From ed3444c2f0dd3b5c68f624cda2d74bb1d1157ec6 Mon Sep 17 00:00:00 2001
From: Jerel Miller <jerelmiller@gmail.com>
Date: Wed, 14 Oct 2020 03:00:58 -0700
Subject: [PATCH] feat: handle proper diffing on each step

---
 src/components/Tutorial.js       | 13 ++++---
 src/components/TutorialEditor.js | 62 ++++++++++++++++++++------------
 src/components/TutorialStep.js   |  6 ++--
 3 files changed, 48 insertions(+), 33 deletions(-)

diff --git a/src/components/Tutorial.js b/src/components/Tutorial.js
index edd5848f7..2503d5c1e 100644
--- a/src/components/Tutorial.js
+++ b/src/components/Tutorial.js
@@ -34,17 +34,16 @@ const Tutorial = ({ children }) => {
           .find(Boolean) || initialState
       );
 
-      const { fileName, code, language } = parseCodeBlockProps(codeBlock);
-      const { code: prevCode } = previousStep.get(fileName);
+      const props = parseCodeBlockProps(codeBlock);
+      const { code: prevCode } = previousStep.get(props.fileName);
 
       return [
         ...steps,
         cloneElement(stepElement, {
-          initialSelectedFile: fileName,
-          step: previousStep.set(fileName, {
-            code,
-            language,
-            diff: diffLines(prevCode, code),
+          codeBlock: { ...props, diff: diffLines(prevCode, props.code) },
+          step: previousStep.set(props.fileName, {
+            code: props.code,
+            language: props.language,
           }),
           index: idx,
           totalSteps: arr.length,
diff --git a/src/components/TutorialEditor.js b/src/components/TutorialEditor.js
index b56815d5e..4fe809ecb 100644
--- a/src/components/TutorialEditor.js
+++ b/src/components/TutorialEditor.js
@@ -5,31 +5,47 @@ import path from 'path';
 import { css } from '@emotion/core';
 import { darken } from 'polished';
 
-const TutorialEditor = ({ initialSelectedFile, files }) => {
-  const [selectedFile, setSelectedFile] = useState(initialSelectedFile);
-  const { diff } = files.get(selectedFile);
+const last = (arr) => arr[arr.length - 1];
 
-  const [highlightedLines] = diff.reduce(
-    ([highlightedLines, lineNumber], change) => {
-      const { count, added, removed } = change;
-      // Include current line when counting the end of the range
-      const rangeEnd = lineNumber + count - 1;
+const diffHighlightedLines = (diff) => {
+  const { highlightedLines } = diff.reduce(
+    ({ highlightedLines, currentLineNumber }, change) => {
+      const { count, added, removed, value } = change;
 
-      return [
-        added
-          ? [
-              ...highlightedLines,
-              lineNumber === rangeEnd
-                ? lineNumber
-                : `${lineNumber}-${lineNumber + count - 1}`,
-            ]
-          : highlightedLines,
-        removed ? lineNumber : lineNumber + count,
-      ];
+      if (!added) {
+        return {
+          highlightedLines,
+          currentLineNumber: removed
+            ? currentLineNumber
+            : currentLineNumber + count,
+        };
+      }
+
+      const lines = value.split('\n').slice(0, count);
+
+      // Don't highlight the last line if the last line is blank. Subtract at
+      // least 1 because we want to include the current line in the range.
+      const subtractAmount = last(lines) === '' ? 2 : 1;
+      const rangeEnd = currentLineNumber + count - subtractAmount;
+      const range =
+        currentLineNumber === rangeEnd
+          ? currentLineNumber
+          : `${currentLineNumber}-${rangeEnd}`;
+
+      return {
+        highlightedLines: [...highlightedLines, range],
+        currentLineNumber: currentLineNumber + count,
+      };
     },
-    [[], 1]
+    { highlightedLines: [], currentLineNumber: 1 }
   );
 
+  return highlightedLines.join(',');
+};
+
+const TutorialEditor = ({ codeBlock, files }) => {
+  const [selectedFile, setSelectedFile] = useState(codeBlock.fileName);
+
   return (
     <div>
       <div
@@ -69,7 +85,9 @@ const TutorialEditor = ({ initialSelectedFile, files }) => {
           language={language}
           fileName={fileName}
           highlightedLines={
-            fileName === selectedFile ? highlightedLines.join(',') : null
+            fileName === codeBlock.fileName && codeBlock.diff
+              ? diffHighlightedLines(codeBlock.diff)
+              : null
           }
           css={css`
             display: ${fileName === selectedFile ? 'block' : 'none'};
@@ -88,7 +106,7 @@ const TutorialEditor = ({ initialSelectedFile, files }) => {
 };
 
 TutorialEditor.propTypes = {
-  initialSelectedFile: PropTypes.string.isRequired,
+  codeBlock: PropTypes.object.isRequired,
   files: PropTypes.instanceOf(Map).isRequired,
 };
 
diff --git a/src/components/TutorialStep.js b/src/components/TutorialStep.js
index 07d88522b..8a85cbe71 100644
--- a/src/components/TutorialStep.js
+++ b/src/components/TutorialStep.js
@@ -6,6 +6,7 @@ import Markdown from './Markdown';
 
 const TutorialStep = ({
   children,
+  codeBlock,
   initialSelectedFile,
   step,
   index,
@@ -47,10 +48,7 @@ const TutorialStep = ({
           `}
         >
           <div>{children}</div>
-          <TutorialEditor
-            files={step}
-            initialSelectedFile={initialSelectedFile}
-          />
+          <TutorialEditor codeBlock={codeBlock} files={step} />
         </div>
       ) : (
         children