import * as os from 'node:os';

import { basename } from 'node:path';

const packageJson = require('../package.json');

/**

* Replaces occurrences of '/' with ':' in a string, since '/' is meaningful inside User-Agent strings as a separator.

*/

function replaceSlashes(s: string): string {

return s.replace('/', ':');

}

const MAX_LATIN1_CODE = 0xff;

/**

* Ensures a string is safe for use in HTTP headers by URI-encoding characters outside the Latin-1 (ISO-8859-1) range.

* Latin-1 characters (code points 0x00–0xFF) are preserved as-is; all others are percent-encoded via encodeURIComponent.

*/

function toLatin1Safe(s: string): string {

let result = '';

for (const char of s) {

result += char.charCodeAt(0) <= MAX_LATIN1_CODE ? char : encodeURIComponent(char);

}

return result;

}

// TODO: for the deno build (see the `npm run build:deno` npm run script), we could replace the `os-browserify` npm

// module shim with our own shim leveraging the deno beta compatibility layer for node's `os` module (for more info

// see https://deno.land/[email protected]/node/os.ts). At the time of writing this TODO (2021/11/25), this required deno

// v1.16.2 and use of the --unstable flag. Once support for this exists without the --unstable flag, we can improve

// the `os` module deno shim to correctly report operating system from a deno runtime. Until then, the below `os`-

// based code will report "browser/undefined" from a deno runtime.

const baseUserAgent =

`${replaceSlashes(packageJson.name)}/${packageJson.version} ` +

`${toLatin1Safe(basename(process.title))}/${process.version.replace('v', '')} ` +

`${os.platform()}/${os.release()}`;

const appMetadata: { [key: string]: string } = {};

/**

* Appends the app metadata into the User-Agent value

* @param appMetadata.name - name of tool to be counted in instrumentation

* @param appMetadata.version - version of tool to be counted in instrumentation

*/

export function addAppMetadata({ name, version }: { name: string; version: string }): void {

appMetadata[replaceSlashes(name)] = version;

}

/**

* Returns the current User-Agent value for instrumentation

*/

export function getUserAgent(): string {

const appIdentifier = Object.entries(appMetadata)

.map(([name, version]) => `${name}/${version}`)

.join(' ');

// only prepend the appIdentifier when it's not empty

return (appIdentifier.length > 0 ? `${appIdentifier} ` : '') + baseUserAgent;

}