package util

import (
	"net/netip"
	"strings"
)

// ParseNetPrefixes parses a list of IP addresses and CIDR ranges, e.g. for a
// list of trusted proxies. Entries are trimmed and blank ones skipped. A CIDR
// range is masked to its network address (10.1.2.3/8 becomes 10.0.0.0/8), and
// an address becomes a prefix holding only that address, with an IPv4-mapped
// IPv6 address (::ffff:1.2.3.4) unmapped to IPv4. The first entry that can't
// be parsed returns an error naming it.
func ParseNetPrefixes(list []string) ([]netip.Prefix, error) {
	prefixes := make([]netip.Prefix, 0, len(list))

	for _, entry := range list {
		entry = strings.TrimSpace(entry)
		if entry == "" {
			continue
		}

		if strings.Contains(entry, "/") {
			prefix, err := netip.ParsePrefix(entry)
			if err != nil {
				return nil, err
			}
			prefixes = append(prefixes, prefix.Masked())
			continue
		}

		addr, err := netip.ParseAddr(entry)
		if err != nil {
			return nil, err
		}

		addr = addr.Unmap()
		prefixes = append(prefixes, netip.PrefixFrom(addr, addr.BitLen()))
	}
	return prefixes, nil
}