A basic implementation of how files to be ignored in 'ignore' files are found and ignored

ignored_files.ts

import * as path from "path"
import * as fs from "fs"

// find all files that match the corresponding splitted directory component
// find all files and folders that match the regular expression of the corresponding path
// filter out all unmatched files/folders from the list based on splitted path
function getIgnoredFiles(ignorePath: string) :string[]{
    const allFiles = walk(process.cwd(), [], {})
    const regex = buildRegex(ignorePath)

    return allFiles.filter((file) => {
        return file.match(regex)
    })
}

function buildRegex(ignorePath: string): RegExp {
    const fileDirectoryPath: string[] = ignorePath.split(path.sep)
    fileDirectoryPath.unshift(...process.cwd().split(path.sep))

    const regexString = fileDirectoryPath.map((str) => {
        if(str === "**"){
            return "(.*?)+"
        }
        else if(str === "*"){
            return `[^\\${path.sep}]+`
        }
        else if(str.match(/\*\.\w+/)){
            return `[\\w]+\\.${str.slice(str.indexOf('.')+1)}`
        }
        else {
            return str
        }
    })

    return new RegExp(regexString.join(`${path.sep}${path.sep}`))
}

function walk(filePath: string, unvisited: string[], visited: {[key: string]: boolean}) : string []{
    let allFiles =  fs.readdirSync(filePath, {
        recursive: true,
    })

    unvisited = unvisited.concat((allFiles as string[]).map((file) => {
        return `${filePath}${path.sep}${file}`
    }))
    while(unvisited.length){
        let file = unvisited.pop()
        if(!fs.statSync(file).isDirectory()){
            visited[file] = true
            continue
        }
        return walk(file, unvisited, visited)
    }

    return Object.keys(visited)
}