defaultLayout.mjs

import { existsSync } from "fs";
import { join } from "path";

const pagesPath = "src/pages";
const layoutPath = "src/layouts";
const layoutAlias = "@layouts";
const defaultLayout = "Layout";

const pascalCache = {};
function toPascalCase(str) {
  pascalCache[str] =
    pascalCache[str] ||
    (/^[\p{L}\d]+$/iu.test(str) &&
      str.charAt(0).toUpperCase() + str.slice(1)) ||
    str
      .replace(
        /([\p{L}\d])([\p{L}\d]*)/giu,
        (g0, g1, g2) => g1.toUpperCase() + g2.toLowerCase()
      )
      .replace(/[^\p{L}\d]/giu, "");

  return pascalCache[str];
}

const knownLayouts = new Set();
const knownNotLayouts = new Set();

export default function defaultLayoutPlugin() {
  return function (tree, file) {
    const filePathFull = file.history[0].replace(/\/[^\/]+$/, "");
    const pagesPathFull = join(file.cwd, pagesPath);
    const nestedDirs = filePathFull.slice(pagesPathFull.length + 1);
    const directories = nestedDirs ? nestedDirs.split("/").reverse() : [];
    let layout = defaultLayout;
    directories.some((directory) => {
      const layoutName = toPascalCase(directory);
      if (
        knownLayouts.has(layoutName) ||
        (!knownNotLayouts.has(layoutName) &&
          existsSync(join(layoutPath, layoutName + ".astro")))
      ) {
        knownLayouts.add(layoutName);
        layout = layoutName;
        return true;
      } else {
        knownNotLayouts.add(layoutName);
      }
    });
    file.data.astro.frontmatter.layout = `${layoutAlias}/${layout}.astro`;
  };
}