import { readFile } from 'node:fs/promises';
import path from 'node:path';
const APP_SCRIPT_TAG = '<script src="mcp-app.js"></script>';
const SHARED_THEME_TOKENS_PLACEHOLDER = '/* @shared-theme-tokens */';
function inlineSharedThemeTokens(
html: string,
sharedThemeTokens: string,
htmlPath: string,
): string {
const placeholderSections = html.split(SHARED_THEME_TOKENS_PLACEHOLDER);
if (placeholderSections.length === 1) {
return html;
}
if (placeholderSections.length !== 2) {
throw new Error(`Expected exactly one shared theme placeholder in ${htmlPath}.`);
}
return `${placeholderSections[0]}${sharedThemeTokens.trim()}${placeholderSections[1]}`;
}
function toSafeInlineScript(script: string): string {
return script.replace(/<\/script/gi, '<\\/script');
}
/**
* Resolves an MCP app HTML template by inlining the bundled JS.
*
* Lookup order:
* 1. Read the sibling `mcp-app.js` next to `htmlPath` and inline it.
* 2. Fall back to the pre-built HTML in `distHtmlPath` (already inlined by esbuild).
* 3. Throw if neither source is available.
*/
export async function resolveAppHtml(
htmlPath: string,
distHtmlPath: string,
): Promise<string> {
const htmlTemplate = await readFile(htmlPath, 'utf-8');
let html = htmlTemplate;
if (htmlTemplate.includes(SHARED_THEME_TOKENS_PLACEHOLDER)) {
const sharedThemePath = path.join(path.dirname(htmlPath), '..', 'shared', 'theme-tokens.css');
const sharedThemeTokens = await readFile(sharedThemePath, 'utf-8');
html = inlineSharedThemeTokens(htmlTemplate, sharedThemeTokens, htmlPath);
}
if (!html.includes(APP_SCRIPT_TAG)) {
return html;
}
const scriptPath = path.join(path.dirname(htmlPath), 'mcp-app.js');
try {
const appScript = await readFile(scriptPath, 'utf-8');
return html.replace(APP_SCRIPT_TAG, `<script>\n${toSafeInlineScript(appScript)}</script>`);
}
catch {
// In source-mode runs, the JS bundle may not exist yet.
}
if (path.resolve(distHtmlPath) !== path.resolve(htmlPath)) {
try {
const distHtml = await readFile(distHtmlPath, 'utf-8');
if (!distHtml.includes(APP_SCRIPT_TAG)) {
return distHtml;
}
}
catch {
// Ignore and throw a focused error below.
}
}
throw new Error(
'UI bundle is missing. Run "pnpm run build" to generate an inline mcp-app bundle for CSP-safe loading.',
);
}
