From 86d1f119dce3d8020b2e3f54cb9f2dba9a13b058 Mon Sep 17 00:00:00 2001
From: "Kent C. Dodds" <me+github@kentcdodds.com>
Date: Mon, 29 Nov 2021 15:12:39 -0700
Subject: [PATCH] feat: only save files if they are unchanged

Closes #320
---
 index.js                           | 11 +++++++++--
 test/fixtures/unchanged-input.css  |  3 +++
 test/fixtures/unchanged-output.css |  5 +++++
 test/unchanged.js                  | 17 +++++++++++++++++
 4 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 test/fixtures/unchanged-input.css
 create mode 100644 test/fixtures/unchanged-output.css
 create mode 100644 test/unchanged.js

diff --git a/index.js b/index.js
index a5286f7..615638c 100755
--- a/index.js
+++ b/index.js
@@ -250,11 +250,11 @@ function css(css, file) {
           const tasks = []
 
           if (options.to) {
-            tasks.push(fs.outputFile(options.to, result.css))
+            tasks.push(outputFile(options.to, result.css))
 
             if (result.map) {
               const mapfile = getMapfile(options)
-              tasks.push(fs.outputFile(mapfile, result.map.toString()))
+              tasks.push(outputFile(mapfile, result.map.toString()))
             }
           } else process.stdout.write(result.css, 'utf8')
 
@@ -278,6 +278,13 @@ function css(css, file) {
     .catch((err) => {
       throw err
     })
+
+  async function outputFile(file, string) {
+    const fileExists = await fs.pathExists(file)
+    const currentValue = fileExists ? await fs.readFile(file, 'utf8') : null
+    if (currentValue === string) return
+    return fs.outputFile(file, string)
+  }
 }
 
 function dependencies(results) {
diff --git a/test/fixtures/unchanged-input.css b/test/fixtures/unchanged-input.css
new file mode 100644
index 0000000..60f1eab
--- /dev/null
+++ b/test/fixtures/unchanged-input.css
@@ -0,0 +1,3 @@
+body {
+  color: red;
+}
diff --git a/test/fixtures/unchanged-output.css b/test/fixtures/unchanged-output.css
new file mode 100644
index 0000000..6521159
--- /dev/null
+++ b/test/fixtures/unchanged-output.css
@@ -0,0 +1,5 @@
+body {
+  color: red;
+}
+
+/*# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbInVuY2hhbmdlZC1pbnB1dC5jc3MiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBQUEiLCJmaWxlIjoidW5jaGFuZ2VkLW91dHB1dC5jc3MiLCJzb3VyY2VzQ29udGVudCI6WyJib2R5IHtcbiAgY29sb3I6IHJlZDtcbn1cbiJdfQ== */
\ No newline at end of file
diff --git a/test/unchanged.js b/test/unchanged.js
new file mode 100644
index 0000000..4598530
--- /dev/null
+++ b/test/unchanged.js
@@ -0,0 +1,17 @@
+import fs from 'fs-extra'
+import test from 'ava'
+
+import cli from './helpers/cli.js'
+
+test('files are not saved if the contents are the same', async (t) => {
+  const input = 'test/fixtures/unchanged-input.css'
+  const output = 'test/fixtures/unchanged-output.css'
+  const intialStat = await fs.stat(output)
+
+  const { error, stderr } = await cli([input, '-o', output])
+
+  t.falsy(error, stderr)
+
+  const finalStat = await fs.stat(output)
+  t.is(finalStat.mtimeMs, intialStat.mtimeMs)
+})