1 files changed, 105 insertions, 0 deletions
diff --git a/toolkit/content/widgets/moz-button-group/moz-button-group.mjs b/toolkit/content/widgets/moz-button-group/moz-button-group.mjs
new file mode 100644
index 0000000000..0706f94762
--- /dev/null
+++ b/toolkit/content/widgets/moz-button-group/moz-button-group.mjs
@@ -0,0 +1,105 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import { html } from "chrome://global/content/vendor/lit.all.mjs";
+import { MozLitElement } from "chrome://global/content/lit-utils.mjs";
+
+export const PLATFORM_LINUX = "linux";
+export const PLATFORM_MACOS = "macosx";
+export const PLATFORM_WINDOWS = "win";
+
+/**
+ * A grouping of buttons. Primary button order will be set automatically based
+ * on class="primary", type="submit" or autofocus attribute. Set slot="primary"
+ * on a primary button that does not have primary styling to set its position.
+ *
+ * @tagname moz-button-group
+ * @property {string} platform - The detected platform, set automatically.
+ */
+export default class MozButtonGroup extends MozLitElement {
+  static queries = {
+    defaultSlotEl: "slot:not([name])",
+    primarySlotEl: "slot[name=primary]",
+  };
+
+  static properties = {
+    platform: { state: true },
+  };
+
+  constructor() {
+    super();
+    this.#detectPlatform();
+  }
+
+  #detectPlatform() {
+    if (typeof AppConstants !== "undefined") {
+      this.platform = AppConstants.platform;
+    } else if (navigator.platform.includes("Linux")) {
+      this.platform = PLATFORM_LINUX;
+    } else if (navigator.platform.includes("Mac")) {
+      this.platform = PLATFORM_MACOS;
+    } else {
+      this.platform = PLATFORM_WINDOWS;
+    }
+  }
+
+  onSlotchange(e) {
+    for (let child of this.defaultSlotEl.assignedNodes()) {
+      if (!(child instanceof Element)) {
+        // Text nodes won't support classList or getAttribute.
+        continue;
+      }
+      // Bug 1791816: These should check moz-button instead of button.
+      if (
+        child.localName == "button" &&
+        (child.classList.contains("primary") ||
+          child.getAttribute("type") == "submit" ||
+          child.hasAttribute("autofocus") ||
+          child.hasAttribute("default"))
+      ) {
+        child.slot = "primary";
+      }
+    }
+    this.#reorderLightDom();
+  }
+
+  #reorderLightDom() {
+    let primarySlottedChildren = [...this.primarySlotEl.assignedNodes()];
+    if (this.platform == PLATFORM_WINDOWS) {
+      primarySlottedChildren.reverse();
+      for (let child of primarySlottedChildren) {
+        child.parentElement.prepend(child);
+      }
+    } else {
+      for (let child of primarySlottedChildren) {
+        // Ensure the primary buttons are at the end of the light DOM.
+        child.parentElement.append(child);
+      }
+    }
+  }
+
+  updated(changedProperties) {
+    if (changedProperties.has("platform")) {
+      this.#reorderLightDom();
+    }
+  }
+
+  render() {
+    let slots = [
+      html` <slot @slotchange=${this.onSlotchange}></slot> `,
+      html` <slot name="primary"></slot> `,
+    ];
+    if (this.platform == PLATFORM_WINDOWS) {
+      slots = [slots[1], slots[0]];
+    }
+    return html`
+      <link
+        rel="stylesheet"
+        href="chrome://global/content/elements/moz-button-group.css"
+      />
+      ${slots}
+    `;
+  }
+}
+customElements.define("moz-button-group", MozButtonGroup);