Convert backend code to ES modules

Bundling code now with Rollup for its flat bundling and tree shaking
support. Front end code still goes through Webpack for browser support.

lib/ui.js

@@ -1,19 +1,19 @@
 "use strict";
 
-const Koa = require("koa");
-const Router = require("koa-router");
-const koaStatic = require("koa-static");
-const koaCompress = require("koa-compress");
-const koaBodyParser = require("koa-bodyparser");
-const koaJwt = require("koa-jwt");
-const jwt = require("jsonwebtoken");
-
-const config = require("./config");
-const api = require("./ui/api");
-const Authorizer = require("./common/authorizer");
-const expression = require("./common/expression");
-const logger = require("./logger");
-const localCache = require("./local-cache");
+import { Z_SYNC_FLUSH } from "zlib";
+import Koa from "koa";
+import Router from "koa-router";
+import * as jwt from "jsonwebtoken";
+import koaStatic from "koa-static";
+import koaCompress from "koa-compress";
+import koaBodyParser from "koa-bodyparser";
+import koaJwt from "koa-jwt";
+import * as config from "./config";
+import api from "./ui/api";
+import Authorizer from "./common/authorizer";
+import { parse } from "./common/expression-parser";
+import * as logger from "./logger";
+import * as localCache from "./local-cache";
 
 const koa = new Koa();
 const router = new Router();
@@ -41,7 +41,7 @@ function getPermissionSets(ctx) {
           ].includes(k)
         ) {
           if (v.filter == null || v.filter === "") v.filter = true;
-          else v.filter = expression.parse(v.filter);
+          else v.filter = parse(v.filter);
         }
       }
       return p;
@@ -175,11 +175,11 @@ router.get("/", async ctx => {
 
 koa.use(
   koaCompress({
-    flush: require("zlib").Z_SYNC_FLUSH
+    flush: Z_SYNC_FLUSH
   })
 );
 
 koa.use(router.routes());
 koa.use(koaStatic("./public"));
 
-exports.listener = koa.callback();
+export const listener = koa.callback();