let mermaidPromise;

async function getMermaid() {
  if (!mermaidPromise) {
    mermaidPromise = import("https://cdn.jsdelivr.net/npm/mermaid@11/dist/mermaid.esm.min.mjs").then(
      (module) => {
        const mermaid = module.default ?? module;
        mermaid.initialize({ startOnLoad: false });
        return mermaid;
      },
    );
  }

  return mermaidPromise;
}

function readDiagramSource(block) {
  const code = block.querySelector("code");
  return (code?.textContent ?? block.textContent ?? "").trim();
}

async function renderBlock(block) {
  if (block.dataset.mermaidOverrideState) {
    return;
  }

  const source = readDiagramSource(block);
  if (!source) {
    block.dataset.mermaidOverrideState = "empty";
    return;
  }

  block.dataset.mermaidOverrideState = "pending";

  try {
    const mermaid = await getMermaid();
    const replacement = document.createElement("div");
    replacement.className = "mermaid";
    replacement.textContent = source;
    replacement.dataset.mermaidOverrideState = "rendered";
    block.replaceWith(replacement);
    await mermaid.run({ nodes: [replacement] });
  } catch (error) {
    block.dataset.mermaidOverrideState = "failed";
    console.warn("Mermaid override failed", error);
  }
}

function findBlocks(root = document) {
  const blocks = [];

  if (root instanceof Element && root.matches("pre.mermaid")) {
    blocks.push(root);
  }

  if (root instanceof Document || root instanceof Element) {
    blocks.push(...root.querySelectorAll("pre.mermaid"));
  }

  return blocks;
}

function renderAll(root = document) {
  for (const block of findBlocks(root)) {
    void renderBlock(block);
  }
}

function installObserver() {
  if (!(document.body instanceof HTMLBodyElement)) {
    return;
  }

  const observer = new MutationObserver((mutations) => {
    for (const mutation of mutations) {
      for (const node of mutation.addedNodes) {
        if (node instanceof Element) {
          renderAll(node);
        }
      }
    }
  });

  observer.observe(document.body, { childList: true, subtree: true });
}

if (document.readyState === "loading") {
  document.addEventListener("DOMContentLoaded", () => {
    renderAll();
    installObserver();
  });
} else {
  renderAll();
  installObserver();
}

window.addEventListener("pageshow", () => renderAll());
window.addEventListener("popstate", () => renderAll());