function loadStencilCompiler(doc = document) {
  const s = doc.createElement('script');
  // loading from jsdelivr because skypack is not converting this file correctly
  s.src = 'https://cdn.jsdelivr.net/npm/@stencil/core@latest/compiler/stencil.min.js';
  return new Promise((resolve, reject) => {
    s.onload = () => resolve(window.stencil.transpile);
    s.onerror = reject;
    doc.body.appendChild(s);
  }); 
}

// auto inject the h import, to reduce boilerplace required in source
const h = "import { h } from 'https://cdn.skypack.dev/@stencil/core';\n"

export async function compileStencil(source, doc = document) {
  if (!source) { throw new Error('no source code provided to compile') }
  // async load the stencil compiler and get the transpile function
  const transpile = await loadStencilCompiler(doc);
  // transpile source and grab code from result
  const { code } = await transpile(h + source, { sourceMap: false });
  // replace import url with one the browser can resolve
  return code.replace('@stencil/core/internal/client', 'https://cdn.skypack.dev/@stencil/core/internal/client');
}

export async function runStencil(source, doc = document) {
  if (!source) { throw new Error('no source code provided to compile') }

  // async load the stencil compiler and get the transpile function
  const code = await compileStencil(source, doc);

  // make a script tag of type module and set script tag's content to the transpiled code
  const s = doc.createElement('script');
  s.type = 'module';
  s.innerHTML = code
  
  // append script tag to execute transpiled code
  doc.body.appendChild(s);
}

export async function parseFromHTML(selector, doc = document) {
  let list = [];

  if (typeof selector === 'string') {
    list = doc.querySelectorAll(selector)
  } else if (selector.innerHTML) {
    list = [selector]
  } else if (list.forEach) {
    list= selector; 
  }
  
  list.forEach(el => runStencil(el.textContent, doc));
}