From 23885b73340c96d9a6c3221b66484abfa814c8b8 Mon Sep 17 00:00:00 2001
From: Joel Wetzell <jwetzell@yahoo.com>
Date: Thu, 26 Dec 2024 12:27:17 -0600
Subject: [PATCH] add encoding

---
 packages/ddp/src/index.ts         | 65 +++++++++++++++++++++++++++++++
 packages/ddp/tests/encode.test.js | 31 ++++++++++++++-
 2 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/packages/ddp/src/index.ts b/packages/ddp/src/index.ts
index 9e2bde3..f94bde5 100644
--- a/packages/ddp/src/index.ts
+++ b/packages/ddp/src/index.ts
@@ -114,3 +114,68 @@ export function decode(bytes: Uint8Array): DDPPacket {
     data: bytes.subarray(dataStart),
   };
 }
+
+export function encode(packet: DDPPacket): Uint8Array {
+  let flagByte = packet.header.flags.version << 6;
+
+  let headerLength = 10;
+
+  if (packet.header.flags.timecode) {
+    flagByte += 16;
+    headerLength = 14;
+  }
+
+  if (packet.header.flags.storage) {
+    flagByte += 8;
+  }
+  if (packet.header.flags.reply) {
+    flagByte += 4;
+  }
+  if (packet.header.flags.query) {
+    flagByte += 2;
+  }
+  if (packet.header.flags.push) {
+    flagByte += 1;
+  }
+
+  let dataTypeByte = 0;
+
+  if (!packet.header.dataType.standard) {
+    dataTypeByte += 128;
+  }
+
+  dataTypeByte += packet.header.dataType.type << 3;
+
+  if (packet.header.dataType.bitsPerPixel === 1) {
+    dataTypeByte += 1;
+  } else if (packet.header.dataType.bitsPerPixel === 4) {
+    dataTypeByte += 2;
+  } else if (packet.header.dataType.bitsPerPixel === 8) {
+    dataTypeByte += 3;
+  } else if (packet.header.dataType.bitsPerPixel === 16) {
+    dataTypeByte += 4;
+  } else if (packet.header.dataType.bitsPerPixel === 24) {
+    dataTypeByte += 5;
+  } else if (packet.header.dataType.bitsPerPixel === 32) {
+    dataTypeByte += 6;
+  } else if (packet.header.dataType.bitsPerPixel === 0) {
+    dataTypeByte += 0;
+  } else {
+    throw new Error('DDP packet has unsupported bits per pixel value');
+  }
+
+  const bytes = new Uint8Array(headerLength);
+  const view = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
+
+  view.setUint8(0, flagByte);
+  view.setUint8(1, packet.header.sequenceNumber);
+  view.setUint8(2, dataTypeByte);
+  view.setUint8(3, packet.header.sourceOrDestinationID);
+  view.setUint32(4, packet.header.dataOffset);
+  view.setUint16(8, packet.header.dataLength);
+
+  // const bytes = new Uint8Array([flagByte, sequenceNumberByte, dataTypeByte, packet.header.sourceOrDestinationID])
+  const headerBytes = new Uint8Array(view.buffer, view.byteOffset, view.byteLength);
+
+  return new Uint8Array([...headerBytes, ...packet.data]);
+}
diff --git a/packages/ddp/tests/encode.test.js b/packages/ddp/tests/encode.test.js
index 3bea32c..ad0b792 100644
--- a/packages/ddp/tests/encode.test.js
+++ b/packages/ddp/tests/encode.test.js
@@ -2,14 +2,41 @@ const { deepEqual, throws } = require('assert');
 const { describe, it } = require('node:test');
 const ddp = require('../dist/cjs/index');
 
-const goodTests = [];
+const goodTests = [
+  {
+    description: 'simple DDP packet',
+    expected: new Uint8Array([0x40, 0x0f, 0x92, 0x01, 0x45, 0x67, 0x89, 0x10, 0x10, 0x11]),
+    packet: {
+      header: {
+        flags: {
+          version: 1,
+          timecode: false,
+          storage: false,
+          reply: false,
+          query: false,
+          push: false,
+        },
+        sequenceNumber: 15,
+        dataType: {
+          standard: false,
+          type: 2,
+          bitsPerPixel: 4,
+        },
+        sourceOrDestinationID: 1,
+        dataOffset: 1164413200,
+        dataLength: 4113,
+      },
+      data: new Uint8Array([]),
+    },
+  },
+];
 
 const badTests = [];
 
 describe('DDP Message Encoding Pass', () => {
   goodTests.forEach((messageTest) => {
     it(messageTest.description, () => {
-      const encoded = ddp.encode(messageTest.message);
+      const encoded = ddp.encode(messageTest.packet);
       deepEqual(encoded, messageTest.expected);
     });
   });