diff --git a/hydro/handler/base.js b/hydro/handler/base.js
index 826204e60..6a932b24b 100644
--- a/hydro/handler/base.js
+++ b/hydro/handler/base.js
@@ -44,10 +44,7 @@ MIDDLEWARE(async (ctx, next) => {
                 }
             }
         };
-        ctx.back = () => {
-            console.log(122143);
-            ctx.redirect(ctx.request.headers.referer || '/');
-        };
+        ctx.back = () => ctx.redirect(ctx.request.headers.referer || '/');
         ctx.csrf_token = await token.add(token.TYPE_CSRF_TOKEN, 600, ctx.path);
         await next();
         if (ctx.session.sid)
diff --git a/templates/partials/problem_sidebar_normal.html b/templates/partials/problem_sidebar_normal.html
index dbf823e75..70216ef4c 100644
--- a/templates/partials/problem_sidebar_normal.html
+++ b/templates/partials/problem_sidebar_normal.html
@@ -100,16 +100,12 @@
       {% if pdoc['psdoc']['status'] %}
         <span class="icon record-status--icon {{ builtin.STATUS_CODES[pdoc['psdoc']['status']] }}"></span>
         <a href="/r/{{ pdoc['psdoc']['rid'] }}" class="record-status--text {{ builtin.STATUS_CODES[pdoc['psdoc']['status']] }}">
-          {{ status.STATUS_TEXTS[pdoc['psdoc']['status']] }}
+          {{ builtin.STATUS_TEXTS[pdoc['psdoc']['status']] }}
         </a>
       {% else %}
         {{ _('(None)') }}
       {% endif %}
       </dd>
-      {% if pdoc['ac_msg'] and pdoc['psdoc']['status'] == status.STATUS_ACCEPTED %}
-        <dt>{{ _('AC Message') }}</dt>
-        <dd>{{ pdoc['ac_msg'] }}</dd>
-      {% endif %}
     {% endif %}
     {% endif %}
       <dt>{{ _('Difficulty') }}</dt>
diff --git a/templates/problem_detail.html b/templates/problem_detail.html
index 0d1e9809d..f7ae2e1ee 100644
--- a/templates/problem_detail.html
+++ b/templates/problem_detail.html
@@ -4,9 +4,9 @@
 <script>
   var Context = {
     'problemId': "{{ pdoc.pid }}",
-    'postSubmitUrl': "/p/{{ pdoc.pid }}",
-    'getSubmissionsUrl': "/p/{{ pdoc.pid }}",
-    'getRecordDetailUrl': "/r/{{ rid }}",
+    'postSubmitUrl': "/p/{{ pdoc.pid }}/submit",
+    'getSubmissionsUrl': "/p/{{ pdoc.pid }}/submit",
+    'getRecordDetailUrl': "/r/{rid}",
     'code_lang': "{{ handler.user.codeLang }}",
     'code_template': "{{ handler.user.codeTemplate }}",
   };
@@ -43,8 +43,8 @@
     </div>
   </div>
   <div class="medium-3 columns">
-    {% set owner_udoc=udoc %}
-    {% set owner_dudoc=dudoc %}
+    {% set owner_udoc = udoc %}
+    {% set owner_dudoc = dudoc %}
     {% include "partials/problem_sidebar.html" %}
   </div>
 </div>
diff --git a/ui/build/config/webpack.js b/ui/build/config/webpack.js
index 4540c6ab7..58c2858c4 100644
--- a/ui/build/config/webpack.js
+++ b/ui/build/config/webpack.js
@@ -4,6 +4,7 @@ import _ from 'lodash';
 import webpack from 'webpack';
 import fs from 'fs-extra';
 
+import MonacoWebpackPlugin from 'monaco-editor-webpack-plugin';
 import FriendlyErrorsPlugin from 'friendly-errors-webpack-plugin';
 import OptimizeCssAssetsPlugin from 'optimize-css-assets-webpack-plugin';
 import ExtractTextPlugin from 'extract-text-webpack-plugin';
@@ -183,9 +184,10 @@ export default function (env = {}) {
       // don't include momentjs locale files
       new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
 
-      // don't include timeago.js locale files
-      // no use. FIXME.
-      // new webpack.IgnorePlugin(/locales\//, /timeago/),
+      new MonacoWebpackPlugin({
+        // available options are documented at https://github.com/Microsoft/monaco-editor-webpack-plugin#options
+        languages: ['cpp', 'csharp', 'java', 'javascript', 'python', 'rust', 'ruby', 'php', 'pascal', 'go']
+      }),
 
       // extract stylesheets into a standalone file
       env.watch
diff --git a/ui/components/scratchpad/ScratchpadEditorContainer.js b/ui/components/scratchpad/ScratchpadEditorContainer.js
index 1f6d1f1b0..b1934bcb1 100644
--- a/ui/components/scratchpad/ScratchpadEditorContainer.js
+++ b/ui/components/scratchpad/ScratchpadEditorContainer.js
@@ -1,26 +1,12 @@
 import React from 'react';
 import { connect } from 'react-redux';
-import CodeMirror from 'react-codemirror';
-
-import 'codemirror/addon/edit/matchbrackets';
-import 'codemirror/mode/clike/clike';
-import 'codemirror/mode/pascal/pascal';
-import 'codemirror/mode/python/python';
-import 'codemirror/mode/php/php';
-import 'codemirror/mode/rust/rust';
-import 'codemirror/mode/haskell/haskell';
-import 'codemirror/mode/javascript/javascript';
-import 'codemirror/mode/go/go';
-import 'codemirror/mode/ruby/ruby';
+import MonacoEditor from 'react-monaco-editor';
 
 import * as languageEnum from 'vj/constant/language';
 
 const getOptions = lang => ({
   lineNumbers: true,
-  tabSize: 4,
-  indentUnit: 4,
-  indentWithTabs: true,
-  mode: languageEnum.LANG_CODEMIRROR_MODES[lang],
+  mode: languageEnum.LANG_MONACO_MODES[lang],
 });
 
 const mapStateToProps = state => ({
@@ -39,17 +25,15 @@ const mapDispatchToProps = dispatch => ({
 
 @connect(mapStateToProps, mapDispatchToProps)
 export default class ScratchpadEditorContainer extends React.PureComponent {
-  componentDidMount() {
-    this.refs.editor.getCodeMirror().setOption('theme', 'vjcm');
-  }
-
   render() {
     return (
-      <CodeMirror
+      <MonacoEditor
+        language={languageEnum.LANG_MONACO_MODES[this.props.lang]}
+        theme="vs-dark"
         value={this.props.code}
-        onChange={code => this.props.handleUpdateCode(code)}
         options={getOptions(this.props.lang)}
         ref="editor"
+        onChange={code => this.props.handleUpdateCode(code)}
       />
     );
   }
diff --git a/ui/constant/language.js b/ui/constant/language.js
index 5687f66ff..b8fba576d 100644
--- a/ui/constant/language.js
+++ b/ui/constant/language.js
@@ -32,19 +32,18 @@ export const LANG_HIGHLIGHT_ID = {
   rb: 'ruby',
 };
 
-export const LANG_CODEMIRROR_MODES = {
-  c: 'text/x-csrc',
-  cc: 'text/x-c++src',
-  cs: 'text/x-csharp',
-  pas: 'text/x-pascal',
-  java: 'text/x-java',
-  py: 'text/x-python',
-  py3: 'text/x-python',
-  php: 'text/x-php',
-  rs: 'text/x-rustsrc',
-  hs: 'text/x-haskell',
-  js: 'text/javascript',
-  go: 'text/x-go',
-  rb: 'text/x-ruby',
+export const LANG_MONACO_MODES = {
+  c: 'cpp',
+  cc: 'cpp',
+  cs: 'csharp',
+  pas: 'pascal',
+  java: 'java',
+  py: 'python',
+  py3: 'python',
+  php: 'php',
+  rs: 'rust',
+  hs: 'haskell',
+  js: 'javascript',
+  go: 'go',
+  rb: 'ruby',
 };
-attachObjectMeta(LANG_CODEMIRROR_MODES, 'exportToPython', false);
diff --git a/ui/package.json b/ui/package.json
index 1ec060d11..799cba531 100644
--- a/ui/package.json
+++ b/ui/package.json
@@ -51,6 +51,7 @@
     "imports-loader": "^0.8.0",
     "js-yaml": "^3.13.1",
     "json-loader": "^0.5.7",
+    "monaco-editor-webpack-plugin": "^1.9.0",
     "optimize-css-assets-webpack-plugin": "^3.2.0",
     "postcss-loader": "^3.0.0",
     "rupture": "^0.7.1",
@@ -89,6 +90,7 @@
     "react": "^15.6.1",
     "react-codemirror": "^1.0.0",
     "react-dom": "^15.6.1",
+    "react-monaco-editor": "^0.35.0",
     "react-redux": "^5.0.6",
     "react-split-pane": "^0.1.65",
     "redux": "^3.7.2",
diff --git a/ui/pages/problem_detail.page.js b/ui/pages/problem_detail.page.js
index 41f7207e5..22d1e82db 100644
--- a/ui/pages/problem_detail.page.js
+++ b/ui/pages/problem_detail.page.js
@@ -1,13 +1,8 @@
 import Tether from 'tether';
 import { NamedPage } from 'vj/misc/PageLoader';
 import Navigation from 'vj/components/navigation';
-import Notification from 'vj/components/notification';
-import { ActionDialog } from 'vj/components/dialog';
-import DomainSelectAutoComplete from 'vj/components/autocomplete/DomainSelectAutoComplete';
 import loadReactRedux from 'vj/utils/loadReactRedux';
 import delay from 'vj/utils/delay';
-import request from 'vj/utils/request';
-import i18n from 'vj/utils/i18n';
 
 class ProblemPageExtender {
   constructor() {
@@ -19,12 +14,8 @@ class ProblemPageExtender {
   }
 
   async extend() {
-    if (this.inProgress) {
-      return;
-    }
-    if (this.isExtended) {
-      return;
-    }
+    if (this.inProgress) return;
+    if (this.isExtended) return;
     this.inProgress = true;
 
     const bound = this.$contentBound
@@ -38,7 +29,6 @@ class ProblemPageExtender {
     Navigation.instance.logoVisible.set('scratchpad', true);
     Navigation.instance.expanded.set('scratchpad', true);
     $('body').addClass('header--collapsed mode--scratchpad');
-
     await this.$scratchpadContainer
       .css({
         left: bound.left,
@@ -67,12 +57,8 @@ class ProblemPageExtender {
   }
 
   async collapse() {
-    if (this.inProgress) {
-      return;
-    }
-    if (!this.isExtended) {
-      return;
-    }
+    if (this.inProgress) return;
+    if (!this.isExtended) return;
     this.inProgress = true;
 
     $(window).scrollTop(0);
@@ -109,11 +95,8 @@ class ProblemPageExtender {
   }
 
   toggle() {
-    if (this.isExtended) {
-      this.collapse();
-    } else {
-      this.extend();
-    }
+    if (this.isExtended) this.collapse();
+    else this.extend();
   }
 }
 
@@ -174,10 +157,7 @@ const page = new NamedPage(['problem_detail', 'contest_detail_problem', 'homewor
   }
 
   async function loadReact() {
-    if (reactLoaded) {
-      return;
-    }
-
+    if (reactLoaded) return;
     $('.loader-container').show();
 
     const SockJs = await import('sockjs-client');
@@ -204,61 +184,13 @@ const page = new NamedPage(['problem_detail', 'contest_detail_problem', 'homewor
         $('#scratchpad').get(0),
       );
     };
-
     unmountReact = () => {
       unmountComponentAtNode($('#scratchpad').get(0));
     };
-
     reactLoaded = true;
-
     $('.loader-container').hide();
   }
 
-  const domainSelector = DomainSelectAutoComplete.getOrConstruct($('.dialog__body--copy-to [name="domain_id"]'));
-  const copyProblemToDialog = new ActionDialog({
-    $body: $('.dialog__body--copy-to > div'),
-    onDispatch(action) {
-      if (action === 'ok' && domainSelector.value() === null) {
-        domainSelector.focus();
-        return false;
-      }
-      return true;
-    },
-  });
-  copyProblemToDialog.clear = function () {
-    domainSelector.clear();
-    return this;
-  };
-
-
-  async function handleClickCopyProblem() {
-    const action = await copyProblemToDialog.clear().open();
-    if (action !== 'ok') {
-      return;
-    }
-    const domainId = copyProblemToDialog.$dom.find('[name="domain_id"]').val();
-    const useNumericId = copyProblemToDialog.$dom.find('[name="numeric_pid"]').prop('checked');
-    const isHidden = copyProblemToDialog.$dom.find('[name="hidden"]').prop('checked');
-    const payload = {
-      operation: 'copy_to_domain',
-      dest_domain_id: domainId,
-    };
-    if (useNumericId) {
-      payload.numeric_pid = 'on';
-    }
-    if (isHidden) {
-      payload.hidden = 'on';
-    }
-    try {
-      const data = await request.post('', payload);
-      Notification.success(i18n('Problem is successfully copied.'));
-      await delay(1000);
-      window.location.href = data.new_problem_url;
-    } catch (error) {
-      Notification.error(error.message);
-    }
-  }
-
   async function enterScratchpadMode() {
     await extender.extend();
     await loadReact();
@@ -284,10 +216,6 @@ const page = new NamedPage(['problem_detail', 'contest_detail_problem', 'homewor
     leaveScratchpadMode();
     ev.preventDefault();
   });
-  $(document).on('click', '[name="problem-sidebar__copy-to"]', (ev) => {
-    handleClickCopyProblem();
-    ev.preventDefault();
-  });
   $(document).on('click', '[name="problem-sidebar__show-category"]', (ev) => {
     $(ev.currentTarget).hide();
     $('[name="problem-sidebar__categories"]').show();
diff --git a/ui/yarn.lock b/ui/yarn.lock
index cef81b264..e4dfec879 100644
--- a/ui/yarn.lock
+++ b/ui/yarn.lock
@@ -1000,11 +1000,24 @@
   resolved "https://registry.yarnpkg.com/@types/node/-/node-13.11.0.tgz#390ea202539c61c8fa6ba4428b57e05bc36dc47b"
   integrity sha512-uM4mnmsIIPK/yeO+42F2RQhGUIs39K2RFmugcJANppXe6J1nvH87PvzPZYpza7Xhhs8Yn9yIAVdLZ84z61+0xQ==
 
+"@types/prop-types@*":
+  version "15.7.3"
+  resolved "https://registry.yarnpkg.com/@types/prop-types/-/prop-types-15.7.3.tgz#2ab0d5da2e5815f94b0b9d4b95d1e5f243ab2ca7"
+  integrity sha512-KfRL3PuHmqQLOG+2tGpRO26Ctg+Cq1E01D2DMriKEATHgWLfeNDmq9e29Q9WIky0dQ3NPkd1mzYH8Lm936Z9qw==
+
 "@types/q@^1.5.1":
   version "1.5.2"
   resolved "https://registry.yarnpkg.com/@types/q/-/q-1.5.2.tgz#690a1475b84f2a884fd07cd797c00f5f31356ea8"
   integrity sha512-ce5d3q03Ex0sy4R14722Rmt6MT07Ua+k4FwDfdcToYJcMKNtRVQvJ6JCAPdAmAnbRb6CsX6aYb9m96NGod9uTw==
 
+"@types/react@^15.x || ^16.x":
+  version "16.9.33"
+  resolved "https://registry.yarnpkg.com/@types/react/-/react-16.9.33.tgz#a5274520f0d28cbbb73c8652ddd48646fd4bcae5"
+  integrity sha512-ovgoy7p9999HDzwv8Sewhl8GJjn/r0GRsFrM9UMwp1uodh0kQ0pwIHLQ6LNfqGSyjNzJ8II/HIg0BL7Yn/B9yA==
+  dependencies:
+    "@types/prop-types" "*"
+    csstype "^2.2.0"
+
 a-sync-waterfall@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/a-sync-waterfall/-/a-sync-waterfall-1.0.1.tgz#75b6b6aa72598b497a125e7a2770f14f4c8a1fa7"
@@ -2705,6 +2718,11 @@ csso@~2.3.1:
     clap "^1.0.9"
     source-map "^0.5.3"
 
+csstype@^2.2.0:
+  version "2.6.10"
+  resolved "https://registry.yarnpkg.com/csstype/-/csstype-2.6.10.tgz#e63af50e66d7c266edb6b32909cfd0aabe03928b"
+  integrity sha512-D34BqZU4cIlMCY93rZHbrq9pjTAQJ3U8S8rfBqjwHxkGPThWFjzZDQpgMJY0QViLxth6ZKYiwFBo14RdN44U/w==
+
 cubic2quad@^1.0.0:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/cubic2quad/-/cubic2quad-1.1.1.tgz#69b19c61a3f5b41ecf2f1d5fae8fb03415aa8b15"
@@ -5360,7 +5378,7 @@ loader-runner@^2.3.0:
   resolved "https://registry.yarnpkg.com/loader-runner/-/loader-runner-2.4.0.tgz#ed47066bfe534d7e84c4c7b9998c2a75607d9357"
   integrity sha512-Jsmr89RcXGIwivFY21FcRrisYZfvLMTWx5kOLc+JTxtpBOG6xML0vzbc6SEQG2FO9/4Fc3wW4LVcB5DmGflaRw==
 
-loader-utils@^1.0.2, loader-utils@^1.1.0, loader-utils@^1.4.0:
+loader-utils@^1.0.2, loader-utils@^1.1.0, loader-utils@^1.2.3, loader-utils@^1.4.0:
   version "1.4.0"
   resolved "https://registry.yarnpkg.com/loader-utils/-/loader-utils-1.4.0.tgz#c579b5e34cb34b1a74edc6c1fb36bfa371d5a613"
   integrity sha512-qH0WSMBtn/oHuwjy/NucEgbx5dbxxnxup9s4PVXJUDHZBQY+s0NWA9rJf53RBnQZxfch7euUui7hpoAPvALZdA==
@@ -5818,6 +5836,18 @@ moment@^2.24.0:
   resolved "https://registry.yarnpkg.com/moment/-/moment-2.24.0.tgz#0d055d53f5052aa653c9f6eb68bb5d12bf5c2b5b"
   integrity sha512-bV7f+6l2QigeBBZSM/6yTNq4P2fNpSWj/0e7jQcy87A8e7o2nAfP/34/2ky5Vw4B9S446EtIhodAzkFCcR4dQg==
 
+monaco-editor-webpack-plugin@^1.9.0:
+  version "1.9.0"
+  resolved "https://registry.yarnpkg.com/monaco-editor-webpack-plugin/-/monaco-editor-webpack-plugin-1.9.0.tgz#5b547281b9f404057dc5d8c5722390df9ac90be6"
+  integrity sha512-tOiiToc94E1sb50BgZ8q8WK/bxus77SRrwCqIpAB5er3cpX78SULbEBY4YPOB8kDolOzKRt30WIHG/D6gz69Ww==
+  dependencies:
+    loader-utils "^1.2.3"
+
+monaco-editor@*:
+  version "0.20.0"
+  resolved "https://registry.yarnpkg.com/monaco-editor/-/monaco-editor-0.20.0.tgz#5d5009343a550124426cb4d965a4d27a348b4dea"
+  integrity sha512-hkvf4EtPJRMQlPC3UbMoRs0vTAFAYdzFQ+gpMb8A+9znae1c43q8Mab9iVsgTcg/4PNiLGGn3SlDIa8uvK1FIQ==
+
 move-concurrently@^1.0.1:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/move-concurrently/-/move-concurrently-1.0.1.tgz#be2c005fda32e0b29af1f05d7c4b33214c701f92"
@@ -7493,6 +7523,15 @@ react-lifecycles-compat@^3.0.0, react-lifecycles-compat@^3.0.4:
   resolved "https://registry.yarnpkg.com/react-lifecycles-compat/-/react-lifecycles-compat-3.0.4.tgz#4f1a273afdfc8f3488a8c516bfda78f872352362"
   integrity sha512-fBASbA6LnOU9dOU2eW7aQ8xmYBSXUIWr+UmF9b1efZBazGNO+rcXT/icdKnYm2pTwcRylVUYwW7H1PHfLekVzA==
 
+react-monaco-editor@^0.35.0:
+  version "0.35.0"
+  resolved "https://registry.yarnpkg.com/react-monaco-editor/-/react-monaco-editor-0.35.0.tgz#ceaaca4f292571e95957871145bd7c5f76a4fd33"
+  integrity sha512-iQbJykYPgKko0yqphTVWi1vHFokFShv5qpWnFV2TvtliKG45x2LVF4/HC06MDVK4fBfp2lCrun+NUcEYMzAnNQ==
+  dependencies:
+    "@types/react" "^15.x || ^16.x"
+    monaco-editor "*"
+    prop-types "^15.7.2"
+
 react-redux@^5.0.6:
   version "5.1.2"
   resolved "https://registry.yarnpkg.com/react-redux/-/react-redux-5.1.2.tgz#b19cf9e21d694422727bf798e934a916c4080f57"