chore: Move editor into codebase (#2930)

shared/editor/marks/Underline.ts

@@ -0,0 +1,51 @@
+import { toggleMark } from "prosemirror-commands";
+import { MarkSpec, MarkType } from "prosemirror-model";
+import markInputRule from "../lib/markInputRule";
+import underlinesRule from "../rules/underlines";
+import Mark from "./Mark";
+
+export default class Underline extends Mark {
+  get name() {
+    return "underline";
+  }
+
+  get schema(): MarkSpec {
+    return {
+      parseDOM: [
+        { tag: "u" },
+        {
+          style: "text-decoration",
+          getAttrs: (value) => (value === "underline" ? {} : undefined),
+        },
+      ],
+      toDOM: () => ["u", 0],
+    };
+  }
+
+  get rulePlugins() {
+    return [underlinesRule];
+  }
+
+  inputRules({ type }: { type: MarkType }) {
+    return [markInputRule(/(?:__)([^_]+)(?:__)$/, type)];
+  }
+
+  keys({ type }: { type: MarkType }) {
+    return {
+      "Mod-u": toggleMark(type),
+    };
+  }
+
+  toMarkdown() {
+    return {
+      open: "__",
+      close: "__",
+      mixable: true,
+      expelEnclosingWhitespace: true,
+    };
+  }
+
+  parseMarkdown() {
+    return { mark: "underline" };
+  }
+}