/**
 * /finder URL contract, shared by the page (server + client) and the API helpers. The site URL and the API use
 * the SAME encoding: repeated `f=slug:op:value` (between → `slug:between:a..b`), `mode=and|or`, `region`, `income`,
 * `sort=slug:asc|desc`.
 */
export type FinderOp = 'gt' | 'gte' | 'lt' | 'lte' | 'eq' | 'between';
export const FINDER_OPS: readonly FinderOp[] = ['gt', 'gte', 'lt', 'lte', 'eq', 'between'];

export interface FinderFilterInput {
  slug: string;
  op: FinderOp;
  value: number;
  value2?: number | null;
}

export interface FinderState {
  filters: FinderFilterInput[];
  mode: 'and' | 'or';
  region: string | null;
  income: string | null;
  sort: string | null;
}

const SLUG = /^[a-z0-9][a-z0-9-]*$/;

export function finderFilterParam(f: FinderFilterInput): string {
  return f.op === 'between' ? `${f.slug}:between:${f.value}..${f.value2 ?? f.value}` : `${f.slug}:${f.op}:${f.value}`;
}

export function parseFinderFilter(raw: string): FinderFilterInput | null {
  const m = /^([a-z0-9][a-z0-9-]*):(gt|gte|lt|lte|eq|between):(.+)$/.exec(raw.trim().toLowerCase());
  if (!m) return null;
  const [, slug, op, rest] = m;
  if (op === 'between') {
    const [a, b] = rest!.split('..');
    const v1 = Number(a);
    const v2 = Number(b);
    if (!Number.isFinite(v1) || !Number.isFinite(v2)) return null;
    return { slug: slug!, op: 'between', value: Math.min(v1, v2), value2: Math.max(v1, v2) };
  }
  const v = Number(rest);
  if (!Number.isFinite(v)) return null;
  return { slug: slug!, op: op as FinderOp, value: v };
}

export function finderQuery(filters: FinderFilterInput[], q: { mode?: 'and' | 'or'; region?: string | null; income?: string | null; sort?: string | null; limit?: number } = {}): string {
  const p = new URLSearchParams();
  for (const f of filters) p.append('f', finderFilterParam(f));
  if (q.mode && q.mode !== 'and') p.set('mode', q.mode);
  if (q.region) p.set('region', q.region);
  if (q.income) p.set('income', q.income);
  if (q.sort) p.set('sort', q.sort);
  if (q.limit) p.set('limit', String(q.limit));
  const s = p.toString();
  return s ? `?${s}` : '';
}

type ParamsLike = { getAll(name: string): string[]; get(name: string): string | null } | Record<string, string | string[] | undefined>;

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

export function parseFinderState(params: ParamsLike): FinderState {
  const filters = all(params, 'f').map(parseFinderFilter).filter((f): f is FinderFilterInput => !!f).slice(0, 8);
  const mode = one(params, 'mode') === 'or' ? 'or' : 'and';
  const clean = (v: string | null) => (v && SLUG.test(v.toLowerCase()) ? v.toLowerCase() : null);
  const sortRaw = one(params, 'sort');
  const sort = sortRaw && /^[a-z0-9][a-z0-9-]*:(asc|desc)$/.test(sortRaw.toLowerCase()) ? sortRaw.toLowerCase() : null;
  return { filters, mode, region: clean(one(params, 'region')), income: clean(one(params, 'income')), sort };
}

export function finderStateQuery(s: FinderState): string {
  return finderQuery(s.filters, { mode: s.mode, region: s.region, income: s.income, sort: s.sort });
}