From 3902ba61049c491f4683ec95e1effeaeec5a1bba Mon Sep 17 00:00:00 2001
From: Joshua Tenner <tenner.joshua@gmail.com>
Date: Mon, 29 Jul 2019 13:02:54 -0400
Subject: [PATCH] [Implement] subarray

---
 assembly/buffer/index.ts | 13 +++++++++++++
 package-lock.json        |  2 +-
 tests/buffer.spec.ts     | 36 +++++++++++++++++++++++++++++++++---
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/assembly/buffer/index.ts b/assembly/buffer/index.ts
index fb5d4ca..caff5ac 100644
--- a/assembly/buffer/index.ts
+++ b/assembly/buffer/index.ts
@@ -27,6 +27,19 @@ export class Buffer extends Uint8Array {
     return value instanceof Buffer;
   }
 
+  // Adapted from https://github.com/AssemblyScript/assemblyscript/blob/master/std/assembly/typedarray.ts
+  public subarray(begin: i32 = 0, end: i32 = 0x7fffffff): Buffer {
+    var len = <i32>this.dataLength;
+    begin = begin < 0 ? max(len + begin, 0) : min(begin, len);
+    end   = end   < 0 ? max(len + end,   0) : min(end,   len);
+    end   = max(end, begin);
+    var out = changetype<Buffer>(__alloc(offsetof<Buffer>(), idof<Buffer>())); // retains
+    out.data = this.data; // retains
+    out.dataStart = this.dataStart + <usize>begin;
+    out.dataLength = end - begin;
+    return out;
+  }
+
   readInt8(offset: i32 = 0): i8 {
     if(i32(offset < 0) | i32(<u32>offset >= this.dataLength)) throw new RangeError(E_INDEXOUTOFRANGE);
     return load<i8>(this.dataStart + <usize>offset);
diff --git a/package-lock.json b/package-lock.json
index 1d4efe9..05a35d2 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -38,7 +38,7 @@
       }
     },
     "assemblyscript": {
-      "version": "github:assemblyscript/assemblyscript#4c938f7689c39e3a1ad813356781e2689fd4ec70",
+      "version": "github:assemblyscript/assemblyscript#227c626921175ab19701752397fa513171750d38",
       "from": "github:assemblyscript/assemblyscript",
       "dev": true,
       "requires": {
diff --git a/tests/buffer.spec.ts b/tests/buffer.spec.ts
index ba4ff36..5fc3ac2 100644
--- a/tests/buffer.spec.ts
+++ b/tests/buffer.spec.ts
@@ -102,7 +102,7 @@ describe("buffer", () => {
     // expectFn(() => {
     //   let newBuff = new Buffer(1);
     //   newBuff.writeInt8(5,10);
-    // }).toThrow();    
+    // }).toThrow();
   });
 
   test("#writeUInt8", () => {
@@ -115,8 +115,8 @@ describe("buffer", () => {
     // expectFn(() => {
     //   let newBuff = new Buffer(1);
     //   newBuff.writeUInt8(5,10);
-    // }).toThrow();    
-  });  
+    // }).toThrow();
+  });
 
   test("#readInt16LE", () => {
     let buff = create<Buffer>([0x0,0x05,0x0]);
@@ -213,4 +213,34 @@ describe("buffer", () => {
     //   newBuff.writeUInt16BE(0);
     // }).toThrow();
   });
+
+  test("#subarray", () => {
+    let example = create<Buffer>([1, 2, 3, 4, 5, 6, 7, 8]);
+
+    // no parameters means copy the Buffer
+    let actual = example.subarray();
+    expect<Buffer>(actual).toStrictEqual(example);
+    expect<ArrayBuffer>(actual.buffer).toBe(example.buffer); // should use the same buffer
+
+    // start at offset 5
+    actual = example.subarray(5);
+    let expected = create<Buffer>([6, 7, 8]);
+    // trace("length", 1, expected.length);
+    expect<Buffer>(actual).toStrictEqual(expected);
+
+    // negative start indicies, start at (8 - 5)
+    actual = example.subarray(-5);
+    expected = create<Buffer>([4, 5, 6, 7, 8]);
+    expect<Buffer>(actual).toStrictEqual(expected);
+
+    // two parameters
+    actual = example.subarray(2, 6);
+    expected = create<Buffer>([3, 4, 5, 6]);
+    expect<Buffer>(actual).toStrictEqual(expected);
+
+    // negative end index
+    actual = example.subarray(4, -1);
+    expected = create<Buffer>([5, 6, 7]);
+    expect<Buffer>(actual).toStrictEqual(expected);
+  });
 });