/**
 * Reading list renderer — turns the curated reading list data file into
 * category-grouped HTML. Pure string builder (no DOM), so it can be unit
 * tested in Node; the browser wiring at the bottom is guarded accordingly.
 */
import { READING_LIST } from "../data/reading-list.js";

/** HTML-escape a value so it is safe to embed in markup. */
export function escapeHtml(value) {
  return String(value)
    .replaceAll("&", "&")
    .replaceAll("<", "&lt;")
    .replaceAll(">", "&gt;")
    .replaceAll('"', "&quot;")
    .replaceAll("'", "&#39;");
}

/** True when the value is an absolute http(s) URL. */
export function isValidUrl(value) {
  try {
    const url = new URL(String(value));
    return url.protocol === "http:" || url.protocol === "https:";
  } catch {
    return false;
  }
}

/** True when the entry has everything needed to render. */
export function isValidEntry(entry) {
  return Boolean(
    entry &&
      typeof entry.title === "string" &&
      entry.title.length > 0 &&
      isValidUrl(entry.url)
  );
}

/**
 * Group valid entries by category, preserving first-seen category order and
 * entry order within each category. Entries without a category fall under
 * "Uncategorized". Invalid entries are skipped.
 */
export function groupByCategory(entries) {
  const groups = new Map();
  for (const entry of entries) {
    if (!isValidEntry(entry)) continue;
    const category = entry.category || "Uncategorized";
    if (!groups.has(category)) groups.set(category, []);
    groups.get(category).push(entry);
  }
  return groups;
}

/** Slugify a category name into a stable, unique HTML id. */
function slugify(value) {
  return value
    .toLowerCase()
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "");
}

/** Render one entry: a title link plus an optional one-line note. */
function renderEntry(entry) {
  const note = entry.note
    ? `<p class="reading-note">${escapeHtml(entry.note)}</p>`
    : "";
  return (
    `<li class="reading-entry">` +
    `<a class="reading-link" href="${escapeHtml(entry.url)}">${escapeHtml(entry.title)}</a>` +
    note +
    `</li>`
  );
}

/**
 * Render the full reading list as an HTML string, grouped by category.
 *
 * @param {Array<{title: string, url: string, note?: string, category?: string}>} entries
 * @returns {string} HTML string ready to be injected into `#reading-list`
 */
export function renderReadingList(entries) {
  const groups = groupByCategory(entries);
  if (groups.size === 0) {
    return '<p class="reading-empty">The reading list is empty.</p>';
  }

  const usedIds = new Set();
  const sections = [];
  for (const [category, items] of groups) {
    let id = slugify(category) || "category";
    while (usedIds.has(id)) id = `${id}-${usedIds.size + 1}`;
    usedIds.add(id);

    sections.push(
      `<section class="reading-category" aria-labelledby="${id}">` +
        `<h2 id="${id}">${escapeHtml(category)}</h2>` +
        `<ul class="reading-list">${items.map(renderEntry).join("")}</ul>` +
        `</section>`
    );
  }
  return sections.join("");
}

// Browser-only wiring — render the data file into the page. Guarded so this
// module stays importable (and testable) in Node.
if (typeof window !== "undefined" && typeof document !== "undefined") {
  const container = document.getElementById("reading-list");
  if (container) {
    container.innerHTML = renderReadingList(READING_LIST);
  }
}