Save cached config to standard directories

Instead of placing the configuration file in the home directory it should be placed in the [appropriate directory](https://wiki.archlinux.org/index.php/XDG_Base_Directory_support) per OS.

Breaking change: resolves issue #37

config-path.js

@@ -0,0 +1,33 @@
+const path = require('path');
+const userHome = require('user-home');
+
+const env = process.env;
+const name = 'js-v8flags';
+
+function macos () {
+  const library = path.join(userHome, 'Library');
+  return path.join(library, 'Caches', name);
+}
+
+function windows () {
+  const appData = env.LOCALAPPDATA || path.join(userHome, 'AppData', 'Local');
+  return path.join(appData, name, 'Cache');
+}
+
+// https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
+function linux () {
+  const username = path.basename(userHome);
+  return path.join(env.XDG_CACHE_HOME || path.join(userHome, '.cache'), name);
+}
+
+module.exports = function (platform) {
+  if (platform === 'darwin') {
+    return macos();
+  }
+
+  if (platform === 'win32') {
+    return windows();
+  }
+
+  return linux();
+};

index.js

@@ -7,6 +7,7 @@ const fs = require('fs');
 const path = require('path');
 const crypto = require('crypto');
 const execFile = require('child_process').execFile;
+const configPath = require('./config-path.js')(process.platform);
 const env = process.env;
 const user = env.LOGNAME || env.USER || env.LNAME || env.USERNAME || '';
 const exclusions = ['--help'];
@@ -33,10 +34,12 @@ function openConfig (cb) {
     return tryOpenConfig(path.join(os.tmpdir(), configfile), cb);
   }
 
-  tryOpenConfig(path.join(userHome, configfile), function (err, fd) {
-    if (err) return tryOpenConfig(path.join(os.tmpdir(), configfile), cb);
-    return cb(null, fd);
-  });
+  fs.mkdir(configPath, function () {
+    tryOpenConfig(path.join(configPath, configfile), function (err, fd) {
+      if (err) return tryOpenConfig(path.join(os.tmpdir(), configfile), cb);
+      return cb(null, fd);
+    });
+  })
 }
 
 function tryOpenConfig (configpath, cb) {
@@ -131,3 +134,4 @@ module.exports = function (cb) {
 };
 
 module.exports.configfile = configfile;
+module.exports.configPath = configPath;

test.js

@@ -16,6 +16,8 @@ function eraseHome() {
   delete env.USER;
   delete env.LNAME;
   delete env.USERNAME;
+  delete env.XDG_CACHE_HOME;
+  delete env.LOCALAPPDATA;
 }
 
 function setTemp(dir) {
@@ -24,11 +26,9 @@ function setTemp(dir) {
 
 function cleanup () {
   var v8flags = require('./');
-  var userHome = require('user-home');
-  if (userHome === null) userHome = __dirname;
 
   var files = [
-    path.resolve(userHome, v8flags.configfile),
+    path.resolve(v8flags.configPath, v8flags.configfile),
     path.resolve(os.tmpdir(), v8flags.configfile),
   ];
   files.forEach(function (file) {
@@ -47,7 +47,7 @@ describe('v8flags', function () {
 
   it('should cache and call back with the v8 flags for the running process', function (done) {
     var v8flags = require('./');
-    var configfile = path.resolve(require('user-home'), v8flags.configfile);
+    var configfile = path.resolve(v8flags.configPath, v8flags.configfile);
     v8flags(function (err, flags) {
       expect(flags).to.be.a('array');
       expect(fs.existsSync(configfile)).to.be.true;
@@ -62,7 +62,7 @@ describe('v8flags', function () {
 
   it('should not append the file when multiple calls happen concurrently and the config file does not yet exist', function (done) {
     var v8flags = require('./');
-    var configfile = path.resolve(require('user-home'), v8flags.configfile);
+    var configfile = path.resolve(v8flags.configPath, v8flags.configfile);
     async.parallel([v8flags, v8flags, v8flags], function (err, result) {
       v8flags(function (err2, res) {
         done();
@@ -83,7 +83,11 @@ describe('v8flags', function () {
   it('should fall back to writing to a temp dir if user home is unwriteable', function (done) {
     eraseHome();
     env.HOME = path.join(__dirname, 'does-not-exist');
+    // Clear require cached modules so the modified environment variable HOME is used
+    delete require.cache[require.resolve('./')];
+    delete require.cache[require.resolve('./config-path.js')];
     var v8flags = require('./');
+    v8flags.configPath = env.HOME;
     var configfile = path.resolve(os.tmpdir(), v8flags.configfile);
     v8flags(function (err, flags) {
       expect(fs.existsSync(configfile)).to.be.true;
@@ -133,6 +137,46 @@ describe('v8flags', function () {
     v8flags(function (err, flags) {
       expect(err).to.be.null;
       done();
-    })
+    });
+  });
+});
+
+describe('config-path', function () {
+  const moduleName = 'js-v8flags';
+
+  beforeEach(function() {
+    env.HOME = 'somehome';
+    cleanup();
+  });
+  afterEach(cleanup);
+
+  it('should return default linux path in other environments', function(done) {
+    delete require.cache[require.resolve('./config-path.js')];
+    const configPath = require('./config-path.js')('other');
+
+    expect(configPath).to.equal(
+      path.join(env.HOME, '.cache', moduleName)
+    );
+    done();
+  });
+
+  it('should return default macos path in darwin environment', function(done) {
+    delete require.cache[require.resolve('./config-path.js')];
+    const configPath = require('./config-path.js')('darwin');
+
+    expect(configPath).to.equal(
+      path.join(env.HOME, 'Library', 'Caches', moduleName)
+    );
+    done();
+  });
+
+  it('should return default windows path in win32 environment', function(done) {
+    delete require.cache[require.resolve('./config-path.js')];
+    const configPath = require('./config-path.js')('win32');
+
+    expect(configPath).to.equal(
+      path.join(env.HOME, 'AppData', 'Local', moduleName, 'Cache')
+    );
+    done();
   });
 });