package auth

import (
	"crypto/rand"
	"encoding/base64"
	"errors"
	"fmt"
	"net"
	"net/http"
	"strings"
	"sync"
	"time"

	"codeberg.org/SquidSE/ClusterCanvas/service/internal/settings"
)

const (
	SessionCookieName = "__Host-ClusterCanvas-Session"
	sessionIDBytes    = 32
	sessionRotateAfter = time.Hour
)

var (
	ErrSessionNotFound = errors.New("session not found")
	ErrSessionIdle     = errors.New("session idle")
)

// SessionManager persists sessions in sessions.enc and sets hardened cookies.
type SessionManager struct {
	configDir string
	key       []byte
	mu        sync.Mutex
}

func NewSessionManager(configDir string, key []byte) *SessionManager {
	return &SessionManager{configDir: configDir, key: key}
}

// CreateSession invalidates prior sessions for the user, stores a new session, and sets the cookie.
func (manager *SessionManager) CreateSession(
	writer http.ResponseWriter,
	userID string,
	security settings.SecuritySettings,
) (settings.SessionRecord, error) {
	manager.mu.Lock()
	defer manager.mu.Unlock()

	store, err := settings.LoadSessionsOrEmpty(manager.configDir, manager.key)
	if err != nil {
		return settings.SessionRecord{}, err
	}

	now := time.Now().UTC()
	lifetime := time.Duration(security.SessionLifetimeHours) * time.Hour
	filtered := make([]settings.SessionRecord, 0, len(store.Sessions))
	for _, session := range store.Sessions {
		if session.UserID == userID {
			continue
		}
		if session.ExpiresAt.Before(now) {
			continue
		}
		filtered = append(filtered, session)
	}

	sessionID, err := newSessionID()
	if err != nil {
		return settings.SessionRecord{}, err
	}

	record := settings.SessionRecord{
		ID:           sessionID,
		UserID:       userID,
		CreatedAt:    now,
		LastSeenAt:   now,
		LastReauthAt: now,
		ExpiresAt:    now.Add(lifetime),
	}
	filtered = append(filtered, record)
	store.Sessions = filtered

	if err := settings.SaveSessions(manager.configDir, store, manager.key); err != nil {
		return settings.SessionRecord{}, err
	}

	setSessionCookie(writer, sessionID, int(lifetime.Seconds()))
	return record, nil
}

// LookupValidSession finds a non-expired, non-idle session and may rotate it.
func (manager *SessionManager) LookupValidSession(
	writer http.ResponseWriter,
	request *http.Request,
	security settings.SecuritySettings,
) (settings.SessionRecord, error) {
	cookie, err := request.Cookie(SessionCookieName)
	if err != nil || strings.TrimSpace(cookie.Value) == "" {
		return settings.SessionRecord{}, ErrSessionNotFound
	}

	manager.mu.Lock()
	defer manager.mu.Unlock()

	store, err := settings.LoadSessionsOrEmpty(manager.configDir, manager.key)
	if err != nil {
		return settings.SessionRecord{}, err
	}

	now := time.Now().UTC()
	idleLimit := time.Duration(security.IdleTimeoutMinutes) * time.Minute
	lifetime := time.Duration(security.SessionLifetimeHours) * time.Hour

	var found *settings.SessionRecord
	idleMatched := false
	remaining := make([]settings.SessionRecord, 0, len(store.Sessions))
	for index := range store.Sessions {
		session := store.Sessions[index]
		if session.ExpiresAt.Before(now) {
			continue
		}
		if session.ID == cookie.Value {
			if now.Sub(session.LastSeenAt) > idleLimit {
				idleMatched = true
				continue
			}
			copySession := session
			found = &copySession
			continue
		}
		remaining = append(remaining, session)
	}

	if found == nil {
		store.Sessions = remaining
		_ = settings.SaveSessions(manager.configDir, store, manager.key)
		clearSessionCookie(writer)
		if idleMatched {
			return settings.SessionRecord{}, ErrSessionIdle
		}
		return settings.SessionRecord{}, ErrSessionNotFound
	}

	shouldRotate := now.Sub(found.CreatedAt) >= sessionRotateAfter ||
		now.Sub(found.CreatedAt) >= lifetime/2

	found.LastSeenAt = now
	if shouldRotate {
		newID, err := newSessionID()
		if err != nil {
			return settings.SessionRecord{}, err
		}
		found.ID = newID
		found.CreatedAt = now
		// LastReauthAt is preserved across rotation.
		setSessionCookie(writer, newID, int(found.ExpiresAt.Sub(now).Seconds()))
	}

	remaining = append(remaining, *found)
	store.Sessions = remaining
	if err := settings.SaveSessions(manager.configDir, store, manager.key); err != nil {
		return settings.SessionRecord{}, err
	}
	return *found, nil
}

// MarkReauth updates LastReauthAt for the session identified by sessionID.
func (manager *SessionManager) MarkReauth(sessionID string) error {
	manager.mu.Lock()
	defer manager.mu.Unlock()

	store, err := settings.LoadSessionsOrEmpty(manager.configDir, manager.key)
	if err != nil {
		return err
	}

	now := time.Now().UTC()
	found := false
	for index := range store.Sessions {
		if store.Sessions[index].ID != sessionID {
			continue
		}
		store.Sessions[index].LastReauthAt = now
		found = true
		break
	}
	if !found {
		return ErrSessionNotFound
	}
	return settings.SaveSessions(manager.configDir, store, manager.key)
}

// InvalidateUserSessions removes all persisted sessions for the given user ID.
func (manager *SessionManager) InvalidateUserSessions(userID string) error {
	manager.mu.Lock()
	defer manager.mu.Unlock()

	store, err := settings.LoadSessionsOrEmpty(manager.configDir, manager.key)
	if err != nil {
		return err
	}

	filtered := make([]settings.SessionRecord, 0, len(store.Sessions))
	for _, session := range store.Sessions {
		if session.UserID == userID {
			continue
		}
		filtered = append(filtered, session)
	}
	store.Sessions = filtered
	return settings.SaveSessions(manager.configDir, store, manager.key)
}

// DestroySession removes the presented session and clears the cookie.
func (manager *SessionManager) DestroySession(writer http.ResponseWriter, request *http.Request) error {
	cookie, err := request.Cookie(SessionCookieName)
	clearSessionCookie(writer)
	if err != nil || cookie.Value == "" {
		return nil
	}

	manager.mu.Lock()
	defer manager.mu.Unlock()

	store, err := settings.LoadSessionsOrEmpty(manager.configDir, manager.key)
	if err != nil {
		return err
	}

	filtered := make([]settings.SessionRecord, 0, len(store.Sessions))
	for _, session := range store.Sessions {
		if session.ID == cookie.Value {
			continue
		}
		filtered = append(filtered, session)
	}
	store.Sessions = filtered
	return settings.SaveSessions(manager.configDir, store, manager.key)
}

func newSessionID() (string, error) {
	buffer := make([]byte, sessionIDBytes)
	if _, err := rand.Read(buffer); err != nil {
		return "", fmt.Errorf("session id: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(buffer), nil
}

func setSessionCookie(writer http.ResponseWriter, sessionID string, maxAgeSeconds int) {
	if maxAgeSeconds < 0 {
		maxAgeSeconds = 0
	}
	http.SetCookie(writer, &http.Cookie{
		Name:     SessionCookieName,
		Value:    sessionID,
		Path:     "/",
		MaxAge:   maxAgeSeconds,
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteStrictMode,
	})
}

func clearSessionCookie(writer http.ResponseWriter) {
	http.SetCookie(writer, &http.Cookie{
		Name:     SessionCookieName,
		Value:    "",
		Path:     "/",
		MaxAge:   -1,
		HttpOnly: true,
		Secure:   true,
		SameSite: http.SameSiteStrictMode,
	})
}

// ClientIP extracts the remote IP, preferring X-Forwarded-For when present.
func ClientIP(request *http.Request) string {
	if forwarded := strings.TrimSpace(request.Header.Get("X-Forwarded-For")); forwarded != "" {
		parts := strings.Split(forwarded, ",")
		return strings.TrimSpace(parts[0])
	}
	host, _, err := net.SplitHostPort(request.RemoteAddr)
	if err != nil {
		return request.RemoteAddr
	}
	return host
}