import { existsSync, readFileSync } from 'fs';

function readFile(path: string): string {
    if (existsSync(path)) {
        return readFileSync(path);
    } else {
        // Callers of readFile have no way of knowing the function can fail
        throw new Error('invalid path');
    }
}

// This line may fail unexpectedly without warnings from typescript
const text = readFile('test.txt');

import { existsSync, readFileSync } from 'fs';
import { Ok, Err, Result } from 'ts-results-es';

function readFile(path: string): Result<string, 'invalid path'> {
    if (existsSync(path)) {
        return new Ok(readFileSync(path)); // new is optional here
    } else {
        return new Err('invalid path'); // new is optional here
    }
}

// Typescript now forces you to check whether you have a valid result at compile time.
const result = readFile('test.txt');
if (result.isOk()) {
    // text contains the file's content
    const text = result.value;
} else {
    // err equals 'invalid path'
    const err = result.error;
}

declare function getLoggedInUsername(): string | undefined;

declare function getImageURLForUsername(username: string): string | undefined;

function getLoggedInImageURL(): string | undefined {
    const username = getLoggedInUsername();
    if (!username) {
        return undefined;
    }

    return getImageURLForUsername(username);
}

const stringUrl = getLoggedInImageURL();
const optionalUrl = stringUrl ? new URL(stringUrl) : undefined;
console.log(optionalUrl);

import { Option, Some, None } from 'ts-results-es';

declare function getLoggedInUsername(): Option<string>;

declare function getImageForUsername(username: string): Option<string>;

function getLoggedInImage(): Option<string> {
    return getLoggedInUsername().andThen(getImageForUsername);
}

const optionalUrl = getLoggedInImage().map((url) => new URL(stringUrl));
console.log(optionalUrl); // Some(URL('...'))

// To extract the value, do this:
if (optionalUrl.some) {
    const url: URL = optionalUrl.value;
}