/**
 * Server-safe helpers for the explorer pages (no 'use client' — the shared `toIndicatorOption` in
 * components/controls/indicator-select.tsx and `parseYear` in lib/url-state.ts live in client modules and cannot
 * be invoked from server components).
 */
import type { IndicatorOption } from '@/components/controls/indicator-select';
import type { IndicatorSummary } from '@/lib/types';

export function indicatorOption(i: IndicatorSummary): IndicatorOption {
  return { slug: i.slug, name: i.name ?? i.slug, short_name: i.short_name, topic: i.topic, unit: i.unit, featured: i.featured, first_year: i.first_year, last_year: i.last_year, n_countries: i.n_countries };
}

export function parseYearParam(v: string | null | undefined): number | null {
  if (!v) return null;
  const n = Number(v);
  return Number.isInteger(n) && n >= 1750 && n <= 2100 ? n : null;
}

const SLUG = /^[a-z0-9][a-z0-9-]*$/;
export function slugParam(v: string | null | undefined, fallback: string | null = null): string | null {
  const s = (v ?? '').toLowerCase();
  return SLUG.test(s) ? s : fallback;
}

export function listParam(v: string | null | undefined, max = 8): string[] {
  if (!v) return [];
  const out: string[] = [];
  for (const part of v.split(',')) {
    const s = part.trim();
    if (s && /^[A-Za-z0-9-]+$/.test(s) && !out.includes(s)) out.push(s);
    if (out.length >= max) break;
  }
  return out;
}

export type SP = Record<string, string | string[] | undefined>;
export function firstParam(sp: SP, k: string): string | null {
  const v = sp[k];
  return (Array.isArray(v) ? v[0] : v) ?? null;
}

/** Annual indicators with enough countries for cross-country views. */
export function explorerIndicators(items: IndicatorSummary[], minCountries = 20): IndicatorOption[] {
  return items.filter((i) => (i.frequency ?? 'A') === 'A' && (i.n_countries ?? 0) >= minCountries).map(indicatorOption);
}

export type ExplorerView = 'map' | 'rank' | 'trend' | 'distribution';
export const EXPLORER_VIEWS: ExplorerView[] = ['map', 'rank', 'trend', 'distribution'];
export const DEFAULT_EXPLORER_INDICATOR = 'gdp-per-capita-ppp';
export const DEFAULT_TRAJ = { x: 'gdp-per-capita-ppp', y: 'life-expectancy', size: 'population' } as const;