package hasher

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"fmt"
	"os"
	"strings"

	"golang.org/x/crypto/argon2"
	"golang.org/x/crypto/bcrypt"
)

var enabled = true

type params struct {
	memory      uint32
	iterations  uint32
	parallelism uint8
	saltLength  uint32
	keyLength   uint32
}

var p = &params{
	memory:      64 * 1024,
	iterations:  3,
	parallelism: 2,
	saltLength:  16,
	keyLength:   32,
}

func init() { // nolint: gochecknoinits
	disableHas := os.Getenv("UNSAFE_DISABLE_PASSWORD_PROJECTION") == "yes_i_am_sure"

	if disableHas {
		fmt.Println("WARNING: Password protection is disabled. This is unsafe in production.")
		enabled = false
	}
}

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

func HashPassword(password string) (string, error) {
	if !enabled {
		return password, nil
	}

	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, 64*1024, 3, 2, b64Salt, b64Hash)
	return encodedHash, err
}

// CheckPasswordHash checks if the provided password matches the hash.
// Additionally, it returns a boolean indicating whether the password should be rehashed.
func CheckPasswordHash(password, hash string) (bool, bool) {
	if !enabled {
		return password == hash, false
	}

	// Compare Argon2id hash first
	match, err := comparePasswordAndHash(password, hash)
	if err != nil || !match {
		// If argon2id hash fails or doesn't match, try bcrypt
		err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
		if err == nil {
			// If bcrypt hash matches, return true and indicate rehashing
			return true, true
		} else {
			// If both fail, return false and indicate no rehashing
			return false, false
		}
	}
	return match, false
}

func comparePasswordAndHash(password, encodedHash string) (match bool, err error) {
	// Extract the parameters, salt and derived key from the encoded password
	// hash.
	p, salt, hash, err := decodeHash(encodedHash)
	if err != nil {
		return false, err
	}

	// Derive the key from the other password using the same parameters.
	otherHash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)

	// Check that the contents of the hashed passwords are identical. Note
	// that we are using the subtle.ConstantTimeCompare() function for this
	// to help prevent timing attacks.
	if subtle.ConstantTimeCompare(hash, otherHash) == 1 {
		return true, nil
	}
	return false, nil
}

func decodeHash(encodedHash string) (p *params, salt, hash []byte, err error) {
	vals := strings.Split(encodedHash, "$")
	if len(vals) != 6 {
		return nil, nil, nil, fmt.Errorf("invalid hash format")
	}

	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, fmt.Errorf("unsupported argon2 version: %d", version)
	}

	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.Strict().DecodeString(vals[4])
	if err != nil {
		return nil, nil, nil, err
	}
	p.saltLength = uint32(len(salt))

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

	return p, salt, hash, nil
}