package web

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"net"
	"net/http"
	"sync"
	"time"
)

const (
	sessionCookieName = "opengfw_session"
	sessionTTL        = 7 * 24 * time.Hour
	maxLoginFailures  = 8
	loginBanDuration  = 5 * time.Minute
)

type authenticator struct {
	secret string

	mu       sync.Mutex
	sessions map[string]time.Time // token -> expiry
	failures map[string]*failureRecord
}

type failureRecord struct {
	count int
	until time.Time
}

func newAuthenticator(secret string) *authenticator {
	return &authenticator{
		secret:   secret,
		sessions: make(map[string]time.Time),
		failures: make(map[string]*failureRecord),
	}
}

// RandomSecret generates a secret to be used when the user did not set one.
func RandomSecret() string {
	b := make([]byte, 12)
	if _, err := rand.Read(b); err != nil {
		return "opengfw"
	}
	return hex.EncodeToString(b)
}

func newToken() string {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return ""
	}
	return hex.EncodeToString(b)
}

// login verifies the password and returns a new session token.
func (a *authenticator) login(remoteAddr, password string) (string, time.Time, error) {
	ip := hostOnly(remoteAddr)
	a.mu.Lock()
	defer a.mu.Unlock()
	now := time.Now()
	if rec, ok := a.failures[ip]; ok && rec.count >= maxLoginFailures && now.Before(rec.until) {
		return "", time.Time{}, errTooManyAttempts
	}
	if subtle.ConstantTimeCompare([]byte(password), []byte(a.secret)) != 1 {
		rec, ok := a.failures[ip]
		if !ok || now.After(rec.until) {
			rec = &failureRecord{}
			a.failures[ip] = rec
		}
		rec.count++
		rec.until = now.Add(loginBanDuration)
		return "", time.Time{}, errBadCredentials
	}
	delete(a.failures, ip)
	token := newToken()
	if token == "" {
		return "", time.Time{}, errInternal
	}
	expiry := now.Add(sessionTTL)
	a.sessions[token] = expiry
	a.gcLocked(now)
	return token, expiry, nil
}

func (a *authenticator) logout(token string) {
	if token == "" {
		return
	}
	a.mu.Lock()
	delete(a.sessions, token)
	a.mu.Unlock()
}

func (a *authenticator) valid(token string) bool {
	if token == "" {
		return false
	}
	a.mu.Lock()
	defer a.mu.Unlock()
	expiry, ok := a.sessions[token]
	if !ok {
		return false
	}
	if time.Now().After(expiry) {
		delete(a.sessions, token)
		return false
	}
	return true
}

func (a *authenticator) gcLocked(now time.Time) {
	for t, exp := range a.sessions {
		if now.After(exp) {
			delete(a.sessions, t)
		}
	}
	for ip, rec := range a.failures {
		if now.After(rec.until) {
			delete(a.failures, ip)
		}
	}
}

// bearerToken returns the token carried by the Authorization header, if any.
func bearerToken(r *http.Request) string {
	const prefix = "Bearer "
	h := r.Header.Get("Authorization")
	if len(h) > len(prefix) && h[:len(prefix)] == prefix {
		return h[len(prefix):]
	}
	return ""
}

// cookieToken returns the token carried by the session cookie, if any.
func cookieToken(r *http.Request) string {
	c, err := r.Cookie(sessionCookieName)
	if err != nil {
		return ""
	}
	return c.Value
}

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