From 3d0ec27038c104ce1738e2d02f5e4e874ea6b09d Mon Sep 17 00:00:00 2001
From: Elian Doran <contact@eliandoran.me>
Date: Mon, 31 Mar 2025 18:54:57 +0300
Subject: [PATCH] fix(mermaid): fix export to PNG for some diagram types

---
 src/public/app/services/utils.spec.ts | 22 +++++++++++++
 src/public/app/services/utils.ts      | 46 +++++++++++++++++++++------
 2 files changed, 58 insertions(+), 10 deletions(-)
 create mode 100644 src/public/app/services/utils.spec.ts

diff --git a/src/public/app/services/utils.spec.ts b/src/public/app/services/utils.spec.ts
new file mode 100644
index 000000000..2885fa270
--- /dev/null
+++ b/src/public/app/services/utils.spec.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { getSizeFromSvg } from "./utils.js";
+
+describe("getSizeFromSvg", () => {
+    it("parses width & height attribute", () => {
+        const svg = `<svg aria-roledescription="sequence" role="graphics-document document" viewBox="-50 -10 714 574" height="574" xmlns="http://www.w3.org/2000/svg" width="714" id="mermaid-graph-2"></svg>`;
+        const result = getSizeFromSvg(svg);
+        expect(result).toMatchObject({
+            width: 714,
+            height: 574,
+        });
+    });
+
+    it("parses viewbox", () => {
+        const svg = `<svg aria-roledescription="er" role="graphics-document document" viewBox="0 0 872.2750244140625 655" style="max-width: 872.2750244140625px;" class="erDiagram" xmlns="http://www.w3.org/2000/svg" width="100%" id="mermaid-graph-2">`;
+        const result = getSizeFromSvg(svg);
+        expect(result).toMatchObject({
+            width: 872.2750244140625,
+            height: 655
+        });
+    });
+});
diff --git a/src/public/app/services/utils.ts b/src/public/app/services/utils.ts
index 9d39bb279..bb85729ba 100644
--- a/src/public/app/services/utils.ts
+++ b/src/public/app/services/utils.ts
@@ -2,6 +2,8 @@ import dayjs from "dayjs";
 import { Modal } from "bootstrap";
 import type { ViewScope } from "./link.js";
 
+const SVG_MIME = "image/svg+xml";
+
 function reloadFrontendApp(reason?: string) {
     if (reason) {
         logInfo(`Frontend app reload: ${reason}`);
@@ -654,27 +656,23 @@ function triggerDownload(fileName: string, dataUrl: string) {
  */
 function downloadSvgAsPng(nameWithoutExtension: string, svgContent: string) {
     return new Promise<void>((resolve, reject) => {
-        const mime = "image/svg+xml";
-
         // First, we need to determine the width and the height from the input SVG.
-        const svgDocument = (new DOMParser()).parseFromString(svgContent, mime);
-        const width = svgDocument.documentElement?.getAttribute("width");
-        const height = svgDocument.documentElement?.getAttribute("height");
-
-        if (!width || !height) {
+        const result = getSizeFromSvg(svgContent);
+        if (!result) {
             reject();
             return;
         }
 
         // Convert the image to a blob.
+        const { width, height } = result;
         const svgBlob = new Blob([ svgContent ], {
-            type: mime
+            type: SVG_MIME
         })
 
         // Create an image element and load the SVG.
         const imageEl = new Image();
-        imageEl.width = parseFloat(width);
-        imageEl.height = parseFloat(height);
+        imageEl.width = width;
+        imageEl.height = height;
         imageEl.onload = () => {
             try {
                 // Draw the image with a canvas.
@@ -704,6 +702,34 @@ function downloadSvgAsPng(nameWithoutExtension: string, svgContent: string) {
     });
 }
 
+export function getSizeFromSvg(svgContent: string) {
+    const svgDocument = (new DOMParser()).parseFromString(svgContent, SVG_MIME);
+
+    // Try to use width & height attributes if available.
+    let width = svgDocument.documentElement?.getAttribute("width");
+    let height = svgDocument.documentElement?.getAttribute("height");
+
+    // If not, use the viewbox.
+    if (!width || !height) {
+        const viewBox = svgDocument.documentElement?.getAttribute("viewBox");
+        if (viewBox) {
+            const viewBoxParts = viewBox.split(" ");
+            width = viewBoxParts[2];
+            height = viewBoxParts[3];
+        }
+    }
+
+    if (width && height) {
+        return {
+            width: parseFloat(width),
+            height: parseFloat(height)
+        }
+    } else {
+        console.warn("SVG export error", svgDocument.documentElement);
+        return null;
+    }
+}
+
 /**
  * Compares two semantic version strings.
  * Returns: