/**
 * URL contract of `/rankings/[indicator]`:
 *   ?year=2020            ranking year (default: latest; the API falls back to the nearest available year)
 *   &group=oecd           group slug (world · regions · continents · income groups · organisations); default world
 *   &income=high-income   income-group slug applied client-side on top of the group (hic/umc/lmc/lic slugs)
 *   &minpop=1000000       minimum population (client-side; 0/absent = none)
 *   &mincov=2             minimum coverage: rows whose year ≥ ranking year − N (client-side)
 *   &view=table|bars|map  presentation (default table)
 *   &sort=asc|desc        default = the API's ("asc" when lower is better, else "desc")
 *   &highlight=canada     country slug pinned at the top of the list
 *   &q=fra                text filter within the ranking
 *   &history=CAN,USA,FRA  countries of the rank-over-time panel (≤ 5 ISO3)
 * Canonical URL = path + `group` (when not world); everything else is volatile.
 */
export type RankingView = 'table' | 'bars' | 'map';
export const RANKING_VIEWS: readonly RankingView[] = ['table', 'bars', 'map'];
export const MIN_POP_OPTIONS = [0, 1_000_000, 5_000_000, 10_000_000, 50_000_000] as const;
export const MIN_COV_OPTIONS = [0, 1, 2, 5] as const;

export interface RankingState {
  year: number | null;
  group: string;
  income: string | null;
  minpop: number | null;
  mincov: number | null;
  view: RankingView;
  sort: 'asc' | 'desc' | null;
  highlight: string | null;
  q: string;
  history: string[];
}

type ParamsLike = { get(name: string): string | null } | Record<string, string | string[] | undefined>;
function read(params: ParamsLike, key: string): string | null {
  if (typeof (params as { get?: unknown }).get === 'function') return (params as { get(name: string): string | null }).get(key);
  const v = (params as Record<string, string | string[] | undefined>)[key];
  return Array.isArray(v) ? (v[0] ?? null) : (v ?? null);
}

export function parseRankingState(params: ParamsLike): RankingState {
  const y = Number(read(params, 'year'));
  const sort = read(params, 'sort');
  const group = (read(params, 'group') ?? 'world').toLowerCase().replace(/[^a-z0-9-]/g, '') || 'world';
  const income = (read(params, 'income') ?? '').toLowerCase().replace(/[^a-z0-9-]/g, '') || null;
  const minpop = Number(read(params, 'minpop'));
  const mincov = Number(read(params, 'mincov'));
  const viewRaw = read(params, 'view');
  const highlight = (read(params, 'highlight') ?? '').toLowerCase().replace(/[^a-z0-9-]/g, '') || null;
  const history = (read(params, 'history') ?? '')
    .split(',')
    .map((s) => s.trim().toUpperCase())
    .filter((s) => /^[A-Z]{3}$/.test(s))
    .slice(0, 5);
  return {
    year: Number.isInteger(y) && y >= 1800 && y <= 2100 ? y : null,
    group,
    income,
    minpop: Number.isFinite(minpop) && minpop > 0 ? minpop : null,
    mincov: Number.isFinite(mincov) && mincov > 0 ? mincov : null,
    view: (RANKING_VIEWS as readonly string[]).includes(viewRaw ?? '') ? (viewRaw as RankingView) : 'table',
    sort: sort === 'asc' || sort === 'desc' ? sort : null,
    highlight,
    q: (read(params, 'q') ?? '').slice(0, 60),
    history,
  };
}

export function rankingQuery(state: Partial<RankingState>): string {
  const p = new URLSearchParams();
  if (state.year != null) p.set('year', String(state.year));
  if (state.group && state.group !== 'world') p.set('group', state.group);
  if (state.income) p.set('income', state.income);
  if (state.minpop) p.set('minpop', String(state.minpop));
  if (state.mincov) p.set('mincov', String(state.mincov));
  if (state.view && state.view !== 'table') p.set('view', state.view);
  if (state.sort) p.set('sort', state.sort);
  if (state.highlight) p.set('highlight', state.highlight);
  if (state.q) p.set('q', state.q);
  if (state.history?.length) p.set('history', state.history.join(','));
  const s = p.toString();
  return s ? `?${s}` : '';
}