package rproxy_test

import (
	"bytes"
	"crypto/rand"
	"io"
	"maps"
	"net/http"
	"slices"
	"strconv"
	"strings"
	"testing"

	"sneak.berlin/go/smallwebwaf/internal/proxy"
)

// questionBodyMaxBytes is the most of a body a question carries.
const questionBodyMaxBytes = proxy.QuestionBodyMaxBytes

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

	servewaf := startServeWAF(t, allow)
	app := startApp(t, greet)
	addr, _ := startRProxy(t, servewaf.URL, app.URL, nil)

	const target = "/some%2Fpath/with%20space?b=2&a=1&bad=%zz;x"

	req := newRequest(t, http.MethodDelete, addr, target, http.NoBody)
	req.Host = site
	req.Header.Set("X-Test", "from the visitor")
	req.Header.Set(forwardedForHeader, "198.51.100.1")
	req.Header.Set(forwardedProtoHeader, "gopher")
	req.Header.Set(requestIDHeader, "the-visitor's")
	req.Header.Set(proxy.ClientHeader, "198.51.100.2")
	req.Header.Set(proxy.PeerHeader, "198.51.100.3")
	req.Header.Set(proxy.ContentLengthHeader, "12345")
	// Go's client then sends no User-Agent, so that one in the question would be
	// Go's own.
	req.Header["User-Agent"] = nil

	wantGreeting(t, visit(t, req))

	asked := servewaf.question(t)
	if asked.method != http.MethodDelete || asked.target != target ||
		asked.host != site {
		t.Errorf("asked about %s %s at %s", asked.method, asked.target, asked.host)
	}

	if asked.header.Get(requestIDHeader) == "the-visitor's" {
		t.Error("the question carries the visitor's id")
	}

	// Exactly these: visit's connection has the visitor send Connection: close.
	want := http.Header{}
	want.Set("Connection", "close")
	want.Set("X-Test", "from the visitor")
	want.Set(forwardedForHeader, "198.51.100.1")
	want.Set(forwardedProtoHeader, "http")
	want.Set(requestIDHeader, asked.header.Get(requestIDHeader))
	want.Set(proxy.ClientHeader, localhost)
	want.Set(proxy.PeerHeader, localhost)

	if !maps.EqualFunc(asked.header, want, slices.Equal) {
		t.Errorf("the question's headers are %v, want %v", asked.header, want)
	}
}

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

	const visitor = "203.0.113.9"

	for _, tc := range []struct {
		name, trusted, client, proto, forwarded string
	}{
		{
			"from a trusted proxy", localhost + "/32", visitor, "https",
			visitor + ", " + localhost,
		},
		{"from a peer not trusted", "10.0.0.0/8", localhost, "http", localhost},
	} {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			servewaf := startServeWAF(t, allow)
			forwarded := make(chan http.Header, 1)
			app := startApp(t, func(w http.ResponseWriter, r *http.Request) {
				forwarded <- r.Header.Clone()

				greet(w, r)
			})
			addr, out := startRProxy(t, servewaf.URL, app.URL, map[string]string{
				trustedProxies: tc.trusted,
			})

			req := newRequest(t, http.MethodGet, addr, "/", http.NoBody)
			req.Header.Set(forwardedForHeader, visitor)
			req.Header.Set(forwardedProtoHeader, "https")
			wantGreeting(t, visit(t, req))

			asked := servewaf.question(t)
			if asked.header.Get(proxy.ClientHeader) != tc.client ||
				asked.header.Get(proxy.PeerHeader) != localhost ||
				asked.header.Get(forwardedForHeader) != visitor ||
				asked.header.Get(forwardedProtoHeader) != tc.proto {
				t.Errorf("the question's headers are %v", asked.header)
			}

			if line := out.requestLine(t); line["client_ip"] != tc.client {
				t.Errorf("line %v, want client_ip %s", line, tc.client)
			}

			if got := (<-forwarded).Get(forwardedForHeader); got != tc.forwarded {
				t.Errorf("the app saw %s %q, want %q", forwardedForHeader, got, tc.forwarded)
			}
		})
	}
}

// randomBytes returns n random bytes.
func randomBytes(n int) []byte {
	body := make([]byte, n)
	_, _ = rand.Read(body) // it never returns an error

	return body
}

func TestFirst64KiBReachServeWAFAndTheWholeBodyTheApp(t *testing.T) {
	t.Parallel()

	for _, size := range []int{
		1, questionBodyMaxBytes - 1, questionBodyMaxBytes, questionBodyMaxBytes + 1,
		5 * questionBodyMaxBytes,
	} {
		for _, announced := range []bool{true, false} {
			name := strconv.Itoa(size) + " bytes, length announced: " +
				strconv.FormatBool(announced)

			t.Run(name, func(t *testing.T) {
				t.Parallel()

				body := randomBytes(size)
				servewaf := startServeWAF(t, allow)
				received := make(chan []byte, 1)
				app := startApp(t, func(w http.ResponseWriter, r *http.Request) {
					whole, _ := io.ReadAll(r.Body)
					received <- whole

					greet(w, r)
				})
				addr, _ := startRProxy(t, servewaf.URL, app.URL, nil)

				req := newRequest(t, http.MethodPost, addr, "/", bytes.NewReader(body))
				if !announced {
					// Go's client sends a body of unknown length in chunks.
					req.ContentLength = -1
				}

				wantGreeting(t, visit(t, req))

				asked := servewaf.question(t)
				want := body[:min(size, questionBodyMaxBytes)]
				wantQuestionBody(t, asked, want, size, announced)

				if !bytes.Equal(<-received, body) {
					t.Error("the app did not get the whole body")
				}

				if report := servewaf.report(t); report.RequestBytes != int64(size) {
					t.Errorf("report %+v, of %d bytes", report, size)
				}
			})
		}
	}
}

// wantQuestionBody checks the body a question carries, want, and how it gives
// the length of the visitor's body, of size bytes.
func wantQuestionBody(
	t *testing.T, asked question, want []byte, size int, announced bool,
) {
	t.Helper()

	if !bytes.Equal(asked.body, want) {
		t.Errorf("the question carries %d bytes, want the first %d", len(asked.body),
			len(want))
	}

	values := asked.header.Values(proxy.ContentLengthHeader)

	if announced {
		if !slices.Equal(values, []string{strconv.Itoa(size)}) ||
			asked.contentLength != int64(len(want)) {
			t.Errorf("announced %v and length %d, want %d and %d", values,
				asked.contentLength, size, len(want))
		}

		return
	}

	if len(values) != 0 || !slices.Equal(asked.transferEncoding, []string{"chunked"}) {
		t.Errorf("announced %v and encoded %v, want none and chunked", values,
			asked.transferEncoding)
	}
}

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

	servewaf := startServeWAF(t, deny)
	app := startApp(t, greet)
	addr, _ := startRProxy(t, servewaf.URL, app.URL, nil)

	// Far more announced than sent. Go's server does not wait for that much, so
	// the answer comes at once.
	conn := dial(t, addr)
	send(t, conn, post+announcedLength(100*questionBodyMaxBytes)+
		strings.Repeat("x", questionBodyMaxBytes))

	if status := readStatus(t, conn); status != http.StatusForbidden {
		t.Errorf("status %d, want servewaf's 403", status)
	}

	if report := servewaf.report(t); report.RequestBytes != questionBodyMaxBytes {
		t.Errorf("report %+v, want the first part's bytes", report)
	}
}