Initial commit 🎉

fbshipit-source-id: b6fc29740c6875d2e78953b8a7123890a67930f2
Co-authored-by: Sebastian McKenzie <sebmck@fb.com>
Co-authored-by: John Knox <jknox@fb.com>
Co-authored-by: Emil Sjölander <emilsj@fb.com>
Co-authored-by: Pritesh Nandgaonkar <prit91@fb.com>

src/ui/styled/sheet.js

@@ -0,0 +1,92 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+const invariant = require('invariant');
+
+function makeStyleTag(): HTMLStyleElement {
+  const tag = document.createElement('style');
+  tag.type = 'text/css';
+  tag.appendChild(document.createTextNode(''));
+
+  const {head} = document;
+  invariant(head, 'expected head');
+  head.appendChild(tag);
+
+  return tag;
+}
+
+export class StyleSheet {
+  constructor(isSpeedy?: boolean) {
+    this.injected = false;
+    this.isSpeedy = Boolean(isSpeedy);
+
+    this.flush();
+    this.inject();
+  }
+
+  ruleIndexes: Array<string>;
+  injected: boolean;
+  isSpeedy: boolean;
+  tag: HTMLStyleElement;
+
+  getRuleCount(): number {
+    return this.ruleIndexes.length;
+  }
+
+  flush() {
+    this.ruleIndexes = [];
+    if (this.tag) {
+      this.tag.innerHTML = '';
+    }
+  }
+
+  inject() {
+    if (this.injected) {
+      throw new Error('already injected stylesheet!');
+    }
+
+    this.tag = makeStyleTag();
+    this.injected = true;
+  }
+
+  delete(key: string) {
+    const index = this.ruleIndexes.indexOf(key);
+    if (index < 0) {
+      // TODO maybe error
+      return;
+    }
+
+    this.ruleIndexes.splice(index, 1);
+
+    const tag = this.tag;
+    if (this.isSpeedy) {
+      const sheet = tag.sheet;
+      invariant(sheet, 'expected sheet');
+
+      // $FlowFixMe: sheet is actually CSSStylesheet
+      sheet.deleteRule(index);
+    } else {
+      tag.removeChild(tag.childNodes[index + 1]);
+    }
+  }
+
+  insert(key: string, rule: string) {
+    const tag = this.tag;
+
+    if (this.isSpeedy) {
+      const sheet = tag.sheet;
+      invariant(sheet, 'expected sheet');
+
+      // $FlowFixMe: sheet is actually CSSStylesheet
+      sheet.insertRule(rule, sheet.cssRules.length);
+    } else {
+      tag.appendChild(document.createTextNode(rule));
+    }
+
+    this.ruleIndexes.push(key);
+  }
+}