package internal

// Minimal protobuf wire helpers (bytes/string fields only).

const (
	errCodeOverflow = -2
	errCodeTruncated = -1
)

func consumeVarint(b []byte) (uint64, int) {
	var x uint64
	var s uint
	for i, c := range b {
		if c < 0x80 {
			if i > 9 || i == 9 && c > 1 {
				return 0, errCodeOverflow
			}
			return x | uint64(c)<<s, i + 1
		}
		x |= uint64(c&0x7f) << s
		s += 7
	}
	return 0, errCodeTruncated
}

// ConsumeBytes parses a length-delimited bytes field.
func ConsumeBytes(b []byte) ([]byte, int) {
	v, n := consumeVarint(b)
	if n < 0 {
		return nil, n
	}
	if v > uint64(len(b)-n) {
		return nil, errCodeOverflow
	}
	return b[n : n+int(v)], n + int(v)
}

// ConsumeString parses a length-delimited string field.
func ConsumeString(b []byte) (string, int) {
	v, n := ConsumeBytes(b)
	if n < 0 {
		return "", n
	}
	return string(v), n
}

func parseError(code int) error {
	switch code {
	case errCodeOverflow:
		return errOverflow
	case errCodeTruncated:
		return errTruncated
	default:
		return errTruncated
	}
}

var (
	errOverflow  = &parseErr{"overflow"}
	errTruncated = &parseErr{"truncated"}
)

type parseErr struct{ msg string }

func (e *parseErr) Error() string { return "protowire: " + e.msg }