// Package middleware provides HTTP middleware.
package middleware

import (
	"context"
	"log/slog"
	"math"
	"net"
	"net/http"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/99designs/basicauth-go"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/go-chi/cors"
	"github.com/gorilla/csrf"
	"go.uber.org/fx"
	"golang.org/x/time/rate"

	"git.eeqj.de/sneak/upaas/internal/config"
	"git.eeqj.de/sneak/upaas/internal/database"
	"git.eeqj.de/sneak/upaas/internal/globals"
	"git.eeqj.de/sneak/upaas/internal/logger"
	"git.eeqj.de/sneak/upaas/internal/models"
	"git.eeqj.de/sneak/upaas/internal/service/auth"
)

// corsMaxAge is the maximum age for CORS preflight responses in seconds.
const corsMaxAge = 300

// apiUserContextKey is the context key for the authenticated API user.
type apiUserContextKey struct{}

// Params contains dependencies for Middleware.
type Params struct {
	fx.In

	Logger   *logger.Logger
	Globals  *globals.Globals
	Config   *config.Config
	Auth     *auth.Service
	Database *database.Database
}

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

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

// loggingResponseWriter wraps http.ResponseWriter to capture status code.
type loggingResponseWriter struct {
	http.ResponseWriter

	statusCode int
}

func newLoggingResponseWriter(
	writer http.ResponseWriter,
) *loggingResponseWriter {
	return &loggingResponseWriter{writer, http.StatusOK}
}

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

// Logging returns a request logging middleware.
func (m *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 := middleware.GetReqID(ctx)
				m.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", realIP(request),
					"status", lrw.statusCode,
					"latency_ms", latency.Milliseconds(),
				)
			}()

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

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

	return host
}

// trustedProxyNets are RFC1918 and loopback CIDRs whose proxy headers we trust.
//
//nolint:gochecknoglobals // package-level constant nets parsed once
var trustedProxyNets = func() []*net.IPNet {
	cidrs := []string{
		"10.0.0.0/8",
		"172.16.0.0/12",
		"192.168.0.0/16",
		"127.0.0.0/8",
		"::1/128",
		"fc00::/7",
	}

	nets := make([]*net.IPNet, 0, len(cidrs))

	for _, cidr := range cidrs {
		_, n, _ := net.ParseCIDR(cidr)
		nets = append(nets, n)
	}

	return nets
}()

// isTrustedProxy reports whether ip is in an RFC1918, loopback, or ULA range.
func isTrustedProxy(ip net.IP) bool {
	for _, n := range trustedProxyNets {
		if n.Contains(ip) {
			return true
		}
	}

	return false
}

// realIP extracts the client's real IP address from the request.
// Proxy headers (X-Real-IP, X-Forwarded-For) are only trusted when the
// direct connection originates from an RFC1918/loopback address.
// Otherwise, headers are ignored and RemoteAddr is used (fail closed).
func realIP(r *http.Request) string {
	addr := ipFromHostPort(r.RemoteAddr)
	remoteIP := net.ParseIP(addr)

	// Only trust proxy headers from private/loopback sources.
	if remoteIP == nil || !isTrustedProxy(remoteIP) {
		return addr
	}

	// 1. X-Real-IP (set by Traefik/nginx)
	if ip := strings.TrimSpace(r.Header.Get("X-Real-IP")); ip != "" {
		return ip
	}

	// 2. X-Forwarded-For: take the first (leftmost/client) IP
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		if parts := strings.SplitN(xff, ",", 2); len(parts) > 0 { //nolint:mnd
			if ip := strings.TrimSpace(parts[0]); ip != "" {
				return ip
			}
		}
	}

	// 3. Fall back to RemoteAddr
	return addr
}

// CORS returns CORS middleware.
func (m *Middleware) CORS() func(http.Handler) http.Handler {
	return cors.Handler(cors.Options{
		AllowedOrigins:   []string{"*"},
		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "X-CSRF-Token"},
		ExposedHeaders:   []string{"Link"},
		AllowCredentials: false,
		MaxAge:           corsMaxAge,
	})
}

// MetricsAuth returns basic auth middleware for metrics endpoint.
func (m *Middleware) MetricsAuth() func(http.Handler) http.Handler {
	if m.params.Config.MetricsUsername == "" {
		return func(next http.Handler) http.Handler {
			return next
		}
	}

	return basicauth.New(
		"metrics",
		map[string][]string{
			m.params.Config.MetricsUsername: {m.params.Config.MetricsPassword},
		},
	)
}

// SessionAuth returns middleware that requires authentication.
func (m *Middleware) SessionAuth() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			writer http.ResponseWriter,
			request *http.Request,
		) {
			user, err := m.params.Auth.GetCurrentUser(request.Context(), request)
			if err != nil || user == nil {
				http.Redirect(writer, request, "/login", http.StatusSeeOther)

				return
			}

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

// CSRF returns CSRF protection middleware using gorilla/csrf.
func (m *Middleware) CSRF() func(http.Handler) http.Handler {
	return csrf.Protect(
		[]byte(m.params.Config.SessionSecret),
		csrf.Secure(false), // Allow HTTP for development; reverse proxy handles TLS
		csrf.Path("/"),
	)
}

// loginRateLimit configures the login rate limiter.
const (
	loginRateLimit      = rate.Limit(5.0 / 60.0) // 5 requests per 60 seconds
	loginBurst          = 5                       // allow burst of 5
	limiterExpiry       = 10 * time.Minute        // evict entries not seen in 10 minutes
	limiterCleanupEvery = 1 * time.Minute         // sweep interval
)

// ipLimiterEntry stores a rate limiter with its last-seen timestamp.
type ipLimiterEntry struct {
	limiter  *rate.Limiter
	lastSeen time.Time
}

// ipLimiter tracks per-IP rate limiters for login attempts with automatic
// eviction of stale entries to prevent unbounded memory growth.
type ipLimiter struct {
	mu       sync.Mutex
	limiters map[string]*ipLimiterEntry
	lastSweep time.Time
}

func newIPLimiter() *ipLimiter {
	return &ipLimiter{
		limiters:  make(map[string]*ipLimiterEntry),
		lastSweep: time.Now(),
	}
}

// sweep removes entries not seen within limiterExpiry. Must be called with mu held.
func (i *ipLimiter) sweep(now time.Time) {
	for ip, entry := range i.limiters {
		if now.Sub(entry.lastSeen) > limiterExpiry {
			delete(i.limiters, ip)
		}
	}

	i.lastSweep = now
}

func (i *ipLimiter) getLimiter(ip string) *rate.Limiter {
	i.mu.Lock()
	defer i.mu.Unlock()

	now := time.Now()

	// Lazy sweep: clean up stale entries periodically.
	if now.Sub(i.lastSweep) >= limiterCleanupEvery {
		i.sweep(now)
	}

	entry, exists := i.limiters[ip]
	if !exists {
		entry = &ipLimiterEntry{
			limiter: rate.NewLimiter(loginRateLimit, loginBurst),
		}
		i.limiters[ip] = entry
	}

	entry.lastSeen = now

	return entry.limiter
}

// loginLimiter is the singleton IP rate limiter for login attempts.
//
//nolint:gochecknoglobals // intentional singleton for rate limiting state
var loginLimiter = newIPLimiter()

// LoginRateLimit returns middleware that rate-limits login attempts per IP.
// It allows 5 attempts per minute and returns 429 Too Many Requests when exceeded.
func (m *Middleware) LoginRateLimit() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			writer http.ResponseWriter,
			request *http.Request,
		) {
			ip := realIP(request)
			limiter := loginLimiter.getLimiter(ip)

			if !limiter.Allow() {
				m.log.WarnContext(request.Context(), "login rate limit exceeded",
					"remoteIP", ip,
				)

				// Compute seconds until the next token is available.
				reservation := limiter.Reserve()
				delay := reservation.Delay()
				reservation.Cancel()

				retryAfter := max(int(math.Ceil(delay.Seconds())), 1)
				writer.Header().Set("Retry-After", strconv.Itoa(retryAfter))

				http.Error(
					writer,
					"Too Many Requests",
					http.StatusTooManyRequests,
				)

				return
			}

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

// APITokenAuth returns middleware that authenticates requests via Bearer token.
// It looks up the token hash in the database and stores the user in context.
func (m *Middleware) APITokenAuth() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			writer http.ResponseWriter,
			request *http.Request,
		) {
			authHeader := request.Header.Get("Authorization")
			if authHeader == "" {
				http.Error(writer, `{"error":"missing Authorization header"}`, http.StatusUnauthorized)

				return
			}

			const bearerPrefix = "Bearer "
			if !strings.HasPrefix(authHeader, bearerPrefix) {
				http.Error(writer, `{"error":"invalid Authorization header"}`, http.StatusUnauthorized)

				return
			}

			rawToken := strings.TrimPrefix(authHeader, bearerPrefix)
			if rawToken == "" {
				http.Error(writer, `{"error":"empty token"}`, http.StatusUnauthorized)

				return
			}

			hash := models.HashAPIToken(rawToken)

			apiToken, err := models.FindAPITokenByHash(request.Context(), m.params.Database, hash)
			if err != nil {
				m.log.Error("api token lookup error", "error", err)
				http.Error(writer, `{"error":"internal server error"}`, http.StatusInternalServerError)

				return
			}

			if apiToken == nil {
				http.Error(writer, `{"error":"invalid token"}`, http.StatusUnauthorized)

				return
			}

			// Touch last used (best-effort, don't block on error)
			_ = apiToken.TouchLastUsed(request.Context())

			user, userErr := models.FindUser(request.Context(), m.params.Database, apiToken.UserID)
			if userErr != nil || user == nil {
				http.Error(writer, `{"error":"token user not found"}`, http.StatusUnauthorized)

				return
			}

			ctx := context.WithValue(request.Context(), apiUserContextKey{}, user)
			next.ServeHTTP(writer, request.WithContext(ctx))
		})
	}
}

// APIUserFromContext extracts the authenticated API user from the context.
func APIUserFromContext(ctx context.Context) *models.User {
	user, _ := ctx.Value(apiUserContextKey{}).(*models.User)

	return user
}

// SetupRequired returns middleware that redirects to setup if no user exists.
func (m *Middleware) SetupRequired() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			writer http.ResponseWriter,
			request *http.Request,
		) {
			setupRequired, err := m.params.Auth.IsSetupRequired(request.Context())
			if err != nil {
				m.log.Error("failed to check setup status", "error", err)
				http.Error(
					writer,
					"Internal Server Error",
					http.StatusInternalServerError,
				)

				return
			}

			if setupRequired {
				// Allow access to setup page
				if request.URL.Path == "/setup" {
					next.ServeHTTP(writer, request)

					return
				}

				http.Redirect(writer, request, "/setup", http.StatusSeeOther)

				return
			}

			// Block setup page if already set up
			if request.URL.Path == "/setup" {
				http.Redirect(writer, request, "/", http.StatusSeeOther)

				return
			}

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