From 60238e81fe02432661b617aee180aa009fc8d2d5 Mon Sep 17 00:00:00 2001
From: Phil Pluckthun <phil@kitten.sh>
Date: Mon, 15 Apr 2024 00:51:47 +0100
Subject: [PATCH] Add writing utility

---
 .../src/commands/generate-output/runner.ts    |  9 +--
 .../src/commands/generate-schema/runner.ts    | 11 ++--
 .../cli-utils/src/commands/shared/index.ts    |  2 +
 .../cli-utils/src/commands/shared/utils.ts    | 57 +++++++++++++++++++
 4 files changed, 69 insertions(+), 10 deletions(-)
 create mode 100644 packages/cli-utils/src/commands/shared/index.ts
 create mode 100644 packages/cli-utils/src/commands/shared/utils.ts

diff --git a/packages/cli-utils/src/commands/generate-output/runner.ts b/packages/cli-utils/src/commands/generate-output/runner.ts
index dbc75f4d..03041bbd 100644
--- a/packages/cli-utils/src/commands/generate-output/runner.ts
+++ b/packages/cli-utils/src/commands/generate-output/runner.ts
@@ -12,6 +12,8 @@ import {
 } from '@gql.tada/internal';
 
 import type { TTY } from '../../term';
+import type { WriteTarget } from '../shared';
+import { writeOutput } from '../shared';
 import * as logger from './logger';
 
 interface Options {
@@ -57,10 +59,9 @@ export async function* run(tty: TTY, opts: Options) {
     throw logger.externalError('Could not generate introspection output', error);
   }
 
-  let destination: string;
+  let destination: WriteTarget;
   if (!opts.output && tty.pipeTo) {
-    tty.pipeTo.write(contents);
-    return;
+    destination = tty.pipeTo;
   } else if (opts.output) {
     destination = path.resolve(process.cwd(), opts.output);
   } else if (pluginConfig.tadaOutputLocation) {
@@ -80,7 +81,7 @@ export async function* run(tty: TTY, opts: Options) {
   }
 
   try {
-    await fs.writeFile(destination, contents);
+    await writeOutput(destination, contents);
   } catch (error) {
     throw logger.externalError('Something went wrong while writing the introspection file', error);
   }
diff --git a/packages/cli-utils/src/commands/generate-schema/runner.ts b/packages/cli-utils/src/commands/generate-schema/runner.ts
index e6568d56..ab579772 100644
--- a/packages/cli-utils/src/commands/generate-schema/runner.ts
+++ b/packages/cli-utils/src/commands/generate-schema/runner.ts
@@ -6,8 +6,8 @@ import type { GraphQLSPConfig, LoadConfigResult } from '@gql.tada/internal';
 import { load, loadConfig, parseConfig } from '@gql.tada/internal';
 
 import type { TTY } from '../../term';
-import { getGraphQLSPConfig } from '../../lsp';
-import { getTsConfig } from '../../tsconfig';
+import type { WriteTarget } from '../shared';
+import { writeOutput } from '../shared';
 import * as logger from './logger';
 
 interface Options {
@@ -32,10 +32,9 @@ export async function* run(tty: TTY, opts: Options) {
     throw logger.errorMessage('Failed to load schema.');
   }
 
-  let destination: string;
+  let destination: WriteTarget;
   if (!opts.output && tty.pipeTo) {
-    tty.pipeTo.write(printSchema(schema));
-    return;
+    destination = tty.pipeTo;
   } else if (opts.output) {
     destination = path.resolve(process.cwd(), opts.output);
   } else {
@@ -70,7 +69,7 @@ export async function* run(tty: TTY, opts: Options) {
   }
 
   try {
-    await fs.writeFile(destination, printSchema(schema));
+    await writeOutput(destination, printSchema(schema));
   } catch (error) {
     throw logger.externalError('Something went wrong while writing the introspection file', error);
   }
diff --git a/packages/cli-utils/src/commands/shared/index.ts b/packages/cli-utils/src/commands/shared/index.ts
new file mode 100644
index 00000000..8ff45f49
--- /dev/null
+++ b/packages/cli-utils/src/commands/shared/index.ts
@@ -0,0 +1,2 @@
+export * from './logger';
+export * from './utils';
diff --git a/packages/cli-utils/src/commands/shared/utils.ts b/packages/cli-utils/src/commands/shared/utils.ts
new file mode 100644
index 00000000..5e847f59
--- /dev/null
+++ b/packages/cli-utils/src/commands/shared/utils.ts
@@ -0,0 +1,57 @@
+import type { WriteStream } from 'node:tty';
+import type { PathLike } from 'node:fs';
+import * as fs from 'node:fs/promises';
+
+/** Checks whether a file exists on disk */
+export const fileExists = (file: PathLike): Promise<boolean> =>
+  fs
+    .stat(file)
+    .then((stat) => stat.isFile())
+    .catch(() => false);
+
+const touchFile = async (file: PathLike): Promise<void> => {
+  try {
+    const now = new Date();
+    await fs.utimes(file, now, now);
+  } catch (_error) {}
+};
+
+export type WriteTarget = PathLike | WriteStream;
+
+/** Writes a file to a swapfile then moves it into place to prevent excess change events. */
+export const writeOutput = async (target: WriteTarget, contents: string): Promise<void> => {
+  if (target && typeof target === 'object' && 'writable' in target) {
+    // If we get a WritableStream (e.g. stdout), we write to that
+    // but we listen for errors and wait for it to flush fully
+    return await new Promise((resolve, reject) => {
+      target.write(contents, (error) => {
+        if (error) {
+          reject(error);
+        } else {
+          resolve();
+        }
+      });
+    });
+  } else if (!(await fileExists(target))) {
+    // If the file doesn't exist, we can write directly, and not
+    // try-catch so the error falls through
+    await fs.writeFile(target, contents);
+  } else {
+    // If the file exists, we write to a swap-file, then rename (i.e. move)
+    // the file into place. No try-catch around `writeFile` for proper
+    // directory/permission errors
+    const tempTarget = target + '.tmp';
+    await fs.writeFile(tempTarget, contents);
+    try {
+      await fs.rename(tempTarget, target);
+    } catch (error) {
+      await fs.unlink(tempTarget);
+      throw error;
+    } finally {
+      // When we move the file into place, we also update its access and
+      // modification time manually, in case the rename doesn't trigger
+      // a change event
+      await touchFile(target);
+    }
+  }
+};