package proxy_test

import (
	"bufio"
	"bytes"
	"encoding/json"
	"io"
	"maps"
	"net"
	"net/http"
	"net/http/httptest"
	"strings"
	"sync"
	"testing"
	"time"

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

const (
	// shortTimeout is what a test sets a timeout to, to see it run out.
	shortTimeout = 300 * time.Millisecond
	// shortTimeoutSetting is shortTimeout as a setting's value.
	shortTimeoutSetting = "300ms"
	// longTimeoutSetting is a timeout that does not run out in a test.
	longTimeoutSetting = "10s"
	// waitLimit bounds how long a test waits for what should happen.
	waitLimit = 10 * time.Second
	// pollInterval is how often a test looks for a log line.
	pollInterval = 10 * time.Millisecond
	// localhost is where every test server listens, and so the address
	// smallwebwaf sees each test's requests come from.
	localhost = "127.0.0.1"
)

// The settings the tests set.
const (
	clientRequestTimeout    = "SWWAF_CLIENT_REQUEST_TIMEOUT"
	clientResponseTimeout   = "SWWAF_CLIENT_RESPONSE_TIMEOUT"
	upstreamRequestTimeout  = "SWWAF_UPSTREAM_REQUEST_TIMEOUT"
	upstreamResponseTimeout = "SWWAF_UPSTREAM_RESPONSE_TIMEOUT"
	requestMaxBytes         = "SWWAF_REQUEST_MAX_BYTES"
	responseMaxBytes        = "SWWAF_RESPONSE_MAX_BYTES"
	trustedProxies          = "SWWAF_TRUSTED_PROXIES"
	rateLimitPerMinute      = "SWWAF_RATE_LIMIT_PER_MINUTE"
)

// output collects what smallwebwaf writes on stdout.
type output struct {
	mu  sync.Mutex
	buf bytes.Buffer
}

// Write adds lines smallwebwaf writes.
func (o *output) Write(p []byte) (int, error) {
	o.mu.Lock()
	defer o.mu.Unlock()

	return o.buf.Write(p)
}

// lines returns every line written so far, decoded.
func (o *output) lines(t *testing.T) []map[string]any {
	t.Helper()
	o.mu.Lock()
	defer o.mu.Unlock()

	var lines []map[string]any

	for text := range strings.Lines(o.buf.String()) {
		var line map[string]any

		err := json.Unmarshal([]byte(text), &line)
		if err != nil {
			t.Fatalf("output line %q is not JSON: %v", text, err)
		}

		lines = append(lines, line)
	}

	return lines
}

// logLine is a request log line, as typed fields and as the JSON object
// it was written as.
type logLine struct {
	requestlog.Line

	fields map[string]any
}

// requestLines waits for count request log lines and returns them.
func (o *output) requestLines(t *testing.T, count int) []logLine {
	t.Helper()

	deadline := time.Now().Add(waitLimit)
	for time.Now().Before(deadline) {
		var found []logLine

		for _, fields := range o.lines(t) {
			if fields["type"] == "request" {
				found = append(found, decodeLine(t, fields))
			}
		}

		if len(found) >= count {
			return found
		}

		time.Sleep(pollInterval)
	}

	t.Fatalf("fewer than %d request log lines after %s", count, waitLimit)

	return nil
}

// requestLine waits for the request log line of a test's one request.
func (o *output) requestLine(t *testing.T) logLine {
	t.Helper()

	return o.requestLines(t, 1)[0]
}

// decodeLine reads a request log line's fields into a logLine.
func decodeLine(t *testing.T, fields map[string]any) logLine {
	t.Helper()

	encoded, err := json.Marshal(fields)
	if err != nil {
		t.Fatalf("encode %v: %v", fields, err)
	}

	line := logLine{fields: fields}

	err = json.Unmarshal(encoded, &line.Line)
	if err != nil {
		t.Fatalf("decode %s: %v", encoded, err)
	}

	return line
}

// startApp starts app as the app smallwebwaf passes requests to.
func startApp(t *testing.T, app http.HandlerFunc) *httptest.Server {
	t.Helper()

	server := httptest.NewServer(app)
	t.Cleanup(server.Close)

	return server
}

// startProxy starts smallwebwaf in front of the app at appURL, with the
// settings in env on top of the defaults, and returns where it listens and
// what it writes.
func startProxy(t *testing.T, appURL string, env map[string]string) (string, *output) {
	t.Helper()

	settings := map[string]string{"SWWAF_UPSTREAM_URL": appURL}
	maps.Copy(settings, env)

	cfg, err := config.FromEnvironment(func(name string) (string, bool) {
		value, ok := settings[name]

		return value, ok
	})
	if err != nil {
		t.Fatalf("settings %v: %v", settings, err)
	}

	out := &output{}
	server := proxy.New(proxy.Params{
		Config:     cfg,
		RequestLog: out,
		ProcessLog: requestlog.NewProcessLogger(out),
	})

	listener, err := (&net.ListenConfig{}).Listen(t.Context(), "tcp", localhost+":0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}

	go func() {
		_ = server.Serve(listener)
	}()

	t.Cleanup(func() {
		_ = server.Close()
	})

	return listener.Addr().String(), out
}

// newClient returns an HTTP client that sends requests as they are made,
// with no compression of its own.
func newClient(t *testing.T) *http.Client {
	t.Helper()

	transport := &http.Transport{DisableCompression: true}
	t.Cleanup(transport.CloseIdleConnections)

	return &http.Client{Transport: transport}
}

// answer is a response as a test reads it: the status, the headers, as
// much of the body as arrived, and the error that ended the reading, nil
// when the whole body arrived.
type answer struct {
	status int
	header http.Header
	body   []byte
	err    error
}

// readAnswer reads all of res, and closes its body.
func readAnswer(res *http.Response) answer {
	body, err := io.ReadAll(res.Body)
	_ = res.Body.Close()

	return answer{status: res.StatusCode, header: res.Header, body: body, err: err}
}

// newRequest makes a request for path to smallwebwaf at addr.
func newRequest(t *testing.T, method, addr, path string, body io.Reader) *http.Request {
	t.Helper()

	req, err := http.NewRequestWithContext(t.Context(), method, "http://"+addr+path, body)
	if err != nil {
		t.Fatalf("new request: %v", err)
	}

	return req
}

// do sends req and reads the answer.
func do(t *testing.T, req *http.Request) answer {
	t.Helper()

	res, err := newClient(t).Do(req)
	if err != nil {
		t.Fatalf("%s %s: %v", req.Method, req.URL.Path, err)
	}

	return readAnswer(res)
}

// get sends a GET request for path to smallwebwaf at addr.
func get(t *testing.T, addr, path string) answer {
	t.Helper()

	return do(t, newRequest(t, http.MethodGet, addr, path, http.NoBody))
}

// dial opens a connection to smallwebwaf at addr, for requests the HTTP
// client cannot make, such as one that stops sending halfway.
func dial(t *testing.T, addr string) net.Conn {
	t.Helper()

	conn, err := (&net.Dialer{}).DialContext(t.Context(), "tcp", addr)
	if err != nil {
		t.Fatalf("dial %s: %v", addr, err)
	}

	t.Cleanup(func() {
		_ = conn.Close()
	})

	return conn
}

// send writes text to conn.
func send(t *testing.T, conn net.Conn, text string) {
	t.Helper()

	_, err := io.WriteString(conn, text)
	if err != nil {
		t.Fatalf("send: %v", err)
	}
}

// readResponse reads the answer to a request sent on conn.
func readResponse(t *testing.T, conn net.Conn) answer {
	t.Helper()

	err := conn.SetReadDeadline(time.Now().Add(waitLimit))
	if err != nil {
		t.Fatalf("set read deadline: %v", err)
	}

	res, err := http.ReadResponse(bufio.NewReader(conn), nil)
	if err != nil {
		t.Fatalf("read response: %v", err)
	}

	return readAnswer(res)
}

// wantLine checks the request log line's status and action.
func wantLine(t *testing.T, line logLine, status int, action string) {
	t.Helper()

	if line.Status != status || line.Action != action {
		t.Errorf("log line has status %d and action %q, want %d and %q",
			line.Status, line.Action, status, action)
	}
}

// wantStatus checks an answer's status.
func wantStatus(t *testing.T, got answer, status int) {
	t.Helper()

	if got.status != status {
		t.Errorf("status %d, want %d", got.status, status)
	}
}

// wantTimedOut checks that what began at start ended once shortTimeout
// had run out, and not much later.
func wantTimedOut(t *testing.T, start time.Time) {
	t.Helper()

	took := time.Since(start)
	if took < shortTimeout || took > shortTimeout+waitLimit/2 {
		t.Errorf("took %s, want %s", took, shortTimeout)
	}
}