import { marked } from "marked";
import { mediaUrl } from "@/app/lib/media";

export interface EbookChunk {
  html: string;
  estimatedHeight: number;
}

export interface EbookData {
  chunks: EbookChunk[];
  headers: string[];
}

function rewriteMediaTag(tag: string): string {
  return tag.replace(/\s(src|poster)=(["'])(.*?)\2/gi, (match, attr: string, quote: string, value: string) => {
    const rewritten = mediaUrl(value);
    return rewritten ? ` ${attr}=${quote}${rewritten}${quote}` : match;
  });
}

function rewriteEmbeddedMedia(html: string): string {
  return html.replace(/<(img|video|audio|source)\b[^>]*>/gi, rewriteMediaTag);
}

export function parseEbookMarkdown(source: string): EbookData {
  const html = marked.parse(source, { breaks: true, gfm: true }) as string;
  const mediaHtml = rewriteEmbeddedMedia(html);
  const lazyHtml = mediaHtml.replace(/<img /g, '<img loading="lazy" decoding="async" ');

  let rawChunks = lazyHtml.split(/(?=<h1[\s>])/i).filter((c) => c.trim());
  if (rawChunks.length <= 1) {
    rawChunks = lazyHtml.split(/(?=<h2[\s>])/i).filter((c) => c.trim());
  }

  const headers: string[] = [];
  const headerRegex = /<h1[^>]*>(.*?)<\/h1>/gi;
  let m;
  while ((m = headerRegex.exec(lazyHtml)) !== null) {
    headers.push(m[1].replace(/<[^>]+>/g, ""));
  }
  if (headers.length === 0) {
    const h2Regex = /<h2[^>]*>(.*?)<\/h2>/gi;
    while ((m = h2Regex.exec(lazyHtml)) !== null) {
      headers.push(m[1].replace(/<[^>]+>/g, ""));
    }
  }

  const chunks: EbookChunk[] = rawChunks.map((chunkHtml) => {
    const imgCount = (chunkHtml.match(/<img\b/g) || []).length;
    const textLen = chunkHtml.replace(/<[^>]+>/g, "").length;
    const estimatedHeight = Math.max(300, Math.round(textLen * 0.6 + imgCount * 350));
    return { html: chunkHtml, estimatedHeight };
  });

  return { chunks, headers };
}