atbb / apps / web / src / middleware / theme.ts

import type { MiddlewareHandler } from "hono";
import type { WebAppEnv } from "../lib/theme-resolution.js";
import { resolveTheme, FALLBACK_THEME } from "../lib/theme-resolution.js";
import { ThemeCache } from "../lib/theme-cache.js";
import { logger } from "../lib/logger.js";

const DEFAULT_CACHE_TTL_MS = 5 * 60 * 1000; // 5 minutes

export function createThemeMiddleware(
  appviewUrl: string,
  cacheTtlMs: number = DEFAULT_CACHE_TTL_MS
): MiddlewareHandler<WebAppEnv> {
  // Intentionally outside the request handler: one shared instance per server
  // startup. Moving this inside the handler would create a new cache per
  // request, silently defeating the feature.
  const cache = new ThemeCache(cacheTtlMs);
  return async (c, next) => {
    const cookieHeader = c.req.header("Cookie");
    const colorSchemeHint = c.req.header("Sec-CH-Prefers-Color-Scheme");
    let theme;
    try {
      theme = await resolveTheme(appviewUrl, cookieHeader, colorSchemeHint, cache);
    } catch (error) {
      logger.error("createThemeMiddleware: resolveTheme threw unexpectedly — using fallback", {
        operation: "createThemeMiddleware",
        error: error instanceof Error ? error.message : String(error),
      });
      theme = FALLBACK_THEME;
    }
    c.set("theme", theme);
    await next();
  };
}