Templater update to handle html and inline erb

Update templater pre-processing approach to
flag (and thus mitigate) duplicate matches
during the "flag content as code" step

app/assets/javascripts/static_site_editor/services/templater.js

+/**
+ * The purpose of this file is to modify Markdown source such that templated code (embedded ruby currently) can be temporarily wrapped and unwrapped in codeblocks:
+ * 1. `wrap()`: temporarily wrap in codeblocks (useful for a WYSIWYG editing experience)
+ * 2. `unwrap()`: undo the temporarily wrapped codeblocks (useful for Markdown editing experience and saving edits)
+ *
+ * Without this `templater`, the templated code is otherwise interpreted as Markdown content resulting in loss of spacing, indentation, escape characters, etc.
+ *
+ */
+
 const ticks = '```';
 const marker = 'sse';
-const prefix = `${ticks} ${marker}\n`; // Space intentional due to https://github.com/nhn/tui.editor/blob/6bcec75c69028570d93d973aa7533090257eaae0/libs/to-mark/src/renderer.gfm.js#L26
-const postfix = `\n${ticks}`;
-const flagPrefix = `${marker}-${Date.now()}`;
-const template = `.| |\\t|\\n(?!(\\n|${flagPrefix}))`;
-const templatedRegex = new RegExp(`(^${prefix}(${template})+?${postfix}$)`, 'gm');
-
-const nonErbMarkupRegex = new RegExp(`^((<(?!%).+>){1}(${template})+(</.+>){1})$`, 'gm');
-const embeddedRubyBlockRegex = new RegExp(`(^<%(${template})+%>$)`, 'gm');
-const embeddedRubyInlineRegex = new RegExp(`(^.*[<|&lt;]%(${template})+$)`, 'gm');
-
-// Order is intentional (general to specific) where HTML markup is flagged first, then ERB blocks, then inline ERB
-// Order in combo with the `flag()` algorithm is used to mitigate potential duplicate pattern matches (ERB nested in HTML for example)
-const orderedPatterns = [nonErbMarkupRegex, embeddedRubyBlockRegex, embeddedRubyInlineRegex];
-
-const unwrap = source => {
-  let text = source;
-  const matches = text.match(templatedRegex);
+const wrapPrefix = `${ticks} ${marker}\n`; // Space intentional due to https://github.com/nhn/tui.editor/blob/6bcec75c69028570d93d973aa7533090257eaae0/libs/to-mark/src/renderer.gfm.js#L26
+const wrapPostfix = `\n${ticks}`;
+const markPrefix = `${marker}-${Date.now()}`;
 
-  if (matches) {
-    matches.forEach(match => {
-      const initial = match.replace(`${prefix}`, '').replace(`${postfix}`, '');
-      text = text.replace(match, initial);
-    });
-  }
+const reHelpers = {
+  template: `.| |\\t|\\n(?!(\\n|${markPrefix}))`,
+  openTag: '<[a-zA-Z]+.*?>',
+  closeTag: '</.+>',
+};
+const reTemplated = new RegExp(`(^${wrapPrefix}(${reHelpers.template})+?${wrapPostfix}$)`, 'gm');
+const rePreexistingCodeBlocks = new RegExp(`(^${ticks}.*\\n(.|\\s)+?${ticks}$)`, 'gm');
+const reHtmlMarkup = new RegExp(
+  `^((${reHelpers.openTag}){1}(${reHelpers.template})*(${reHelpers.closeTag}){1})$`,
+  'gm',
+);
+const reEmbeddedRubyBlock = new RegExp(`(^<%(${reHelpers.template})+%>$)`, 'gm');
+const reEmbeddedRubyInline = new RegExp(`(^.*[<|&lt;]%(${reHelpers.template})+$)`, 'gm');
 
-  return text;
+const patternGroups = {
+  ignore: [rePreexistingCodeBlocks],
+  // Order is intentional (general to specific) where HTML markup is marked first, then ERB blocks, then inline ERB
+  // Order in combo with the `mark()` algorithm is used to mitigate potential duplicate pattern matches (ERB nested in HTML for example)
+  allow: [reHtmlMarkup, reEmbeddedRubyBlock, reEmbeddedRubyInline],
 };
 
-const flag = (source, patterns) => {
+const mark = (source, groups) => {
   let text = source;
   let id = 0;
   const hash = {};
 
-  patterns.forEach(pattern => {
-    const matches = text.match(pattern);
-    if (matches) {
-      matches.forEach(match => {
-        const key = `${flagPrefix}${id}`;
-        text = text.replace(match, key);
-        hash[key] = match;
-        id += 1;
-      });
-    }
+  Object.entries(groups).forEach(([groupKey, group]) => {
+    group.forEach(pattern => {
+      const matches = text.match(pattern);
+      if (matches) {
+        matches.forEach(match => {
+          const key = `${markPrefix}-${groupKey}-${id}`;
+          text = text.replace(match, key);
+          hash[key] = match;
+          id += 1;
+        });
+      }
+    });
   });
 
   return { text, hash };
 };
 
-const wrap = source => {
-  const { text, hash } = flag(unwrap(source), orderedPatterns);
+const unmark = (text, hash) => {
+  let source = text;
 
-  let wrappedSource = text;
   Object.entries(hash).forEach(([key, value]) => {
-    wrappedSource = wrappedSource.replace(key, `${prefix}${value}${postfix}`);
+    const newVal = key.includes('ignore') ? value : `${wrapPrefix}${value}${wrapPostfix}`;
+    source = source.replace(key, newVal);
   });
 
-  return wrappedSource;
+  return source;
+};
+
+const unwrap = source => {
+  let text = source;
+  const matches = text.match(reTemplated);
+
+  if (matches) {
+    matches.forEach(match => {
+      const initial = match.replace(`${wrapPrefix}`, '').replace(`${wrapPostfix}`, '');
+      text = text.replace(match, initial);
+    });
+  }
+
+  return text;
+};
+
+const wrap = source => {
+  const { text, hash } = mark(unwrap(source), patternGroups);
+  return unmark(text, hash);
 };
 
 export default { wrap, unwrap };

changelogs/unreleased/38834-templater-exclude-pre-existing-codeblocks.yml

+---
+title: Add pre-processing step so preexisting codeblocks are preserved prior to flagging content as code in the static site editor's WYSIWYG mode.
+merge_request: 38834
+author:
+type: added

spec/frontend/static_site_editor/services/templater_spec.js

@@ -30,6 +30,15 @@ Below this line is a block of HTML.
   <h1>Heading</h1>
   <p>Some paragraph...</p>
 </div>
+
+Below this line is a codeblock of the same HTML that should be ignored and preserved.
+
+\`\`\` html
+<div>
+  <h1>Heading</h1>
+  <p>Some paragraph...</p>
+</div>
+\`\`\`
 `;
   const sourceTemplated = `Below this line is a simple ERB (single-line erb block) example.
 
@@ -69,6 +78,15 @@ Below this line is a block of HTML.
   <p>Some paragraph...</p>
 </div>
 \`\`\`
+
+Below this line is a codeblock of the same HTML that should be ignored and preserved.
+
+\`\`\` html
+<div>
+  <h1>Heading</h1>
+  <p>Some paragraph...</p>
+</div>
+\`\`\`
 `;
 
   it.each`