package main

import (
	"crypto/sha512"
	"fmt"
	"io"
	"os"
)

func checkFile(filepath string, checksum string) (bool, error) {
	if _, err := os.Stat(filepath); os.IsNotExist(err) {
		return false, nil
	}

	// file exists, check checksum
	lsum, err := hash(filepath)
	if err != nil {
		return false, err
	}

	if checksum != fmt.Sprintf("%x", lsum) {
		return false, nil
	}

	return true, nil
}

func hash(filepath string) ([]byte, error) {
	file, err := os.Open(filepath)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	hasher := sha512.New()
	if _, err := io.Copy(hasher, file); err != nil {
		return nil, err
	}

	return hasher.Sum(nil), nil
}