package httpapi

import (
	"net"
	"net/http"
	"net/netip"
	"os"
	"strings"
)

// trustedProxyPrefixes returns no trusted peers when any configured CIDR is invalid.
// An empty configuration deliberately treats every connection as direct.
func trustedProxyPrefixes() []netip.Prefix {
	raw := strings.TrimSpace(os.Getenv("EVOBGP_TRUSTED_PROXY_CIDRS"))
	if raw == "" {
		return nil
	}
	parts := strings.Split(raw, ",")
	prefixes := make([]netip.Prefix, 0, len(parts))
	for _, part := range parts {
		prefix, err := netip.ParsePrefix(strings.TrimSpace(part))
		if err != nil {
			return nil
		}
		if prefix.Addr().Is4In6() {
			if prefix.Bits() < 96 {
				return nil
			}
			prefix = netip.PrefixFrom(prefix.Addr().Unmap(), prefix.Bits()-96)
		}
		prefixes = append(prefixes, prefix.Masked())
	}
	return prefixes
}

func peerAddress(r *http.Request) (netip.Addr, bool) {
	if r == nil {
		return netip.Addr{}, false
	}
	host, _, err := net.SplitHostPort(strings.TrimSpace(r.RemoteAddr))
	if err != nil {
		host = strings.TrimSpace(r.RemoteAddr)
	}
	ip, err := netip.ParseAddr(host)
	if err != nil {
		return netip.Addr{}, false
	}
	return ip.WithZone("").Unmap(), true
}

func isTrustedProxy(ip netip.Addr, prefixes []netip.Prefix) bool {
	for _, prefix := range prefixes {
		if prefix.Contains(ip) || prefix.Contains(ip.Unmap()) {
			return true
		}
	}
	return false
}

func clientIPWithTrustedProxies(r *http.Request, prefixes []netip.Prefix) string {
	peer, ok := peerAddress(r)
	if !ok {
		if r == nil {
			return ""
		}
		return strings.TrimSpace(r.RemoteAddr)
	}
	if !isTrustedProxy(peer, prefixes) {
		return peer.String()
	}
	values := r.Header.Values("X-Forwarded-For")
	if len(values) != 1 || strings.TrimSpace(values[0]) == "" {
		return peer.String()
	}
	hops := strings.Split(values[0], ",")
	current := peer
	for i := len(hops) - 1; i >= 0; i-- {
		if !isTrustedProxy(current, prefixes) {
			return current.String()
		}
		next, err := netip.ParseAddr(strings.TrimSpace(hops[i]))
		if err != nil {
			return peer.String()
		}
		if next.Zone() != "" {
			return peer.String()
		}
		current = next.Unmap()
	}
	return current.String()
}