package auth

import (
	"net/http"
	"testing"
)

// The spoofing cases below are the reason this function exists rather than a
// one-line r.RemoteAddr read, so they're asserted explicitly rather than
// folded into the happy-path table.
func TestClientIP(t *testing.T) {
	tests := []struct {
		name       string
		remoteAddr string
		forwarded  string
		realIP     string
		want       string
	}{
		{
			name:       "direct connection, no proxy headers",
			remoteAddr: "203.0.113.5:51234",
			want:       "203.0.113.5",
		},
		{
			// The attack this guards against: a client connecting straight to
			// us claims to be someone else. RemoteAddr is public, so it did
			// NOT come through our proxy, so its XFF is worthless.
			name:       "direct connection ignores forged X-Forwarded-For",
			remoteAddr: "203.0.113.5:51234",
			forwarded:  "198.51.100.99",
			want:       "203.0.113.5",
		},
		{
			name:       "direct connection ignores forged X-Real-IP",
			remoteAddr: "203.0.113.5:51234",
			realIP:     "198.51.100.99",
			want:       "203.0.113.5",
		},
		{
			name:       "behind proxy, single forwarded client",
			remoteAddr: "172.18.0.1:40000",
			forwarded:  "203.0.113.5",
			want:       "203.0.113.5",
		},
		{
			// A client that prepends a lie to XFF only pollutes the LEFT end;
			// the proxy appends the address it actually saw on the right. The
			// right-to-left walk reaches the truth first.
			name:       "behind proxy, forged prefix is skipped for the appended truth",
			remoteAddr: "10.0.0.2:40000",
			forwarded:  "198.51.100.99, 203.0.113.5",
			want:       "203.0.113.5",
		},
		{
			name:       "behind proxy chain, internal hops skipped",
			remoteAddr: "10.0.0.2:40000",
			forwarded:  "203.0.113.5, 10.0.0.7, 172.18.0.3",
			want:       "203.0.113.5",
		},
		{
			name:       "behind proxy, X-Real-IP used when no forwarded header",
			remoteAddr: "127.0.0.1:40000",
			realIP:     "203.0.113.5",
			want:       "203.0.113.5",
		},
		{
			// LAN client through a LAN proxy: everything is private, so there
			// is no public address to find. Reporting the peer is honest.
			name:       "behind proxy, all-private chain falls back to remote",
			remoteAddr: "172.18.0.1:40000",
			forwarded:  "192.168.1.50, 172.18.0.3",
			want:       "172.18.0.1",
		},
		{
			name:       "behind proxy, malformed forwarded entries ignored",
			remoteAddr: "172.18.0.1:40000",
			forwarded:  "not-an-ip, 203.0.113.5, also-garbage",
			want:       "203.0.113.5",
		},
		{
			name:       "remote addr without a port is tolerated",
			remoteAddr: "203.0.113.5",
			want:       "203.0.113.5",
		},
		{
			name:       "ipv6 remote addr",
			remoteAddr: "[2001:db8::1]:51234",
			want:       "2001:db8::1",
		},
		{
			name:       "ipv6 forwarded client behind proxy",
			remoteAddr: "[fd00::1]:40000",
			forwarded:  "2001:db8::5",
			want:       "2001:db8::5",
		},
		{
			name:       "empty remote addr yields empty",
			remoteAddr: "",
			want:       "",
		},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			r, err := http.NewRequest(http.MethodGet, "/api/me/sessions", nil)
			if err != nil {
				t.Fatalf("NewRequest: %v", err)
			}
			r.RemoteAddr = tc.remoteAddr
			if tc.forwarded != "" {
				r.Header.Set("X-Forwarded-For", tc.forwarded)
			}
			if tc.realIP != "" {
				r.Header.Set("X-Real-IP", tc.realIP)
			}
			if got := ClientIP(r); got != tc.want {
				t.Errorf("ClientIP() = %q, want %q", got, tc.want)
			}
		})
	}
}