Merge remote-tracking branch 'origin/ghc-8.10' into ghc-9.0

4 files changed, 559 insertions, 192 deletions

diff --git a/haddock-api/resources/html/js-src/details-helper.ts b/haddock-api/resources/html/js-src/details-helper.ts
deleted file mode 100644
index f13ac905..00000000
--- a/haddock-api/resources/html/js-src/details-helper.ts
+++ /dev/null
@@ -1,106 +0,0 @@
-import {getCookie} from "./cookies";
-
-interface HTMLDetailsElement extends HTMLElement {
-  open: boolean
-}
-
-interface DetailsInfo {
-  element: HTMLDetailsElement
-  openByDefault: boolean
-  toggles: HTMLElement[]
-}
-
-// Global state
-const detailsRegistry: { [id: string]: DetailsInfo } = {};
-const toggled: { [id: string]: true } = {}; /* stores which <details> are not in their default state */
-
-function lookupDetailsRegistry(id: string): DetailsInfo {
-  const info = detailsRegistry[id];
-  if (info == undefined) { throw new Error(`could not find <details> element with id '${id}'`); }
-  return info;
-}
-
-function onDetailsToggle(ev: Event) {
-  const element = ev.target as HTMLDetailsElement;
-  const id = element.id;
-  const info = lookupDetailsRegistry(id);
-  const isOpen = info.element.open;
-  for (const toggle of info.toggles) {
-    if (toggle.classList.contains('details-toggle-control')) {
-      toggle.classList.add(isOpen ? 'collapser' : 'expander');
-      toggle.classList.remove(isOpen ? 'expander' : 'collapser');
-    }
-  }
-  if (element.open == info.openByDefault) {
-    delete toggled[id];
-  } else {
-    toggled[id] = true;
-  }
-  rememberToggled();
-}
-
-function gatherDetailsElements() {
-  const els: HTMLDetailsElement[] = Array.prototype.slice.call(document.getElementsByTagName('details'));
-  for (const el of els) {
-    if (typeof el.id == "string" && el.id.length > 0) {
-      detailsRegistry[el.id] = {
-        element: el,
-        openByDefault: !!el.open,
-        toggles: [] // added later
-      };
-      el.addEventListener('toggle', onDetailsToggle);
-    }
-  }
-}
-
-function toggleDetails(id: string) {
-  const {element} = lookupDetailsRegistry(id);
-  element.open = !element.open;
-}
-
-function rememberToggled() {
-  const sections: string[] = Object.keys(toggled);
-  // cookie specific to this page; don't use setCookie which sets path=/
-  document.cookie = "toggled=" + encodeURIComponent(sections.join('+'));
-}
-
-function restoreToggled() {
-  const cookie = getCookie("toggled");
-  if (!cookie) { return; }
-  const ids = cookie.split('+');
-  for (const id of ids) {
-    const info = detailsRegistry[id];
-    toggled[id] = true;
-    if (info) {
-      info.element.open = !info.element.open;
-    }
-  }
-}
-
-function onToggleClick(ev: MouseEvent) {
-  ev.preventDefault();
-  const toggle = ev.currentTarget as HTMLElement;
-  const id = toggle.getAttribute('data-details-id');
-  if (!id) { throw new Error("element with class 'details-toggle' has no 'data-details-id' attribute!"); }
-  toggleDetails(id);
-}
-
-function initCollapseToggles() {
-  const toggles: HTMLElement[] = Array.prototype.slice.call(document.getElementsByClassName('details-toggle'));
-  toggles.forEach(toggle => {
-    const id = toggle.getAttribute('data-details-id');
-    if (!id) { throw new Error("element with class 'details-toggle' has no 'data-details-id' attribute!"); }
-    const info = lookupDetailsRegistry(id);
-    info.toggles.push(toggle);
-    toggle.addEventListener('click', onToggleClick);
-    if (toggle.classList.contains('details-toggle-control')) {
-      toggle.classList.add(info.element.open ? 'collapser' : 'expander');
-    }
-  });
-}
-
-export function init() {
-  gatherDetailsElements();
-  restoreToggled();
-  initCollapseToggles();
-}
\ No newline at end of file
diff --git a/haddock-api/resources/html/js-src/details-helper.tsx b/haddock-api/resources/html/js-src/details-helper.tsx
new file mode 100644
index 00000000..871b5417
--- /dev/null
+++ b/haddock-api/resources/html/js-src/details-helper.tsx
@@ -0,0 +1,464 @@
+// This file implements the UI and logic for collapsing and expanding
+// instance lists ("details").
+//
+// A configuration ('GlobalConfig') controlled by the UI is persisted
+// in local storage in the user's browser. The configuration includes:
+//
+// * a global default state ('defaultInstanceState') for all instance
+//   lists. The possible values for the global default are "collapsed"
+//   and "expanded".
+//
+// * a global boolean option ('rememberToggles') to remember which
+//   specific instance lists are not in the default state (e.g. which
+//   instance lists are expanded when the default is "collapsed").
+//
+// * a local / per-page record of which specific instance lists are
+//   not in the default state, when the global option
+//   ('rememberToggles') to remember this info is enabled.
+//
+// The UI consists of an Instances menu with buttons for expanding and
+// collapsing all instance lists in the current module, a checkbox for
+// setting the global default state, and a checkbox to enable
+// remembering which instance lists are not in the global default
+// state. Also, each instance list on each module page has buttons for
+// collapsing and expanding.
+//
+// The logic of the UI is as follows:
+//
+// * setting the global default state erases any record of which
+//   specific instances are in the non-default state, and collapses or
+//   expands all instance lists on the current page to be in the
+//   global default state.
+//
+// * changing boolean option for remembering which specific instance
+//   lists are not in the default state erases any existing record of
+//   which instances are not in the default state across all pages,
+//   and updates the record for the current page when the option is
+//   set to true. No collapsing or expanding is done.
+//
+// * toggling the collapse/expand state of a specific instance list
+//   causes the state of that specific instance list to be recorded in
+//   the persisted configuration iff the new state of that specific
+//   instance list is different from the global default state, and the
+//   option to remember instance list states is enabled. There are two
+//   ways to toggle the collapse/expand state of a specific instance,
+//   by clicking its collapse/expand button, and by clicking the
+//   "collapse all" or "expand all" button in the Instances menu.
+//
+// This file also implements an association between elements (with
+// class "details-toggle" and "details-toggle-control") that can be
+// clicked to expand/collapse <details> elements, and the details
+// elements themselves. Note that this covers both <details> elements
+// that list instances -- what the above explained UI and logic is
+// concerned with -- and details about individual instances themselves
+// -- which the above is not concerend with. The association includes
+// adding event listeners that change CSS classes back and forth
+// between "expander" and "collapser"; these classes determine whether
+// an element is adorned with a right arrow ("expander") or a down
+// arrow ("collapser"). I don't understand why we don't directly use
+// the the HTML <summary> element type to allow the <details> elements
+// to be directly clickable.
+import preact = require("preact");
+
+const { h, Component } = preact;
+
+enum DefaultState { Closed, Open }
+
+interface GlobalConfig {
+  defaultInstanceState: DefaultState
+  rememberToggles: boolean
+}
+
+// Hackage domain-wide config
+const globalConfig: GlobalConfig = {
+  defaultInstanceState: DefaultState.Open,
+  rememberToggles: true,
+};
+
+class PreferencesButton extends Component<any, any> {
+  render(props: { title: string, onClick: () => void }) {
+    function onClick(e: Event) {
+      e.preventDefault();
+      props.onClick();
+    }
+    return <li><a href="#" onClick={onClick}>{props.title}</a></li>;
+  }
+}
+
+function addPreferencesButton(action: () => void) {
+  const pageMenu = document.querySelector('#page-menu') as HTMLUListElement;
+  const dummy = document.createElement('li');
+  pageMenu.insertBefore(dummy, pageMenu.firstChild);
+  preact.render(<PreferencesButton onClick={action} title="Instances" />, pageMenu, dummy);
+}
+
+type PreferencesProps = {
+  showHideTrigger: (action: () => void) => void
+}
+
+type PreferencesState = {
+  isVisible: boolean
+}
+
+class Preferences extends Component<PreferencesProps, PreferencesState> {
+  componentWillMount() {
+    document.addEventListener('mousedown', this.hide.bind(this));
+
+    document.addEventListener('keydown', (e) => {
+      if (this.state.isVisible) {
+        if (e.key === 'Escape') {
+          this.hide();
+        }
+      }
+    })
+  }
+
+  hide() {
+    this.setState({ isVisible: false });
+  }
+
+  show() {
+    if (!this.state.isVisible) {
+      this.setState({ isVisible: true });
+    }
+  }
+
+  toggleVisibility() {
+    if (this.state.isVisible) {
+      this.hide();
+    } else {
+      this.show();
+    }
+  }
+
+  componentDidMount() {
+    this.props.showHideTrigger(this.toggleVisibility.bind(this));
+  }
+
+  render(props: PreferencesProps, state: PreferencesState) {
+    const stopPropagation = (e: Event) => { e.stopPropagation(); };
+
+    return <div id="preferences" class={state.isVisible ? '' : 'hidden'}>
+        <div id="preferences-menu" class="dropdown-menu" onMouseDown={stopPropagation}>
+          <PreferencesMenu />
+        </div>
+      </div>;
+  }
+}
+
+function storeGlobalConfig() {
+  const json = JSON.stringify(globalConfig);
+  try {
+    // https://developer.mozilla.org/en-US/docs/Web/API/Storage/setItem#Exceptions.
+    localStorage.setItem('global', json);
+  } catch (e) {}
+}
+
+var globalConfigLoaded: boolean = false;
+
+function loadGlobalConfig() {
+  if (globalConfigLoaded) { return; }
+  globalConfigLoaded = true;
+  const global = localStorage.getItem('global');
+  if (!global) { return; }
+  try {
+    const globalConfig_ = JSON.parse(global);
+    globalConfig.defaultInstanceState = globalConfig_.defaultInstanceState;
+    globalConfig.rememberToggles = globalConfig_.rememberToggles;
+  } catch(e) {
+    // Gracefully handle errors related to changed config format.
+    if (e instanceof SyntaxError || e instanceof TypeError) {
+      localStorage.removeItem('global');
+    } else {
+      throw e;
+    }
+  }
+}
+
+function setDefaultInstanceState(s: DefaultState) {
+  return (e: Event) => {
+    globalConfig.defaultInstanceState = s;
+    putInstanceListsInDefaultState();
+    storeGlobalConfig();
+    clearLocalStorage();
+    storeLocalConfig();
+  }
+}
+
+function setRememberToggles(e: Event) {
+  const checked: boolean = (e as any).target.checked;
+  globalConfig.rememberToggles = checked;
+  storeGlobalConfig();
+  clearLocalStorage();
+  storeLocalConfig();
+}
+
+// Click event consumer for "default collapse" instance menu check box.
+function defaultCollapseOnClick(e: Event) {
+  const us = document.getElementById('default-collapse-instances') as HTMLInputElement;
+  if (us !== null) {
+    if (us.checked) {
+      setDefaultInstanceState(DefaultState.Closed)(e);
+    } else {
+      setDefaultInstanceState(DefaultState.Open)(e);
+    }
+  }
+}
+
+// Instances menu.
+function PreferencesMenu() {
+  loadGlobalConfig();
+  return <div>
+      <div>
+        <button type="button"
+                onClick={expandAllInstances}>
+        Expand All Instances
+        </button>
+        <button type="button"
+                onClick={collapseAllInstances}>
+        Collapse All Instances
+        </button>
+      </div>
+      <div>
+        <input type="checkbox"
+               id="default-collapse-instances"
+               name="default-instance-state"
+               checked={globalConfig.defaultInstanceState===DefaultState.Closed}
+               onClick={defaultCollapseOnClick}></input>
+
+        <span>Collapse All Instances By Default</span>
+      </div>
+      <div>
+        <input type="checkbox"
+               id="remember-toggles"
+               name="remember-toggles"
+               checked={globalConfig.rememberToggles}
+               onClick={setRememberToggles}></input>
+        <label for="remember-toggles">Remember Manually Collapsed/Expanded Instances</label>
+      </div>
+    </div>;
+}
+
+interface HTMLDetailsElement extends HTMLElement {
+  open: boolean
+}
+
+interface DetailsInfo {
+  element: HTMLDetailsElement
+  // Here 'toggles' is the list of all elements of class
+  // 'details-toggle-control' that control toggling 'element'. I
+  // believe this list is always length zero or one.
+  toggles: HTMLElement[]
+}
+
+// Mapping from <details> elements to their info.
+const detailsRegistry: { [id: string]: DetailsInfo } = {};
+
+function lookupDetailsRegistry(id: string): DetailsInfo {
+  const info = detailsRegistry[id];
+  if (info == undefined) { throw new Error(`could not find <details> element with id '${id}'`); }
+  return info;
+}
+
+// Return true iff instance lists are open by default.
+function getDefaultOpenSetting(): boolean {
+  return globalConfig.defaultInstanceState == DefaultState.Open;
+}
+
+// Event handler for "toggle" events, which are triggered when a
+// <details> element's "open" property changes.  We don't deal with
+// any config stuff here, because we only change configs in response
+// to mouse clicks. In contrast, for example, this event is triggred
+// automatically once for every <details> element when the user clicks
+// the "collapse all elements" button.
+function onToggleEvent(ev: Event) {
+  const element = ev.target as HTMLDetailsElement;
+  const id = element.id;
+  const info = lookupDetailsRegistry(id);
+  const isOpen = info.element.open;
+  // Update the CSS of the toggle element users can click on to toggle
+  // 'element'. The "collapser" and "expander" classes control what
+  // kind of arrow appears next to the 'toggle' element.
+  for (const toggle of info.toggles) {
+    if (toggle.classList.contains('details-toggle-control')) {
+      toggle.classList.add(isOpen ? 'collapser' : 'expander');
+      toggle.classList.remove(isOpen ? 'expander' : 'collapser');
+    }
+  }
+}
+
+function gatherDetailsElements() {
+  const els: HTMLDetailsElement[] = Array.prototype.slice.call(document.getElementsByTagName('details'));
+  for (const el of els) {
+    if (typeof el.id == "string" && el.id.length > 0) {
+      detailsRegistry[el.id] = {
+        element: el,
+        toggles: [] // Populated later by 'initCollapseToggles'.
+      };
+      el.addEventListener('toggle', onToggleEvent);
+    }
+  }
+}
+
+// Return the id of the <details> element that the given 'toggle'
+// element toggles.
+function getDataDetailsId(toggle: Element): string {
+  const id = toggle.getAttribute('data-details-id');
+  if (!id) { throw new Error("element with class " + toggle + " has no 'data-details-id' attribute!"); }
+  return id;
+}
+
+// Toggle the "open" state of a <details> element when that element's
+// toggle element is clicked.
+function toggleDetails(toggle: Element) {
+  const id = getDataDetailsId(toggle);
+  const {element} = lookupDetailsRegistry(id);
+  element.open = !element.open;
+}
+
+// Prefix for local keys used with local storage. Idea is that other
+// modules could also use local storage with a different prefix and we
+// wouldn't step on each other's toes.
+//
+// NOTE: we're using the browser's "local storage" API via the
+// 'localStorage' object to store both "local" (to the current Haddock
+// page) and "global" (across all Haddock pages) configuration. Be
+// aware of these two different uses of the term "local".
+const localStoragePrefix: string = "local-details-config:";
+
+// Local storage key for the current page.
+function localStorageKey(): string {
+  return localStoragePrefix + document.location.pathname;
+}
+
+// Clear all local storage related to instance list configs.
+function clearLocalStorage() {
+  const keysToDelete: string[] = [];
+  for (var i = 0; i < localStorage.length; ++i) {
+    const key = localStorage.key(i);
+    if (key !== null && key.startsWith(localStoragePrefix)) {
+      keysToDelete.push(key);
+    }
+  }
+  keysToDelete.forEach(key => {
+    localStorage.removeItem(key);
+  });
+}
+
+// Compute and save the set of instance list ids that aren't in the
+// default state.
+function storeLocalConfig() {
+  if (!globalConfig.rememberToggles) return;
+  const instanceListToggles: HTMLElement[] =
+    // Restrict to 'details-toggle' elements for "instances"
+    // *plural*. These are the toggles that control instance lists and
+    // not the list of methods for individual instances.
+    Array.prototype.slice.call(document.getElementsByClassName(
+      'instances details-toggle details-toggle-control'));
+  const nonDefaultInstanceListIds: string[] = [];
+  instanceListToggles.forEach(toggle => {
+    const id = getDataDetailsId(toggle);
+    const details = document.getElementById(id) as HTMLDetailsElement;
+    if (details.open != getDefaultOpenSetting()) {
+      nonDefaultInstanceListIds.push(id);
+    }
+  });
+
+  const json = JSON.stringify(nonDefaultInstanceListIds);
+  try {
+    // https://developer.mozilla.org/en-US/docs/Web/API/Storage/setItem#Exceptions.
+    localStorage.setItem(localStorageKey(), json);
+  } catch (e) {}
+}
+
+function putInstanceListsInDefaultState() {
+  switch (globalConfig.defaultInstanceState) {
+    case DefaultState.Closed: _collapseAllInstances(true); break;
+    case DefaultState.Open: _collapseAllInstances(false); break;
+    default: break;
+  }
+}
+
+// Expand and collapse instance lists according to global and local
+// config.
+function restoreToggled() {
+  loadGlobalConfig();
+  putInstanceListsInDefaultState();
+  if (!globalConfig.rememberToggles) { return; }
+  const local = localStorage.getItem(localStorageKey());
+  if (!local) { return; }
+  try {
+    const nonDefaultInstanceListIds: string[] = JSON.parse(local);
+    nonDefaultInstanceListIds.forEach(id => {
+      const info = lookupDetailsRegistry(id);
+      info.element.open = ! getDefaultOpenSetting();
+    });
+  } catch(e) {
+    // Gracefully handle errors related to changed config format.
+    if (e instanceof SyntaxError || e instanceof TypeError) {
+      localStorage.removeItem(localStorageKey());
+    } else {
+      throw e;
+    }
+  }
+}
+
+// Handler for clicking on the "toggle" element that toggles the
+// <details> element with id given by the 'data-details-id' property
+// of the "toggle" element.
+function onToggleClick(ev: MouseEvent) {
+  ev.preventDefault();
+  const toggle = ev.currentTarget as HTMLElement;
+  toggleDetails(toggle);
+  storeLocalConfig();
+}
+
+// Set event handlers on elements responsible for expanding and
+// collapsing <details> elements.
+//
+// This applies to all 'details-toggle's, not just to to top-level
+// 'details-toggle's that control instance lists.
+function initCollapseToggles() {
+  const toggles: HTMLElement[] = Array.prototype.slice.call(document.getElementsByClassName('details-toggle'));
+  toggles.forEach(toggle => {
+    const id = getDataDetailsId(toggle);
+    const info = lookupDetailsRegistry(id);
+    info.toggles.push(toggle);
+    toggle.addEventListener('click', onToggleClick);
+    if (toggle.classList.contains('details-toggle-control')) {
+      toggle.classList.add(info.element.open ? 'collapser' : 'expander');
+    }
+  });
+}
+
+// Collapse or expand all instances.
+function _collapseAllInstances(collapse: boolean) {
+  const ilists = document.getElementsByClassName('subs instances');
+  [].forEach.call(ilists, function (ilist : Element) {
+    const toggleType = collapse ? 'collapser' : 'expander';
+    const toggle = ilist.getElementsByClassName('instances ' + toggleType)[0];
+    if (toggle) {
+      toggleDetails(toggle);
+    }
+  });
+}
+
+function collapseAllInstances() {
+  _collapseAllInstances(true);
+  storeLocalConfig();
+}
+
+function expandAllInstances() {
+  _collapseAllInstances(false);
+  storeLocalConfig();
+}
+
+export function init(showHide?: (action: () => void) => void) {
+  gatherDetailsElements();
+  initCollapseToggles();
+  restoreToggled();
+  preact.render(
+    <Preferences showHideTrigger={showHide || addPreferencesButton} />,
+    document.body
+  );
+}
diff --git a/haddock-api/resources/html/js-src/init.ts b/haddock-api/resources/html/js-src/init.ts
index 877874ae..1bfa8b3c 100644
--- a/haddock-api/resources/html/js-src/init.ts
+++ b/haddock-api/resources/html/js-src/init.ts
@@ -17,6 +17,6 @@ function onDomReady(callback: () => void) {
 onDomReady(() => {
   document.body.classList.add('js-enabled');
   styleMenu.init();
-  detailsHelper.init();
   quickJump.init();
-});
\ No newline at end of file
+  detailsHelper.init();
+});
diff --git a/haddock-api/resources/html/js-src/style-menu.tsx b/haddock-api/resources/html/js-src/style-menu.tsx
index bab840ca..2eb8344e 100644
--- a/haddock-api/resources/html/js-src/style-menu.tsx
+++ b/haddock-api/resources/html/js-src/style-menu.tsx
@@ -4,91 +4,14 @@ import {getCookie, setCookie, clearCookie} from "./cookies";
 import preact = require("preact");
 
 const { h, Component } = preact;
-const rspace = /\s\s+/g,
-    rtrim = /^\s+|\s+$/g;
-
-function spaced(s: string) { return (" " + s + " ").replace(rspace, " "); }
-function trim(s: string)   { return s.replace(rtrim, ""); }
-
-function hasClass(elem: Element, value: string) {
-  const className = spaced(elem.className || "");
-  return className.indexOf( " " + value + " " ) >= 0;
-}
-
-function addClass(elem: Element, value: string) {
-  const className = spaced(elem.className || "");
-  if ( className.indexOf( " " + value + " " ) < 0 ) {
-    elem.className = trim(className + " " + value);
-  }
-}
-
-function removeClass(elem: Element, value: string) {
-  let className = spaced(elem.className || "");
-  className = className.replace(" " + value + " ", " ");
-  elem.className = trim(className);
-}
-
-function toggleClass(elem: Element, valueOn: string, valueOff: string, bool?: boolean): boolean {
-  if (bool == null) { bool = ! hasClass(elem, valueOn); }
-  if (bool) {
-    removeClass(elem, valueOff);
-    addClass(elem, valueOn);
-  }
-  else {
-    removeClass(elem, valueOn);
-    addClass(elem, valueOff);
-  }
-  return bool;
-}
-
-function makeClassToggle(valueOn: string, valueOff: string): (elem: Element, bool?: boolean) => boolean {
-  return function(elem, bool) {
-    return toggleClass(elem, valueOn, valueOff, bool);
-  }
-}
-
-const toggleShow = makeClassToggle("show", "hide");
 
+// Get all of the styles that are available
 function styles(): HTMLLinkElement[] {
   const es = Array.prototype.slice.call(document.getElementsByTagName("link"));
   return es.filter((a: HTMLLinkElement) => a.rel.indexOf("style") != -1 && a.title);
 }
 
-class StyleMenuButton extends Component<any, any> {
-
-  render(props: { stys: string[] }) {
-    function action() {
-      styleMenu();
-      return false;
-    };
-
-    return <li><div id='style-menu-holder' onClick={action}>
-      <a href='#'>Style &#9662;</a>
-      <ul id='style-menu' class='hide'>
-        {props.stys.map((sty) => {
-              function action() {
-                setActiveStyleSheet(sty);
-                return false;
-              };
-
-              return <li><a href='#' onClick={action}>{sty}</a></li>;
-        })}
-      </ul>
-    </div></li>;
-  }
-
-}
-
-function addStyleMenu() {
-  const stys = styles().map((s) => s.title);
-  if (stys.length > 1) {
-    const pageMenu = document.querySelector('#page-menu') as HTMLUListElement;
-    const dummy = document.createElement('li');
-    pageMenu.appendChild(dummy);
-    preact.render(<StyleMenuButton stys={stys} title="Style"/>, pageMenu, dummy);
-  }
-}
-
+// Set a style (including setting the cookie)
 function setActiveStyleSheet(title: string) {
   const as = styles();
   let found: null | HTMLLinkElement = null;
@@ -110,17 +33,103 @@ function setActiveStyleSheet(title: string) {
   }
 }
 
+// Reset the style based on the cookie
 function resetStyle() {
   const s = getCookie("haddock-style");
   if (s) setActiveStyleSheet(s);
 }
 
-function styleMenu(show?: boolean) {
-  const m = document.getElementById('style-menu');
-  if (m) toggleShow(m, show);
+class StylesButton extends Component<any, any> {
+  render(props: { title: string, onClick: () => void }) {
+    function onClick(e: Event) {
+      e.preventDefault();
+      props.onClick();
+    }
+    return <li><a href="#" onClick={onClick}>{props.title}</a></li>;
+  }
 }
 
-export function init() {
-  addStyleMenu();
+// Add the style menu button
+function addStyleMenu(stys: string[], action: () => void) {
+  if (stys.length > 1) {
+    const pageMenu = document.querySelector('#page-menu') as HTMLUListElement;
+    const dummy = document.createElement('li');
+    pageMenu.appendChild(dummy);
+    preact.render(<StylesButton onClick={action} title="Styles"/>, pageMenu, dummy);
+  }
+}
+
+type StyleProps = {
+  styles: string[]
+  showHideTrigger: (action: () => void) => void
+}
+
+type StyleState = {
+  isVisible: boolean
+}
+
+// Represents the full style dropdown
+class Styles extends Component<StyleProps, StyleState> {
+
+  componentWillMount() {
+    document.addEventListener('mousedown', this.hide.bind(this));
+
+    document.addEventListener('keydown', (e) => {
+      if (this.state.isVisible) {
+        if (e.key === 'Escape') {
+          this.hide();
+        }
+      }
+    })
+  }
+
+  hide() {
+    this.setState({ isVisible: false });
+  }
+
+  show() {
+    if (!this.state.isVisible) {
+      this.setState({ isVisible: true });
+    }
+  }
+
+  toggleVisibility() {
+    if (this.state.isVisible) {
+      this.hide();
+    } else {
+      this.show();
+    }
+  }
+
+  componentDidMount() {
+    this.props.showHideTrigger(this.toggleVisibility.bind(this));
+  }
+
+  render(props: StyleProps, state: StyleState) {
+    const stopPropagation = (e: Event) => { e.stopPropagation(); };
+
+    return <div id="style" class={state.isVisible ? '' : 'hidden'}>
+        <div id="style-menu" class="dropdown-menu" onMouseDown={stopPropagation}>
+          {
+            props.styles.map((sty) =>
+              <button type="button"
+                      onClick={(e) => { this.hide(); setActiveStyleSheet(sty) }}>
+                {sty}
+              </button>
+            )
+          }
+        </div>
+      </div>;
+  }
+}
+
+
+export function init(showHide?: (action: () => void) => void) {
+  const stys = styles().map((s) => s.title);
+  const addStylesButton = (action: () => void) => addStyleMenu(stys, action)
   resetStyle();
+  preact.render(
+    <Styles showHideTrigger={showHide || addStylesButton} styles={stys} />,
+    document.body
+  );
 }