Load configuration file

config.ts

import { loadConfigFile } from "./load";

const { config } = await loadConfigFile("custom.config"); // custom.config.(?:json|[cm]?[tj]s)

console.log(config);

load.ts

import { promises as fsp } from "node:fs";
import { dirname, resolve } from "node:path";
import { loadConfig, LoadConfigOptions, LoadConfigResult } from "unconfig";

type MaybePromise<T> = T | Promise<T>

export async function getResolvedFilePath(filePath: string): Promise<[cwd: string, filePath: string, isOverride: boolean]> {
    let currentDir = process.cwd();
    let isOverride = false;

    const stat = await fsp.stat(filePath).catch(() => null);
    if (stat) {
        const absolutePath = resolve(filePath);
        if (stat.isFile()) {
            isOverride = true;
            filePath = absolutePath;
            currentDir = dirname(filePath);
        } else {
            currentDir = absolutePath;
        }
    }

    return [currentDir, filePath, isOverride];
}

export async function loadConfigFile<T>(
    filePath: string,
    options?: LoadConfigOptions<T> | ((opts: LoadConfigOptions<T>, filePath: string, isOverride: boolean) => MaybePromise<LoadConfigOptions<T>>)
): Promise<LoadConfigResult<T>> {
    const [cwd, resolvedFilePath, isOverride] = await getResolvedFilePath(filePath);
    const sources = isOverride
        ? [{ files: filePath, extensions: [] }]
        : [{ files: resolvedFilePath }];

    options = typeof options === "function"
        ? await options({ cwd, sources }, resolvedFilePath, isOverride)
        : { ...options, sources: Array.isArray(options?.sources) && options.sources?.length ? options.sources : sources };

    return loadConfig<T>({ cwd, ...options });
}