/*
 * ============================================================================
 * Projekt.....: rs2322tcp
 * Datei.......: session.go
 * Copyright (C) 2026 Dieter Lang
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 * Beschreibung:
 * Verwaltung des Lebenszyklus einer Client-Session einschließlich
 * der zugehörigen Netzwerkressourcen, Data-Listener und aktiven
 * Datenverbindungen.
 * ============================================================================
 */
package server

import (
	"fmt"
	"io"
	"net"
	"sync"
)

///////////////////////////////////////////////////////////////////////////////
// Session
///////////////////////////////////////////////////////////////////////////////

// Session represents one active client connection.
//
// All resources belonging to one client connection are associated with
// the session. This includes the control connection, dynamic data
// listeners and active data connections belonging to the configured
// remote devices.
type Session struct {
	id   uint64
	conn net.Conn

	mu              sync.Mutex
	closed          bool
	resources       []io.Closer
	dataListeners   map[string]*DataListener
	dataConnections map[string]*DataConnection
}

///////////////////////////////////////////////////////////////////////////////
// Constructor
///////////////////////////////////////////////////////////////////////////////

// NewSession creates a new client session.
func NewSession(id uint64, conn net.Conn) (*Session, error) {
	if conn == nil {
		return nil, fmt.Errorf("connection is nil")
	}

	if id == 0 {
		return nil, fmt.Errorf("session ID must not be zero")
	}

	return &Session{
		id:              id,
		conn:            conn,
		resources:       make([]io.Closer, 0),
		dataListeners:   make(map[string]*DataListener),
		dataConnections: make(map[string]*DataConnection),
	}, nil
}

///////////////////////////////////////////////////////////////////////////////
// Properties
///////////////////////////////////////////////////////////////////////////////

// ID returns the unique session ID.
func (s *Session) ID() uint64 {
	if s == nil {
		return 0
	}

	return s.id
}

// Conn returns the control connection belonging to the session.
func (s *Session) Conn() net.Conn {
	if s == nil {
		return nil
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	if s.closed {
		return nil
	}

	return s.conn
}

// IsClosed reports whether the session has already been closed.
func (s *Session) IsClosed() bool {
	if s == nil {
		return true
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	return s.closed
}

///////////////////////////////////////////////////////////////////////////////
// Resources
///////////////////////////////////////////////////////////////////////////////

// AddResource adds a resource to the session.
//
// The resource must implement io.Closer. It will automatically be closed
// when the session is closed.
//
// If the session is already closed, the resource is closed immediately
// and an error is returned.
func (s *Session) AddResource(resource io.Closer) error {
	if s == nil {
		if resource != nil {
			_ = resource.Close()
		}

		return fmt.Errorf("session is nil")
	}

	if resource == nil {
		return fmt.Errorf("resource is nil")
	}

	s.mu.Lock()

	if s.closed {
		s.mu.Unlock()

		_ = resource.Close()

		return fmt.Errorf("session is already closed")
	}

	s.resources = append(s.resources, resource)

	s.mu.Unlock()

	return nil
}

// ResourceCount returns the number of resources currently owned by the
// session.
//
// This method is primarily useful for diagnostics and tests.
func (s *Session) ResourceCount() int {
	if s == nil {
		return 0
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	return len(s.resources)
}

///////////////////////////////////////////////////////////////////////////////
// Data listeners
///////////////////////////////////////////////////////////////////////////////

// AddDataListener associates a dynamic data listener with a remote device.
//
// The listener becomes a session resource and is therefore automatically
// closed when the session is closed.
func (s *Session) AddDataListener(
	deviceID string,
	listener *DataListener,
) error {
	if s == nil {
		if listener != nil {
			_ = listener.Close()
		}

		return fmt.Errorf("session is nil")
	}

	if deviceID == "" {
		if listener != nil {
			_ = listener.Close()
		}

		return fmt.Errorf("device ID is empty")
	}

	if listener == nil {
		return fmt.Errorf("data listener is nil")
	}

	s.mu.Lock()

	if s.closed {
		s.mu.Unlock()

		_ = listener.Close()

		return fmt.Errorf("session is already closed")
	}

	if _, exists := s.dataListeners[deviceID]; exists {
		s.mu.Unlock()

		_ = listener.Close()

		return fmt.Errorf(
			"data listener already exists for device %q",
			deviceID,
		)
	}

	s.resources = append(s.resources, listener)
	s.dataListeners[deviceID] = listener

	s.mu.Unlock()

	return nil
}

// DataListener returns the data listener associated with a device.
//
// The second return value reports whether a listener exists for the
// specified device.
func (s *Session) DataListener(
	deviceID string,
) (*DataListener, bool) {
	if s == nil {
		return nil, false
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	if s.closed {
		return nil, false
	}

	listener, ok := s.dataListeners[deviceID]

	return listener, ok
}

// DataPort returns the dynamic TCP data port associated with a device.
//
// It returns 0 if the device has no listener or the session is closed.
func (s *Session) DataPort(deviceID string) int {
	listener, ok := s.DataListener(deviceID)
	if !ok {
		return 0
	}

	return listener.Port()
}

// DataListenerCount returns the number of data listeners currently
// associated with the session.
func (s *Session) DataListenerCount() int {
	if s == nil {
		return 0
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	return len(s.dataListeners)
}

///////////////////////////////////////////////////////////////////////////////
// Active data connections
///////////////////////////////////////////////////////////////////////////////

// AddDataConnection associates an active data connection with a remote
// device.
//
// Only one active data connection is allowed per device. The data
// connection becomes a session resource and is therefore automatically
// closed when the session is closed.
func (s *Session) AddDataConnection(
	deviceID string,
	connection *DataConnection,
) error {
	if s == nil {
		if connection != nil {
			_ = connection.Close()
		}

		return fmt.Errorf("session is nil")
	}

	if deviceID == "" {
		if connection != nil {
			_ = connection.Close()
		}

		return fmt.Errorf("device ID is empty")
	}

	if connection == nil {
		return fmt.Errorf("data connection is nil")
	}

	s.mu.Lock()

	if s.closed {
		s.mu.Unlock()

		_ = connection.Close()

		return fmt.Errorf("session is already closed")
	}

	if _, exists := s.dataConnections[deviceID]; exists {
		s.mu.Unlock()

		_ = connection.Close()

		return fmt.Errorf(
			"data connection already exists for device %q",
			deviceID,
		)
	}

	s.resources = append(s.resources, connection)
	s.dataConnections[deviceID] = connection

	s.mu.Unlock()

	return nil
}

// DataConnection returns the active data connection associated with a
// device.
//
// The second return value reports whether an active connection exists.
func (s *Session) DataConnection(
	deviceID string,
) (*DataConnection, bool) {
	if s == nil {
		return nil, false
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	if s.closed {
		return nil, false
	}

	connection, ok := s.dataConnections[deviceID]

	return connection, ok
}

// RemoveDataConnection removes an active data connection from the
// session.
//
// The connection is closed before it is removed from the session.
// Removing a connection that is not registered is harmless.
func (s *Session) RemoveDataConnection(deviceID string) error {
	if s == nil {
		return nil
	}

	s.mu.Lock()

	connection, exists := s.dataConnections[deviceID]
	if !exists {
		s.mu.Unlock()
		return nil
	}

	delete(s.dataConnections, deviceID)

	for i, resource := range s.resources {
		if resource == connection {
			s.resources = append(
				s.resources[:i],
				s.resources[i+1:]...,
			)
			break
		}
	}

	s.mu.Unlock()

	return connection.Close()
}

// DataConnectionCount returns the number of currently active data
// connections.
func (s *Session) DataConnectionCount() int {
	if s == nil {
		return 0
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	return len(s.dataConnections)
}

///////////////////////////////////////////////////////////////////////////////
// Lifecycle
///////////////////////////////////////////////////////////////////////////////

// Close terminates the session and releases all resources belonging
// to the session.
//
// Close is safe to call multiple times.
//
// Data listeners and other session resources are closed before the
// control connection is closed.
func (s *Session) Close() error {
	if s == nil {
		return nil
	}

	s.mu.Lock()

	if s.closed {
		s.mu.Unlock()
		return nil
	}

	s.closed = true

	conn := s.conn
	s.conn = nil

	resources := s.resources
	s.resources = nil
	s.dataListeners = nil
	s.dataConnections = nil

	s.mu.Unlock()

	var firstErr error

	for _, resource := range resources {
		if resource == nil {
			continue
		}

		if err := resource.Close(); err != nil && firstErr == nil {
			firstErr = err
		}
	}

	if conn != nil {
		if err := conn.Close(); err != nil && firstErr == nil {
			firstErr = err
		}
	}

	return firstErr
}