/**
 * Data explorer URL state (§ "Our World in Data"-style explorer). Pure: shared by the /explore page,
 * the CSV route and unit tests. Defaults that depend on the database (top cancers, year range,
 * available metric/geography) are injected by the caller — nothing is hardcoded here.
 */
import type { SP } from '@/lib/search-params';

export const MAX_CANCERS = 6;
export const TABLE_PAGE_SIZE = 50;
export const VIEWS = ['lines', 'multiples'] as const;
export type ExplorerView = (typeof VIEWS)[number];
export const NORMALIZE = ['none'] as const;
export type ExplorerNormalize = (typeof NORMALIZE)[number];
/** "any" = no sex filter: series become cancer × sex inside a comparable group. */
export const SEX_ANY = 'any';

export interface ExplorerState {
  metric: string;
  cancers: string[]; // cancer slugs (or CI-CAN ids), ≤ MAX_CANCERS, deduplicated, order kept
  geography: string; // geography slug or ISO3
  sex: string; // all | male | female | any
  age: string; // age group label, 'all' by default
  from: number | null;
  to: number | null;
  view: ExplorerView;
  normalize: ExplorerNormalize;
  page: number; // observations table page (1-based)
}

export interface ExplorerDefaults {
  metric: string;
  geography: string;
  cancers: string[];
  sex?: string;
  age?: string;
  from?: number | null;
  to?: number | null;
}

const SLUG_RE = /^[a-z0-9][a-z0-9-]{0,99}$/;
const CI_ID_RE = /^CI-CAN-\d{8}$/i;
const METRIC_RE = /^[a-z][a-z0-9_]{1,63}$/;
const GEO_RE = /^[a-z0-9][a-z0-9-]{0,99}$/i;
const AGE_RE = /^[A-Za-z0-9+_\- ]{1,24}$/; // e.g. "all", "0-14", "65+", "85 and over"
const SEX_RE = /^[a-z_]{1,16}$/;
const YEAR_MIN = 1900;
const YEAR_MAX = 2100;

function first(v: string | string[] | undefined): string {
  const s = Array.isArray(v) ? v[0] : v;
  return (s ?? '').toString().trim();
}

/**
 * Cancer references from `cancers=a,b,c`, repeated `cancers=a&cancers=b`, or a mix (checkboxes + a free
 * comma-separated input share the same name). Lower-cases slugs, upper-cases CI ids, drops invalid tokens
 * and duplicates, keeps at most `max` in the order given.
 */
export function parseCancerList(v: string | string[] | undefined, max = MAX_CANCERS): string[] {
  const raw = (Array.isArray(v) ? v : v == null ? [] : [v]).flatMap((s) => String(s).split(/[,\s]+/));
  const out: string[] = [];
  for (const tok of raw) {
    const t = tok.trim();
    if (!t) continue;
    const norm = CI_ID_RE.test(t) ? t.toUpperCase() : t.toLowerCase();
    if (!CI_ID_RE.test(norm) && !SLUG_RE.test(norm)) continue;
    if (out.includes(norm)) continue;
    out.push(norm);
    if (out.length >= max) break;
  }
  return out;
}

function parseYear(v: string, fallback: number | null): number | null {
  if (v === '') return fallback;
  const n = Number.parseInt(v, 10);
  if (!Number.isFinite(n) || n < YEAR_MIN || n > YEAR_MAX) return fallback;
  return n;
}

/** Parse the search params into a complete state, filling gaps from the (database-computed) defaults. */
export function parseExplorerParams(sp: SP, d: ExplorerDefaults): ExplorerState {
  const metricRaw = first(sp.metric).toLowerCase();
  const geoRaw = first(sp.geography);
  const sexRaw = first(sp.sex).toLowerCase();
  const ageRaw = first(sp.age);
  const viewRaw = first(sp.view).toLowerCase();
  const normRaw = first(sp.normalize).toLowerCase();
  const cancers = parseCancerList(sp.cancers);
  let from = parseYear(first(sp.from), d.from ?? null);
  let to = parseYear(first(sp.to), d.to ?? null);
  if (from != null && to != null && from > to) [from, to] = [to, from];
  const pageN = Number.parseInt(first(sp.page), 10);
  return {
    metric: METRIC_RE.test(metricRaw) ? metricRaw : d.metric,
    cancers: cancers.length > 0 ? cancers : d.cancers.slice(0, MAX_CANCERS),
    geography: GEO_RE.test(geoRaw) ? (geoRaw.length === 3 ? geoRaw.toUpperCase() : geoRaw.toLowerCase()) : d.geography,
    sex: SEX_RE.test(sexRaw) ? sexRaw : (d.sex ?? 'all'),
    age: AGE_RE.test(ageRaw) ? ageRaw : (d.age ?? 'all'),
    from,
    to,
    view: (VIEWS as readonly string[]).includes(viewRaw) ? (viewRaw as ExplorerView) : 'lines',
    normalize: (NORMALIZE as readonly string[]).includes(normRaw) ? (normRaw as ExplorerNormalize) : 'none',
    page: Number.isFinite(pageN) && pageN > 1 ? Math.min(pageN, 100_000) : 1,
  };
}

/**
 * Serialize a state to a query string. Every dimension is written explicitly so a permalink is
 * self-describing and stable when the computed defaults change; `view`, `normalize` and `page` are
 * omitted at their default values. `cancers` is comma-separated.
 */
export function serializeExplorerParams(s: ExplorerState, overrides: Partial<ExplorerState> = {}): string {
  const m = { ...s, ...overrides };
  const qs = new URLSearchParams();
  qs.set('metric', m.metric);
  if (m.cancers.length > 0) qs.set('cancers', m.cancers.join(','));
  qs.set('geography', m.geography);
  qs.set('sex', m.sex);
  qs.set('age', m.age);
  if (m.from != null) qs.set('from', String(m.from));
  if (m.to != null) qs.set('to', String(m.to));
  if (m.view !== 'lines') qs.set('view', m.view);
  if (m.normalize !== 'none') qs.set('normalize', m.normalize);
  if (m.page > 1) qs.set('page', String(m.page));
  return `?${qs.toString()}`;
}

/** Same filters expressed for the public API (`/api/v1/epidemiology`) — repeated `cancer=` params, `from`/`to`. */
export function apiQueryFor(s: ExplorerState, limit = 200): string {
  const qs = new URLSearchParams();
  qs.set('metric', s.metric);
  for (const c of s.cancers) qs.append('cancer', c);
  qs.set('geography', s.geography);
  if (s.sex !== SEX_ANY) qs.set('sex', s.sex);
  qs.set('age', s.age);
  if (s.from != null) qs.set('from', String(s.from));
  if (s.to != null) qs.set('to', String(s.to));
  qs.set('limit', String(limit));
  return `?${qs.toString()}`;
}

/** Year label for headers and captions: "1999–2024", "2024" or "all years". */
export function yearRangeLabel(from: number | null, to: number | null): string {
  if (from != null && to != null) return from === to ? String(from) : `${from}–${to}`;
  if (from != null) return `from ${from}`;
  if (to != null) return `to ${to}`;
  return 'all years';
}

export function sexLabel(sex: string): string {
  switch (sex) {
    case 'all':
      return 'both sexes';
    case 'male':
      return 'male';
    case 'female':
      return 'female';
    case SEX_ANY:
      return 'by sex';
    default:
      return sex.replace(/_/g, ' ');
  }
}

export function ageLabel(age: string): string {
  return age === 'all' ? 'all ages' : `ages ${age}`;
}