/*---------------------------------------------------------
 * Copyright (C) Microsoft Corporation. All rights reserved.
 * Modification copyright 2020 The Go Authors. All rights reserved.
 * Licensed under the MIT License. See LICENSE in the project root for license information.
 *--------------------------------------------------------*/

'use strict';

import cp = require('child_process');
import fs = require('fs');
import moment from 'moment';
import path = require('path');
import semver = require('semver');
import util = require('util');
import vscode = require('vscode');
import { InitializeParams } from 'vscode-languageserver-protocol';
import {
	CancellationToken,
	CloseAction,
	ConfigurationParams,
	ConfigurationRequest,
	ErrorAction,
	ExecuteCommandParams,
	ExecuteCommandRequest,
	ExecuteCommandSignature,
	InitializeError,
	InitializeResult,
	LanguageClientOptions,
	Message,
	ProgressToken,
	ProvideCodeLensesSignature,
	ProvideCompletionItemsSignature,
	ProvideDocumentFormattingEditsSignature,
	Hover,
	ResponseError,
	RevealOutputChannelOn
} from 'vscode-languageclient';
import { Executable, ServerOptions, LanguageClient } from 'vscode-languageclient/node';
import { getGoConfig, getGoplsConfig, extensionInfo } from '../config';
import { toolExecutionEnvironment } from '../goEnv';
import { GoDocumentFormattingEditProvider, getFormatTool } from './legacy/goFormat';
import { installTools, latestModuleVersion, promptForMissingTool, promptForUpdatingTool } from '../goInstallTools';
import { getTool, Tool } from '../goTools';
import { updateGlobalState, updateWorkspaceState } from '../stateUtils';
import {
	getBinPath,
	getCheckForToolsUpdatesConfig,
	getCurrentGoPath,
	getGoVersion,
	getWorkspaceFolderPath
} from '../util';
import { getToolFromToolPath } from '../utils/pathUtils';
import fetch from 'node-fetch';
import { CompletionItemKind, FoldingContext } from 'vscode';
import { ProvideFoldingRangeSignature } from 'vscode-languageclient';
import { daysBetween, getStateConfig, maybePromptForGoplsSurvey, timeDay, timeMinute } from '../goSurvey';
import { maybePromptForDeveloperSurvey } from '../developerSurvey/prompt';
import { CommandFactory } from '../commands';
import { updateLanguageServerIconGoStatusBar } from '../goStatus';
import { URI } from 'vscode-uri';
import { VulncheckReport, writeVulns } from '../goVulncheck';
import { ActiveProgressTerminals, IProgressTerminal, ProgressTerminal } from '../progressTerminal';
import { createHash } from 'crypto';
import { GoExtensionContext } from '../context';
import { GoDiagnosticsFeature } from '../diagnostics/diagnostics';
import { GoDocumentSelector } from '../goMode';
import { GOPLS_ADD_TEST_COMMAND } from '../goGenerateTests';
import { GOPLS_MODIFY_TAGS_COMMAND } from '../goModifytags';
import { GOPLS_IMPLEMENT_INTERFACE_COMMAND } from '../goImpl';
import { TelemetryKey, telemetryReporter } from '../goTelemetry';
import {
	InteractiveExecuteCommandParams,
	InteractiveResolveCommandSignature,
	InteractiveFormsFeature,
	InteractiveMiddleware
} from './form';
import { GoSemanticTokensFeature } from './goSemanticTokens';

export interface LanguageServerConfig {
	serverName: string;
	path: string;
	version?: { version: string; goVersion?: string };
	modtime?: Date;
	enabled: boolean;
	flags: string[];
	env: any;
	features: {
		// A custom formatter can be configured to run instead of gopls.
		// This is enabled when the user has configured a specific format
		// tool in the "go.formatTool" setting.
		formatter?: GoDocumentFormattingEditProvider;
	};
	checkForUpdates: string;
}

export interface ServerInfo {
	Name: string;
	Version?: string;
	GoVersion?: string;
	Commands?: string[];
}

export function updateRestartHistory(goCtx: GoExtensionContext, reason: RestartReason, enabled: boolean) {
	// Keep the history limited to 10 elements.
	goCtx.restartHistory = goCtx.restartHistory ?? [];
	while (goCtx.restartHistory.length > 10) {
		goCtx.restartHistory = goCtx.restartHistory.slice(1);
	}
	goCtx.restartHistory.push(new Restart(reason, new Date(), enabled));
}

export enum RestartReason {
	ACTIVATION = 'activation',
	MANUAL = 'manual',
	CONFIG_CHANGE = 'config change',
	INSTALLATION = 'installation'
}

export class Restart {
	reason: RestartReason;
	timestamp: Date;
	enabled: boolean;

	constructor(reason: RestartReason, timestamp: Date, enabled: boolean) {
		this.reason = reason;
		this.timestamp = timestamp;
		this.enabled = enabled;
	}
}

// computes a bigint fingerprint of the machine id.
function hashMachineID(salt?: string): number {
	const hash = createHash('md5').update(`${vscode.env.machineId}${salt}`).digest('hex');
	return parseInt(hash.substring(0, 8), 16);
}

// returns true if the proposed upgrade version is mature, or we are selected for staged rollout.
export async function okForStagedRollout(
	tool: Tool,
	ver: semver.SemVer,
	hashFn: (key?: string) => number
): Promise<boolean> {
	// patch release is relatively safe to upgrade. Moreover, the patch
	// can carry a fix for security which is better to apply sooner.
	if (ver.patch !== 0 || ver.prerelease?.length > 0) return true;

	const published = await getTimestampForVersion(tool, ver);
	if (!published) return true;

	const days = daysBetween(new Date(), published.toDate());
	if (days <= 1) {
		return hashFn(ver.version) % 100 < 10; // upgrade with 10% chance for the first day.
	}
	if (days <= 3) {
		return hashFn(ver.version) % 100 < 30; // upgrade with 30% chance for the first 3 days.
	}
	return true;
}

// scheduleGoplsSuggestions sets timeouts for the various gopls-specific
// suggestions. We check user's gopls versions once per day to prompt users to
// update to the latest version. We also check if we should prompt users to
// fill out the survey.
export function scheduleGoplsSuggestions(goCtx: GoExtensionContext) {
	if (extensionInfo.isInCloudIDE) {
		return;
	}
	// Some helper functions.
	const usingGo = (): boolean => {
		return vscode.workspace.textDocuments.some((doc) => doc.languageId === 'go');
	};
	const installGopls = async (cfg: LanguageServerConfig) => {
		const tool: Tool = getTool('gopls')!;
		const versionToUpdate = await shouldUpdateLanguageServer(tool, cfg);
		if (!versionToUpdate) {
			return;
		}
		// If the user has opted in to automatic tool updates, we can update
		// without prompting.
		const toolsManagementConfig = getGoConfig()['toolsManagement'];
		if (toolsManagementConfig && toolsManagementConfig['autoUpdate'] === true) {
			if (extensionInfo.isPreview || (await okForStagedRollout(tool, versionToUpdate, hashMachineID))) {
				const goVersion = await getGoVersion();
				const toolVersion = { ...tool, version: versionToUpdate }; // ToolWithVersion
				await installTools([toolVersion], goVersion, { silent: true });
			} else {
				console.log(`gopls ${versionToUpdate} is too new, try to update later`);
			}
		} else {
			void promptForUpdatingTool(tool.name, versionToUpdate);
		}
	};
	const update = async () => {
		setTimeout(update, timeDay);
		const cfg = goCtx.latestConfig;
		// trigger periodic update check only if the user is already using gopls.
		// Otherwise, let's check again tomorrow.
		if (!cfg || !cfg.enabled || cfg.serverName !== 'gopls') {
			return;
		}
		await installGopls(cfg);
	};
	const survey = async () => {
		setTimeout(survey, timeDay);
		// Only prompt for the survey if the user is working on Go code.
		if (!usingGo) {
			return;
		}
		maybePromptForGoplsSurvey(goCtx);
		void maybePromptForDeveloperSurvey(goCtx);
	};
	const telemetry = () => {
		if (!usingGo) {
			return;
		}
		maybePromptForTelemetry(goCtx);
	};
	setTimeout(update, 10 * timeMinute);
	setTimeout(survey, 30 * timeMinute);
	setTimeout(telemetry, 6 * timeMinute);
}

// Ask users to fill out opt-out survey.
export async function promptAboutGoplsOptOut(goCtx: GoExtensionContext) {
	// Check if the configuration is set in the workspace.
	const useLanguageServer = getGoConfig().inspect('useLanguageServer');
	const workspace = useLanguageServer?.workspaceFolderValue === false || useLanguageServer?.workspaceValue === false;

	let cfg = getGoplsOptOutConfig(workspace);
	const promptFn = async (): Promise<GoplsOptOutConfig> => {
		if (cfg.prompt === false) {
			return cfg;
		}
		// Prompt the user ~once a month.
		if (cfg.lastDatePrompted && daysBetween(new Date(), cfg.lastDatePrompted) < 30) {
			return cfg;
		}
		cfg.lastDatePrompted = new Date();
		await promptForGoplsOptOutSurvey(
			goCtx,
			cfg,
			"It looks like you've disabled the Go language server. Would you be willing to tell us why you've disabled it, so that we can improve it?"
		);
		return cfg;
	};
	cfg = await promptFn();
	flushGoplsOptOutConfig(cfg, workspace);
}

async function promptForGoplsOptOutSurvey(
	goCtx: GoExtensionContext,
	cfg: GoplsOptOutConfig,
	msg: string
): Promise<GoplsOptOutConfig> {
	const s = await vscode.window.showInformationMessage(msg, { title: 'Yes' }, { title: 'No' });
	if (!s) {
		return cfg;
	}
	const localGoplsVersion = await getLocalGoplsVersion(goCtx.latestConfig);
	const goplsVersion = localGoplsVersion?.version || 'na';
	const goV = await getGoVersion();
	let goVersion = 'na';
	if (goV) {
		goVersion = goV.format(true);
	}
	switch (s.title) {
		case 'Yes':
			cfg.prompt = false;
			await vscode.env.openExternal(
				vscode.Uri.parse(
					`https://google.qualtrics.com/jfe/form/SV_doId0RNgV3pHovc?gopls=${goplsVersion}&go=${goVersion}&os=${process.platform}`
				)
			);
			break;
		case 'No':
			break;
	}
	return cfg;
}

export interface GoplsOptOutConfig {
	prompt?: boolean;
	lastDatePrompted?: Date;
}

const goplsOptOutConfigKey = 'goplsOptOutConfig';

export const getGoplsOptOutConfig = (workspace: boolean): GoplsOptOutConfig => {
	return getStateConfig(goplsOptOutConfigKey, workspace) as GoplsOptOutConfig;
};

export const flushGoplsOptOutConfig = (cfg: GoplsOptOutConfig, workspace: boolean) => {
	if (workspace) {
		updateWorkspaceState(goplsOptOutConfigKey, JSON.stringify(cfg));
	}
	updateGlobalState(goplsOptOutConfigKey, JSON.stringify(cfg));
};

// exported for testing.
export async function stopLanguageClient(goCtx: GoExtensionContext) {
	const c = goCtx.languageClient;
	goCtx.crashCount = 0;
	goCtx.telemetryService = undefined;
	goCtx.languageClient = undefined;
	if (!c) return false;

	if (c.diagnostics) {
		c.diagnostics.clear();
	}
	// LanguageClient.stop may hang if the language server
	// crashes during shutdown before responding to the
	// shutdown request. Enforce client-side timeout.
	c.stop(2000).catch((e) => {
		c.outputChannel?.appendLine(`Failed to stop client: ${e}`);
	});
}

export function toServerInfo(res?: InitializeResult): ServerInfo | undefined {
	if (!res) return undefined;

	const info: ServerInfo = {
		Commands: res.capabilities?.executeCommandProvider?.commands || [],
		Name: res.serverInfo?.name || 'unknown'
	};

	try {
		interface serverVersionJSON {
			GoVersion?: string;
			Version?: string;
			// before gopls 0.8.0
			version?: string;
		}
		const v = <serverVersionJSON>(res.serverInfo?.version ? JSON.parse(res.serverInfo.version) : {});
		info.Version = v.Version || v.version;
		info.GoVersion = v.GoVersion;
	} catch {
		// gopls is not providing any info, that's ok.
	}
	return info;
}

export class GoLanguageClient extends LanguageClient implements vscode.Disposable {
	constructor(
		id: string,
		name: string,
		serverOptions: ServerOptions,
		clientOptions: LanguageClientOptions,
		private onDidChangeVulncheckResultEmitter: vscode.EventEmitter<VulncheckEvent>
	) {
		super(id, name, serverOptions, clientOptions);
	}

	dispose(timeout?: number) {
		this.onDidChangeVulncheckResultEmitter.dispose();
		return super.dispose(timeout);
	}

	public get onDidChangeVulncheckResult(): vscode.Event<VulncheckEvent> {
		return this.onDidChangeVulncheckResultEmitter.event;
	}

	protected fillInitializeParams(params: InitializeParams): void {
		super.fillInitializeParams(params);

		// VSCode-Go honors most client capabilities from the vscode-languageserver-node
		// library. Experimental capabilities not used by vscode-languageserver-node
		// can be used for custom communication between vscode-go and gopls.
		// See https://github.com/microsoft/vscode-languageserver-node/issues/1607
		const experimental = (params.capabilities.experimental as any) || {};
		experimental.progressMessageStyles = ['log'];

		params.capabilities.experimental = experimental;
	}
}

type VulncheckEvent = {
	URI?: URI;
	message?: string;
};

// buildLanguageClient returns a language client built using the given language server config.
// The returned language client need to be started before use.
export async function buildLanguageClient(
	goCtx: GoExtensionContext,
	cfg: LanguageServerConfig
): Promise<GoLanguageClient> {
	// Reuse the same output channel for each instance of the server.
	if (cfg.enabled) {
		if (!goCtx.serverOutputChannel) {
			goCtx.serverOutputChannel = vscode.window.createOutputChannel(cfg.serverName + ' (server)', { log: true });
		}
		if (!goCtx.serverTraceChannel) {
			goCtx.serverTraceChannel = vscode.window.createOutputChannel(cfg.serverName, { log: true });
		}
	}

	await getLocalGoplsVersion(cfg); // populate and cache cfg.version
	const goplsWorkspaceConfig = await adjustGoplsWorkspaceConfiguration(cfg, getGoplsConfig(), 'gopls', undefined);

	// when initialization is failed after the connection is established,
	// we want to handle the connection close error case specially. Capture the error
	// in initializationFailedHandler and handle it in the connectionCloseHandler.
	let initializationError: ResponseError<InitializeError> | undefined = undefined;

	// TODO(hxjiang): deprecate special handling for async call gopls.run_govulncheck.
	let govulncheckTerminal: IProgressTerminal | undefined;
	const pendingVulncheckProgressToken = new Map<ProgressToken, any>();
	const onDidChangeVulncheckResultEmitter = new vscode.EventEmitter<VulncheckEvent>();

	// VSCode-Go prepares the information needed to start the language server.
	// vscode-languageclient-node.LanguageClient will spin up the language
	// server based on the provided information below.
	const serverOption: Executable = {
		command: cfg.path,
		args: cfg.flags,
		options: { env: cfg.env }
	};

	// cfg is captured by closures for later use during error report.
	const c = new GoLanguageClient(
		'go', // id
		cfg.serverName, // name e.g. gopls
		serverOption as ServerOptions,
		{
			initializationOptions: goplsWorkspaceConfig,
			documentSelector: GoDocumentSelector,
			uriConverters: {
				// Apply file:/// scheme to all file paths.
				code2Protocol: (uri: vscode.Uri): string =>
					(uri.scheme ? uri : uri.with({ scheme: 'file' })).toString(),
				protocol2Code: (uri: string) => vscode.Uri.parse(uri)
			},
			outputChannel: goCtx.serverOutputChannel,
			traceOutputChannel: goCtx.serverTraceChannel,
			revealOutputChannelOn: RevealOutputChannelOn.Never,
			initializationFailedHandler: (error: ResponseError<InitializeError>): boolean => {
				initializationError = error;
				return false;
			},
			errorHandler: {
				error: (error: Error, message: Message, count: number) => {
					// Allow 5 crashes before shutdown.
					if (count < 5) {
						return {
							message: '', // suppresses error popups
							action: ErrorAction.Continue
						};
					}
					return {
						message: '', // suppresses error popups
						action: ErrorAction.Shutdown
					};
				},
				closed: () => {
					if (initializationError !== undefined) {
						void suggestActionAfterGoplsStartError(goCtx, cfg);
						initializationError = undefined;
						// In case of initialization failure, do not try to restart.
						return {
							message: '', // suppresses error popups - there will be other popups. :-(
							action: CloseAction.DoNotRestart
						};
					}

					// Allow 5 crashes before shutdown.
					const { crashCount = 0 } = goCtx;
					goCtx.crashCount = crashCount + 1;
					if (goCtx.crashCount < 5) {
						updateLanguageServerIconGoStatusBar(c, true);
						return {
							message: '', // suppresses error popups
							action: CloseAction.Restart
						};
					}
					void suggestActionAfterGoplsStartError(goCtx, cfg);
					updateLanguageServerIconGoStatusBar(c, true);
					return {
						message: '', // suppresses error popups - there will be other popups.
						action: CloseAction.DoNotRestart
					};
				}
			},
			middleware: {
				provideTypeDefinition: async (doc, pos, token, next) => {
					if (!goCtx.languageClient) {
						return await next(doc, pos, token);
					}

					const editor = vscode.window.activeTextEditor;
					if (!editor || doc !== editor.document) {
						return await next(doc, pos, token);
					}

					const selection = editor?.selection;
					if (selection.isEmpty || !selection.contains(pos)) {
						return await next(doc, pos, token);
					}

					// Attaching selected range to gopls type def request.
					const param = goCtx.languageClient.code2ProtocolConverter.asTextDocumentPositionParams(doc, pos);
					(param as any).range = goCtx.languageClient.code2ProtocolConverter.asRange(selection);

					const result: any = await c.sendRequest('textDocument/typeDefinition', param);
					return goCtx.languageClient.protocol2CodeConverter.asDefinitionResult(result);
				},
				provideHover: async (doc, pos, token, next) => {
					const editor = vscode.window.activeTextEditor;
					if (!editor || doc !== editor.document) {
						return await next(doc, pos, token);
					}

					const selection = editor?.selection;
					if (selection.isEmpty || !selection.contains(pos)) {
						return await next(doc, pos, token);
					}

					if (!goCtx.languageClient) {
						return await next(doc, pos, token);
					}

					// Attaching selected range to gopls hover request.
					// See golang/go#69058.
					const param = goCtx.languageClient.code2ProtocolConverter.asTextDocumentPositionParams(doc, pos);
					(param as any).range = goCtx.languageClient.code2ProtocolConverter.asRange(selection);

					const result: Hover = await c.sendRequest('textDocument/hover', param);

					return goCtx.languageClient.protocol2CodeConverter.asHover(result);
				},
				handleWorkDoneProgress: async (token, params, next) => {
					switch (params.kind) {
						case 'begin':
							if (typeof params.message === 'string') {
								const paragraphs = params.message.split('\n\n', 2);
								const metadata = paragraphs[0].trim();
								if (!metadata.startsWith('style: ')) {
									break;
								}
								const style = metadata.substring('style: '.length);
								if (style === 'log') {
									const term = ProgressTerminal.Open(params.title, token);
									if (paragraphs.length > 1) {
										term.appendLine(paragraphs[1]);
									}
									term.show();
								}
							}
							break;
						case 'report':
							if (params.message) {
								ActiveProgressTerminals.get(token)?.appendLine(params.message);
							}
							if (pendingVulncheckProgressToken.has(token) && params.message) {
								govulncheckTerminal?.appendLine(params.message);
							}
							break;
						case 'end':
							if (params.message) {
								ActiveProgressTerminals.get(token)?.appendLine(params.message);
							}
							if (pendingVulncheckProgressToken.has(token)) {
								const out = pendingVulncheckProgressToken.get(token);
								pendingVulncheckProgressToken.delete(token);
								// success. In case of failure, it will be 'failed'
								onDidChangeVulncheckResultEmitter.fire({ URI: out.URI, message: params.message });
							}
					}
					next(token, params);
				},
				resolveCommand: async (
					param: InteractiveExecuteCommandParams,
					next: InteractiveResolveCommandSignature
				) => {
					// Avoid resolving for frequently triggered commands.
					if (param.command === 'gopls.package_symbols') {
						return param;
					}
					return await next(param);
				},
				executeCommand: async (command: string, args: any[], next: ExecuteCommandSignature) => {
					try {
						if (command === 'gopls.tidy' || command === 'gopls.vulncheck') {
							await vscode.workspace.saveAll(false);
						}
						if (command === 'gopls.run_govulncheck' && args.length && args[0].URI) {
							if (govulncheckTerminal) {
								vscode.window.showErrorMessage(
									'cannot start vulncheck while another vulncheck is in progress'
								);
								return;
							}
							await vscode.workspace.saveAll(false);
							const uri = args[0].URI ? URI.parse(args[0].URI) : undefined;
							const dir = uri?.fsPath?.endsWith('.mod') ? path.dirname(uri.fsPath) : uri?.fsPath;
							govulncheckTerminal = ProgressTerminal.Open('govulncheck');
							govulncheckTerminal.appendLine(`⚡ govulncheck -C ${dir} ./...\n\n`);
							govulncheckTerminal.show();
						}

						const res: any = await next(command, args);

						const progressToken = res?.Token as ProgressToken;
						// The progressToken from executeCommand indicates that
						// gopls may trigger a related workDoneProgress
						// notification, either before or after the command
						// completes.
						// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#serverInitiatedProgress
						if (progressToken !== undefined) {
							switch (command) {
								case 'gopls.run_govulncheck':
									pendingVulncheckProgressToken.set(progressToken, args[0]);
									break;
								case 'gopls.vulncheck':
									// Write the vulncheck report to the terminal.
									if (ActiveProgressTerminals.has(progressToken)) {
										void writeVulns(
											res.Result,
											ActiveProgressTerminals.get(progressToken),
											cfg.path
										);
									}
									break;
								default:
									// By default, dump the result to the terminal.
									ActiveProgressTerminals.get(progressToken)?.appendLine(res.Result);
							}
						}

						return res;
					} catch (e) {
						// Suppress error messages for frequently triggered
						// or programmatically triggered commads.
						if (command === 'gopls.package_symbols') {
							return null;
						}
						// TODO: how to print ${e} reliably???
						const answer = await vscode.window.showErrorMessage(
							`Command '${command}' failed: ${e}.`,
							'Show Trace'
						);
						if (answer === 'Show Trace') {
							goCtx.serverOutputChannel?.show();
						}
						return null;
					}
				},
				provideFoldingRanges: async (
					doc: vscode.TextDocument,
					context: FoldingContext,
					token: CancellationToken,
					next: ProvideFoldingRangeSignature
				) => {
					const ranges = await next(doc, context, token);
					if ((!ranges || ranges.length === 0) && doc.lineCount > 0) {
						return undefined;
					}
					return ranges;
				},
				provideCodeLenses: async (
					doc: vscode.TextDocument,
					token: vscode.CancellationToken,
					next: ProvideCodeLensesSignature
				): Promise<vscode.CodeLens[]> => {
					const codeLens = await next(doc, token);
					if (!codeLens || codeLens.length === 0) {
						return codeLens ?? [];
					}
					return codeLens.reduce((lenses: vscode.CodeLens[], lens: vscode.CodeLens) => {
						switch (lens.command?.title) {
							case 'run test': {
								return [...lenses, ...createTestCodeLens(lens)];
							}
							case 'run benchmark': {
								return [...lenses, ...createBenchmarkCodeLens(lens)];
							}
							default: {
								return [...lenses, lens];
							}
						}
					}, []);
				},
				provideDocumentFormattingEdits: async (
					document: vscode.TextDocument,
					options: vscode.FormattingOptions,
					token: vscode.CancellationToken,
					next: ProvideDocumentFormattingEditsSignature
				) => {
					// If a custom formatter is configured, use it.
					if (cfg.features.formatter) {
						return cfg.features.formatter.provideDocumentFormattingEdits(document, options, token);
					}
					// Otherwise, fall back to gopls.
					return next(document, options, token);
				},
				provideCompletionItem: async (
					document: vscode.TextDocument,
					position: vscode.Position,
					context: vscode.CompletionContext,
					token: vscode.CancellationToken,
					next: ProvideCompletionItemsSignature
				) => {
					const list = await next(document, position, context, token);
					if (!list) {
						return list;
					}
					const items = Array.isArray(list) ? list : list.items;

					// Give all the candidates the same filterText to trick VSCode
					// into not reordering our candidates. All the candidates will
					// appear to be equally good matches, so VSCode's fuzzy
					// matching/ranking just maintains the natural "sortText"
					// ordering. We can only do this in tandem with
					// "incompleteResults" since otherwise client side filtering is
					// important.
					if (!Array.isArray(list) && list.isIncomplete && list.items.length > 1) {
						let hardcodedFilterText = items[0].filterText;
						if (!hardcodedFilterText) {
							// tslint:disable:max-line-length
							// According to LSP spec,
							// https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_completion
							// if filterText is falsy, the `label` should be used.
							// But we observed that's not the case.
							// Even if vscode picked the label value, that would
							// cause to reorder candiates, which is not ideal.
							// Force to use non-empty `label`.
							// https://github.com/golang/vscode-go/issues/441
							let { label } = items[0];
							if (typeof label !== 'string') label = label.label;
							hardcodedFilterText = label;
						}
						for (const item of items) {
							item.filterText = hardcodedFilterText;
						}
					}
					const paramHints = vscode.workspace.getConfiguration('editor.parameterHints', {
						languageId: 'go',
						uri: document.uri
					});
					// If the user has parameterHints (signature help) enabled,
					// trigger it for function or method completion items.
					if (paramHints.get<boolean>('enabled') === true) {
						for (const item of items) {
							if (item.kind === CompletionItemKind.Method || item.kind === CompletionItemKind.Function) {
								item.command = {
									title: 'triggerParameterHints',
									command: 'editor.action.triggerParameterHints'
								};
							}
						}
					}
					return list;
				},
				// Keep track of the last file change in order to not prompt
				// user if they are actively working.
				didOpen: async (e, next) => {
					goCtx.lastUserAction = new Date();
					void next(e);
				},
				didChange: async (e, next) => {
					goCtx.lastUserAction = new Date();
					void next(e);
				},
				didClose: async (e, next) => {
					goCtx.lastUserAction = new Date();
					void next(e);
				},
				didSave: async (e, next) => {
					goCtx.lastUserAction = new Date();
					void next(e);
				},
				workspace: {
					configuration: async (
						params: ConfigurationParams,
						token: CancellationToken,
						next: ConfigurationRequest.HandlerSignature
					): Promise<any[] | ResponseError<void>> => {
						const configs = await next(params, token);
						if (!configs || !Array.isArray(configs)) {
							return configs;
						}
						const ret = [] as any[];
						for (let i = 0; i < configs.length; i++) {
							let workspaceConfig = configs[i];
							if (!!workspaceConfig && typeof workspaceConfig === 'object') {
								const scopeUri = params.items[i].scopeUri;
								const resource = scopeUri ? vscode.Uri.parse(scopeUri) : undefined;
								const section = params.items[i].section;
								workspaceConfig = await adjustGoplsWorkspaceConfiguration(
									cfg,
									workspaceConfig,
									section,
									resource
								);
							}
							ret.push(workspaceConfig);
						}
						return ret;
					}
				},
				resolveCodeAction: async (item, token, next) => {
					if (item.command) {
						switch (item.command.command) {
							case GOPLS_ADD_TEST_COMMAND:
								telemetryReporter.add(TelemetryKey.COMMAND_TRIGGER_GOPLS_ADD_TEST_CODE_ACTION, 1);
								break;
							case GOPLS_IMPLEMENT_INTERFACE_COMMAND:
								telemetryReporter.add(
									TelemetryKey.COMMAND_TRIGGER_GOPLS_IMPLEMENT_INTERFACE_CODE_ACTION,
									1
								);
								break;
							case GOPLS_MODIFY_TAGS_COMMAND:
								telemetryReporter.add(TelemetryKey.COMMAND_TRIGGER_GOPLS_MODIFY_TAGS_CODE_ACTION, 1);
								break;
						}
					}
					try {
						return await next(item, token);
					} catch (e) {
						const answer = await vscode.window.showErrorMessage(
							`code action resolve failed: ${e}.`,
							'Show Trace'
						);
						if (answer === 'Show Trace') {
							goCtx.serverOutputChannel?.show();
						}
						return null;
					}
				}
			} as InteractiveMiddleware
		} as LanguageClientOptions,
		onDidChangeVulncheckResultEmitter
	);
	c.registerFeature(new InteractiveFormsFeature(c));
	c.registerFeature(new GoSemanticTokensFeature());
	c.registerFeature(new GoDiagnosticsFeature(c, goCtx));
	onDidChangeVulncheckResultEmitter.event(async (e: VulncheckEvent) => {
		if (!govulncheckTerminal) {
			return;
		}
		if (!e || !e.URI) {
			govulncheckTerminal.appendLine(`unexpected vulncheck event: ${JSON.stringify(e)}`);
			return;
		}

		try {
			if (e.message === 'completed') {
				const res = await goplsFetchVulncheckResult(goCtx, e.URI.toString());
				if (res!.Vulns) {
					vscode.window.showWarningMessage(
						'upgrade gopls (v0.14.0 or newer) to see the details about detected vulnerabilities'
					);
				} else {
					await writeVulns(res, govulncheckTerminal, cfg.path);
				}
			} else {
				govulncheckTerminal.appendLine(`terminated without result: ${e.message}`);
			}
		} catch (e) {
			govulncheckTerminal.appendLine(`Fetching govulncheck output from gopls failed ${e}`);
		} finally {
			govulncheckTerminal.show();
			govulncheckTerminal = undefined;
		}
	});
	return c;
}

// filterGoplsDefaultConfigValues removes the entries filled based on the default values
// and selects only those the user explicitly specifies in their settings.
// This returns a new object created based on the filtered properties of workspaceConfig.
// Exported for testing.
export function filterGoplsDefaultConfigValues(workspaceConfig: any, resource?: vscode.Uri): any {
	if (!workspaceConfig) {
		workspaceConfig = {};
	}
	const cfg = getGoplsConfig(resource);
	const filtered = {} as { [key: string]: any };
	for (const [key, value] of Object.entries(workspaceConfig)) {
		if (typeof value === 'function') {
			continue;
		}
		const c = cfg.inspect(key);
		// select only the field whose current value comes from non-default setting.
		if (
			!c ||
			!util.isDeepStrictEqual(c.defaultValue, value) ||
			// c.defaultValue !== value would be most likely sufficient, except
			// when gopls' default becomes different from extension's default.
			// So, we also forward the key if ever explicitely stated in one of the
			// settings layers.
			c.globalLanguageValue !== undefined ||
			c.globalValue !== undefined ||
			c.workspaceFolderLanguageValue !== undefined ||
			c.workspaceFolderValue !== undefined ||
			c.workspaceLanguageValue !== undefined ||
			c.workspaceValue !== undefined
		) {
			filtered[key] = value;
		}
	}
	return filtered;
}

// passGoConfigToGoplsConfigValues passes some of the relevant 'go.' settings to gopls settings.
// This assumes `goplsWorkspaceConfig` is an output of filterGoplsDefaultConfigValues,
// so it is modifiable and doesn't contain properties that are not explicitly set.
//   - go.buildTags and go.buildFlags are passed as gopls.build.buildFlags
//     if goplsWorkspaceConfig doesn't explicitly set it yet.
// Exported for testing.
export function passGoConfigToGoplsConfigValues(goplsWorkspaceConfig: any, goWorkspaceConfig: any): any {
	if (!goplsWorkspaceConfig) {
		goplsWorkspaceConfig = {};
	}

	const buildFlags = [] as string[];
	if (goWorkspaceConfig?.buildFlags) {
		buildFlags.push(...goWorkspaceConfig.buildFlags);
	}
	if (goWorkspaceConfig?.buildTags && buildFlags.indexOf('-tags') === -1) {
		buildFlags.push('-tags', goWorkspaceConfig?.buildTags);
	}
	// If gopls.build.buildFlags is set, don't touch it.
	if (buildFlags.length > 0 && goplsWorkspaceConfig['build.buildFlags'] === undefined) {
		goplsWorkspaceConfig['build.buildFlags'] = buildFlags;
	}

	return goplsWorkspaceConfig;
}

// adjustGoplsWorkspaceConfiguration filters unnecessary options and adds any necessary, additional
// options to the gopls config. See filterGoplsDefaultConfigValues, passGoConfigToGoplsConfigValues.
// If this is for the nightly extension, we also request to activate features under experiments.
async function adjustGoplsWorkspaceConfiguration(
	cfg: LanguageServerConfig,
	workspaceConfig: any,
	section?: string,
	resource?: vscode.Uri
): Promise<any> {
	// We process only gopls config
	if (section !== 'gopls') {
		return workspaceConfig;
	}

	workspaceConfig = filterGoplsDefaultConfigValues(workspaceConfig, resource) || {};
	// note: workspaceConfig is a modifiable, valid object.
	const goConfig = getGoConfig(resource);
	workspaceConfig = passGoConfigToGoplsConfigValues(workspaceConfig, goConfig);
	workspaceConfig = await passInlayHintConfigToGopls(cfg, workspaceConfig, goConfig);
	workspaceConfig = await passVulncheckConfigToGopls(cfg, workspaceConfig, goConfig);
	workspaceConfig = await passLinkifyShowMessageToGopls(cfg, workspaceConfig);

	// Only modify the user's configurations for the Nightly.
	if (!extensionInfo.isPreview) {
		return workspaceConfig;
	}
	if (workspaceConfig && !workspaceConfig['allExperiments']) {
		workspaceConfig['allExperiments'] = true;
	}
	return workspaceConfig;
}

async function passInlayHintConfigToGopls(cfg: LanguageServerConfig, goplsConfig: any, goConfig: any) {
	const goplsVersion = await getLocalGoplsVersion(cfg);
	if (!goplsVersion) return goplsConfig ?? {};
	const version = semver.parse(goplsVersion.version);
	if ((version?.compare('0.8.4') ?? 1) > 0) {
		const { inlayHints } = goConfig;
		if (inlayHints) {
			goplsConfig['ui.inlayhint.hints'] = { ...inlayHints };
		}
	}
	return goplsConfig;
}

async function passVulncheckConfigToGopls(cfg: LanguageServerConfig, goplsConfig: any, goConfig: any) {
	const goplsVersion = await getLocalGoplsVersion(cfg);
	if (!goplsVersion) return goplsConfig ?? {};
	const version = semver.parse(goplsVersion.version);
	if ((version?.compare('0.10.1') ?? 1) > 0) {
		const vulncheck = goConfig.get('diagnostic.vulncheck');
		if (vulncheck) {
			goplsConfig['ui.vulncheck'] = vulncheck;
		}
	}
	return goplsConfig;
}

async function passLinkifyShowMessageToGopls(cfg: LanguageServerConfig, goplsConfig: any) {
	goplsConfig = goplsConfig ?? {};

	const goplsVersion = await getLocalGoplsVersion(cfg);
	if (!goplsVersion) return goplsConfig;

	const version = semver.parse(goplsVersion.version);
	// The linkifyShowMessage option was added in v0.14.0-pre.1.
	if ((version?.compare('0.13.99') ?? 1) > 0) {
		goplsConfig['linkifyShowMessage'] = true;
	}
	return goplsConfig;
}

// createTestCodeLens adds the go.test.cursor and go.debug.cursor code lens
function createTestCodeLens(lens: vscode.CodeLens): vscode.CodeLens[] {
	// CodeLens argument signature in gopls is [fileName: string, testFunctions: string[], benchFunctions: string[]],
	// so this needs to be deconstructured here
	// Note that there will always only be one test function name in this context
	if ((lens.command?.arguments?.length ?? 0) < 2 || (lens.command?.arguments?.[1].length ?? 0) < 1) {
		return [lens];
	}
	return [
		new vscode.CodeLens(lens.range, {
			title: '',
			...lens.command,
			command: 'go.test.cursor',
			arguments: [{ functionName: lens.command?.arguments?.[1][0] }]
		}),
		new vscode.CodeLens(lens.range, {
			title: 'debug test',
			command: 'go.debug.cursor',
			arguments: [{ functionName: lens.command?.arguments?.[1][0] }]
		})
	];
}

function createBenchmarkCodeLens(lens: vscode.CodeLens): vscode.CodeLens[] {
	// CodeLens argument signature in gopls is [fileName: string, testFunctions: string[], benchFunctions: string[]],
	// so this needs to be deconstructured here
	// Note that there will always only be one benchmark function name in this context
	if ((lens.command?.arguments?.length ?? 0) < 3 || (lens.command?.arguments?.[2].length ?? 0) < 1) {
		return [lens];
	}
	return [
		new vscode.CodeLens(lens.range, {
			title: '',
			...lens.command,
			command: 'go.benchmark.cursor',
			arguments: [{ functionName: lens.command?.arguments?.[2][0] }]
		}),
		new vscode.CodeLens(lens.range, {
			title: 'debug benchmark',
			command: 'go.debug.cursor',
			arguments: [{ functionName: lens.command?.arguments?.[2][0] }]
		})
	];
}

export async function buildLanguageServerConfig(
	goConfig: vscode.WorkspaceConfiguration
): Promise<LanguageServerConfig> {
	let formatter: GoDocumentFormattingEditProvider | undefined;
	if (getFormatTool(goConfig) !== '') {
		formatter = new GoDocumentFormattingEditProvider();
	}

	const cfg: LanguageServerConfig = {
		serverName: '', // remain empty if gopls binary can't be found.
		path: '',
		enabled: goConfig['useLanguageServer'] === true,
		flags: goConfig['languageServerFlags'] || [],
		features: {
			// TODO: We should have configs that match these names.
			// Ultimately, we should have a centralized language server config rather than separate fields.
			formatter: formatter
		},
		env: toolExecutionEnvironment(),
		checkForUpdates: getCheckForToolsUpdatesConfig(goConfig)
	};
	// user has opted out of using the language server.
	if (!cfg.enabled) {
		return cfg;
	}

	// locate the configured language server tool.
	const languageServerPath = getLanguageServerToolPath();
	if (!languageServerPath) {
		// Assume the getLanguageServerToolPath will show the relevant
		// errors to the user. Disable the language server.
		cfg.enabled = false;
		return cfg;
	}
	cfg.path = languageServerPath;
	cfg.serverName = getToolFromToolPath(cfg.path) ?? '';

	// Get the mtime of the language server binary so that we always pick up
	// the right version.
	const stats = fs.statSync(languageServerPath);
	if (!stats) {
		vscode.window.showErrorMessage(`Unable to stat path to language server binary: ${languageServerPath}.
Please try reinstalling it.`);
		// Disable the language server.
		cfg.enabled = false;
		return cfg;
	}
	cfg.modtime = stats.mtime;
	cfg.version = await getLocalGoplsVersion(cfg);
	return cfg;
}

/**
 *
 * Return the absolute path to the correct binary. If the required tool is not available,
 * prompt the user to install it. Only gopls is officially supported.
 */
export function getLanguageServerToolPath(): string | undefined {
	const goConfig = getGoConfig();
	// Check that all workspace folders are configured with the same GOPATH.
	if (!allFoldersHaveSameGopath()) {
		vscode.window.showInformationMessage(
			`The Go language server is currently not supported in a multi-root set-up with different GOPATHs (${gopathsPerFolder()}).`
		);
		return;
	}
	// Get the path to gopls (getBinPath checks for alternate tools).
	const goplsBinaryPath = getBinPath('gopls');
	if (path.isAbsolute(goplsBinaryPath)) {
		return goplsBinaryPath;
	}
	const alternateTools = goConfig['alternateTools'];
	if (alternateTools) {
		// The user's alternate language server was not found.
		const goplsAlternate = alternateTools['gopls'];
		if (goplsAlternate) {
			vscode.window.showErrorMessage(
				`Cannot find the alternate tool ${goplsAlternate} configured for gopls.
Please install it and reload this VS Code window.`
			);
			return;
		}
	}

	// Prompt the user to install gopls.
	void promptForMissingTool('gopls');
}

function allFoldersHaveSameGopath(): boolean {
	if (!vscode.workspace.workspaceFolders || vscode.workspace.workspaceFolders.length <= 1) {
		return true;
	}
	const tempGopath = getCurrentGoPath(vscode.workspace.workspaceFolders[0].uri);
	return vscode.workspace.workspaceFolders.find((x) => tempGopath !== getCurrentGoPath(x.uri)) ? false : true;
}

function gopathsPerFolder(): string[] {
	const result: string[] = [];
	for (const folder of vscode.workspace.workspaceFolders ?? []) {
		result.push(getCurrentGoPath(folder.uri));
	}
	return result;
}

export async function shouldUpdateLanguageServer(
	tool: Tool,
	cfg?: LanguageServerConfig,
	mustCheck?: boolean
): Promise<semver.SemVer | null | undefined> {
	if (!cfg) {
		return null;
	}
	// Only support updating gopls for now.
	if (tool.name !== 'gopls' || (!mustCheck && (cfg.checkForUpdates === 'off' || extensionInfo.isInCloudIDE))) {
		return null;
	}
	if (!cfg.enabled) {
		return null;
	}

	// If the Go version is too old, don't update.
	const goVersion = await getGoVersion();
	if (!goVersion || (tool.minimumGoVersion && goVersion.lt(tool.minimumGoVersion.format()))) {
		return null;
	}

	// First, run the "gopls version" command and parse its results.
	// TODO(rstambler): Confirm that the gopls binary's modtime matches the
	// modtime in the config. Update it if needed.
	const usersVersion = await getLocalGoplsVersion(cfg);

	// We might have a developer version. Don't make the user update.
	if (
		usersVersion &&
		(usersVersion.version === '(devel)' ||
			// "+dirty" suffix is considered as a developer version.
			// See golang/go#50603.
			usersVersion.version.endsWith('+dirty'))
	) {
		return null;
	}

	let version = tool.latestVersion;
	if (cfg.checkForUpdates === 'proxy') {
		// Allow installation of gopls pre-releases on insider versions of the extension.
		const latest = await latestModuleVersion(tool.modulePath, extensionInfo.isPreview);
		if (latest) {
			version = latest;
		}
	}

	// If "gopls" is so old that it doesn't have the "gopls version" command,
	// or its version doesn't match our expectations, usersVersion will be empty or invalid.
	// Suggest the latestVersion.
	if (!usersVersion || !semver.valid(usersVersion.version)) {
		return version;
	}

	// The user may have build the gopls from the source (without a build tag)
	// which means that they have a pseudoversion.
	const usersTime = parseTimestampFromPseudoversion(usersVersion.version);
	// If the user has a pseudoversion, get the timestamp for the latest gopls version and compare.
	if (usersTime) {
		let latestTime = cfg.checkForUpdates
			? await getTimestampForVersion(tool, version!)
			: tool.latestVersionTimestamp;
		if (!latestTime) {
			latestTime = tool.latestVersionTimestamp;
		}
		return usersTime.isBefore(latestTime) ? version : null;
	}

	// If the user's version does not contain a timestamp,
	// default to a semver comparison of the two versions.
	const usersVersionSemver = semver.parse(usersVersion.version, {
		loose: true
	});
	return semver.lt(usersVersionSemver!, version!) ? version : null;
}

// Copied from src/cmd/vendor/golang.org/x/mod/module/pseudo.go
const pseudoVersionRE =
	/^v[0-9]+\.(0\.0-|\d+\.\d+-([^+]*\.)?0\.)\d{14}-[A-Za-z0-9]+(\+[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?$/;

// parseTimestampFromPseudoversion returns the timestamp for the given
// pseudoversion. The timestamp is the center component, and it has the
// format "YYYYMMDDHHmmss".
function parseTimestampFromPseudoversion(version: string): moment.Moment | null {
	const split = version.split('-');
	if (split.length < 2) {
		return null;
	}
	if (!semver.valid(version)) {
		return null;
	}
	if (!pseudoVersionRE.test(version)) {
		return null;
	}
	const sv = semver.coerce(version);
	if (!sv) {
		return null;
	}

	// Copied from src/cmd/vendor/golang.org/x/mod/module/pseudo.go
	const build = sv.build.join('.');
	const buildIndex = version.lastIndexOf(build);
	if (buildIndex >= 0) {
		version = version.substring(0, buildIndex);
	}
	const lastDashIndex = version.lastIndexOf('-');
	version = version.substring(0, lastDashIndex);
	const firstDashIndex = version.lastIndexOf('-');
	const dotIndex = version.lastIndexOf('.');
	let timestamp: string;
	if (dotIndex > firstDashIndex) {
		// "vX.Y.Z-pre.0" or "vX.Y.(Z+1)-0"
		timestamp = version.substring(dotIndex + 1);
	} else {
		// "vX.0.0"
		timestamp = version.substring(firstDashIndex + 1);
	}
	return moment.utc(timestamp, 'YYYYMMDDHHmmss');
}

export const getTimestampForVersion = async (tool: Tool, version: semver.SemVer) => {
	const data = await goProxyRequest(tool, `v${version.format()}.info`);
	if (!data) {
		return null;
	}
	const time = moment(data['Time']);
	return time;
};

interface GoplsVersionOutput {
	GoVersion: string;
	Main: {
		Path: string;
		Version: string;
	};
}

// getLocalGoplsVersion returns the version of gopls that is currently
// installed on the user's machine. This is determined by running the
// `gopls version` command.
//
// If this command has already been executed, it returns the saved result.
export const getLocalGoplsVersion = async (cfg?: LanguageServerConfig) => {
	if (!cfg) {
		return;
	}
	if (cfg.version) {
		return cfg.version;
	}
	if (cfg.path === '') {
		return;
	}
	const env = toolExecutionEnvironment();
	const cwd = getWorkspaceFolderPath();

	const execFile = util.promisify(cp.execFile);
	try {
		const { stdout } = await execFile(cfg.path, ['version', '-json'], { env, cwd });

		const v = <GoplsVersionOutput>JSON.parse(stdout);
		if (v?.Main.Version) {
			cfg.version = { version: v.Main.Version, goVersion: v.GoVersion };
			return cfg.version;
		}
	} catch {
		// do nothing
	}

	// fall back to the old way (pre v0.8.0)
	let output = '';
	try {
		const { stdout } = await execFile(cfg.path, ['version'], { env, cwd });
		output = stdout;
	} catch {
		// The "gopls version" command is not supported, or something else went wrong.
		// TODO: Should we propagate this error?
		return;
	}

	const lines = output.trim().split('\n');
	switch (lines.length) {
		case 0:
			// No results, should update.
			// Worth doing anything here?
			return;
		case 1:
			// Built in $GOPATH mode. Should update.
			// TODO: Should we check the Go version here?
			// Do we even allow users to enable gopls if their Go version is too low?
			return;
		case 2:
			// We might actually have a parseable version.
			break;
		default:
			return;
	}

	// The second line should be the sum line.
	// It should look something like this:
	//
	//    golang.org/x/tools/gopls@v0.1.3 h1:CB5ECiPysqZrwxcyRjN+exyZpY0gODTZvNiqQi3lpeo=
	//
	// TODO(stamblerre): We should use a regex to match this, but for now, we split on the @ symbol.
	// The reasoning for this is that gopls still has a golang.org/x/tools/cmd/gopls binary,
	// so users may have a developer version that looks like "golang.org/x/tools@(devel)".
	const moduleVersion = lines[1].trim().split(' ')[0];

	// Get the relevant portion, that is:
	//
	//    golang.org/x/tools/gopls@v0.1.3
	//
	const split = moduleVersion.trim().split('@');
	if (split.length < 2) {
		return;
	}
	// The version comes after the @ symbol:
	//
	//    v0.1.3
	//
	cfg.version = { version: split[1] };
	return cfg.version;
};

async function goProxyRequest(tool: Tool, endpoint: string): Promise<any> {
	// Get the user's value of GOPROXY.
	// If it is not set, we cannot make the request.
	const output = process.env['GOPROXY'];
	if (!output || !output.trim()) {
		return null;
	}
	// Try each URL set in the user's GOPROXY environment variable.
	// If none is set, don't make the request.
	const proxies = output.trim().split(/,|\|/);
	for (const proxy of proxies) {
		if (proxy === 'direct') {
			continue;
		}
		const url = `${proxy}/${tool.importPath}/@v/${endpoint}`;
		let data: string;
		try {
			const response = await fetch(url);
			data = await response.text();
		} catch (e) {
			console.log(`Error sending request to ${proxy}: ${e}`);
			return null;
		}
		return data;
	}
	return null;
}

// errorKind refers to the different possible kinds of gopls errors.
export enum errorKind {
	initializationFailure,
	crash,
	manualRestart
}

// suggestActionAfterStartError potentially suggests actions to the user when gopls fails to start, either
// updating the language server or double checking their go.languageServerFlags setting.
export async function suggestActionAfterGoplsStartError(
	goCtx: GoExtensionContext,
	cfg: LanguageServerConfig // config used when starting this gopls.
) {
	// cfg is the config used when starting this crashed gopls instance, while
	// goCtx.latestConfig is the config used by the latest gopls instance.
	// They may be different if gopls upgrade occurred in between.
	if (JSON.stringify(goCtx.latestConfig?.version) !== JSON.stringify(cfg.version)) {
		return;
	}

	// The user may have an outdated version of gopls, in which case we should
	// just prompt them to update.
	const tool: Tool = getTool('gopls')!;
	const versionToUpdate = await shouldUpdateLanguageServer(tool, goCtx.latestConfig, true);
	if (versionToUpdate) {
		void promptForUpdatingTool(tool.name, versionToUpdate, true);
		return;
	}

	// Show the user the output channel content to alert them to the issue.
	goCtx.serverOutputChannel?.show();

	if (goCtx.latestConfig?.serverName !== 'gopls') {
		return;
	}

	const isIncorrectUsage = await isIncorrectCommandUsage(goCtx);

	// If the user has invalid values for "go.languageServerFlags", we may get
	// this error. Prompt them to double check their flags.
	let selected: string | undefined;
	if (isIncorrectUsage) {
		const languageServerFlags = getGoConfig()['languageServerFlags'] as string[];
		if (languageServerFlags && languageServerFlags.length > 0) {
			selected = await vscode.window.showErrorMessage(
				`The extension was unable to start the language server.
You may have an invalid value in your "go.languageServerFlags" setting.
It is currently set to [${languageServerFlags}].
Please correct the setting.`,
				'Open Settings',
				'I need more help.'
			);
			switch (selected) {
				case 'Open Settings':
					await vscode.commands.executeCommand('workbench.action.openSettings', 'go.languageServerFlags');
					return;
				case 'I need more help':
					// Fall through the automated issue report.
					break;
			}
		}
	}
}

export const showServerOutputChannel: CommandFactory = (ctx, goCtx) => () => {
	if (!goCtx.languageServerIsRunning) {
		vscode.window.showInformationMessage('gopls is not running');
		return;
	}
	// likely show() is asynchronous, despite the documentation
	goCtx.serverOutputChannel?.show();
	let found: vscode.TextDocument | undefined;
	for (const doc of vscode.workspace.textDocuments) {
		if (doc.fileName.indexOf('extension-output-') !== -1) {
			// despite show() above, this might not get the output we want, so check
			const contents = doc.getText();
			if (contents.indexOf('[Info  - ') === -1) {
				continue;
			}
			if (found !== undefined) {
				vscode.window.showInformationMessage('multiple docs named extension-output-...');
			}
			found = doc;
			// .log, as some decoration is better than none
			vscode.workspace.openTextDocument({ language: 'log', content: contents });
		}
	}
	if (found === undefined) {
		vscode.window.showErrorMessage('make sure "gopls (server)" output is showing');
	}
};

function sleep(ms: number) {
	return new Promise((resolve) => setTimeout(resolve, ms));
}

async function isIncorrectCommandUsage(goCtx: GoExtensionContext): Promise<boolean> {
	goCtx.serverOutputChannel?.show();
	// Find the logs in the output channel. There is no way to read
	// an output channel directly, but we can find the open text
	// document, since we just surfaced the output channel to the user.
	// See https://github.com/microsoft/vscode/issues/65108.
	let logs: string | undefined;
	for (let i = 0; i < 10; i++) {
		// try a couple of times until successfully finding the channel.
		for (const doc of vscode.workspace.textDocuments) {
			if (doc.languageId !== 'Log') {
				continue;
			}
			if (doc.isDirty || doc.isClosed) {
				continue;
			}
			if (doc.fileName.indexOf('gopls (server)') > -1) {
				logs = doc.getText();
				break;
			}
		}
		if (logs) {
			break;
		}
		// sleep a bit before the next try. The choice of the sleep time is arbitrary.
		await sleep((i + 1) * 100);
	}
	return logs ? logs.lastIndexOf('Usage:') > -1 : false;
}

const GOPLS_FETCH_VULNCHECK_RESULT = 'gopls.fetch_vulncheck_result';
// Fetches vulncheck result and throws an error if the result is not found.
// uri is a string representation of URI or DocumentURI.
async function goplsFetchVulncheckResult(goCtx: GoExtensionContext, uri: string): Promise<VulncheckReport> {
	const { languageClient } = goCtx;
	const params: ExecuteCommandParams = {
		command: GOPLS_FETCH_VULNCHECK_RESULT,
		arguments: [{ URI: uri }]
	};
	const res: { [modFile: string]: VulncheckReport } = await languageClient?.sendRequest(
		ExecuteCommandRequest.type,
		params
	);

	// res may include multiple results, but we only need one for the given uri.
	// Gopls uses normalized URI (https://cs.opensource.google/go/x/tools/+/refs/tags/gopls/v0.14.2:gopls/internal/span/uri.go;l=78)
	// but VS Code URI (uri) may not be normalized. For comparison, we use URI.fsPath
	// that provides a normalization implementation.
	// https://github.com/microsoft/vscode-uri/blob/53e4ca6263f2e4ddc35f5360c62bc1b1d30f27dd/src/uri.ts#L204
	const uriFsPath = URI.parse(uri).fsPath;
	for (const modFile in res) {
		try {
			const modFileURI = URI.parse(modFile);
			if (modFileURI.fsPath === uriFsPath) {
				return res[modFile];
			}
		} catch {
			console.log(`gopls returned an unparseable file uri in govulncheck result: ${modFile}`);
		}
	}
	throw new Error(`no matching go.mod ${uriFsPath} (${uri.toString()}) in the returned result: ${Object.keys(res)}`);
}

export function maybePromptForTelemetry(goCtx: GoExtensionContext) {
	const callback = async () => {
		const { lastUserAction = new Date() } = goCtx;
		const currentTime = new Date();

		// Make sure the user has been idle for at least 5 minutes.
		const idleTime = currentTime.getTime() - lastUserAction.getTime();
		if (idleTime < 5 * timeMinute) {
			setTimeout(callback, 5 * timeMinute - Math.max(idleTime, 0));
			return;
		}
		void goCtx.telemetryService?.promptForTelemetry();
	};
	void callback();
}