From 8c1bd481c09f25255aa3ff2c73fbdeb9e9aa9d86 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sun, 6 Oct 2019 17:23:02 +0100
Subject: [PATCH] WIP tests 1

---
 package-lock.json  | 12 ++++++
 package.json       |  4 +-
 test/index.test.js |  3 ++
 test/streams.js    | 99 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 test/streams.js

diff --git a/package-lock.json b/package-lock.json
index 12855d2..f4dda2d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -353,6 +353,12 @@
         "@types/yargs": "^13.0.0"
       }
     },
+    "@offirmo/random": {
+      "version": "2.0.4",
+      "resolved": "https://registry.npmjs.org/@offirmo/random/-/random-2.0.4.tgz",
+      "integrity": "sha1-bnHQosawDnicL/A1YpKd72nIk9A=",
+      "dev": true
+    },
     "@overlookmotel/eslint-config": {
       "version": "4.3.2",
       "resolved": "https://registry.npmjs.org/@overlookmotel/eslint-config/-/eslint-config-4.3.2.tgz",
@@ -5191,6 +5197,12 @@
       "integrity": "sha1-NbCYdbT/SfJqd35QmzCQoyJr8ks=",
       "dev": true
     },
+    "stream-gen": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/stream-gen/-/stream-gen-2.0.1.tgz",
+      "integrity": "sha512-v8XTQUS49pphqUqPAJjPtEzkC7rPcZwK27QstEk2+WlPmftxI+LF0eo9btw4boIcArYhUYfyfl4MD92TAiWRjA==",
+      "dev": true
+    },
     "string-length": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/string-length/-/string-length-2.0.0.tgz",
diff --git a/package.json b/package.json
index 56974ef..b42561b 100644
--- a/package.json
+++ b/package.json
@@ -15,6 +15,7 @@
   },
   "dependencies": {},
   "devDependencies": {
+    "@offirmo/random": "^2.0.4",
     "@overlookmotel/eslint-config": "^4.3.2",
     "@overlookmotel/eslint-config-jest": "^2.1.0",
     "coveralls": "^3.0.6",
@@ -25,7 +26,8 @@
     "eslint-plugin-import": "^2.18.2",
     "eslint-plugin-jest": "^22.17.0",
     "eslint-plugin-node": "^10.0.0",
-    "jest": "^24.9.0"
+    "jest": "^24.9.0",
+    "stream-gen": "^2.0.1"
   },
   "keywords": [
     "stream",
diff --git a/test/index.test.js b/test/index.test.js
index 4ca049e..83a73c6 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -8,6 +8,9 @@
 // Modules
 const streamChop = require('../index');
 
+// Imports
+const {createReadStream} = require('./streams.js');
+
 // Init
 require('./support');
 
diff --git a/test/streams.js b/test/streams.js
new file mode 100644
index 0000000..18867f0
--- /dev/null
+++ b/test/streams.js
@@ -0,0 +1,99 @@
+/* --------------------
+ * stream-chop
+ * Functions to create test streams
+ * ------------------*/
+
+/* eslint-disable no-bitwise */
+
+'use strict';
+
+// Modules
+const {GeneratorReadStream, GeneratorWriteStream} = require('stream-gen'),
+	Random = require('@offirmo/random');
+
+// Constants
+const SEED = 0;
+
+// Exports
+
+module.exports = {
+	createReadStream,
+	createWriteStream
+};
+
+/**
+ * Create readable byte stream of specified length.
+ * Stream of bytes is drawn from MT pseudo-random generator.
+ * Output for same `start` and `len` is deterministic.
+ *
+ * @param {number} start - Start bytes of sequence
+ * @param {number} len - Length of sequence
+ * @returns {Stream} - Readable data stream
+ */
+function createReadStream(start, len) {
+	const gen = createGenerator(start, len);
+	return new GeneratorReadStream(gen);
+}
+
+/**
+ * Create writable stream.
+ * It checks that data piped into it matches expected
+ * i.e. same data as in stream from `createReadStream()`.
+ * Callback is called with error if data does not match, or with `null` when stream ends without error.
+ *
+ * @param {number} start - Start bytes of sequence
+ * @param {number} len - Length of sequence
+ * @param {function} cb - Callback - called with `null` when stream ends, or an error if matching fail
+ * @returns {Stream} - Readable data stream
+ */
+function createWriteStream(start, len, cb) {
+	const gen = createGenerator(start, len);
+	return new GeneratorWriteStream(gen, cb);
+}
+
+function createGenerator(start, len) {
+	// Init MT pseudo-random number generator
+	const mt = Random.engines.mt19937();
+	mt.seed(SEED);
+
+	// Init empty buffer
+	let leftover = 0,
+		leftoverBytes = 0;
+
+	// Discard start
+	if (start > 0) {
+		const discardBytes = start % 4,
+			discardQuads = (start - discardBytes) / 4;
+		if (discardQuads > 0) mt.discard(discardQuads);
+
+		if (discardBytes > 0) {
+			// Get new 32-bit number, discard unneeded bytes, and put rest in leftover
+			leftover = mt();
+			leftover >>= discardBytes * 8;
+			leftoverBytes = 4 - discardBytes;
+		}
+	}
+
+	// Create generator to produce bytes
+	let bytesRemaining = len;
+	function next() {
+		// If finished, end generator
+		if (bytesRemaining === 0) return {value: undefined, done: true};
+
+		// If no leftover, pull another 32-bit number from MT.
+		if (leftoverBytes === 0) {
+			leftover = mt();
+			leftoverBytes = 4;
+		}
+
+		// Pull lowest byte from leftover
+		const value = leftover & 0xFF;
+		leftover >>= 8;
+		leftoverBytes--;
+		bytesRemaining--;
+
+		return {value, done: false};
+	}
+
+	return () => ({next});
+}