From c174c19ddda6d3a82d2c62c1e60b0402b73f9c9b Mon Sep 17 00:00:00 2001
From: Nolan Lawson <nolan@nolanlawson.com>
Date: Wed, 23 Oct 2019 18:07:24 -0700
Subject: [PATCH] fix: fix tesseract.js progress bar (#1599)

* fix: fix tesseract.js progress bar

* fixup
---
 src/routes/_utils/runTesseract.js | 68 ++++++++++++++++++-------------
 1 file changed, 40 insertions(+), 28 deletions(-)

diff --git a/src/routes/_utils/runTesseract.js b/src/routes/_utils/runTesseract.js
index 171e569c..1896213d 100644
--- a/src/routes/_utils/runTesseract.js
+++ b/src/routes/_utils/runTesseract.js
@@ -2,24 +2,49 @@ import { importTesseractWorker } from '../_utils/asyncModules'
 
 const DESTROY_WORKER_DELAY = 300000 // 5 minutes
 
-// TODO: it's flaky to try to estimate tesseract's total progress this way
-const steps = [
-  { status: 'loading tesseract core', proportion: 0.05 },
-  { status: 'initializing tesseract', proportion: 0.05 },
-  { status: 'loading language traineddata', proportion: 0.1 },
-  { status: 'initializing api', proportion: 0.2 },
-  { status: 'recognizing text', proportion: 0.6 }
-]
-
 let worker
 let destroyWorkerHandle
 
-async function initWorker () {
+// TODO: it seems hacky that we have to spy on the tesseract worker to figure out its progress
+const steps = [
+  { status: 'loading tesseract core', proportion: 0.1 },
+  { status: 'initializing tesseract', proportion: 0.05 },
+  { status: 'loading language traineddata', proportion: 0.1 },
+  { status: 'initializing api', proportion: 0.2 },
+  { status: 'recognizing text', proportion: 0.55 }
+]
+
+if (process.env.NODE_ENV !== 'production') {
+  if (steps.map(_ => _.proportion).reduce((a, b) => a + b, 0) !== 1) {
+    console.error('Steps do not add up to 1! You should probably fix this.')
+  }
+}
+
+async function spyOnWorkerProgress (onProgress, runnable) {
+  const listener = event => {
+    const { data } = event
+    if (onProgress && data.status === 'progress' && steps.find(({ status }) => status === data.data.status)) {
+      onProgress(getTotalProgress(data.data))
+    }
+  }
+
+  worker.worker.addEventListener('message', listener)
+  try {
+    const res = await runnable()
+    return res
+  } finally {
+    worker.worker.removeEventListener('message', listener)
+  }
+}
+
+async function initWorker (onProgress) {
   if (!worker) {
     worker = (await importTesseractWorker())()
-    await worker.load()
-    await worker.loadLanguage('eng')
-    await worker.initialize('eng')
+    await spyOnWorkerProgress(onProgress, async () => {
+      await worker.load()
+      await worker.loadLanguage('eng')
+      await worker.initialize('eng')
+    })
   }
 }
 
@@ -55,25 +80,12 @@ function getTotalProgress (progressInfo) {
 }
 
 async function recognize (url, onProgress) {
-  // TODO: it seems hacky that we have to spy on the tesseract worker to figure out its progress
-  const listener = event => {
-    const { data } = event
-    if (onProgress && data.status === 'progress' && steps.find(({ status }) => status === data.data.status)) {
-      onProgress(getTotalProgress(data.data))
-    }
-  }
-  worker.worker.addEventListener('message', listener)
-  try {
-    const res = await worker.recognize(url, 'eng')
-    return res
-  } finally {
-    worker.worker.removeEventListener('message', listener)
-  }
+  return spyOnWorkerProgress(onProgress, () => worker.recognize(url, 'eng'))
 }
 
 export async function runTesseract (url, onProgress) {
   cancelDestroyWorker()
-  await initWorker()
+  await initWorker(onProgress)
   try {
     const res = await recognize(url, onProgress)
     console.log('result', res)