hcengineering · ArtyomSavchenko · Feb 3, 2026 · Feb 3, 2026 · Feb 3, 2026
diff --git a/packages/theme/styles/prose.scss b/packages/theme/styles/prose.scss
@@ -574,13 +574,24 @@ pre.proseCodeBlock>pre.proseCode {
   .mermaidPreviewContainer {
     padding: 0.5rem;
     cursor: default;
-    overflow-x: auto;
+    overflow: auto;
   }
 
   &:not(.folded) .mermaidPreviewContainer {
     border-top: 1px solid var(--border-color);
     min-height: 6rem;
   }
+
+  .mermaidPreview {
+    width: 100%;
+
+    svg {
+      width: 100%;
+      max-width: 100%;
+      height: auto;
+      display: block;
+    }
+  }
 }
 
 .proseInlineCommentHighlight {
@@ -602,4 +613,4 @@ pre.proseCodeBlock>pre.proseCode {
 
 .theme-light {
   @include meta.load-css('./github-light.scss');
-}
+}
diff --git a/plugins/text-editor-resources/src/components/extension/codeSnippets/MermaidPopup.svelte b/plugins/text-editor-resources/src/components/extension/codeSnippets/MermaidPopup.svelte
@@ -0,0 +1,73 @@
+<!--
+//
+// Copyright © 2026 Hardcore Engineering Inc.
+//
+// Licensed under the Eclipse Public License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License. You may
+// obtain a copy of the License at https://www.eclipse.org/legal/epl-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+-->
+<script lang="ts">
+  import { Html, Modal, ButtonIcon, IconClose, IconMaximize, IconMinimize, Scroller } from '@hcengineering/ui'
+  import { createEventDispatcher } from 'svelte'
+
+  export let svg: string
+  export let fullSize = false
+
+  const dispatch = createEventDispatcher()
+</script>
+
+<Modal type={'type-component'} padding={'0.5rem'} bottomPadding={'0'} on:fullsize on:close>
+  <svelte:fragment slot="beforeTitle">
+    <ButtonIcon
+      icon={IconClose}
+      kind={'tertiary'}
+      size={'small'}
+      noPrint
+      on:click={() => {
+        dispatch('close')
+      }}
+    />
+    <div class="hulyHeader-divider short no-line no-print" />
+    <ButtonIcon
+      icon={!fullSize ? IconMaximize : IconMinimize}
+      kind={'tertiary'}
+      size={'small'}
+      noPrint
+      on:click={() => {
+        fullSize = !fullSize
+        dispatch('fullsize', fullSize)
+      }}
+    />
+    <div class="hulyHeader-divider short no-print" />
+  </svelte:fragment>
+
+  <Scroller horizontal stickedScrollBars thinScrollBars>
+    <div class="mermaid-container">
+      <Html value={svg} />
+    </div>
+  </Scroller>
+</Modal>
+
+<style>
+  .mermaid-container {
+    display: flex;
+    justify-content: center;
+    align-items: flex-start;
+    width: 100%;
+  }
+
+  .mermaid-container :global(svg) {
+    max-width: 100%;
+    height: auto;
+    display: block;
+    margin: 0 auto;
+  }
+</style>
diff --git a/plugins/text-editor-resources/src/components/extension/codeSnippets/mermaid.ts b/plugins/text-editor-resources/src/components/extension/codeSnippets/mermaid.ts
@@ -15,16 +15,19 @@
 
 import { codeBlockOptions } from '@hcengineering/text'
 import { getCurrentTheme, isThemeDark, themeStore } from '@hcengineering/theme'
+import { showPopup } from '@hcengineering/ui'
+import { mergeAttributes } from '@tiptap/core'
 import { CodeBlockLowlight, type CodeBlockLowlightOptions } from '@tiptap/extension-code-block-lowlight'
 import { type Node as ProseMirrorNode } from '@tiptap/pm/model'
 import { NodeSelection, Plugin, PluginKey, TextSelection, type Transaction } from '@tiptap/pm/state'
 import { Decoration, DecorationSet, type EditorView } from '@tiptap/pm/view'
 import { createLowlight } from 'lowlight'
 import type { MermaidConfig } from 'mermaid'
+import { createRelativePositionFromTypeIndex, type RelativePosition, type Doc as YDoc } from 'yjs'
+
 import { isChangeEditable } from '../hooks/editable'
 
-import { mergeAttributes } from '@tiptap/core'
-import { createRelativePositionFromTypeIndex, type RelativePosition, type Doc as YDoc } from 'yjs'
+import MermaidPopup from './MermaidPopup.svelte'
 
 export interface MermaidOptions extends CodeBlockLowlightOptions {
   ydoc?: YDoc
@@ -156,6 +159,9 @@ export const MermaidExtension = CodeBlockLowlight.extend<MermaidOptions>({
         diagramBuilder: () => null,
         textContent: node.textContent
       }
+      let pendingSelection = false
+      let pendingSelectionPos: number | null = null
+      let pendingSelectionTimer: number | null = null
 
       const toggleFoldState = (newState: boolean, event?: MouseEvent): void => {
         event?.preventDefault()
@@ -187,16 +193,56 @@ export const MermaidExtension = CodeBlockLowlight.extend<MermaidOptions>({
       toggleButtonNode.onmousedown = (e) => {
         toggleFoldState(!nodeState.folded, e)
       }
-      previewNode.ondblclick = (e) => {
-        toggleFoldState(!nodeState.folded, e)
-      }
 
       previewNode.onclick = (e) => {
         if (typeof getPos !== 'function') return
-        const pos = getPos()
-        const selection = NodeSelection.create(editor.view.state.doc, pos)
-        editor.view.dispatch(editor.view.state.tr.setSelection(selection))
+        if (node?.type.name !== MermaidExtension.name) return
+
         e.preventDefault()
+        e.stopPropagation()
+
+        const pos = getPos()
+
+        const { selection } = editor.view.state
+        const mermaid = editor.view.state.doc.nodeAt(pos)
+        const isSelected =
+          containerNode.classList.contains('selected') ||
+          nodeState.selected ||
+          (pendingSelection && pendingSelectionPos === pos) ||
+          (selection instanceof NodeSelection &&
+            mermaid !== null &&
+            selection.from === pos &&
+            selection.to === pos + mermaid.nodeSize)
+
+        if (!isSelected) {
+          const nodePatch: NodePatchSpec = {
+            pos,
+            folded: nodeState.folded,
+            selected: true
+          }
+
+          const selection = NodeSelection.create(editor.view.state.doc, pos)
+          const tr = setTxMeta(editor.view.state.tr, { nodePatch })
+          tr.setSelection(selection)
+
+          editor.view.dispatch(tr)
+          pendingSelection = true
+          pendingSelectionPos = pos
+          if (pendingSelectionTimer !== null) {
+            clearTimeout(pendingSelectionTimer)
+          }
+          pendingSelectionTimer = window.setTimeout(() => {
+            pendingSelection = false
+            pendingSelectionPos = null
+            pendingSelectionTimer = null
+          }, 1000)
+          return
+        }
+
+        const diagram = nodeState.diagramBuilder?.(editor.view)
+        if (diagram?.svg != null) {
+          showPopup(MermaidPopup, { svg: diagram.svg, fullSize: true }, 'centered')
+        }
       }
 
       const syncState = (decorations: readonly Decoration[]): void => {
@@ -228,8 +274,10 @@ export const MermaidExtension = CodeBlockLowlight.extend<MermaidOptions>({
 
         if (nodeState.selected) {
           containerNode.classList.add('selected')
+          previewNode.style.cursor = 'zoom-in'
         } else {
           containerNode.classList.remove('selected')
+          previewNode.style.cursor = 'default'
         }
 
         if (!isEmpty && error !== null) {
@@ -255,6 +303,15 @@ export const MermaidExtension = CodeBlockLowlight.extend<MermaidOptions>({
         if (!allowFold && nodeState.folded) {
           toggleFoldState(false)
         }
+
+        if (nodeState.selected && pendingSelection) {
+          pendingSelection = false
+          pendingSelectionPos = null
+          if (pendingSelectionTimer !== null) {
+            clearTimeout(pendingSelectionTimer)
+            pendingSelectionTimer = null
+          }
+        }
       }
 
       const toggleSelection = (newState: boolean): void => {
@@ -416,14 +473,24 @@ function buildState (
     // Ensure SVG maintains its natural size
     const svg = container.querySelector('svg')
     if (svg !== null) {
+      svg.style.width = '100%'
+      svg.style.maxWidth = '100%'
       svg.style.height = 'auto'
+      svg.style.display = 'block'
       // Remove any width/height attributes that might cause stretching
       if (!svg.hasAttribute('viewBox')) {
         const width = svg.getAttribute('width')
         const height = svg.getAttribute('height')
-        if (width !== null && height !== null) {
-          svg.setAttribute('viewBox', `0 0 ${width} ${height}`)
+        const widthValue = width !== null ? Number.parseFloat(width) : NaN
+        const heightValue = height !== null ? Number.parseFloat(height) : NaN
+        if (Number.isFinite(widthValue) && Number.isFinite(heightValue)) {
+          svg.setAttribute('viewBox', `0 0 ${widthValue} ${heightValue}`)
+          svg.removeAttribute('width')
+          svg.removeAttribute('height')
         }
+      } else {
+        svg.removeAttribute('width')
+        svg.removeAttribute('height')
       }
     }