/**
 * The search engines this extension knows how to drive.
 *
 * Every selector and every URL parameter below was read off the real SERP in
 * castle's Chrome, not recalled or inferred. That is not pedantry: Google's own
 * Tools menu writes `tbs=qdr:*`, which renders an *empty* page on that profile,
 * while the undocumented-looking `as_qdr=*` works. Anything in here that was not
 * observed is a bug waiting to be reported as "no results".
 *
 * Two extraction modes, because the engines genuinely differ:
 *
 *   - "items"    — the SERP has a clean per-result container (`li.b_algo`,
 *                  `.result`, `.snippet[data-type=web]`). Straightforward.
 *   - "headings" — Google has no stable result container, so results are found
 *                  from each <h3> outward. Kept as its own mode rather than
 *                  forced into the item shape, because it is the one that has
 *                  been through the most verification.
 */

export type EngineId = "google" | "duckduckgo" | "bing" | "brave";

export type Recency = "day" | "week" | "month" | "year";

export const RECENCY_VALUES = ["day", "week", "month", "year"] as const;

export const ENGINE_IDS: readonly EngineId[] = ["google", "duckduckgo", "bing", "brave"];

/** Aliases accepted from humans and from the model. */
const ENGINE_ALIASES: Record<string, EngineId> = {
  google: "google",
  g: "google",
  duckduckgo: "duckduckgo",
  ddg: "duckduckgo",
  duck: "duckduckgo",
  bing: "bing",
  b: "bing",
  brave: "brave",
};

/**
 * How the in-page script should read one engine's results. Passed into the
 * browser as JSON, so everything here must be plain data.
 */
export type ExtractionConfig = {
  mode: "items" | "headings";
  /** Results container candidates, first match wins. */
  roots: string[];
  /**
   * Present only on the engine's own "nothing matched" page. Without it a page
   * that genuinely has zero hits is indistinguishable from broken markup, and
   * the error blames the extractor for what is just an over-narrow query.
   */
  emptyMarker?: string;
  /** "items" mode: one result. */
  item?: string;
  /** Anchor carrying the outbound link, relative to the item. */
  link?: string;
  /** Title element, relative to the item. Falls back to the anchor's text. */
  title?: string;
  /** Description element, relative to the item. */
  snippet?: string;
  /**
   * "items" mode with no snippet selector: text from these is subtracted from
   * the item's text to leave the description behind.
   */
  subtract?: string[];
  /** Items matching any of these are ads or non-web cards, and are skipped. */
  exclude?: string[];
  /** How outbound links are wrapped, if they are. */
  unwrap: "none" | "ddg" | "bing" | "google";
  /** Hosts belonging to the engine itself; links to them are not results. */
  selfHostPattern: string;
};

export type EngineDefinition = {
  readonly id: EngineId;
  readonly label: string;
  /** Human-facing note about what makes this engine worth choosing. */
  readonly note: string;
  /**
   * Recency windows this engine can actually express, mapped to the parameter
   * value. A window that is absent is one the engine does not support — never
   * one that is silently dropped.
   */
  readonly recency: Partial<Record<Recency, string>>;
  readonly buildUrl: (query: string, numResults: number, recency: Recency | undefined) => string;
  readonly extraction: ExtractionConfig;
};

const GOOGLE: EngineDefinition = {
  id: "google",
  label: "Google",
  note: "best result quality; blocks aggressively under repeated automated queries",
  recency: { day: "d", week: "w", month: "m", year: "y" },
  buildUrl: (query, numResults, recency) => {
    const params = new URLSearchParams({ q: query, num: String(numResults), hl: "en" });
    // `udm=14` is the plain "Web" tab: no AI overview, no carousels. But any
    // date restriction combined with it renders an empty page, and `tbs=qdr:*`
    // renders an empty page on its own — both observed. So a time-limited
    // search drops udm and uses the older as_qdr instead.
    if (recency) params.set("as_qdr", GOOGLE.recency[recency] as string);
    else params.set("udm", "14");
    return `https://www.google.com/search?${params.toString()}`;
  },
  extraction: {
    mode: "headings",
    roots: ["#rso", "#search"],
    // Every result is `google.com/goto?url=<opaque token>` (since at least
    // 2026-11-06). The page cannot unwrap it; search.ts resolves it afterwards.
    // It must not count as Google's own link, hence the lookahead.
    unwrap: "google",
    selfHostPattern: String.raw`^https?://(www\.)?google\.[a-z.]+/(?!goto\?)`,
  },
};

const DUCKDUCKGO: EngineDefinition = {
  id: "duckduckgo",
  label: "DuckDuckGo",
  note: "no-JS endpoint, the most stable markup here and the least likely to challenge",
  // Read off DuckDuckGo's own <select name="df">: "", d, w, m, y.
  recency: { day: "d", week: "w", month: "m", year: "y" },
  buildUrl: (query, _numResults, recency) => {
    // The html endpoint renders server-side with no JavaScript, which makes it
    // both faster and far less fragile than the app at duckduckgo.com. It has
    // no result-count parameter — it returns a full page and the caller slices.
    const params = new URLSearchParams({ q: query });
    if (recency) params.set("df", DUCKDUCKGO.recency[recency] as string);
    return `https://html.duckduckgo.com/html/?${params.toString()}`;
  },
  extraction: {
    mode: "items",
    roots: [".results", "#links"],
    // Seen 2026-11-06: `<div class="result results_links no-results">` — it is
    // itself a `.result`, which is why the extractor finds a container and no hits.
    emptyMarker: ".no-results",
    item: ".result",
    link: "a.result__a[href]",
    title: "a.result__a",
    snippet: ".result__snippet",
    exclude: [".result--ad", ".badge--ad"],
    unwrap: "ddg",
    selfHostPattern: String.raw`^https?://(html\.|www\.)?duckduckgo\.com/`,
  },
};

const BING: EngineDefinition = {
  id: "bing",
  label: "Bing",
  note: "good coverage; supports day/week/month only — it has no year filter",
  // ez1/ez2/ez3 verified to filter (results carried "4 hours ago", "1 day ago").
  // There is deliberately no year: Bing's UI offers no such window, and the
  // ez5 custom-range form returned nothing when tried.
  recency: { day: "ez1", week: "ez2", month: "ez3" },
  buildUrl: (query, numResults, recency) => {
    const params = new URLSearchParams({ q: query });
    if (recency) {
      // `count` silently cancels `filters` — with ez1 alone every result is
      // hours old, and adding count in either order brings back months-old
      // ones. Observed directly, and it fails silently: the results look
      // perfectly plausible, just unfiltered. Exactly the same trap as Google's
      // udm+as_qdr, so the same answer — drop the count parameter and let the
      // caller slice the list it gets.
      params.set("filters", `ex1:"${BING.recency[recency] as string}"`);
    } else {
      params.set("count", String(numResults));
    }
    return `https://www.bing.com/search?${params.toString()}`;
  },
  extraction: {
    mode: "items",
    // Organic results only. Bing's answer cards also contain <h2>s, which is
    // why this targets li.b_algo rather than walking headings.
    roots: ["#b_results"],
    item: "li.b_algo",
    link: "h2 a[href]",
    title: "h2",
    snippet: ".b_caption p, .b_algoSlug, p",
    exclude: [".b_ad", ".b_adBottom"],
    unwrap: "bing",
    selfHostPattern: String.raw`^https?://(www\.)?bing\.com/`,
  },
};

const BRAVE: EngineDefinition = {
  id: "brave",
  label: "Brave Search",
  note: "independent index, direct links; challenges after 1-2 queries, clears in ~15-20 min",
  // Left empty deliberately — see the note in README. Brave's filter UI is
  // client-rendered and the `tf=` values could not be confirmed against a page
  // that was not simultaneously serving a bot check, so no window is claimed
  // rather than one being guessed at.
  recency: {},
  buildUrl: (query, _numResults, _recency) => {
    const params = new URLSearchParams({ q: query });
    return `https://search.brave.com/search?${params.toString()}`;
  },
  extraction: {
    mode: "items",
    // `#results` is gone from the live page (2026-11-06); `#main` and `main`
    // wrap the results. Left first so the older layout still matches.
    roots: ["#results", "#main", "main"],
    // data-type="web" excludes the AI summariser, video and news cards, which
    // share the .snippet class but are not ranked web results.
    item: '.snippet[data-type="web"]',
    link: "a[href]",
    title: ".title",
    // No dedicated description element. The item's text is
    // "source | breadcrumb | title | description", so the extractor keeps only
    // the lines after the title. These selectors are the fallback for when the
    // title is not on a line of its own.
    subtract: [".title", "cite"],
    unwrap: "none",
    selfHostPattern: String.raw`^https?://(search\.)?brave\.com/`,
  },
};

const BY_ID: Record<EngineId, EngineDefinition> = {
  google: GOOGLE,
  duckduckgo: DUCKDUCKGO,
  bing: BING,
  brave: BRAVE,
};

export const getEngine = (id: EngineId): EngineDefinition => BY_ID[id];

export const allEngines = (): readonly EngineDefinition[] => ENGINE_IDS.map((id) => BY_ID[id]);

/** Parse a user- or model-supplied engine name. Null when unrecognised. */
export const parseEngineId = (raw: string): EngineId | null =>
  ENGINE_ALIASES[raw.trim().toLowerCase()] ?? null;

/** The names accepted for an engine, for help text and error messages. */
export const engineAliases = (): readonly string[] => Object.keys(ENGINE_ALIASES);

/** Which engines can express a given recency window. */
export const enginesSupportingRecency = (recency: Recency): readonly EngineId[] =>
  ENGINE_IDS.filter((id) => BY_ID[id].recency[recency] !== undefined);

/** Human-readable list of the windows an engine supports, or "none". */
export const describeRecencySupport = (engine: EngineDefinition): string => {
  const windows = RECENCY_VALUES.filter((r) => engine.recency[r] !== undefined);
  return windows.length > 0 ? windows.join(", ") : "none";
};