/csv; charset=utf-8').header('content-disposition', 'attachment; filename="rareindex-export.csv"').send(toCsv(rows));
  return reply.send(envelope(rows, meta));
}