// author: simon-pierre boucher <contact@spboucher.ai>
import { Readability } from "@mozilla/readability";
import { parse, stripChrome } from "./dom.js";

const MIN_READABILITY_CHARS = 200;

function textLen(el: Element): number {
  return (el.textContent ?? "").replace(/\s+/g, " ").trim().length;
}

function linkTextLen(el: Element): number {
  let sum = 0;
  for (const a of Array.from(el.querySelectorAll("a"))) sum += textLen(a);
  return sum;
}

/**
 * Density-based main-content fallback (§8.2). For each candidate block, score it
 * by `textLength^2 / (1 + linkTextLength)` — favouring large, low-link subtrees —
 * and return the winner's HTML. This is the safety net for listing/product pages
 * where Readability silently returns almost nothing.
 */
export function densityExtract(document: Document): string {
  const candidates = Array.from(document.querySelectorAll("article, main, section, div, td"));
  let best: Element | null = document.body;
  let bestScore = -1;
  for (const el of candidates) {
    const t = textLen(el);
    if (t < 100) continue;
    const score = (t * t) / (1 + linkTextLen(el));
    if (score > bestScore) {
      bestScore = score;
      best = el;
    }
  }
  return (best ?? document.body).innerHTML;
}

export interface MainContent {
  readonly html: string;
  readonly usedReadability: boolean;
}

export function extractMainContent(html: string, onlyMainContent: boolean): MainContent {
  if (!onlyMainContent) {
    const { document } = parse(html);
    return { html: document.body.innerHTML, usedReadability: false };
  }

  try {
    const { document } = parse(html);
    const article = new Readability(document as unknown as Document, { charThreshold: MIN_READABILITY_CHARS }).parse();
    if (article && (article.textContent ?? "").trim().length >= MIN_READABILITY_CHARS && article.content) {
      return { html: article.content, usedReadability: true };
    }
  } catch {
    /* fall through to density */
  }

  const { document } = parse(html);
  stripChrome(document);
  return { html: densityExtract(document), usedReadability: false };
}