package xor

import (
	"encoding/base64"
	"fmt"
)

// XORBytes takes two byte slices and XORs them together, returning the final
// byte slice. It is an error to pass in two byte slices that do not have the
// same length.
func XORBytes(a, b []byte) ([]byte, error) {
	if len(a) != len(b) {
		return nil, fmt.Errorf("length of byte slices is not equivalent: %d != %d", len(a), len(b))
	}

	buf := make([]byte, len(a))

	for i := range a {
		buf[i] = a[i] ^ b[i]
	}

	return buf, nil
}

// XORBase64 takes two base64-encoded strings and XORs the decoded byte slices
// together, returning the final byte slice. It is an error to pass in two
// strings that do not have the same length to their base64-decoded byte slice.
func XORBase64(a, b string) ([]byte, error) {
	aBytes, err := base64.StdEncoding.DecodeString(a)
	if err != nil {
		return nil, fmt.Errorf("error decoding first base64 value: %w", err)
	}
	if aBytes == nil || len(aBytes) == 0 {
		return nil, fmt.Errorf("decoded first base64 value is nil or empty")
	}

	bBytes, err := base64.StdEncoding.DecodeString(b)
	if err != nil {
		return nil, fmt.Errorf("error decoding second base64 value: %w", err)
	}
	if bBytes == nil || len(bBytes) == 0 {
		return nil, fmt.Errorf("decoded second base64 value is nil or empty")
	}

	return XORBytes(aBytes, bBytes)
}
