error on too small signature

app/javascript/submission_form/crop_canvas.js

@@ -1,4 +1,4 @@
-function cropCanvasAndExportToPNG (canvas) {
+function cropCanvasAndExportToPNG (canvas, { errorOnTooSmall } = { errorOnTooSmall: false }) {
   const ctx = canvas.getContext('2d')
 
   const width = canvas.width
@@ -33,6 +33,10 @@ function cropCanvasAndExportToPNG (canvas) {
   croppedCanvas.height = croppedHeight
   const croppedCtx = croppedCanvas.getContext('2d')
 
+  if (errorOnTooSmall && (croppedWidth < 20 || croppedHeight < 20)) {
+    return Promise.reject(new Error('Image too small'))
+  }
+
   croppedCtx.drawImage(canvas, leftmost, topmost, croppedWidth, croppedHeight, 0, 0, croppedWidth, croppedHeight)
 
   return new Promise((resolve, reject) => {

app/javascript/submission_form/form.vue

@@ -1000,7 +1000,11 @@ export default {
           this.isSubmitting = false
         })
       }).catch(error => {
+        if (error?.message === 'Image too small') {
+          alert('Signature is too small - please redraw.')
+        } else {
           console.log(error)
+        }
       }).finally(() => {
         this.isSubmitting = false
       })

app/javascript/submission_form/signature_step.vue

@@ -41,7 +41,7 @@
           <a
             id="type_text_button"
             href="#"
-            class="btn btn-outline btn-sm font-medium"
+            class="btn btn-outline btn-sm font-medium inline-flex flex-nowrap"
             @click.prevent="toggleTextInput"
           >
             <IconTextSize :width="16" />
@@ -56,7 +56,7 @@
           :data-tip="t('take_photo')"
         >
           <label
-            class="btn btn-outline btn-sm font-medium"
+            class="btn btn-outline btn-sm font-medium inline-flex flex-nowrap"
           >
             <IconCamera :width="16" />
             <input
@@ -386,8 +386,8 @@ export default {
         return Promise.resolve({})
       }
 
-      return new Promise((resolve) => {
+      return new Promise((resolve, reject) => {
-        cropCanvasAndExportToPNG(this.$refs.canvas).then(async (blob) => {
+        cropCanvasAndExportToPNG(this.$refs.canvas, { errorOnTooSmall: true }).then(async (blob) => {
           const file = new File([blob], 'signature.png', { type: 'image/png' })
 
           if (this.isDirectUpload) {
@@ -429,6 +429,8 @@ export default {
               return resolve(attachment)
             })
           }
+        }).catch((error) => {
+          return reject(error)
         })
       })
     }