packages/cli: separate handlers for different template files in diff

packages/cli/package.json

@@ -29,6 +29,7 @@
     "backstage-cli": "bin/backstage-cli"
   },
   "devDependencies": {
+    "@types/diff": "^4.0.2",
     "@types/fs-extra": "^8.1.0",
     "@types/html-webpack-plugin": "^3.2.2",
     "@types/inquirer": "^6.5.0",
@@ -58,6 +59,7 @@
     "chokidar": "^3.3.1",
     "commander": "^4.1.1",
     "dashify": "^2.0.0",
+    "diff": "^4.0.2",
     "eslint-plugin-import": "^2.20.2",
     "eslint-plugin-monorepo": "^0.2.1",
     "fork-ts-checker-webpack-plugin": "^4.0.5",

packages/cli/src/commands/plugin/diff/index.ts

@@ -16,10 +16,12 @@
 
 import fs from 'fs-extra';
 import { relative as relativePath } from 'path';
-import handlebars from 'handlebars';
+import { diffLines } from 'diff';
+import handlebars, { Template } from 'handlebars';
 import recursiveReadDir from 'recursive-readdir';
 import { paths } from 'lib/paths';
 import { version } from 'lib/version';
+import chalk from 'chalk';
 
 type PluginInfo = {
   id: string;
@@ -121,14 +123,87 @@ async function readTemplate(
   return templateFiles;
 }
 
+async function packageJsonHandler(file: TemplateFile) {
+  if (!file.targetExists) {
+    throw new Error(`${file.targetPath} doesn't exist`);
+  }
+
+  console.log(`pkg.json handler: ${file.targetPath}`);
+  const pkg = JSON.parse(file.templateContents);
+  console.log('DEBUG: pkg =', pkg);
+  const targetPkg = JSON.parse(file.targetContents);
+  console.log('DEBUG: targetPkg =', targetPkg);
+}
+
+async function diffHandler(file: TemplateFile) {
+  if (!file.targetExists) {
+    // TODO: prompt to write template file
+    return;
+  }
+  if (file.targetContents === file.templateContents) {
+    return;
+  }
+
+  const diffs = diffLines(file.targetContents, file.templateContents);
+
+  for (const diff of diffs) {
+    if (diff.added) {
+      process.stdout.write(chalk.green(`+${diff.value}`));
+    } else if (diff.removed) {
+      process.stdout.write(chalk.red(`-${diff.value}`));
+    } else {
+      process.stdout.write(` ${diff.value}`);
+    }
+  }
+}
+
+async function skipHandler(file: TemplateFile) {
+  console.log(`Skipping ${file.targetPath}`);
+}
+
+type FileHandler = {
+  patterns: Array<string | RegExp>;
+  handler: (file: TemplateFile) => Promise<void>;
+};
+
+const fileHandlers: FileHandler[] = [
+  {
+    patterns: ['package.json'],
+    handler: packageJsonHandler,
+  },
+  {
+    patterns: ['.eslintrc.js', 'tsconfig.json'],
+    handler: diffHandler,
+  },
+  {
+    patterns: ['README.md', /^^src\//],
+    handler: skipHandler,
+  },
+];
+
 export default async () => {
   const pluginInfo = await readPluginInfo();
   const templateVars = { version, ...pluginInfo };
-  console.log('DEBUG: templateVars =', templateVars);
 
   const templateDir = paths.resolveOwn('templates/default-plugin');
-  console.log('DEBUG: templateDir =', templateDir);
 
   const templateFiles = await readTemplate(templateDir, templateVars);
-  console.log('DEBUG: templateFiles =', templateFiles);
+
+  for (const templateFile of templateFiles) {
+    const { targetPath } = templateFile;
+    const fileHandler = fileHandlers.find(handler =>
+      handler.patterns.some(pattern =>
+        typeof pattern === 'string'
+          ? pattern === targetPath
+          : pattern.test(targetPath),
+      ),
+    );
+    if (fileHandler) {
+      await fileHandler.handler(templateFile);
+    } else {
+      throw new Error(`No template file handler found for ${targetPath}`);
+    }
+  }
+
+  console.log(`DEBUG: done!`);
 };

yarn.lock

@@ -3915,6 +3915,11 @@
   resolved "https://registry.npmjs.org/@types/debug/-/debug-4.1.5.tgz#b14efa8852b7768d898906613c23f688713e02cd"
   integrity sha512-Q1y515GcOdTHgagaVFhHnIFQ38ygs/kmxdNpvpou+raI9UO3YZcHDngBSYKQklcKlvA7iuQlmIKbzvmxcOE9CQ==
 
+"@types/diff@^4.0.2":
+  version "4.0.2"
+  resolved "https://registry.npmjs.org/@types/diff/-/diff-4.0.2.tgz#2e9bb89f9acc3ab0108f0f3dc4dbdcf2fff8a99c"
+  integrity sha512-mIenTfsIe586/yzsyfql69KRnA75S8SVXQbTLpDejRrjH0QSJcpu3AUOi/Vjnt9IOsXKxPhJfGpQUNMueIU1fQ==
+
 "@types/eslint-visitor-keys@^1.0.0":
   version "1.0.0"
   resolved "https://registry.npmjs.org/@types/eslint-visitor-keys/-/eslint-visitor-keys-1.0.0.tgz#1ee30d79544ca84d68d4b3cdb0af4f205663dd2d"
@@ -8114,7 +8119,7 @@ diff-sequences@^25.1.0:
   resolved "https://registry.npmjs.org/diff-sequences/-/diff-sequences-25.1.0.tgz#fd29a46f1c913fd66c22645dc75bffbe43051f32"
   integrity sha512-nFIfVk5B/NStCsJ+zaPO4vYuLjlzQ6uFvPxzYyHlejNZ/UGa7G/n7peOXVrVNvRuyfstt+mZQYGpjxg9Z6N8Kw==
 
-diff@^4.0.1:
+diff@^4.0.1, diff@^4.0.2:
   version "4.0.2"
   resolved "https://registry.npmjs.org/diff/-/diff-4.0.2.tgz#60f3aecb89d5fae520c11aa19efc2bb982aade7d"
   integrity sha512-58lmxKSA4BNyLz+HHMUzlOEpg09FV+ev6ZMe3vJihgdxzgcwZ8VoEEPmALCZG9LmqfVoNMMKpttIYTVG6uDY7A==