package utils

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"golang.org/x/crypto/argon2"
	"strings"
)

func generateRandomBytes(n uint32) ([]byte, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)
	if err != nil {
		return nil, err
	}

	return b, nil
}

func decodeHash(encodedHash string) (p *params, salt, hash []byte, err error) {
	vals := strings.Split(encodedHash, "$")
	if len(vals) != 6 {
		return nil, nil, nil, ErrInvalidHash
	}
	var version int
	_, err = fmt.Sscanf(vals[2], "v=%d", &version)
	if err != nil {
		return nil, nil, nil, err
	}
	if version != argon2.Version {
		return nil, nil, nil, ErrIncompatibleVersion
	}
	p = &params{}
	_, err = fmt.Sscanf(vals[3], "m=%d,t=%d,p=%d", &p.memory, &p.iterations, &p.parallelism)
	if err != nil {
		return nil, nil, nil, err
	}
	salt, err = base64.RawStdEncoding.DecodeString(vals[4])
	if err != nil {
		return nil, nil, nil, err
	}
	p.saltLength = uint32(len(salt))

	hash, err = base64.RawStdEncoding.DecodeString(vals[5])
	if err != nil {
		return nil, nil, nil, err
	}
	p.keyLength = uint32(len(hash))

	return p, salt, hash, nil
}

func CompareStringToArgon2Hash(password string, hashedPassword string) (match bool, err error) {
	p, salt, hash, err := decodeHash(hashedPassword)
	if err != nil {
		return false, err
	}
	otherHash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)
	if subtle.ConstantTimeCompare(hash, otherHash) == 1 {
		return true, nil
	}
	return false, nil
}

func HashStringArgon2(password string) (encodedHash string, err error) {
	salt, err := generateRandomBytes(p.saltLength)
	if err != nil {
		return "", err
	}
	hash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)
	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
	b64Hash := base64.RawStdEncoding.EncodeToString(hash)
	encodedHash = fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s", argon2.Version, p.memory, p.iterations, p.parallelism, b64Salt, b64Hash)

	return encodedHash, nil
}

func RandomString(s int) (string, error) {
	b, err := generateRandomBytes(uint32(s))
	return base64.URLEncoding.EncodeToString(b), err
}