update signature validation

app/javascript/draw.js

@@ -1,5 +1,6 @@
 import SignaturePad from 'signature_pad'
 import { cropCanvasAndExportToPNG } from './submission_form/crop_canvas'
+import { isValidSignatureCanvas } from './submission_form/validate_signature'
 
 window.customElements.define('draw-signature', class extends HTMLElement {
   connectedCallback () {
@@ -43,6 +44,8 @@ window.customElements.define('draw-signature', class extends HTMLElement {
 
           return response
         })
+      }).catch(error => {
+        console.log(error)
       }).finally(() => {
         this.submitButton.disabled = false
       })
@@ -65,8 +68,13 @@ window.customElements.define('draw-signature', class extends HTMLElement {
   }
 
   async submitImage () {
-    return new Promise((resolve, reject) => {
+    if (!isValidSignatureCanvas(this.pad.toData())) {
-      cropCanvasAndExportToPNG(this.canvas, { errorOnTooSmall: true }).then(async (blob) => {
+      alert('Signature is too small or simple. Please redraw.')
+
+      return Promise.reject(new Error('Image too small or simple'))
+    }
+
+    return cropCanvasAndExportToPNG(this.canvas).then(async (blob) => {
       const file = new File([blob], 'signature.png', { type: 'image/png' })
 
       const formData = new FormData()
@@ -79,12 +87,7 @@ window.customElements.define('draw-signature', class extends HTMLElement {
       return fetch('/api/attachments', {
         method: 'POST',
         body: formData
-        }).then((resp) => resp.json()).then((attachment) => {
+      }).then(resp => resp.json())
-          return resolve(attachment)
-        })
-      }).catch((error) => {
-        return reject(error)
-      })
     })
   }
 

app/javascript/submission_form/crop_canvas.js

@@ -1,4 +1,4 @@
-function cropCanvasAndExportToPNG (canvas, { errorOnTooSmall } = { errorOnTooSmall: false }) {
+function cropCanvasAndExportToPNG (canvas) {
   const ctx = canvas.getContext('2d')
 
   const width = canvas.width
@@ -33,10 +33,6 @@ function cropCanvasAndExportToPNG (canvas, { errorOnTooSmall } = { errorOnTooSma
   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

@@ -1445,11 +1445,7 @@ export default {
           this.isSubmittingComplete = false
         })
       }).catch(error => {
-        if (error?.message === 'Image too small') {
-          alert(this.t('signature_is_too_small_please_redraw'))
-        } else {
         console.log(error)
-        }
       }).finally(() => {
         this.isSubmitting = false
         this.isSubmittingComplete = false

app/javascript/submission_form/i18n.js

@@ -93,7 +93,7 @@ const en = {
   reupload: 'Reupload',
   upload: 'Upload',
   files: 'Files',
-  signature_is_too_small_please_redraw: 'Signature is too small. Please redraw.',
+  signature_is_too_small_or_simple_please_redraw: 'Signature is too small or simple. Please redraw.',
   wait_countdown_seconds: 'Wait {countdown} seconds'
 }
 
@@ -191,7 +191,7 @@ const es = {
   reupload: 'Volver a subir',
   upload: 'Subir',
   files: 'Archivos',
-  signature_is_too_small_please_redraw: 'La firma es demasiado pequeña. Por favor, dibújala de nuevo.',
+  signature_is_too_small_or_simple_please_redraw: 'La firma es demasiado pequeña o simple. Por favor, vuelve a dibujarla.',
   wait_countdown_seconds: 'Espera {countdown} segundos'
 }
 
@@ -289,7 +289,7 @@ const it = {
   reupload: 'Ricarica',
   upload: 'Carica',
   files: 'File',
-  signature_is_too_small_please_redraw: 'La firma è troppo piccola. Ridisegnala per favore.',
+  signature_is_too_small_or_simple_please_redraw: 'La firma è troppo piccola o semplice. Ridisegnala, per favore.',
   wait_countdown_seconds: 'Attendi {countdown} secondi'
 }
 
@@ -387,7 +387,7 @@ const de = {
   reupload: 'Erneut hochladen',
   upload: 'Hochladen',
   files: 'Dateien',
-  signature_is_too_small_please_redraw: 'Die Unterschrift ist zu klein. Bitte erneut zeichnen.',
+  signature_is_too_small_or_simple_please_redraw: 'Die Unterschrift ist zu klein oder zu einfach. Bitte erneut zeichnen.',
   wait_countdown_seconds: 'Warte {countdown} Sekunden'
 }
 
@@ -485,7 +485,7 @@ const fr = {
   reupload: 'Recharger',
   upload: 'Télécharger',
   files: 'Fichiers',
-  signature_is_too_small_please_redraw: 'La signature est trop petite. Veuillez la redessiner.',
+  signature_is_too_small_or_simple_please_redraw: 'La signature est trop petite ou trop simple. Veuillez la redessiner.',
   wait_countdown_seconds: 'Attendez {countdown} secondes'
 }
 
@@ -583,7 +583,7 @@ const pl = {
   reupload: 'Ponowne przesłanie',
   upload: 'Przesyłanie',
   files: 'Pliki',
-  signature_is_too_small_please_redraw: 'Podpis jest zbyt mały. Proszę narysować go ponownie.'
+  signature_is_too_small_or_simple_please_redraw: 'Podpis jest zbyt mały lub zbyt prosty. Proszę narysować go ponownie.'
 }
 
 const uk = {
@@ -680,7 +680,7 @@ const uk = {
   reupload: 'Перезавантажити',
   upload: 'Завантажити',
   files: 'Файли',
-  signature_is_too_small_please_redraw: 'Підпис занадто малий. Будь ласка, перемалюйте його.',
+  signature_is_too_small_or_simple_please_redraw: 'Підпис занадто маленький або надто простий. Будь ласка, перемалюйте.',
   wait_countdown_seconds: 'Зачекайте {countdown} секунд'
 }
 
@@ -778,7 +778,7 @@ const cs = {
   reupload: 'Znovu nahrát',
   upload: 'Nahrát',
   files: 'Soubory',
-  signature_is_too_small_please_redraw: 'Podpis je příliš malý. Prosím, překreslete ho.',
+  signature_is_too_small_or_simple_please_redraw: 'Podpis je příliš malý nebo jednoduchý. Nakreslete jej prosím znovu.',
   wait_countdown_seconds: 'Počkejte {countdown} sekund'
 }
 
@@ -876,7 +876,7 @@ const pt = {
   reupload: 'Reenviar',
   upload: 'Carregar',
   files: 'Arquivos',
-  signature_is_too_small_please_redraw: 'A assinatura é muito pequena. Por favor, redesenhe-a.',
+  signature_is_too_small_or_simple_please_redraw: 'A assinatura é muito pequena ou simples. Por favor, redesenhe.',
   wait_countdown_seconds: 'Aguarde {countdown} segundos'
 }
 
@@ -975,7 +975,7 @@ const he = {
   reupload: 'העלה שוב',
   upload: 'העלאה',
   files: 'קבצים',
-  signature_is_too_small_please_redraw: 'החתימה קטנה מדי. אנא צייר מחדש.',
+  signature_is_too_small_or_simple_please_redraw: 'החתימה קטנה או פשוטה מדי. אנא חתום מחדש.',
   wait_countdown_seconds: 'המתן {countdown} שניות'
 }
 
@@ -1074,7 +1074,7 @@ const nl = {
   reupload: 'Opnieuw uploaden',
   upload: 'Uploaden',
   files: 'Bestanden',
-  signature_is_too_small_please_redraw: 'De handtekening is te klein. Teken deze opnieuw, alstublieft.',
+  signature_is_too_small_or_simple_please_redraw: 'De handtekening is te klein of te eenvoudig. Teken opnieuw.',
   wait_countdown_seconds: 'Wacht {countdown} seconden'
 }
 
@@ -1172,7 +1172,7 @@ const ar = {
   reupload: 'إعادة التحميل',
   upload: 'تحميل',
   files: 'الملفات',
-  signature_is_too_small_please_redraw: 'التوقيع صغير جدًا. يرجى إعادة الرسم.',
+  signature_is_too_small_or_simple_please_redraw: 'التوقيع صغير جدًا أو بسيط جدًا. يرجى إعادة رسمه.',
   wait_countdown_seconds: 'انتظر {countdown} ثانية'
 }
 
@@ -1269,7 +1269,7 @@ const ko = {
   reupload: '다시 업로드',
   upload: '업로드',
   files: '파일',
-  signature_is_too_small_please_redraw: '서명이 너무 작습니다. 다시 그려주세요.',
+  signature_is_too_small_or_simple_please_redraw: '서명이 너무 작거나 단순합니다. 다시 그려주세요.',
   wait_countdown_seconds: '{countdown}초 기다리세요'
 }
 

app/javascript/submission_form/initials_step.vue

@@ -118,11 +118,17 @@
       :src="attachmentsIndex[modelValue || computedPreviousValue].url"
       class="mx-auto bg-white border border-base-300 rounded max-h-44"
     >
+    <div class="relative">
+      <div
+        v-if="!isDrawInitials"
+        class="absolute top-0 right-0 left-0 bottom-0"
+      />
       <canvas
         v-show="!modelValue && !computedPreviousValue"
         ref="canvas"
         class="bg-white border border-base-300 rounded-2xl w-full draw-canvas"
       />
+    </div>
     <input
       v-if="!isDrawInitials && !modelValue && !computedPreviousValue"
       id="initials_text_input"

app/javascript/submission_form/signature_step.vue

@@ -292,6 +292,7 @@
 <script>
 import { IconReload, IconCamera, IconSignature, IconTextSize, IconArrowsDiagonalMinimize2, IconQrcode, IconX } from '@tabler/icons-vue'
 import { cropCanvasAndExportToPNG } from './crop_canvas'
+import { isValidSignatureCanvas } from './validate_signature'
 import SignaturePad from 'signature_pad'
 import AppearsOn from './appears_on'
 import FileDropzone from './dropzone'
@@ -680,8 +681,14 @@ export default {
         return Promise.resolve({})
       }
 
-      return new Promise((resolve, reject) => {
+      if (this.isSignatureStarted && this.pad.toData().length > 0 && !isValidSignatureCanvas(this.pad.toData())) {
-        cropCanvasAndExportToPNG(this.$refs.canvas, { errorOnTooSmall: true }).then(async (blob) => {
+        alert(this.t('signature_is_too_small_or_simple_please_redraw'))
+
+        return Promise.reject(new Error('Image too small or simple'))
+      }
+
+      return new Promise((resolve) => {
+        cropCanvasAndExportToPNG(this.$refs.canvas).then(async (blob) => {
           const file = new File([blob], 'signature.png', { type: 'image/png' })
 
           if (this.dryRun) {
@@ -717,12 +724,6 @@ export default {
               return resolve(attachment)
             })
           }
-        }).catch((error) => {
-          if (error.message === 'Image too small' && this.field.required === false) {
-            return resolve({})
-          } else {
-            return reject(error)
-          }
         })
       })
     }

app/javascript/submission_form/validate_signature.js

@@ -0,0 +1,38 @@
+function isValidSignatureCanvas (data) {
+  if (data.length === 0) return false
+
+  const strokes = data.filter(stroke => Array.isArray(stroke.points) && stroke.points.length > 2)
+
+  if (strokes.length === 0) return false
+
+  let skippedStraightLine = 0
+
+  const validStrokes = strokes.filter(stroke => {
+    const points = stroke.points
+    const first = points[0]
+    const last = points[points.length - 1]
+    const A = last.y - first.y
+    const B = first.x - last.x
+    const C = last.x * first.y - first.x * last.y
+    const lineLength = Math.sqrt(A * A + B * B)
+
+    const totalDeviation = points.reduce((sum, p) => {
+      const distanceToLine = Math.abs(A * p.x + B * p.y + C) / lineLength
+      return sum + distanceToLine
+    }, 0)
+
+    const avgDeviation = totalDeviation / points.length
+
+    if (avgDeviation < 3 && skippedStraightLine < 2) {
+      skippedStraightLine++
+
+      return false
+    }
+
+    return true
+  })
+
+  return validStrokes.length > 0
+}
+
+export { isValidSignatureCanvas }

spec/signing_form_helper.rb

@@ -4,21 +4,49 @@ module SigningFormHelper
   module_function
 
   def draw_canvas
-    page.find('canvas').click([], { x: 150, y: 100 })
     page.execute_script <<~JS
       const canvas = document.getElementsByTagName('canvas')[0];
-      const ctx = canvas.getContext('2d');
+      const rect = canvas.getBoundingClientRect();
 
-      ctx.beginPath();
+      const startX = rect.left + 50;
-      ctx.moveTo(150, 100);
+      const startY = rect.top + 100;
-      ctx.lineTo(450, 100);
-      ctx.stroke();
 
-      ctx.beginPath();
+      const amplitude = 20;
-      ctx.moveTo(150, 100);
+      const wavelength = 30;
-      ctx.lineTo(150, 150);
+      const length = 300;
-      ctx.stroke();
+
+      function dispatchPointerEvent(type, x, y) {
+        const event = new PointerEvent(type, {
+          pointerId: 1,
+          pointerType: 'pen',
+          isPrimary: true,
+          clientX: x,
+          clientY: y,
+          bubbles: true,
+          pressure: 0.5
+        });
+
+        canvas.dispatchEvent(event);
+      }
+
+      dispatchPointerEvent('pointerdown', startX, startY);
+
+      let x = 0;
+      function drawStep() {
+        if (x > length) {
+          dispatchPointerEvent('pointerup', startX + x, startY);
+          return;
+        }
+
+        const y = startY + amplitude * Math.sin((x / wavelength) * 2 * Math.PI);
+        dispatchPointerEvent('pointermove', startX + x, y);
+        x += 5;
+        requestAnimationFrame(drawStep);
+      }
+
+      drawStep();
     JS
+
     sleep 0.5
   end
 

spec/system/signing_form_spec.rb

@@ -360,6 +360,19 @@ RSpec.describe 'Signing Form', type: :system do
       expect(field_value(submitter, 'Signature')).to be_present
     end
 
+    it 'shows an error message if the canvas is not drawn or too simple' do
+      visit submit_form_path(slug: submitter.slug)
+
+      find('#expand_form_button').click
+      page.find('canvas').click([], { x: 150, y: 100 })
+
+      alert_text = page.accept_alert do
+        click_button 'Sign and Complete'
+      end
+
+      expect(alert_text).to eq 'Signature is too small or simple. Please redraw.'
+    end
+
     it 'completes the form if the canvas is typed' do
       visit submit_form_path(slug: submitter.slug)