package coreruleset_test

import (
	"maps"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"slices"
	"strconv"
	"strings"
	"testing"
	"time"

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

// The bounds on what a visitor can send, as SPEC.md gives them.
const (
	// lineLimit is the longest request line or header line.
	lineLimit = 8 << 10
	// headerLimit is the most bytes rproxy reads of a request line and
	// headers together.
	headerLimit = 32 << 10
	// mostCookies and mostHeaderFields are waf's limits on cookies and header
	// fields.
	mostCookies      = 50
	mostHeaderFields = 100
	// mostBodyRead is the largest SWW_WAF_CORE_RULE_SET_BODY_INSPECTION_SIZE.
	mostBodyRead = 8 << 10
	// mostJSONRead is the largest JSON body the Core Rule Set reads.
	mostJSONRead = 1 << 10
)

// inspectionTimeLimit is the most time the Core Rule Set may take on one
// request. It is the default of rproxy's SWW_RPROXY_WAF_BACKEND_TIMEOUT_MS, 2
// seconds, less the default of SWW_WAF_ASN_AND_COUNTRY_LOOKUP_TIMEOUT_MS, 800
// milliseconds, which a question can also wait for GeoJS, and less 200
// milliseconds for waf's other checks.
const inspectionTimeLimit = time.Second

// text returns n bytes of letters, digits and spaces, which the Core Rule Set
// takes longer over than one letter repeated.
func text(n int) string {
	const words = "select 0x2f from tbl_1 where name like abc_9 "

	return strings.Repeat(words, n/len(words)+1)[:n]
}

// visitorRequest is a request a visitor can send, at the most of one or more
// of the bounds above.
type visitorRequest struct {
	name   string
	target string
	// header holds the headers besides Host.
	header http.Header
	// contentType is the body's type, "" for no body.
	contentType string
	body        string
}

// longestTarget returns a target whose request line, "POST <target>
// HTTP/1.1", is lineLimit bytes long.
func longestTarget() string {
	const around = len("POST /?q= HTTP/1.1")

	return "/?q=" + strings.ReplaceAll(text(lineLimit-around), " ", "+")
}

// cookieLine returns a Cookie value whose line, "Cookie: <value>", is
// lineLimit bytes long, made of count cookies.
func cookieLine(count int) string {
	const linePrefix = len("Cookie: ")

	cookies := make([]string, count)
	for i := range cookies {
		cookies[i] = "c" + strconv.Itoa(i) + "="
	}

	// Each cookie is followed by "; ", but for the last.
	room := lineLimit - linePrefix - len(strings.Join(cookies, "; "))
	for i := range cookies {
		share := room / count
		if i == 0 {
			share += room % count
		}

		cookies[i] += strings.ReplaceAll(text(share), " ", "_")
	}

	return strings.Join(cookies, "; ")
}

// headerValue returns a value whose line, "<name>: <value>", is n bytes long.
func headerValue(name string, n int) string {
	return text(n - len(name) - len(": "))
}

// formFields returns a form body of mostBodyRead bytes holding count fields.
func formFields(count int) string {
	fields := make([]string, count)
	for i := range fields {
		fields[i] = "f" + strconv.Itoa(i) + "="
	}

	room := mostBodyRead - len(strings.Join(fields, "&"))
	for i := range fields {
		share := room / count
		if i == 0 {
			share += room % count
		}

		fields[i] += strings.ReplaceAll(text(share), " ", "+")
	}

	return strings.Join(fields, "&")
}

// multipartBody returns a multipart body of mostBodyRead bytes, with the
// boundary "b", holding fields of about size bytes each.
func multipartBody(size int) string {
	var body strings.Builder

	const end = "--b--\r\n"

	for i := 0; ; i++ {
		head := "--b\r\nContent-Disposition: form-data; name=\"f" +
			strconv.Itoa(i) + "\"\r\n\r\n"

		room := mostBodyRead - body.Len() - len(
			end,
		) - len(
			head,
		) - len(
			"\r\n",
		)
		if room <= 0 {
			break
		}

		body.WriteString(head + text(min(size, room)) + "\r\n")
	}

	body.WriteString(end)

	return body.String()
}

// jsonArrayOfMostElements returns a JSON array of at most mostJSONRead bytes
// holding as many elements as fit, each the number 1.
func jsonArrayOfMostElements() string {
	return "[1" + strings.Repeat(
		",1",
		(mostJSONRead-len("[1]"))/len(",1"),
	) + "]"
}

// jsonOfMostElementsUnderAKey returns a JSON body of mostJSONRead bytes
// holding as many elements as fit, each the number 1, in an array under a
// key of 6 bytes. Coraza names each element "json.<key>.<index>", so a
// longer key makes longer names. 6 bytes is the longest key that keeps the
// names and values of this body within the 8 KiB Coraza allows.
func jsonOfMostElementsUnderAKey() string {
	head := `{"` + text(6) + `":[1`

	return head + strings.Repeat(
		",1",
		(mostJSONRead-len(head+"]}"))/len(",1"),
	) + "]}"
}

// The kinds of body the Core Rule Set reads, and the header that names a
// request's cookies.
const (
	formType      = "application/x-www-form-urlencoded"
	jsonType      = "application/json"
	multipartType = "multipart/form-data; boundary=b"
	cookieHeader  = "Cookie"
)

// fullLine is the length of each of the request line and the three or four
// header lines that together fill rproxy's limit, with room for the line
// endings and the other headers.
const fullLine = lineLimit - 64

// worstCaseRequests are, for each kind of thing a visitor sends, the requests
// that keep the Core Rule Set busiest, within the bounds above. The last
// holds the most of everything at once: Cookie lines keep it busier than
// other header lines, and the JSON body of the most elements under a key
// keeps it busier than the other bodies.
func worstCaseRequests() []visitorRequest {
	fullCookieLine := cookieLine(1)[:fullLine-len("Cookie: ")]

	return append(
		append(worstCaseHeaders(), worstCaseBodies()...),
		visitorRequest{
			name:   "the longest request line, three Cookie lines and body",
			target: longestTarget()[:fullLine-len("POST  HTTP/1.1")],
			header: http.Header{cookieHeader: {
				fullCookieLine, fullCookieLine, fullCookieLine,
			}},
			contentType: jsonType, body: jsonOfMostElementsUnderAKey(),
		},
	)
}

// worstCaseHeaders are the requests of worstCaseRequests with no body.
func worstCaseHeaders() []visitorRequest {
	headerFields := http.Header{}

	for i := range mostHeaderFields - 1 {
		name := "X-Field-" + strconv.Itoa(i)
		headerFields.Set(
			name,
			headerValue(name, headerLimit/mostHeaderFields),
		)
	}

	return []visitorRequest{
		{name: "the longest request line", target: longestTarget()},
		{
			name: "the longest request line, as query parameters",
			target: "/?" + strings.Repeat(
				"a=1&",
				(lineLimit-len("POST /? HTTP/1.1"))/len("a=1&"),
			),
		},
		{
			name:   "the longest Cookie line, as one cookie",
			target: "/",
			header: http.Header{cookieHeader: {cookieLine(1)}},
		},
		{
			name:   "the longest Cookie line, as the most cookies",
			target: "/",
			header: http.Header{cookieHeader: {cookieLine(mostCookies)}},
		},
		{name: "the most header fields", target: "/", header: headerFields},
		{
			name:   "the longest header lines",
			target: "/",
			header: http.Header{
				"User-Agent": {headerValue("User-Agent", fullLine)},
				"Referer":    {headerValue("Referer", fullLine)},
				"Accept":     {headerValue("Accept", fullLine)},
				"X-Long":     {headerValue("X-Long", fullLine)},
			},
		},
	}
}

// worstCaseBodies are the requests of worstCaseRequests whose body holds
// the most the Core Rule Set reads.
func worstCaseBodies() []visitorRequest {
	const nested = (mostJSONRead - len(`{"a":1}`)) / len(`{"a":}`)

	return []visitorRequest{
		{
			name: "a form body of one field", target: "/",
			contentType: formType, body: formFields(1),
		},
		{
			name: "a form body of the most fields Coraza keeps", target: "/",
			contentType: formType, body: formFields(1000),
		},
		{
			name: "a JSON body of one string", target: "/",
			contentType: jsonType,
			body: `{"a":"` + text(
				mostJSONRead-len(`{"a":""}`),
			) + `"}`,
		},
		{
			name: "a JSON body of the most elements", target: "/",
			contentType: jsonType, body: jsonArrayOfMostElements(),
		},
		{
			name: "a JSON body of the most elements under a key", target: "/",
			contentType: jsonType, body: jsonOfMostElementsUnderAKey(),
		},
		{
			name: "a JSON body nested deep", target: "/",
			contentType: jsonType,
			body: strings.Repeat(`{"a":`, nested) + "1" +
				strings.Repeat("}", nested),
		},
		{
			name: "an XML body of many elements", target: "/",
			contentType: "application/xml",
			body: "<a>" + strings.Repeat(
				"<b>x</b>",
				(mostBodyRead-len("<a></a>"))/len("<b>x</b>"),
			) + "</a>",
		},
		{
			name: "a multipart body of one field", target: "/",
			contentType: multipartType, body: multipartBody(mostBodyRead),
		},
		{
			name: "a multipart body of many fields", target: "/",
			contentType: multipartType, body: multipartBody(1),
		},
	}
}

// inspectionTime returns how long crs takes to inspect tc, and fails t unless
// it reads all of tc's body and Coraza parses it.
func inspectionTime(
	t *testing.T, crs *coreruleset.CoreRuleSet, tc visitorRequest,
) time.Duration {
	t.Helper()

	req := httptest.NewRequestWithContext(
		t.Context(), http.MethodPost, tc.target, nil,
	)
	maps.Copy(req.Header, tc.header)

	if tc.contentType != "" {
		req.Header.Set("Content-Type", tc.contentType)
	}

	began := time.Now()
	result, read, _ := crs.Inspect(
		req, netip.MustParseAddr("192.0.2.1"), strings.NewReader(tc.body),
	)
	took := time.Since(began)

	if string(read) != tc.body {
		t.Errorf("read %d bytes of %d", len(read), len(tc.body))
	}

	// Rule 900440 matches a body Coraza could not parse.
	if slices.Contains(result.RuleIDs, 900440) {
		t.Errorf("Coraza could not parse the body")
	}

	return took
}

// TestTheCoreRuleSetInspectsEachWorstCaseRequestInTime runs one at a time, so
// that the tests running in parallel do not slow it. Other work on the host
// can still slow one try, so a request fails only when three tries in a row
// take too long.
//
//nolint:paralleltest // one at a time, as above
func TestTheCoreRuleSetInspectsEachWorstCaseRequestInTime(t *testing.T) {
	const tries = 3

	// The settings that make the Core Rule Set slowest: the highest paranoia
	// level, no rule switched off, and the most of a body read.
	crs := shared(t, coreruleset.Params{
		ParanoiaLevel: 4, BodyInspectionSize: mostBodyRead,
	})

	for _, tc := range worstCaseRequests() {
		t.Run(tc.name, func(t *testing.T) {
			var took time.Duration

			for range tries {
				took = inspectionTime(t, crs, tc)
				if took <= inspectionTimeLimit {
					return
				}
			}

			t.Errorf(
				"took %s on the last of %d tries, over %s",
				took, tries, inspectionTimeLimit,
			)
		})
	}
}