package magna

import (
	"encoding/binary"
)

// getU8 returns the first byte from a byte array at offset.
func getU8(buf []byte, offset int) (uint8, int, error) {
	nextOffset := offset + 1
	if nextOffset > len(buf) {
		return 0, len(buf), &BufferOverflowError{Length: len(buf), Offset: nextOffset}
	}

	return buf[offset], nextOffset, nil
}

// getU16 returns the bigEndian uint16 from a byte array at offset.
func getU16(buf []byte, offset int) (uint16, int, error) {
	nextOffset := offset + 2
	if nextOffset > len(buf) {
		return 0, len(buf), &BufferOverflowError{Length: len(buf), Offset: nextOffset}
	}

	return binary.BigEndian.Uint16(buf[offset:]), nextOffset, nil
}

// getU32 returns the bigEndian uint32 from a byte array at offset.
func getU32(buf []byte, offset int) (uint32, int, error) {
	nextOffset := offset + 4
	if nextOffset > len(buf) {
		return 0, len(buf), &BufferOverflowError{Length: len(buf), Offset: nextOffset}
	}

	return binary.BigEndian.Uint32(buf[offset:]), nextOffset, nil
}

// getSlice returns a slice of bytes from a byte array at an offset and of length.
func getSlice(buf []byte, offset int, length int) ([]byte, int, error) {
	nextOffset := offset + length
	if nextOffset > len(buf) {
		return nil, len(buf), &BufferOverflowError{Length: len(buf), Offset: nextOffset}
	}

	return buf[offset:nextOffset], nextOffset, nil
}