index.js

#!/usr/bin/env node
const { createConnection, TextDocuments, TextDocument, TextDocumentChangeEvent, Diagnostic, DiagnosticSeverity, ProposedFeatures } = require("vscode-languageserver");
const { exec, spawn } = require("child_process");
const fetch = require("node-fetch");
const qs = require("qs");
const getPort = require("get-port")
const fileUrlToPath = require("file-uri-to-path");
const writeGood = require("write-good");
let languageToolClient = async (text) => ([]);

const languageToolServer = {
    listen (port) {
	const server = spawn("java", ["-cp", `${__dirname}/LanguageTool-4.3/languagetool-server.jar`, "org.languagetool.server.HTTPServer", "--port", `${port}`]);
	server.stdout.on("data", (data)=>{
	    console.warn(data.toString());
	    if(data.toString().match(/Server started/)) {
		languageToolClient = async (text) => {
		    const language = 'en-US';
		    const response = await fetch(`http://localhost:${port}/v2/check?${qs.stringify({language, text})}`);
		    const json = await response.json();
		    return json.matches;
		}
	    }
	});
	server.stderr.on("data", (data)=>{
	    console.warn(data.toString());
	});
	process.on('exit', ()=>server.kill());
    }
};

const connection = createConnection(ProposedFeatures.all);

const documents = new TextDocuments();

connection.onInitialize(() => ({
    capabilities: {
	textDocumentSync: documents.syncKind,
    }
}));

const removeMarkdown = (markdown) => {
    return markdown
	.replace(/```[\s\S]*?```/mg, (s) => " ".repeat(s.length))
    	.replace(/~~~[\s\S]*?~~~/mg, (s) => " ".repeat(s.length))
        .replace(/\$\$?[\s\S]*?\$\$?/mg, (s) => " ".repeat(s.length))
	.replace(/(\[)(.*?)(\]\(.*?\))/mg, (_, s, t, u) => " ".repeat(s.length)+t+" ".repeat(u.length))
        .replace(/[-=>`*_ ]*/mg, (s)=>" ".repeat(s.length))
	.replace(/#*/mg, (s)=>" ".repeat(s.length))
}

const removeLaTeX = (latex) => {
    return latex
	.replace(/(\\text.*\{)(.*?)(\})/, (_, s, t, u)=> " ".repeat(s.length)+t+" ".repeat(u.length))
	.replace(/\\\w+(?:\{.*?\}|\[.*?\])*/mg, (s) => " ".repeat(s.length))
	.replace(/\\\(.*?\\\)|\\\[.*?\\\]/mg, (s) => " ".repeat(s.length))
	.replace(/\$\$.*?\$\$/mg, (s) => " ".repeat(s.length))
	.replace(/\$.*?\$/mg, (s) => " ".repeat(s.length))
}

const validateTextDocumentChange = async (change) => {
    const text = process.argv.indexOf("--markdown") > 0 ? removeMarkdown(change.document.getText())
	  : process.argv.indexOf("--latex") > 0 ? removeLaTeX(change.document.getText())
	  : change.document.getText();
    const writeGoodWarnings = await writeGood(text);
    const languageToolErrors = await languageToolClient(text);
    const diagnostics = ([])
	  .concat(writeGoodWarnings.map((warning)=>({
	      severity: DiagnosticSeverity.Hint,
	      code: text.slice(warning.index, warning.index+warning.offset),
	      range: {
		  start: change.document.positionAt(warning.index),
		  end: change.document.positionAt(warning.index + warning.offset)
	      },
	      message: warning.reason,
	      srouce: "write-good"
	  })), languageToolErrors.filter((error) => {
	      return !error.message.match(/repeated a whitespace/)
	  }).map((error)=>({
	      severity: DiagnosticSeverity.Error,
	      code: text.slice(error.offset, error.offset+error.length),
	      range: {
		start: change.document.positionAt(error.offset),
		end: change.document.positionAt(error.offset+error.length)
	    },
	    message: error.message,
	    source: "languagetool"
	  })));
    connection.sendDiagnostics({ uri: change.document.uri, diagnostics });
}


documents.onDidChangeContent(validateTextDocumentChange);

(async()=>{languageToolServer.listen(await getPort());})();

documents.listen(connection);

connection.listen();