Implements Prettier (#701)

* Adds and configures prettier

* Creates format script

* Runs prettier

* Adds npm scripts and checks for formatting in CI

scripts/prettier.js

@@ -0,0 +1,87 @@
+const chalk = require('chalk');
+const fs = require('fs');
+const glob = require('glob');
+const path = require('path');
+const prettier = require('prettier');
+
+const filePattern = `{client,scripts,server,shared}${path.sep}!(assets){${path.sep},}{**${path.sep}*,*}.{js,json,md}`;
+
+const iterateOverFiles = ({onFileRead}) => {
+  return new Promise((resolve, reject) => {
+    glob(filePattern, (error, files) => {
+      if (error) {
+        reject(Error(error));
+      }
+
+      resolve(
+        Promise.all(
+          files.map(file => {
+            const filePath = path.join(process.cwd(), file);
+            const fileContents = fs.readFileSync(filePath, 'utf8');
+            return onFileRead(filePath, fileContents);
+          })
+        )
+      );
+    });
+  });
+};
+
+const format = () => {
+  console.log(chalk.reset('Formatting files...'));
+
+  iterateOverFiles({
+    onFileRead: (filePath, fileContents) => {
+      return prettier.resolveConfig(filePath).then(options => {
+        return new Promise((resolve, reject) => {
+          fs.writeFile(filePath, prettier.format(fileContents, {...options, filepath: filePath}), error => {
+            if (error) {
+              reject(error);
+              return;
+            }
+
+            resolve();
+          });
+        });
+      });
+    },
+  })
+    .then(() => {
+      console.log(chalk.green('Done formatting files.'));
+    })
+    .catch(error => {
+      console.log(chalk.red('Error formatting files:\n'), chalk.reset(error));
+      process.exit(1);
+    });
+};
+
+const check = () => {
+  console.log(chalk.reset('Checking code formatting...'));
+
+  iterateOverFiles({
+    onFileRead: (filePath, fileContents) => {
+      return prettier.resolveConfig(filePath).then(options => {
+        const isCompliant = prettier.check(fileContents, {...options, filepath: filePath});
+
+        if (!isCompliant) {
+          throw filePath;
+        }
+      });
+    },
+  })
+    .then(() => {
+      console.log(chalk.green('Done checking files.'));
+    })
+    .catch(error => {
+      console.log(chalk.red('Unformatted file found:\n'), chalk.reset(error));
+      process.exit(1);
+    });
+};
+
+const commands = {check, format};
+const desiredCommand = process.argv.slice(2)[0];
+
+if (commands[desiredCommand] == null) {
+  throw new Error(`No command ${desiredCommand}.`);
+} else {
+  commands[desiredCommand]();
+}