node-edf/Source/Writer.ts

NodeJS library for reading and writing EDF files.

import * as fs from "fs";
import moment from "moment";
import {ChannelInfo, Chunk, EDFPackage} from "./EDFPackage";

export function WriteEDFPackage(pack: EDFPackage, stream: fs.WriteStream) {
	WriteEDFHeader(pack, stream);
	for (const chunk of pack.chunks) {
		AppendChunk(chunk, stream, pack.channelInfos);
	}
}

function Str(length: number, val: any) {
	const result: string = (val ?? "").toString();
	if (result.length > length) throw new Error(`Val "${result}" exceeded string-length limit of ${length}.`);
	return result.padEnd(length);
}

export function WriteEDFHeader(pack: EDFPackage, stream: fs.WriteStream) {
	stream.write(Str(8, pack.edfVersion));
	stream.write(Str(80, pack.patientID));
	stream.write(Str(80, pack.recordingID));
	stream.write(Str(8, moment(pack.startTime).format("DD.MM.YY")));
	stream.write(Str(8, moment(pack.startTime).format("HH.mm.ss")));
	const headerBytes = 256 + (256 * pack.channelInfos.length); // class itself is 256 bytes, plus 256 per channel-info structure
	stream.write(Str(8, headerBytes));
	stream.write(Str(44, pack.reservedStr));
	stream.write(Str(8, pack.chunks.length));
	stream.write(Str(8, pack.chunkDuration));
	stream.write(Str(4, pack.channelInfos.length));
	pack.channelInfos.forEach(a=>stream.write(Str(16, a.name)));
	pack.channelInfos.forEach(a=>stream.write(Str(80, a.type)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.dimensions)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.physicalMin)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.physicalMax)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.digitalMin)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.digitalMax)));
	pack.channelInfos.forEach(a=>stream.write(Str(80, a.prefilteringInfo)));
	pack.channelInfos.forEach(a=>stream.write(Str(8, a.sampleCountPerChunk)));
	pack.channelInfos.forEach(a=>stream.write(Str(32, a.reservedStr)));
}

export function AppendChunk(chunk: Chunk, stream: fs.WriteStream, channelInfos: ChannelInfo[]) {
	// Data stays in channels x samples configuration
	// 2 Byte signed int litte-endian, 2's complement

	const totalSamplesPerChunk = channelInfos.map(ch=>ch.sampleCountPerChunk).reduce((total, a)=>total + a, 0);
	const buffer = Buffer.alloc(totalSamplesPerChunk * 2, "base64"); // each sample is 2 bytes

	let offset = 0;
	for (const channelSamples of chunk.channelSamples) {
		for (const sample of channelSamples) {
			//buffer.writeInt16LE(parseInt(((sample * 32768) / 188000).toString()), offset);
			//buffer.writeInt16LE(Math.floor((sample * 32768) / 188000), offset);
			buffer.writeInt16LE(sample, offset);
			offset += 2;
		}
	}
	stream.write(buffer, "base64");
}