extensions/html-language-features/server/src/htmlServer.ts/startServer
export function startServer(connection: Connection, runtime: RuntimeEnvironment) {

	// Create a text document manager.
	const documents = new TextDocuments(TextDocument);
	// Make the text document manager listen on the connection
	// for open, change and close text document events
	documents.listen(connection);

	let workspaceFolders: WorkspaceFolder[] = [];

	let languageModes: LanguageModes;

	let clientSnippetSupport = false;
	let dynamicFormatterRegistration = false;
	let scopedSettingsSupport = false;
	let workspaceFoldersSupport = false;
	let foldingRangeLimit = Number.MAX_VALUE;
	let formatterMaxNumberOfEdits = Number.MAX_VALUE;

	const customDataRequestService: CustomDataRequestService = {
		getContent(uri: string) {
			return connection.sendRequest(CustomDataContent.type, uri);
		}
	};

	let globalSettings: Settings = {};
	let documentSettings: { [key: string]: Thenable<Settings> } = {};
	// remove document settings on close
	documents.onDidClose(e => {
		delete documentSettings[e.document.uri];
	});

	function getDocumentSettings(textDocument: TextDocument, needsDocumentSettings: () => boolean): Thenable<Settings | undefined> {
		if (scopedSettingsSupport && needsDocumentSettings()) {
			let promise = documentSettings[textDocument.uri];
			if (!promise) {
				const scopeUri = textDocument.uri;
				const configRequestParam: ConfigurationParams = { items: [{ scopeUri, section: 'css' }, { scopeUri, section: 'html' }, { scopeUri, section: 'javascript' }] };
				promise = connection.sendRequest(ConfigurationRequest.type, configRequestParam).then(s => ({ css: s[0], html: s[1], javascript: s[2] }));
				documentSettings[textDocument.uri] = promise;
			}
			return promise;
		}
		return Promise.resolve(undefined);
	}

	// After the server has started the client sends an initialize request. The server receives
	// in the passed params the rootPath of the workspace plus the client capabilities
	connection.onInitialize((params: InitializeParams): InitializeResult => {
		const initializationOptions = params.initializationOptions;

		workspaceFolders = (<any>params).workspaceFolders;
		if (!Array.isArray(workspaceFolders)) {
			workspaceFolders = [];
			if (params.rootPath) {
				workspaceFolders.push({ name: '', uri: URI.file(params.rootPath).toString() });
			}
		}

		const handledSchemas = initializationOptions?.handledSchemas as string[] ?? ['file'];

		const fileSystemProvider = getFileSystemProvider(handledSchemas, connection, runtime);

		const workspace = {
			get settings() { return globalSettings; },
			get folders() { return workspaceFolders; }
		};

		languageModes = getLanguageModes(initializationOptions?.embeddedLanguages || { css: true, javascript: true }, workspace, params.capabilities, fileSystemProvider);

		const dataPaths: string[] = initializationOptions?.dataPaths || [];
		fetchHTMLDataProviders(dataPaths, customDataRequestService).then(dataProviders => {
			languageModes.updateDataProviders(dataProviders);
		});

		documents.onDidClose(e => {
			languageModes.onDocumentRemoved(e.document);
		});
		connection.onShutdown(() => {
			languageModes.dispose();
		});

		function getClientCapability<T>(name: string, def: T) {
			const keys = name.split('.');
			let c: any = params.capabilities;
			for (let i = 0; c && i < keys.length; i++) {
				if (!c.hasOwnProperty(keys[i])) {
					return def;
				}
				c = c[keys[i]];
			}
			return c;
		}

		clientSnippetSupport = getClientCapability('textDocument.completion.completionItem.snippetSupport', false);
		dynamicFormatterRegistration = getClientCapability('textDocument.rangeFormatting.dynamicRegistration', false) && (typeof initializationOptions?.provideFormatter !== 'boolean');
		scopedSettingsSupport = getClientCapability('workspace.configuration', false);
		workspaceFoldersSupport = getClientCapability('workspace.workspaceFolders', false);
		foldingRangeLimit = getClientCapability('textDocument.foldingRange.rangeLimit', Number.MAX_VALUE);
		formatterMaxNumberOfEdits = params.initializationOptions?.customCapabilities?.rangeFormatting?.editLimit || Number.MAX_VALUE;
		const capabilities: ServerCapabilities = {
			textDocumentSync: TextDocumentSyncKind.Incremental,
			completionProvider: clientSnippetSupport ? { resolveProvider: true, triggerCharacters: ['.', ':', '<', '"', '=', '/'] } : undefined,
			hoverProvider: true,
			documentHighlightProvider: true,
			documentRangeFormattingProvider: params.initializationOptions?.provideFormatter === true,
			documentFormattingProvider: params.initializationOptions?.provideFormatter === true,
			documentLinkProvider: { resolveProvider: false },
			documentSymbolProvider: true,
			definitionProvider: true,
			signatureHelpProvider: { triggerCharacters: ['('] },
			referencesProvider: true,
			colorProvider: {},
			foldingRangeProvider: true,
			selectionRangeProvider: true,
			renameProvider: true,
			linkedEditingRangeProvider: true
		};
		return { capabilities };
	});

	connection.onInitialized(() => {
		if (workspaceFoldersSupport) {
			connection.client.register(DidChangeWorkspaceFoldersNotification.type);

			connection.onNotification(DidChangeWorkspaceFoldersNotification.type, e => {
				const toAdd = e.event.added;
				const toRemove = e.event.removed;
				const updatedFolders = [];
				if (workspaceFolders) {
					for (const folder of workspaceFolders) {
						if (!toRemove.some(r => r.uri === folder.uri) && !toAdd.some(r => r.uri === folder.uri)) {
							updatedFolders.push(folder);
						}
					}
				}
				workspaceFolders = updatedFolders.concat(toAdd);
				documents.all().forEach(triggerValidation);
			});
		}
	});

	let formatterRegistrations: Thenable<Disposable>[] | null = null;

	// The settings have changed. Is send on server activation as well.
	connection.onDidChangeConfiguration((change) => {
		globalSettings = change.settings;
		documentSettings = {}; // reset all document settings
		documents.all().forEach(triggerValidation);

		// dynamically enable & disable the formatter
		if (dynamicFormatterRegistration) {
			const enableFormatter = globalSettings && globalSettings.html && globalSettings.html.format && globalSettings.html.format.enable;
			if (enableFormatter) {
				if (!formatterRegistrations) {
					const documentSelector = [{ language: 'html' }, { language: 'handlebars' }];
					formatterRegistrations = [
						connection.client.register(DocumentRangeFormattingRequest.type, { documentSelector }),
						connection.client.register(DocumentFormattingRequest.type, { documentSelector })
					];
				}
			} else if (formatterRegistrations) {
				formatterRegistrations.forEach(p => p.then(r => r.dispose()));
				formatterRegistrations = null;
			}
		}
	});

	const pendingValidationRequests: { [uri: string]: Disposable } = {};
	const validationDelayMs = 500;

	// The content of a text document has changed. This event is emitted
	// when the text document first opened or when its content has changed.
	documents.onDidChangeContent(change => {
		triggerValidation(change.document);
	});

	// a document has closed: clear all diagnostics
	documents.onDidClose(event => {
		cleanPendingValidation(event.document);
		connection.sendDiagnostics({ uri: event.document.uri, diagnostics: [] });
	});

	function cleanPendingValidation(textDocument: TextDocument): void {
		const request = pendingValidationRequests[textDocument.uri];
		if (request) {
			request.dispose();
			delete pendingValidationRequests[textDocument.uri];
		}
	}

	function triggerValidation(textDocument: TextDocument): void {
		cleanPendingValidation(textDocument);
		pendingValidationRequests[textDocument.uri] = runtime.timer.setTimeout(() => {
			delete pendingValidationRequests[textDocument.uri];
			validateTextDocument(textDocument);
		}, validationDelayMs);
	}

	function isValidationEnabled(languageId: string, settings: Settings = globalSettings) {
		const validationSettings = settings && settings.html && settings.html.validate;
		if (validationSettings) {
			return languageId === 'css' && validationSettings.styles !== false || languageId === 'javascript' && validationSettings.scripts !== false;
		}
		return true;
	}

	async function validateTextDocument(textDocument: TextDocument) {
		try {
			const version = textDocument.version;
			const diagnostics: Diagnostic[] = [];
			if (textDocument.languageId === 'html') {
				const modes = languageModes.getAllModesInDocument(textDocument);
				const settings = await getDocumentSettings(textDocument, () => modes.some(m => !!m.doValidation));
				const latestTextDocument = documents.get(textDocument.uri);
				if (latestTextDocument && latestTextDocument.version === version) { // check no new version has come in after in after the async op
					for (const mode of modes) {
						if (mode.doValidation && isValidationEnabled(mode.getId(), settings)) {
							pushAll(diagnostics, await mode.doValidation(latestTextDocument, settings));
						}
					}
					connection.sendDiagnostics({ uri: latestTextDocument.uri, diagnostics });
				}
			}
		} catch (e) {
			connection.console.error(formatError(`Error while validating ${textDocument.uri}`, e));
		}
	}

	connection.onCompletion(async (textDocumentPosition, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(textDocumentPosition.textDocument.uri);
			if (!document) {
				return null;
			}
			const mode = languageModes.getModeAtPosition(document, textDocumentPosition.position);
			if (!mode || !mode.doComplete) {
				return { isIncomplete: true, items: [] };
			}
			const doComplete = mode.doComplete;

			if (mode.getId() !== 'html') {
				/* __GDPR__
					"html.embbedded.complete" : {
						"languageId" : { "classification": "SystemMetaData", "purpose": "FeatureInsight" }
					}
				 */
				connection.telemetry.logEvent({ key: 'html.embbedded.complete', value: { languageId: mode.getId() } });
			}

			const settings = await getDocumentSettings(document, () => doComplete.length > 2);
			const documentContext = getDocumentContext(document.uri, workspaceFolders);
			return doComplete(document, textDocumentPosition.position, documentContext, settings);

		}, null, `Error while computing completions for ${textDocumentPosition.textDocument.uri}`, token);
	});

	connection.onCompletionResolve((item, token) => {
		return runSafe(runtime, async () => {
			const data = item.data;
			if (data && data.languageId && data.uri) {
				const mode = languageModes.getMode(data.languageId);
				const document = documents.get(data.uri);
				if (mode && mode.doResolve && document) {
					return mode.doResolve(document, item);
				}
			}
			return item;
		}, item, `Error while resolving completion proposal`, token);
	});

	connection.onHover((textDocumentPosition, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(textDocumentPosition.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, textDocumentPosition.position);
				const doHover = mode?.doHover;
				if (doHover) {
					const settings = await getDocumentSettings(document, () => doHover.length > 2);
					return doHover(document, textDocumentPosition.position, settings);
				}
			}
			return null;
		}, null, `Error while computing hover for ${textDocumentPosition.textDocument.uri}`, token);
	});

	connection.onDocumentHighlight((documentHighlightParams, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(documentHighlightParams.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, documentHighlightParams.position);
				if (mode && mode.findDocumentHighlight) {
					return mode.findDocumentHighlight(document, documentHighlightParams.position);
				}
			}
			return [];
		}, [], `Error while computing document highlights for ${documentHighlightParams.textDocument.uri}`, token);
	});

	connection.onDefinition((definitionParams, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(definitionParams.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, definitionParams.position);
				if (mode && mode.findDefinition) {
					return mode.findDefinition(document, definitionParams.position);
				}
			}
			return [];
		}, null, `Error while computing definitions for ${definitionParams.textDocument.uri}`, token);
	});

	connection.onReferences((referenceParams, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(referenceParams.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, referenceParams.position);
				if (mode && mode.findReferences) {
					return mode.findReferences(document, referenceParams.position);
				}
			}
			return [];
		}, [], `Error while computing references for ${referenceParams.textDocument.uri}`, token);
	});

	connection.onSignatureHelp((signatureHelpParms, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(signatureHelpParms.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, signatureHelpParms.position);
				if (mode && mode.doSignatureHelp) {
					return mode.doSignatureHelp(document, signatureHelpParms.position);
				}
			}
			return null;
		}, null, `Error while computing signature help for ${signatureHelpParms.textDocument.uri}`, token);
	});

	async function onFormat(textDocument: TextDocumentIdentifier, range: Range | undefined, options: FormattingOptions): Promise<TextEdit[]> {
		const document = documents.get(textDocument.uri);
		if (document) {
			let settings = await getDocumentSettings(document, () => true);
			if (!settings) {
				settings = globalSettings;
			}
			const unformattedTags: string = settings && settings.html && settings.html.format && settings.html.format.unformatted || '';
			const enabledModes = { css: !unformattedTags.match(/\bstyle\b/), javascript: !unformattedTags.match(/\bscript\b/) };

			const edits = await format(languageModes, document, range ?? getFullRange(document), options, settings, enabledModes);
			if (edits.length > formatterMaxNumberOfEdits) {
				const newText = TextDocument.applyEdits(document, edits);
				return [TextEdit.replace(getFullRange(document), newText)];
			}
			return edits;
		}
		return [];
	}

	connection.onDocumentRangeFormatting((formatParams, token) => {
		return runSafe(runtime, () => onFormat(formatParams.textDocument, formatParams.range, formatParams.options), [], `Error while formatting range for ${formatParams.textDocument.uri}`, token);
	});

	connection.onDocumentFormatting((formatParams, token) => {
		return runSafe(runtime, () => onFormat(formatParams.textDocument, undefined, formatParams.options), [], `Error while formatting ${formatParams.textDocument.uri}`, token);
	});

	connection.onDocumentLinks((documentLinkParam, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(documentLinkParam.textDocument.uri);
			const links: DocumentLink[] = [];
			if (document) {
				const documentContext = getDocumentContext(document.uri, workspaceFolders);
				for (const m of languageModes.getAllModesInDocument(document)) {
					if (m.findDocumentLinks) {
						pushAll(links, await m.findDocumentLinks(document, documentContext));
					}
				}
			}
			return links;
		}, [], `Error while document links for ${documentLinkParam.textDocument.uri}`, token);
	});

	connection.onDocumentSymbol((documentSymbolParms, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(documentSymbolParms.textDocument.uri);
			const symbols: SymbolInformation[] = [];
			if (document) {
				for (const m of languageModes.getAllModesInDocument(document)) {
					if (m.findDocumentSymbols) {
						pushAll(symbols, await m.findDocumentSymbols(document));
					}
				}
			}
			return symbols;
		}, [], `Error while computing document symbols for ${documentSymbolParms.textDocument.uri}`, token);
	});

	connection.onRequest(DocumentColorRequest.type, (params, token) => {
		return runSafe(runtime, async () => {
			const infos: ColorInformation[] = [];
			const document = documents.get(params.textDocument.uri);
			if (document) {
				for (const m of languageModes.getAllModesInDocument(document)) {
					if (m.findDocumentColors) {
						pushAll(infos, await m.findDocumentColors(document));
					}
				}
			}
			return infos;
		}, [], `Error while computing document colors for ${params.textDocument.uri}`, token);
	});

	connection.onRequest(ColorPresentationRequest.type, (params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				const mode = languageModes.getModeAtPosition(document, params.range.start);
				if (mode && mode.getColorPresentations) {
					return mode.getColorPresentations(document, params.color, params.range);
				}
			}
			return [];
		}, [], `Error while computing color presentations for ${params.textDocument.uri}`, token);
	});

	connection.onRequest(AutoInsertRequest.type, (params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				const pos = params.position;
				if (pos.character > 0) {
					const mode = languageModes.getModeAtPosition(document, Position.create(pos.line, pos.character - 1));
					if (mode && mode.doAutoInsert) {
						return mode.doAutoInsert(document, pos, params.kind);
					}
				}
			}
			return null;
		}, null, `Error while computing auto insert actions for ${params.textDocument.uri}`, token);
	});

	connection.onFoldingRanges((params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				return getFoldingRanges(languageModes, document, foldingRangeLimit, token);
			}
			return null;
		}, null, `Error while computing folding regions for ${params.textDocument.uri}`, token);
	});

	connection.onSelectionRanges((params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				return getSelectionRanges(languageModes, document, params.positions);
			}
			return [];
		}, [], `Error while computing selection ranges for ${params.textDocument.uri}`, token);
	});

	connection.onRenameRequest((params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			const position: Position = params.position;

			if (document) {
				const mode = languageModes.getModeAtPosition(document, params.position);

				if (mode && mode.doRename) {
					return mode.doRename(document, position, params.newName);
				}
			}
			return null;
		}, null, `Error while computing rename for ${params.textDocument.uri}`, token);
	});

	connection.languages.onLinkedEditingRange((params, token) => {
		return <any> /* todo remove when microsoft/vscode-languageserver-node#700 fixed */ runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				const pos = params.position;
				if (pos.character > 0) {
					const mode = languageModes.getModeAtPosition(document, Position.create(pos.line, pos.character - 1));
					if (mode && mode.doLinkedEditing) {
						const ranges = await mode.doLinkedEditing(document, pos);
						if (ranges) {
							return { ranges };
						}
					}
				}
			}
			return null;
		}, null, `Error while computing synced regions for ${params.textDocument.uri}`, token);
	});

	let semanticTokensProvider: SemanticTokenProvider | undefined;
	function getSemanticTokenProvider() {
		if (!semanticTokensProvider) {
			semanticTokensProvider = newSemanticTokenProvider(languageModes);
		}
		return semanticTokensProvider;
	}

	connection.onRequest(SemanticTokenRequest.type, (params, token) => {
		return runSafe(runtime, async () => {
			const document = documents.get(params.textDocument.uri);
			if (document) {
				return getSemanticTokenProvider().getSemanticTokens(document, params.ranges);
			}
			return null;
		}, null, `Error while computing semantic tokens for ${params.textDocument.uri}`, token);
	});

	connection.onRequest(SemanticTokenLegendRequest.type, token => {
		return runSafe(runtime, async () => {
			return getSemanticTokenProvider().legend;
		}, null, `Error while computing semantic tokens legend`, token);
	});

	connection.onNotification(CustomDataChangedNotification.type, dataPaths => {
		fetchHTMLDataProviders(dataPaths, customDataRequestService).then(dataProviders => {
			languageModes.updateDataProviders(dataProviders);
		});
	});

	// Listen on the connection
	connection.listen();
}