From 83a0deab20647633a75cb7f0d8cb40d70912aa4e Mon Sep 17 00:00:00 2001
From: Joel Wetzell <jwetzell@yahoo.com>
Date: Wed, 25 Dec 2024 23:14:48 -0600
Subject: [PATCH] bare DDP packet decoding

---
 packages/ddp/src/index.ts         | 116 ++++++++++++++++++++++++++++++
 packages/ddp/tests/decode.test.js |  62 +++++++++++++++-
 2 files changed, 175 insertions(+), 3 deletions(-)

diff --git a/packages/ddp/src/index.ts b/packages/ddp/src/index.ts
index e69de29..e42d759 100644
--- a/packages/ddp/src/index.ts
+++ b/packages/ddp/src/index.ts
@@ -0,0 +1,116 @@
+export enum DDPDataType {
+  UNDEFINED = 0,
+  RGB = 1,
+  HSL = 2,
+  RGBW = 3,
+  GRAYSCALE = 4,
+}
+
+export enum DDPID {
+  JSON_CONTROL = 246,
+  JSON_CONFIG = 250,
+  JSON_STATUS = 251,
+  DMX_TRANSIT = 254,
+  ALL = 255,
+}
+
+export type DDPHeader = {
+  flags: {
+    version: number;
+    timecode: boolean;
+    storage: boolean;
+    reply: boolean;
+    query: boolean;
+    push: boolean;
+  };
+  sequenceNumber: number;
+  dataType: {
+    standard: boolean;
+    type: number;
+    bitsPerPixel: number;
+  };
+  sourceOrDestinationID: number;
+  dataOffset: number;
+  dataLength: number;
+  timecode?: {
+    seconds: number;
+    fractionalSeconds: number;
+  };
+};
+
+export type DDPPacket = {
+  header: DDPHeader;
+  data: Uint8Array;
+};
+
+export function decode(bytes: Uint8Array): DDPPacket {
+  if (bytes.length < 10) {
+    throw new Error('DDP packet must be at least 10 bytes');
+  }
+
+  const flagsByte = bytes[0];
+
+  const flags = {
+    version: (flagsByte & 0xc0) >> 6,
+    timecode: (flagsByte & 0x10) >> 4 === 1,
+    storage: (flagsByte & 0x08) >> 3 === 1,
+    reply: (flagsByte & 0x04) >> 2 === 1,
+    query: (flagsByte & 0x02) >> 1 === 1,
+    push: (flagsByte & 0x01) === 1,
+  };
+  const sequenceNumber = bytes[1] & 0x0f;
+
+  const dataTypeByte = bytes[2];
+
+  const dataType = {
+    standard: dataTypeByte >> 7 === 0,
+    type: (dataTypeByte & 0x38) >> 3,
+    bitsPerPixel: dataTypeByte & 0x07,
+  };
+
+  if (dataType.bitsPerPixel > 1) {
+    if (dataType.bitsPerPixel === 2) {
+      dataType.bitsPerPixel = 4;
+    } else if (dataType.bitsPerPixel === 3) {
+      dataType.bitsPerPixel = 8;
+    } else if (dataType.bitsPerPixel === 4) {
+      dataType.bitsPerPixel = 16;
+    } else if (dataType.bitsPerPixel === 5) {
+      dataType.bitsPerPixel = 24;
+    } else if (dataType.bitsPerPixel === 6) {
+      dataType.bitsPerPixel = 32;
+    } else {
+      throw new Error('unknown DDP size');
+    }
+  }
+
+  const sourceOrDestinationID = bytes[3];
+  const dataOffset = (bytes[4] << 24) + (bytes[5] << 16) + (bytes[6] << 8) + bytes[7];
+  const dataLength = (bytes[8] << 8) + bytes[9];
+
+  const header: DDPHeader = {
+    flags,
+    sequenceNumber,
+    dataType,
+    sourceOrDestinationID,
+    dataOffset,
+    dataLength,
+  };
+
+  let dataStart = 10 
+  if (flags.timecode) {
+    if (bytes.length < 14) {
+      throw new Error('DDP packet with timecode must be at least 14 bytes');
+    }
+    dataStart = 14
+    header.timecode = {
+      seconds: (bytes[10] << 8) + bytes[11],
+      fractionalSeconds: (bytes[12] << 8) + bytes[13],
+    };
+  }
+
+  return {
+    header,
+    data: bytes.subarray(dataStart)
+  };
+}
diff --git a/packages/ddp/tests/decode.test.js b/packages/ddp/tests/decode.test.js
index 7bbb439..d9c6e8f 100644
--- a/packages/ddp/tests/decode.test.js
+++ b/packages/ddp/tests/decode.test.js
@@ -3,16 +3,72 @@ const { describe, it } = require('node:test');
 const ddp = require('../dist/cjs/index');
 
 const goodTests = [
+  {
+    description: 'simple DDP packet',
+    bytes: new Uint8Array([0x40, 0x0f, 0x92, 0x01, 0x45, 0x67, 0x89, 0x10, 0x10, 0x11]),
+    expected: {
+      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([])
+    },
+  },
+  {
+    description: 'DDP packet with timecode',
+    bytes: new Uint8Array([0x50, 0x0f, 0x92, 0x01, 0x45, 0x67, 0x89, 0x10, 0x10, 0x11, 0x10, 0x11, 0x11, 0x10]),
+    expected: {
+      header: {
+        flags: {
+          version: 1,
+          timecode: true,
+          storage: false,
+          reply: false,
+          query: false,
+          push: false,
+        },
+        sequenceNumber: 15,
+        dataType: {
+          standard: false,
+          type: 2,
+          bitsPerPixel: 4,
+        },
+        sourceOrDestinationID: 1,
+        dataOffset: 1164413200,
+        dataLength: 4113,
+        timecode: {
+          seconds: 4113,
+          fractionalSeconds: 4368,
+        },
+      },
+      data: new Uint8Array([])
+
+    },
+  },
 ];
 
-const badTests = [
-  
-];
+const badTests = [];
 
 describe('DDP Message Decoding Pass', () => {
   goodTests.forEach((messageTest) => {
     it(messageTest.description, () => {
       const decoded = ddp.decode(messageTest.bytes);
+      console.log(decoded.header);
       deepEqual(decoded, messageTest.expected);
     });
   });