package clientip_test

import (
	"net/netip"
	"testing"

	"sneak.berlin/go/pixa/internal/clientip"
)

// Addresses reused across the resolver cases.
const (
	trustedRangeV4 = "10.0.0.0/8"
	forwardedV4    = "203.0.113.7"
	untrustedV4    = "198.51.100.9"
	trustedPeer    = "10.0.0.1:5000"
)

// mustPrefixes parses CIDR strings into prefixes for building a resolver.
func mustPrefixes(t *testing.T, cidrs ...string) []netip.Prefix {
	t.Helper()

	prefixes := make([]netip.Prefix, 0, len(cidrs))

	for _, c := range cidrs {
		p, err := netip.ParsePrefix(c)
		if err != nil {
			t.Fatalf("netip.ParsePrefix(%q) error = %v", c, err)
		}

		prefixes = append(prefixes, p)
	}

	return prefixes
}

type resolveCase struct {
	name         string
	trusted      []string
	remoteAddr   string
	forwardedFor []string
	want         string
}

// runResolveCases runs each case against a resolver built from its trusted
// list and checks the resolved address.
func runResolveCases(t *testing.T, cases []resolveCase) {
	t.Helper()

	for _, tt := range cases {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			r := clientip.NewResolver(mustPrefixes(t, tt.trusted...))

			got := r.Resolve(tt.remoteAddr, tt.forwardedFor)
			if got != tt.want {
				t.Errorf("Resolve(%q, %v) = %q, want %q",
					tt.remoteAddr, tt.forwardedFor, got, tt.want)
			}
		})
	}
}

// TestResolvePeerTrust covers the trust decision on the direct peer: a
// forwarded header is believed only from a trusted peer, and a client
// connecting directly cannot spoof its address.
func TestResolvePeerTrust(t *testing.T) {
	t.Parallel()

	runResolveCases(t, []resolveCase{
		{
			name:         "trusted peer honors forwarded client",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{forwardedV4},
			want:         forwardedV4,
		},
		{
			name:         "untrusted peer ignores forwarded header",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   untrustedV4 + ":33333",
			forwardedFor: []string{forwardedV4},
			want:         untrustedV4,
		},
		{
			name:         "spoofed chain from untrusted peer cannot influence result",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   untrustedV4 + ":33333",
			forwardedFor: []string{"1.2.3.4, 10.9.9.9, 127.0.0.1"},
			want:         untrustedV4,
		},
		{
			name:         "empty trusted list always uses peer",
			trusted:      nil,
			remoteAddr:   forwardedV4 + ":80",
			forwardedFor: []string{"10.0.0.5"},
			want:         forwardedV4,
		},
		{
			name:         "trusted peer with no forwarded header uses peer",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: nil,
			want:         "10.0.0.1",
		},
		{
			name:         "unparseable peer is returned unchanged",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   "garbage",
			forwardedFor: []string{forwardedV4},
			want:         "garbage",
		},
	})
}

// TestResolveChainWalk covers walking the X-Forwarded-For chain from a
// trusted peer to the rightmost entry that is not itself a trusted proxy.
func TestResolveChainWalk(t *testing.T) {
	t.Parallel()

	runResolveCases(t, []resolveCase{
		{
			name:         "rightmost untrusted entry across a mixed chain",
			trusted:      []string{trustedRangeV4, "192.168.0.0/16"},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{forwardedV4 + ", 192.168.1.1, 10.0.0.2"},
			want:         forwardedV4,
		},
		{
			name:         "spoofed client behind a trusted proxy is not believed",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{"1.2.3.4, " + untrustedV4},
			want:         untrustedV4,
		},
		{
			name:         "chain split across multiple header lines",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{forwardedV4, "10.0.0.2"},
			want:         forwardedV4,
		},
		{
			name:         "garbage entries are skipped",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{forwardedV4 + ", not-an-ip"},
			want:         forwardedV4,
		},
		{
			name:         "all-trusted chain falls back to peer",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   trustedPeer,
			forwardedFor: []string{"10.0.0.9, 10.0.0.2"},
			want:         "10.0.0.1",
		},
		{
			name:         "trusted IPv6 peer honors forwarded client",
			trusted:      []string{"2001:db8::/32"},
			remoteAddr:   "[2001:db8::1]:9000",
			forwardedFor: []string{forwardedV4},
			want:         forwardedV4,
		},
		{
			name:         "IPv4-mapped peer matches IPv4 trusted range",
			trusted:      []string{trustedRangeV4},
			remoteAddr:   "[::ffff:10.0.0.1]:5000",
			forwardedFor: []string{forwardedV4},
			want:         forwardedV4,
		},
	})
}

func TestContextRoundTrip(t *testing.T) {
	t.Parallel()

	ctx := clientip.WithClientIP(t.Context(), forwardedV4)
	if got := clientip.FromContext(ctx); got != forwardedV4 {
		t.Errorf("FromContext = %q, want %q", got, forwardedV4)
	}
}

func TestFromContextAbsent(t *testing.T) {
	t.Parallel()

	if got := clientip.FromContext(t.Context()); got != "" {
		t.Errorf("FromContext with no value = %q, want empty", got)
	}
}