import * as cheerio from 'cheerio';
import { ExtractedLink, ParserInput, ParserPlugin } from './types.js';

function nearestSection($: cheerio.CheerioAPI, element: any): string | undefined {
  const previous = $(element).prevAll('h1,h2,h3,h4,h5,h6,strong,b').first().text().trim();
  if (previous) {
    return previous;
  }
  const parentPrevious = $(element)
    .parent()
    .prevAll('h1,h2,h3,h4,h5,h6,p,tr')
    .first()
    .text()
    .trim();
  return parentPrevious || undefined;
}

type TextToken = { type: 'text'; text: string };
type AnchorToken = { type: 'anchor'; element: any; text: string };
type Token = TextToken | AnchorToken;

function compactText(value: string): string {
  return value.replace(/\s+/g, ' ').trim();
}

function textBeforeSponsorMarker(value: string): string {
  return compactText(value.split(/\b(?:sponsor|sponsored|advertisement|partner)\b/i)[0] ?? value);
}

function sponsorMarkerText(value: string): string | undefined {
  return value.match(/\b(?:sponsor|sponsored|advertisement|partner)\b/i)?.[0].toUpperCase();
}

function blockTokens($: cheerio.CheerioAPI, node: any): Token[] {
  if (!node) {
    return [];
  }

  if (node.type === 'text') {
    const text = compactText(node.data ?? '');
    return text ? [{ type: 'text', text }] : [];
  }

  if (node.type === 'tag' && node.name === 'a' && $(node).attr('href')) {
    return [{ type: 'anchor', element: node, text: compactText($(node).text()) }];
  }

  return $(node)
    .contents()
    .toArray()
    .flatMap((child) => blockTokens($, child));
}

function localContext($: cheerio.CheerioAPI, element: any, title: string): string {
  const block = $(element).closest('p,li,td,div').first();
  if (block.length === 0) {
    return title;
  }

  const tokens = blockTokens($, block.get(0));
  const anchorIndex = tokens.findIndex(
    (token) => token.type === 'anchor' && token.element === element
  );
  if (anchorIndex === -1) {
    return title;
  }

  const parts: string[] = [];
  const previousText = tokens
    .slice(0, anchorIndex)
    .reverse()
    .find((token): token is TextToken => token.type === 'text')?.text;
  const marker = previousText ? sponsorMarkerText(previousText) : undefined;
  if (marker) {
    parts.push(marker);
  }
  parts.push(title);

  for (const token of tokens.slice(anchorIndex + 1)) {
    if (token.type === 'anchor') {
      break;
    }
    parts.push(textBeforeSponsorMarker(token.text));
  }

  return compactText(parts.join(' '));
}

export const genericParser: ParserPlugin = {
  name: 'generic',
  matches: () => true,
  parse(input: ParserInput): ExtractedLink[] {
    const $ = cheerio.load(input.html);
    return $('a[href]')
      .toArray()
      .map((element) => {
        const anchor = $(element);
        const title = compactText(anchor.text()) || anchor.attr('aria-label') || '';
        const url = anchor.attr('href') ?? '';
        const context = localContext($, element, title);

        return {
          url,
          title,
          description: context && context !== title ? context : '',
          sourceText: title,
          section: nearestSection($, element),
          context
        };
      })
      .filter((link) => Boolean(link.url));
  }
};