Escape markdown sequences (#2208)

* escape inline markdown character

* fix typo

* improve document around custom markdown plugin and add escape sequence utils

* recover inline escape sequences on edit

* remove escape sequences from plain text body

* use `s` for strike-through instead of del

* escape block markdown sequences

* fix remove escape sequence was not removing all slashes from plain text

* recover block sequences on edit

src/app/plugins/markdown/utils.ts

@@ -0,0 +1,83 @@
+import { findAndReplace } from '../../utils/findAndReplace';
+import { ESC_BLOCK_SEQ, UN_ESC_BLOCK_SEQ } from './block/rules';
+import { EscapeRule, INLINE_SEQUENCE_SET } from './inline/rules';
+import { runInlineRule } from './inline/runner';
+import { replaceMatch } from './internal';
+
+/**
+ * Removes escape sequences from markdown inline elements in the given plain-text.
+ * This function unescapes characters that are escaped with backslashes (e.g., `\*`, `\_`)
+ * in markdown syntax, returning the original plain-text with markdown characters in effect.
+ *
+ * @param text - The input markdown plain-text containing escape characters (e.g., `"some \*italic\*"`)
+ * @returns The plain-text with markdown escape sequences removed (e.g., `"some *italic*"`)
+ */
+export const unescapeMarkdownInlineSequences = (text: string): string =>
+  runInlineRule(text, EscapeRule, (t) => {
+    if (t === '') return t;
+    return unescapeMarkdownInlineSequences(t);
+  }) ?? text;
+
+/**
+ * Recovers the markdown escape sequences in the given plain-text.
+ * This function adds backslashes (`\`) before markdown characters that may need escaping
+ * (e.g., `*`, `_`) to ensure they are treated as literal characters and not part of markdown formatting.
+ *
+ * @param text - The input plain-text that may contain markdown sequences (e.g., `"some *italic*"`)
+ * @returns The plain-text with markdown escape sequences added (e.g., `"some \*italic\*"`)
+ */
+export const escapeMarkdownInlineSequences = (text: string): string => {
+  const regex = new RegExp(`(${INLINE_SEQUENCE_SET})`, 'g');
+  const parts = findAndReplace(
+    text,
+    regex,
+    (match) => {
+      const [, g1] = match;
+      return `\\${g1}`;
+    },
+    (t) => t
+  );
+
+  return parts.join('');
+};
+
+/**
+ * Removes escape sequences from markdown block elements in the given plain-text.
+ * This function unescapes characters that are escaped with backslashes (e.g., `\>`, `\#`)
+ * in markdown syntax, returning the original plain-text with markdown characters in effect.
+ *
+ * @param {string} text - The input markdown plain-text containing escape characters (e.g., `\> block quote`).
+ * @param {function} processPart - It takes the plain-text as input and returns a modified version of it.
+ * @returns {string} The plain-text with markdown escape sequences removed and markdown formatting applied.
+ */
+export const unescapeMarkdownBlockSequences = (
+  text: string,
+  processPart: (text: string) => string
+): string => {
+  const match = text.match(ESC_BLOCK_SEQ);
+
+  if (!match) return processPart(text);
+
+  const [, g1] = match;
+  return replaceMatch(text, match, g1, (t) => [processPart(t)]).join('');
+};
+
+/**
+ * Escapes markdown block elements by adding backslashes before markdown characters
+ * (e.g., `\>`, `\#`) that are normally interpreted as markdown syntax.
+ *
+ * @param {string} text - The input markdown plain-text that may contain markdown elements (e.g., `> block quote`).
+ * @param {function} processPart - It takes the plain-text as input and returns a modified version of it.
+ * @returns {string} The plain-text with markdown escape sequences added, preventing markdown formatting.
+ */
+export const escapeMarkdownBlockSequences = (
+  text: string,
+  processPart: (text: string) => string
+): string => {
+  const match = text.match(UN_ESC_BLOCK_SEQ);
+
+  if (!match) return processPart(text);
+
+  const [, g1] = match;
+  return replaceMatch(text, match, `\\${g1}`, (t) => [processPart(t)]).join('');
+};