feat: configure formatting tools (#502)

.gitignore

@@ -6,3 +6,4 @@ apps/stock-price-checker-proxy/cache/
 apps/twitch-proxy/.data/
 apps/twitch-proxy/.logs/
 Caddyfile
+.eslintcache

.husky/pre-commit

@@ -0,0 +1,4 @@
+#!/bin/sh
+. "$(dirname -- "$0")/_/husky.sh"
+
+npx lint-staged

.lintstagedrc.js

@@ -0,0 +1,40 @@
+const { ESLint } = require('eslint');
+
+const cli = new ESLint();
+
+// This lets us abort if we've already run a stage for all files
+const completedStages = new Set();
+
+// if a lot of files are changed, it's faster to run prettier/eslint on the
+// whole project than to run them on each file separately
+module.exports = {
+  '*.(js|jsx|ts|tsx)': async files => {
+    if (completedStages.has('js')) return [];
+
+    const ignoredIds = await Promise.all(
+      files.map(file => cli.isPathIgnored(file))
+    );
+    const lintableFiles = files.filter((_, i) => !ignoredIds[i]);
+    if (files.length > 10) {
+      completedStages.add('js');
+      return ['eslint --max-warnings=0 --cache --fix .', 'prettier --write .'];
+    } else {
+      return [
+        'eslint --max-warnings=0 --cache --fix ' + lintableFiles.join(' '),
+        ...files.map(filename => `prettier --write '${filename}'`)
+      ];
+    }
+  },
+  '*.!(js|jsx|ts|tsx)': files => {
+    if (completedStages.has('not-js')) return [];
+
+    if (files.length > 10) {
+      completedStages.add('not-js');
+      return 'prettier --write .';
+    } else {
+      return files.map(
+        filename => `prettier --write --ignore-unknown '${filename}'`
+      );
+    }
+  }
+};

.prettierignore

@@ -0,0 +1,8 @@
+# Ignore minified libraries
+apps/voting-app/public/*.min.js
+# Ignore bundles
+apps/**/public/bundle.js
+# Ignore test runner files?
+apps/**/assertion-analyser.js
+apps/**/test-runner.js
+apps/**/fcctesting.js