// Package middleware provides HTTP middleware for the neoirc server.
package middleware

import (
	"log/slog"
	"net"
	"net/http"
	"net/netip"
	"slices"
	"strings"
	"time"

	basicauth "github.com/99designs/basicauth-go"
	chimw "github.com/go-chi/chi/v5/middleware"
	metrics "github.com/slok/go-http-metrics/metrics/prometheus"
	ghmm "github.com/slok/go-http-metrics/middleware"
	"github.com/slok/go-http-metrics/middleware/std"
	"github.com/spf13/viper"
	"go.uber.org/fx"
	"go4.org/netipx"
	"sneak.berlin/go/neoirc/internal/config"
	"sneak.berlin/go/neoirc/internal/globals"
	"sneak.berlin/go/neoirc/internal/logger"
)

// Params defines the dependencies for creating Middleware.
type Params struct {
	fx.In

	Logger  *logger.Logger
	Globals *globals.Globals
	Config  *config.Config
}

// Middleware provides HTTP middleware handlers.
type Middleware struct {
	log    *slog.Logger
	params *Params
}

// New creates a new Middleware instance.
func New(
	_ fx.Lifecycle, params Params,
) (*Middleware, error) {
	mware := &Middleware{
		params: &params,
		log:    params.Logger.Get(),
	}

	return mware, nil
}

func ipFromHostPort(hostPort string) string {
	host, _, err := net.SplitHostPort(hostPort)
	if err != nil {
		return ""
	}

	if len(host) > 0 && host[0] == '[' {
		return host[1 : len(host)-1]
	}

	return host
}

// ClientIP returns middleware that replaces request.RemoteAddr with the
// client's address and keeps the port of the TCP connection. The
// X-Forwarded-For and X-Real-IP headers count only when the connection
// comes from an address in TRUSTED_PROXIES.
func (mware *Middleware) ClientIP() func(http.Handler) http.Handler {
	trusted := mware.params.Config.TrustedProxies

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(
			func(
				writer http.ResponseWriter,
				request *http.Request,
			) {
				peer, err := netip.ParseAddrPort(request.RemoteAddr)
				if err == nil {
					client := clientAddr(
						peer.Addr().Unmap(), request.Header, trusted,
					)
					request.RemoteAddr = netip.AddrPortFrom(
						client, peer.Port(),
					).String()
				}

				next.ServeHTTP(writer, request)
			})
	}
}

// clientAddr returns the client's address for a request from peer. A
// peer outside trusted is the client, whatever its headers say. A
// trusted peer is a proxy. Its X-Forwarded-For list is read from the
// right, past the trusted addresses, to the first untrusted one; when
// all are trusted, the client is the leftmost. Without X-Forwarded-For,
// the client is X-Real-IP. An entry that is not an IP address gives
// peer.
func clientAddr(
	peer netip.Addr, header http.Header, trusted *netipx.IPSet,
) netip.Addr {
	if !trusted.Contains(peer) {
		return peer
	}

	forwarded := strings.Join(header.Values("X-Forwarded-For"), ",")
	if forwarded == "" {
		realIP, err := netip.ParseAddr(
			strings.TrimSpace(header.Get("X-Real-IP")),
		)
		if err != nil {
			return peer
		}

		return realIP.Unmap()
	}

	client := peer

	for _, entry := range slices.Backward(strings.Split(forwarded, ",")) {
		addr, err := netip.ParseAddr(strings.TrimSpace(entry))
		if err != nil {
			return peer
		}

		client = addr.Unmap()
		if !trusted.Contains(client) {
			break
		}
	}

	return client
}

type loggingResponseWriter struct {
	http.ResponseWriter

	statusCode int
}

// newLoggingResponseWriter wraps a ResponseWriter
// to capture the status code.
func newLoggingResponseWriter(
	writer http.ResponseWriter,
) *loggingResponseWriter {
	return &loggingResponseWriter{
		ResponseWriter: writer,
		statusCode:     http.StatusOK,
	}
}

func (lrw *loggingResponseWriter) WriteHeader(code int) {
	lrw.statusCode = code
	lrw.ResponseWriter.WriteHeader(code)
}

// Logging returns middleware that logs each HTTP request.
func (mware *Middleware) Logging() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(
			func(
				writer http.ResponseWriter,
				request *http.Request,
			) {
				start := time.Now()
				lrw := newLoggingResponseWriter(writer)
				ctx := request.Context()

				defer func() {
					latency := time.Since(start)

					reqID, _ := ctx.Value(
						chimw.RequestIDKey,
					).(string)

					mware.log.InfoContext(
						ctx, "request",
						"request_start", start,
						"method", request.Method,
						"url", request.URL.String(),
						"useragent", request.UserAgent(),
						"request_id", reqID,
						"referer", request.Referer(),
						"proto", request.Proto,
						"remoteIP",
						ipFromHostPort(request.RemoteAddr),
						"status", lrw.statusCode,
						"latency_ms",
						latency.Milliseconds(),
					)
				}()

				next.ServeHTTP(lrw, request)
			})
	}
}

// Metrics returns middleware that records HTTP metrics.
func (mware *Middleware) Metrics() func(http.Handler) http.Handler {
	metricsMiddleware := ghmm.New(ghmm.Config{ //nolint:exhaustruct // optional fields
		Recorder: metrics.NewRecorder(
			metrics.Config{}, //nolint:exhaustruct // defaults
		),
	})

	return func(next http.Handler) http.Handler {
		return std.Handler("", metricsMiddleware, next)
	}
}

// MetricsAuth returns middleware that protects metrics with basic auth.
func (mware *Middleware) MetricsAuth() func(http.Handler) http.Handler {
	return basicauth.New(
		"metrics",
		map[string][]string{
			viper.GetString("METRICS_USERNAME"): {
				viper.GetString("METRICS_PASSWORD"),
			},
		},
	)
}

// cspPolicy is the Content-Security-Policy header value applied to all
// responses.  The embedded SPA loads scripts and styles from same-origin
// files only (no inline scripts or inline style attributes), so a strict
// policy works without 'unsafe-inline'.
const cspPolicy = "default-src 'self'; " +
	"script-src 'self'; " +
	"style-src 'self'; " +
	"connect-src 'self'; " +
	"img-src 'self'; " +
	"font-src 'self'; " +
	"object-src 'none'; " +
	"frame-ancestors 'none'; " +
	"base-uri 'self'; " +
	"form-action 'self'"

// CSP returns middleware that sets the Content-Security-Policy header on
// every response for defense-in-depth against XSS.
func (mware *Middleware) CSP() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(
			func(
				writer http.ResponseWriter,
				request *http.Request,
			) {
				writer.Header().Set(
					"Content-Security-Policy",
					cspPolicy,
				)
				next.ServeHTTP(writer, request)
			})
	}
}