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/**
* Pure reader-mode extraction — no CDP, no DOM. The in-page script
* (see capture.ts) serializes candidate content blocks; these pure functions
* score them and assemble clean article text, so the selection logic is
* unit-testable against saved fixtures (test/deep-research/readability-test.ts).
*
* Dependency-free by design (no jsdom / Readability): the harness ships no new
* runtime deps. The heuristic favors blocks with high text density and low link
* density, which is what separates article body from nav/ads/boilerplate.
*/
/** One candidate content block captured in-page. */
export type ContentBlock = {
/** Semantic tag: paragraph | heading | listitem | blockquote | other. */
readonly kind: "paragraph" | "heading" | "listitem" | "blockquote" | "other";
readonly text: string;
/** Chars of text that sit inside <a> tags — high ratio ⇒ nav/menu, not prose. */
readonly linkTextLength: number;
/** True when an ancestor is nav/header/footer/aside — structural boilerplate. */
readonly inBoilerplate: boolean;
};
/** The JSON payload capture.ts returns from the page. */
export type PageCapture = {
readonly url: string;
readonly title: string;
readonly blocks: ReadonlyArray<ContentBlock>;
/** Bounded innerText fallback when block extraction finds nothing usable. */
readonly bodyText: string;
};
/** The tool's public output shape. */
export type ReadablePage = {
readonly title: string;
readonly url: string;
readonly text: string;
readonly wordCount: number;
};
const MIN_PARAGRAPH_CHARS = 25;
const MAX_LINK_DENSITY = 0.5;
const MIN_ARTICLE_WORDS = 40;
const linkDensity = (block: ContentBlock): number => {
if (block.text.length === 0) return 1;
return block.linkTextLength / block.text.length;
};
/** A block is article prose if it is substantive, text-dense, and not chrome. */
const isArticleBlock = (block: ContentBlock): boolean => {
if (block.inBoilerplate) return false;
if (linkDensity(block) > MAX_LINK_DENSITY) return false;
if (block.kind === "heading" || block.kind === "blockquote" || block.kind === "listitem") {
return block.text.trim().length > 0;
}
return block.text.trim().length >= MIN_PARAGRAPH_CHARS;
};
const render = (block: ContentBlock): string => {
const text = block.text.trim();
if (block.kind === "heading") return `\n## ${text}\n`;
if (block.kind === "listitem") return `- ${text}`;
if (block.kind === "blockquote") return `> ${text}`;
return text;
};
const wordCountOf = (text: string): number => {
const trimmed = text.trim();
return trimmed.length === 0 ? 0 : trimmed.split(/\s+/).length;
};
/**
* Assemble readable article text from a page capture. Keeps text-dense,
* non-boilerplate blocks; falls back to the bounded body text when the article
* is too thin (e.g. a page with no clear content structure).
*/
export const extractReadable = (capture: PageCapture): ReadablePage => {
const articleText = capture.blocks.filter(isArticleBlock).map(render).join("\n\n").replace(/\n{3,}/g, "\n\n").trim();
const useFallback = wordCountOf(articleText) < MIN_ARTICLE_WORDS;
const text = useFallback ? capture.bodyText.trim() : articleText;
return {
title: capture.title.trim(),
url: capture.url,
text,
wordCount: wordCountOf(text),
};
};
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