Support markdown editor for issue template (#24400)

Fixes #24398

Task:
- [x] Reusing "textarea" like GitHub seems more friendly to users.
- [x] ^V image pasting and file uploading handling.

<details><summary>screenshots</summary>


![image](https://user-images.githubusercontent.com/18380374/235418877-00090552-ebda-411c-8e39-b47246bc8746.png)

![image](https://user-images.githubusercontent.com/18380374/235419073-dc33cad7-7626-4bce-9161-eb205c7384b5.png)
Display only one markdown editor:

![image](https://user-images.githubusercontent.com/18380374/235419098-ee21386d-2b2d-432e-bdb2-18646cc031e7.png)
Support file upload and ^V image pasting

![image](https://user-images.githubusercontent.com/18380374/235419364-7b390fa4-da56-437d-b55e-3847fbc049e7.png)

</details>

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

4 files changed, 88 insertions, 65 deletions

diff --git a/web_src/js/features/comp/ComboMarkdownEditor.js b/web_src/js/features/comp/ComboMarkdownEditor.js
index 90d1bcde5a..103e71daae 100644
--- a/web_src/js/features/comp/ComboMarkdownEditor.js
+++ b/web_src/js/features/comp/ComboMarkdownEditor.js
@@ -5,10 +5,9 @@ import {attachTribute} from '../tribute.js';
 import {hideElem, showElem, autosize} from '../../utils/dom.js';
 import {initEasyMDEImagePaste, initTextareaImagePaste} from './ImagePaste.js';
 import {handleGlobalEnterQuickSubmit} from './QuickSubmit.js';
-import {emojiString} from '../emoji.js';
 import {renderPreviewPanelContent} from '../repo-editor.js';
-import {matchEmoji, matchMention} from '../../utils/match.js';
 import {easyMDEToolbarActions} from './EasyMDEToolbarActions.js';
+import {initTextExpander} from './TextExpander.js';
 
 let elementIdCounter = 0;
 
@@ -43,14 +42,12 @@ class ComboMarkdownEditor {
 
   async init() {
     this.prepareEasyMDEToolbarActions();
+    this.setupContainer();
     this.setupTab();
     this.setupDropzone();
     this.setupTextarea();
-    this.setupExpander();
 
-    if (this.userPreferredEditor === 'easymde') {
-      await this.switchToEasyMDE();
-    }
+    await this.switchToUserPreference();
   }
 
   applyEditorHeights(el, heights) {
@@ -60,6 +57,11 @@ class ComboMarkdownEditor {
     if (heights.maxHeight) el.style.maxHeight = heights.maxHeight;
   }
 
+  setupContainer() {
+    initTextExpander(this.container.querySelector('text-expander'));
+    this.container.addEventListener('ce-editor-content-changed', (e) => this.options?.onContentChanged?.(this, e));
+  }
+
   setupTextarea() {
     this.textarea = this.container.querySelector('.markdown-text-editor');
     this.textarea._giteaComboMarkdownEditor = this;
@@ -103,64 +105,6 @@ class ComboMarkdownEditor {
     }
   }
 
-  setupExpander() {
-    const expander = this.container.querySelector('text-expander');
-    expander?.addEventListener('text-expander-change', ({detail: {key, provide, text}}) => {
-      if (key === ':') {
-        const matches = matchEmoji(text);
-        if (!matches.length) return provide({matched: false});
-
-        const ul = document.createElement('ul');
-        ul.classList.add('suggestions');
-        for (const name of matches) {
-          const emoji = emojiString(name);
-          const li = document.createElement('li');
-          li.setAttribute('role', 'option');
-          li.setAttribute('data-value', emoji);
-          li.textContent = `${emoji} ${name}`;
-          ul.append(li);
-        }
-
-        provide({matched: true, fragment: ul});
-      } else if (key === '@') {
-        const matches = matchMention(text);
-        if (!matches.length) return provide({matched: false});
-
-        const ul = document.createElement('ul');
-        ul.classList.add('suggestions');
-        for (const {value, name, fullname, avatar} of matches) {
-          const li = document.createElement('li');
-          li.setAttribute('role', 'option');
-          li.setAttribute('data-value', `${key}${value}`);
-
-          const img = document.createElement('img');
-          img.src = avatar;
-          li.append(img);
-
-          const nameSpan = document.createElement('span');
-          nameSpan.textContent = name;
-          li.append(nameSpan);
-
-          if (fullname && fullname.toLowerCase() !== name) {
-            const fullnameSpan = document.createElement('span');
-            fullnameSpan.classList.add('fullname');
-            fullnameSpan.textContent = fullname;
-            li.append(fullnameSpan);
-          }
-
-          ul.append(li);
-        }
-
-        provide({matched: true, fragment: ul});
-      }
-    });
-    expander?.addEventListener('text-expander-value', ({detail}) => {
-      if (detail?.item) {
-        detail.value = detail.item.getAttribute('data-value');
-      }
-    });
-  }
-
   setupDropzone() {
     const dropzoneParentContainer = this.container.getAttribute('data-dropzone-parent-container');
     if (dropzoneParentContainer) {
@@ -224,7 +168,16 @@ class ComboMarkdownEditor {
     return processed;
   }
 
+  async switchToUserPreference() {
+    if (this.userPreferredEditor === 'easymde') {
+      await this.switchToEasyMDE();
+    } else {
+      this.switchToTextarea();
+    }
+  }
+
   switchToTextarea() {
+    if (!this.easyMDE) return;
     showElem(this.textareaMarkdownToolbar);
     if (this.easyMDE) {
       this.easyMDE.toTextArea();
@@ -233,6 +186,7 @@ class ComboMarkdownEditor {
   }
 
   async switchToEasyMDE() {
+    if (this.easyMDE) return;
     // EasyMDE's CSS should be loaded via webpack config, otherwise our own styles can not overwrite the default styles.
     const {default: EasyMDE} = await import(/* webpackChunkName: "easymde" */'easymde');
     const easyMDEOpt = {
diff --git a/web_src/js/features/comp/ImagePaste.js b/web_src/js/features/comp/ImagePaste.js
index 9145b24062..dc335495a3 100644
--- a/web_src/js/features/comp/ImagePaste.js
+++ b/web_src/js/features/comp/ImagePaste.js
@@ -25,6 +25,10 @@ function clipboardPastedImages(e) {
   return files;
 }
 
+function triggerEditorContentChanged(target) {
+  target.dispatchEvent(new CustomEvent('ce-editor-content-changed', {bubbles: true}));
+}
+
 class TextareaEditor {
   constructor(editor) {
     this.editor = editor;
@@ -38,6 +42,7 @@ class TextareaEditor {
     editor.selectionStart = startPos;
     editor.selectionEnd = startPos + value.length;
     editor.focus();
+    triggerEditorContentChanged(editor);
   }
 
   replacePlaceholder(oldVal, newVal) {
@@ -54,6 +59,7 @@ class TextareaEditor {
     }
     editor.selectionStart = editor.selectionEnd;
     editor.focus();
+    triggerEditorContentChanged(editor);
   }
 }
 
@@ -70,6 +76,7 @@ class CodeMirrorEditor {
     endPoint.ch = startPoint.ch + value.length;
     editor.setSelection(startPoint, endPoint);
     editor.focus();
+    triggerEditorContentChanged(editor.getTextArea());
   }
 
   replacePlaceholder(oldVal, newVal) {
@@ -84,6 +91,7 @@ class CodeMirrorEditor {
     endPoint.ch += newVal.length;
     editor.setSelection(endPoint, endPoint);
     editor.focus();
+    triggerEditorContentChanged(editor.getTextArea());
   }
 }
 
diff --git a/web_src/js/features/comp/QuickSubmit.js b/web_src/js/features/comp/QuickSubmit.js
index 43424a949f..d598a59655 100644
--- a/web_src/js/features/comp/QuickSubmit.js
+++ b/web_src/js/features/comp/QuickSubmit.js
@@ -6,7 +6,9 @@ export function handleGlobalEnterQuickSubmit(target) {
   if ($form.length) {
     // here use the event to trigger the submit event (instead of calling `submit()` method directly)
     // otherwise the `areYouSure` handler won't be executed, then there will be an annoying "confirm to leave" dialog
-    $form.trigger('submit');
+    if ($form[0].checkValidity()) {
+      $form.trigger('submit');
+    }
   } else {
     // if no form, then the editor is for an AJAX request, dispatch an event to the target, let the target's event handler to do the AJAX request.
     // the 'ce-' prefix means this is a CustomEvent
diff --git a/web_src/js/features/comp/TextExpander.js b/web_src/js/features/comp/TextExpander.js
new file mode 100644
index 0000000000..e2840610df
--- /dev/null
+++ b/web_src/js/features/comp/TextExpander.js
@@ -0,0 +1,59 @@
+import {matchEmoji, matchMention} from '../../utils/match.js';
+import {emojiString} from '../emoji.js';
+
+export function initTextExpander(expander) {
+  expander?.addEventListener('text-expander-change', ({detail: {key, provide, text}}) => {
+    if (key === ':') {
+      const matches = matchEmoji(text);
+      if (!matches.length) return provide({matched: false});
+
+      const ul = document.createElement('ul');
+      ul.classList.add('suggestions');
+      for (const name of matches) {
+        const emoji = emojiString(name);
+        const li = document.createElement('li');
+        li.setAttribute('role', 'option');
+        li.setAttribute('data-value', emoji);
+        li.textContent = `${emoji} ${name}`;
+        ul.append(li);
+      }
+
+      provide({matched: true, fragment: ul});
+    } else if (key === '@') {
+      const matches = matchMention(text);
+      if (!matches.length) return provide({matched: false});
+
+      const ul = document.createElement('ul');
+      ul.classList.add('suggestions');
+      for (const {value, name, fullname, avatar} of matches) {
+        const li = document.createElement('li');
+        li.setAttribute('role', 'option');
+        li.setAttribute('data-value', `${key}${value}`);
+
+        const img = document.createElement('img');
+        img.src = avatar;
+        li.append(img);
+
+        const nameSpan = document.createElement('span');
+        nameSpan.textContent = name;
+        li.append(nameSpan);
+
+        if (fullname && fullname.toLowerCase() !== name) {
+          const fullnameSpan = document.createElement('span');
+          fullnameSpan.classList.add('fullname');
+          fullnameSpan.textContent = fullname;
+          li.append(fullnameSpan);
+        }
+
+        ul.append(li);
+      }
+
+      provide({matched: true, fragment: ul});
+    }
+  });
+  expander?.addEventListener('text-expander-value', ({detail}) => {
+    if (detail?.item) {
+      detail.value = detail.item.getAttribute('data-value');
+    }
+  });
+}