fix(cli): use unique temp dir per invocation

Fixes #183

Author: JamieMason

src/constants.ts

@@ -1,5 +1,6 @@
 import { tmpdir } from 'os';
 import { join } from 'path';
+import { uuid } from './uuid';
 
 export interface IApp {
   readonly bundleId: string;
@@ -39,7 +40,7 @@ export const SUPPORTED_FILE_TYPES = [
   ...supports.jpegmini,
 ].filter((value, i, list) => list.indexOf(value) === i);
 
-export const TMPDIR = join(tmpdir(), 'imageoptim-cli');
+export const TMPDIR = join(tmpdir(), 'imageoptim-cli', uuid());
 export const VERSION = manifest.version;
 export const PNGQUANT_NUMBER_OF_COLORS = '256';
 export const PNGQUANT_QUALITY = '65-80';

src/uuid.ts

@@ -0,0 +1,19 @@
+/**
+ * Cheaply generate a UUID with a low chance of collisions
+ * https://stackoverflow.com/a/8809472/745158
+ */
+export function uuid(): string {
+  let epoch: number = new Date().getTime();
+  let sessionLength: number = Date.now() * 1000 || 0;
+  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (character) => {
+    let randomNumber: number = Math.random() * 16;
+    if (epoch > 0) {
+      randomNumber = (epoch + randomNumber) % 16 | 0;
+      epoch = Math.floor(epoch / 16);
+    } else {
+      randomNumber = (sessionLength + randomNumber) % 16 | 0;
+      sessionLength = Math.floor(sessionLength / 16);
+    }
+    return (character == 'x' ? randomNumber : (randomNumber & 0x7) | 0x8).toString(16);
+  });
+}