package hopp

import "fmt"

type anyInt16 interface { ~uint16 | ~int16 }
type anyInt64 interface { ~uint64 | ~int64 }

// decodeI16 decodes a 16 bit integer from the given data.
func decodeI16[T anyInt16](data []byte) (T, error) {
	if len(data) != 2 { return 0, fmt.Errorf("decoding int16: %w", ErrWrongBufferLength) }
	return T(data[0]) << 8 | T(data[1]), nil
}

// encodeI16 encodes a 16 bit integer into the given buffer.
func encodeI16[T anyInt16](buffer []byte, value T) error {
	if len(buffer) != 2 { return fmt.Errorf("encoding int16: %w", ErrWrongBufferLength) }
	buffer[0] = byte(value >> 8)
	buffer[1] = byte(value)
	return nil
}

// decodeI64 decodes a 64 bit integer from the given data.
func decodeI64[T anyInt64](data []byte) (T, error) {
	if len(data) != 8 { return 0, fmt.Errorf("decoding int64: %w", ErrWrongBufferLength) }
	return T(data[0]) << 56 |
		T(data[1]) << 48 |
		T(data[2]) << 40 |
		T(data[3]) << 32 |
		T(data[4]) << 24 |
		T(data[5]) << 16 |
		T(data[6]) <<  8 |
		T(data[7]), nil
}

// encodeI64 encodes a 64 bit integer into the given buffer.
func encodeI64[T anyInt64](buffer []byte, value T) error {
	if len(buffer) != 8 { return fmt.Errorf("encoding int64: %w", ErrWrongBufferLength) }
	buffer[0] = byte(value >> 56)
	buffer[1] = byte(value >> 48)
	buffer[2] = byte(value >> 40)
	buffer[3] = byte(value >> 32)
	buffer[4] = byte(value >> 24)
	buffer[5] = byte(value >> 16)
	buffer[6] = byte(value >> 8)
	buffer[7] = byte(value)
	return nil
}