import fs from "fs";
import path from "path";

const SECTION_RECT =
  /<rect\b[^>]*\bwidth="1920"[^>]*\bheight="672"[^>]*\bfill="(#[0-9A-Fa-f]{3,8})"/i;

/**
 * First 1920×672 rect fill in a Figma Section banner SVG.
 * Clip-path rects with fill="white" come later and are ignored.
 */
export function extractSectionBannerFill(svg: string): string | null {
  const match = svg.match(SECTION_RECT);
  return match?.[1] ?? null;
}

function sectionBannerDiskPath(slug: string, bannerFileName?: string): string {
  return path.join(
    process.cwd(),
    "public/content/blog",
    bannerFileName ?? `${slug}-section.svg`,
  );
}

/**
 * Page background for an article: section banner fill when that SVG exists,
 * otherwise the markdown `background.color`.
 */
export function resolveBlogPageBackgroundColor({
  slug,
  bannerFileName,
  frontmatterColor,
}: {
  slug: string;
  bannerFileName?: string;
  frontmatterColor?: string;
}): string | undefined {
  try {
    const svg = fs.readFileSync(
      sectionBannerDiskPath(slug, bannerFileName),
      "utf8",
    );
    const fill = extractSectionBannerFill(svg);
    if (fill) {
      return fill;
    }
  } catch {
    // No section SVG yet — fall through to frontmatter.
  }

  return frontmatterColor;
}