package opcua

import (
	"context"
	"errors"
	"fmt"
	"log" //nolint:depguard // just for debug
	"net/url"
	"os"
	"strconv"
	"time"

	"github.com/gopcua/opcua"
	"github.com/gopcua/opcua/debug"
	"github.com/gopcua/opcua/ua"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"
)

type OpcUAWorkarounds struct {
	AdditionalValidStatusCodes []string `toml:"additional_valid_status_codes"`
}

type ConnectionState opcua.ConnState

const (
	Closed       ConnectionState = ConnectionState(opcua.Closed)
	Connected    ConnectionState = ConnectionState(opcua.Connected)
	Connecting   ConnectionState = ConnectionState(opcua.Connecting)
	Disconnected ConnectionState = ConnectionState(opcua.Disconnected)
	Reconnecting ConnectionState = ConnectionState(opcua.Reconnecting)
)

func (c ConnectionState) String() string {
	return opcua.ConnState(c).String()
}

type OpcUAClientConfig struct {
	Endpoint          string          `toml:"endpoint"`
	SecurityPolicy    string          `toml:"security_policy"`
	SecurityMode      string          `toml:"security_mode"`
	Certificate       string          `toml:"certificate"`
	PrivateKey        string          `toml:"private_key"`
	RemoteCertificate string          `toml:"remote_certificate"`
	Username          config.Secret   `toml:"username"`
	Password          config.Secret   `toml:"password"`
	AuthMethod        string          `toml:"auth_method"`
	ConnectTimeout    config.Duration `toml:"connect_timeout"`
	RequestTimeout    config.Duration `toml:"request_timeout"`
	ClientTrace       bool            `toml:"client_trace"`

	OptionalFields []string         `toml:"optional_fields"`
	Workarounds    OpcUAWorkarounds `toml:"workarounds"`
	SessionTimeout config.Duration  `toml:"session_timeout"`
	Locales        []string         `toml:"locales"`
}

func (o *OpcUAClientConfig) Validate() error {
	// Validate endpoint
	if o.Endpoint == "" {
		return fmt.Errorf("%w: endpoint cannot be empty", ErrInvalidEndpoint)
	}
	u, err := url.Parse(o.Endpoint)
	if err != nil {
		return fmt.Errorf("%w: invalid endpoint URL %q: %w", ErrInvalidEndpoint, o.Endpoint, err)
	}
	if u.Scheme != "opc.tcp" {
		return fmt.Errorf("%w: invalid endpoint scheme %q, expected 'opc.tcp'", ErrInvalidEndpoint, u.Scheme)
	}

	// Validate security policy
	switch o.SecurityPolicy {
	case "", "None", "Basic128Rsa15", "Basic256", "Basic256Sha256", "auto":
		// valid
	default:
		return fmt.Errorf("%w: %q, valid options: None, Basic128Rsa15, Basic256, Basic256Sha256, auto", ErrInvalidSecurityPolicy, o.SecurityPolicy)
	}

	// Validate security mode
	switch o.SecurityMode {
	case "", "None", "Sign", "SignAndEncrypt", "auto":
		// valid
	default:
		return fmt.Errorf("%w: %q, valid options: None, Sign, SignAndEncrypt, auto", ErrInvalidSecurityMode, o.SecurityMode)
	}

	// Validate authentication method
	switch o.AuthMethod {
	case "", "Anonymous", "UserName", "Certificate", "auto":
		// valid
	default:
		return fmt.Errorf("%w: %q, valid options: Anonymous, UserName, Certificate, auto", ErrInvalidAuthMethod, o.AuthMethod)
	}

	// Validate certificate configuration
	if err := o.validateCertificateConfiguration(); err != nil {
		return err
	}

	// Validate credentials based on auth method
	if o.AuthMethod == "UserName" {
		if o.Username.Empty() {
			return fmt.Errorf("%w: username required for UserName authentication", ErrInvalidConfiguration)
		}
		if o.Password.Empty() {
			return fmt.Errorf("%w: password required for UserName authentication", ErrInvalidConfiguration)
		}
	}

	// Validate optional fields
	for i, field := range o.OptionalFields {
		if field != "DataType" {
			return fmt.Errorf("%w: unknown optional_fields[%d] value %q, valid options: DataType", ErrInvalidConfiguration, i, field)
		}
	}

	// Validate timeouts
	if o.ConnectTimeout < 0 {
		return fmt.Errorf("%w: connect_timeout must be non-negative, got %v", ErrInvalidConfiguration, o.ConnectTimeout)
	}
	if o.ConnectTimeout != 0 && time.Duration(o.ConnectTimeout) < 100*time.Millisecond {
		return fmt.Errorf("%w: connect_timeout too short (%v), minimum recommended is 100ms", ErrInvalidConfiguration, o.ConnectTimeout)
	}

	if o.RequestTimeout < 0 {
		return fmt.Errorf("%w: request_timeout must be non-negative, got %v", ErrInvalidConfiguration, o.RequestTimeout)
	}
	if o.RequestTimeout != 0 && time.Duration(o.RequestTimeout) < 100*time.Millisecond {
		return fmt.Errorf("%w: request_timeout too short (%v), minimum recommended is 100ms", ErrInvalidConfiguration, o.RequestTimeout)
	}

	if o.SessionTimeout < 0 {
		return fmt.Errorf("%w: session_timeout must be non-negative, got %v", ErrInvalidConfiguration, o.SessionTimeout)
	}
	if o.SessionTimeout != 0 && time.Duration(o.SessionTimeout) < 1*time.Second {
		return fmt.Errorf("%w: session_timeout too short (%v), minimum recommended is 1s", ErrInvalidConfiguration, o.SessionTimeout)
	}

	return nil
}

func (o *OpcUAClientConfig) validateCertificateConfiguration() error {
	// If using None/None security, client certificates are optional
	if o.SecurityPolicy == "None" && o.SecurityMode == "None" {
		return nil
	}

	// Both empty is valid (will generate self-signed)
	if o.Certificate == "" && o.PrivateKey == "" {
		return nil
	}

	// Both must be provided if one is provided
	if o.Certificate == "" {
		return fmt.Errorf("%w: private key provided without certificate", ErrInvalidConfiguration)
	}
	if o.PrivateKey == "" {
		return fmt.Errorf("%w: certificate provided without private key", ErrInvalidConfiguration)
	}

	return nil
}

func (o *OpcUAClientConfig) CreateClient(telegrafLogger telegraf.Logger) (*OpcUAClient, error) {
	err := o.Validate()
	if err != nil {
		return nil, err
	}

	if o.ClientTrace {
		debug.Enable = true
		debug.Logger = log.New(&DebugLogger{Log: telegrafLogger}, "", 0)
	}

	c := &OpcUAClient{
		Config: o,
		Log:    telegrafLogger,
	}
	c.Log.Debug("Initialising OpcUAClient")

	err = c.setupWorkarounds()
	return c, err
}

type OpcUAClient struct {
	Config *OpcUAClientConfig
	Log    telegraf.Logger

	Client         *opcua.Client
	namespaceArray []string

	opts  []opcua.Option
	codes []ua.StatusCode

	// Internal flags
	DisableAutoReconnect bool
}

// determineOrCreateCertificates handles certificate determination and generation logic
func (o *OpcUAClient) determineOrCreateCertificates() error {
	certFile := o.Config.Certificate
	keyFile := o.Config.PrivateKey

	if certFile == "" && keyFile != "" || certFile != "" && keyFile == "" {
		return errors.New("specified only one of certificate or private key")
	}

	var generate, permanent bool
	if certFile == "" && keyFile == "" {
		// Case 1: Both empty, generate a non-permanent file
		generate = true
	} else {
		// Case 2 or 3: Both specified - check if files exist
		var certExists, keyExists bool
		if _, err := os.Stat(certFile); err == nil {
			certExists = true
		} else if !errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("checking certificate %q failed: %w", certFile, err)
		}
		if _, err := os.Stat(keyFile); err == nil {
			keyExists = true
		} else if !errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("checking private key %q failed: %w", keyFile, err)
		}

		// Either both certificate and private key exists or they don't, we don't support mixed setups
		if certExists != keyExists {
			return &CertificateError{
				Operation: "validation",
				Path:      keyFile,
				Err:       fmt.Errorf("only one of certificate %q and private key %q exists", certFile, keyFile),
			}
		}

		generate = !certExists && !keyExists
		permanent = true
	}

	// If both exist, we don't need to do anything, they will be loaded later
	if !generate {
		o.Log.Debugf("Using existing certificates from %q and %q", certFile, keyFile)
		return nil
	}

	if permanent {
		o.Log.Infof("Generating permanent self-signed certificate at %q and %q", certFile, keyFile)
	} else {
		o.Log.Debug("Generating temporary self-signed certificate")
	}

	// Generate the certificates
	cert, privateKey, err := generateCert("urn:telegraf:gopcua:client", 2048, certFile, keyFile, 365*24*time.Hour)
	if err != nil {
		return err
	}

	o.Config.Certificate = cert
	o.Config.PrivateKey = privateKey

	return nil
}

// SetupOptions reads the endpoints from the specified server and sets up all authentication
func (o *OpcUAClient) SetupOptions() error {
	ctx, cancel := context.WithTimeout(context.Background(), time.Duration(o.Config.ConnectTimeout))
	defer cancel()
	// Get a list of the endpoints for our target server
	endpoints, err := opcua.GetEndpoints(ctx, o.Config.Endpoint)
	if err != nil {
		return &EndpointError{
			Endpoint: o.Config.Endpoint,
			Err:      fmt.Errorf("failed to get endpoints: %w", err),
		}
	}

	// A client certificate is only needed when the channel is actually secured.
	// Setting either security_policy or security_mode to "None" collapses the
	// channel to None, so skip certificate creation (which may fail on a
	// read-only filesystem) unless both request security.
	if o.Config.SecurityPolicy != "None" && o.Config.SecurityMode != "None" {
		if err := o.determineOrCreateCertificates(); err != nil {
			return err
		}
	}

	o.Log.Debug("Configuring OPC UA connection options")
	o.opts, err = o.generateClientOpts(endpoints)

	return err
}

func (o *OpcUAClient) setupWorkarounds() error {
	o.codes = []ua.StatusCode{ua.StatusOK}
	for i, c := range o.Config.Workarounds.AdditionalValidStatusCodes {
		val, err := strconv.ParseUint(c, 0, 32) // setting 32 bits to allow for safe conversion
		if err != nil {
			return fmt.Errorf("%w: invalid status code %q at index %d: %w", ErrStatusCodeParsing, c, i, err)
		}
		o.codes = append(o.codes, ua.StatusCode(val))
	}

	return nil
}

func (o *OpcUAClient) StatusCodeOK(code ua.StatusCode) bool {
	for _, val := range o.codes {
		if val == code {
			return true
		}
	}
	return false
}

// Connect to an OPC UA device
func (o *OpcUAClient) Connect(ctx context.Context) error {
	o.Log.Debug("Connecting OPC UA Client to server")
	u, err := url.Parse(o.Config.Endpoint)
	if err != nil {
		return err
	}

	switch u.Scheme {
	case "opc.tcp":
		if err := o.SetupOptions(); err != nil {
			return err
		}

		if o.Client != nil {
			o.Log.Warnf("Closing connection to %q as already connected", u)
			if err := o.Client.Close(ctx); err != nil {
				// Only log the error but do not bail-out here as this prevents
				// reconnections for multiple parties (see e.g. #9523).
				o.Log.Errorf("Closing connection to %s failed: %v", o.Config.Endpoint, err)
			}
		}

		o.Client, err = opcua.NewClient(o.Config.Endpoint, o.opts...)
		if err != nil {
			return &EndpointError{
				Endpoint: o.Config.Endpoint,
				Err:      fmt.Errorf("%w: failed to create client: %w", ErrConnectionFailed, err),
			}
		}
		ctx, cancel := context.WithTimeout(context.Background(), time.Duration(o.Config.ConnectTimeout))
		defer cancel()
		if err := o.Client.Connect(ctx); err != nil {
			return &EndpointError{
				Endpoint: o.Config.Endpoint,
				Err:      fmt.Errorf("%w: %w", ErrConnectionFailed, err),
			}
		}
		o.Log.Debug("Connected to OPC UA Server")

	default:
		return &EndpointError{
			Endpoint: o.Config.Endpoint,
			Err:      fmt.Errorf("%w: unsupported scheme %q, expected opc.tcp", ErrInvalidEndpoint, u.Scheme),
		}
	}
	return nil
}

func (o *OpcUAClient) Disconnect(ctx context.Context) error {
	o.Log.Debug("Disconnecting from OPC UA Server")
	u, err := url.Parse(o.Config.Endpoint)
	if err != nil {
		return &EndpointError{
			Endpoint: o.Config.Endpoint,
			Err:      fmt.Errorf("%w: %w", ErrInvalidEndpoint, err),
		}
	}

	switch u.Scheme {
	case "opc.tcp":
		// We can't do anything about failing to close a connection
		err := o.Client.Close(ctx)
		o.Client = nil
		if err != nil {
			return fmt.Errorf("failed to close connection to %s: %w", o.Config.Endpoint, err)
		}
		return nil
	default:
		return &EndpointError{
			Endpoint: o.Config.Endpoint,
			Err:      fmt.Errorf("%w: unsupported scheme %q", ErrInvalidEndpoint, u.Scheme),
		}
	}
}

func (o *OpcUAClient) State() ConnectionState {
	if o.Client == nil {
		return Disconnected
	}
	return ConnectionState(o.Client.State())
}

// UpdateNamespaceArray fetches the namespace array from the OPC UA server
// The namespace array is stored at the well-known node ns=0;i=2255
func (o *OpcUAClient) UpdateNamespaceArray(ctx context.Context) error {
	if o.Client == nil {
		return errors.New("client not connected")
	}

	nodeID := ua.NewNumericNodeID(0, 2255)
	req := &ua.ReadRequest{
		MaxAge: 2000,
		NodesToRead: []*ua.ReadValueID{
			{NodeID: nodeID},
		},
		TimestampsToReturn: ua.TimestampsToReturnBoth,
	}

	resp, err := o.Client.Read(ctx, req)
	if err != nil {
		return fmt.Errorf("failed to read namespace array: %w", err)
	}

	if len(resp.Results) == 0 {
		return errors.New("no results returned when reading namespace array")
	}

	result := resp.Results[0]
	if result.Status != ua.StatusOK {
		return fmt.Errorf("failed to read namespace array, status: %w", result.Status)
	}

	if result.Value == nil {
		return errors.New("namespace array value is nil")
	}

	// The namespace array is an array of strings
	namespaces, ok := result.Value.Value().([]string)
	if !ok {
		return fmt.Errorf("namespace array is not a string array, got type: %T", result.Value.Value())
	}

	o.namespaceArray = namespaces
	o.Log.Debugf("Fetched namespace array with %d entries", len(namespaces))
	return nil
}

// NamespaceArray returns the cached namespace array
func (o *OpcUAClient) NamespaceArray() []string {
	return o.namespaceArray
}
