// Library for I2Ps SAMv3 bridge (https://geti2p.com)
package sam3

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"math/rand"
	"net"
	"os"
	"strings"

	"github.com/sirupsen/logrus"

	"github.com/go-i2p/i2pkeys"
	"github.com/go-i2p/sam3/common"
	logger "github.com/go-i2p/sam3/log"
)

func init() {
	logger.InitializeSAM3Logger()
}

// Used for controlling I2Ps SAMv3.
// This implements the "Control Socket" for all connections.
type SAM struct {
	address   string
	conn      net.Conn
	keys      *i2pkeys.I2PKeys
	sigType   int
	formatter *common.SAMFormatter
	version   common.Version
	SAMEmit
	*SAMResolver
}

const (
	session_OK             = "SESSION STATUS RESULT=OK DESTINATION="
	session_DUPLICATE_ID   = "SESSION STATUS RESULT=DUPLICATED_ID\n"
	session_DUPLICATE_DEST = "SESSION STATUS RESULT=DUPLICATED_DEST\n"
	session_INVALID_KEY    = "SESSION STATUS RESULT=INVALID_KEY\n"
	session_I2P_ERROR      = "SESSION STATUS RESULT=I2P_ERROR MESSAGE="
)

const (
	Sig_NONE                 = "SIGNATURE_TYPE=EdDSA_SHA512_Ed25519"
	Sig_DSA_SHA1             = "SIGNATURE_TYPE=DSA_SHA1"
	Sig_ECDSA_SHA256_P256    = "SIGNATURE_TYPE=ECDSA_SHA256_P256"
	Sig_ECDSA_SHA384_P384    = "SIGNATURE_TYPE=ECDSA_SHA384_P384"
	Sig_ECDSA_SHA512_P521    = "SIGNATURE_TYPE=ECDSA_SHA512_P521"
	Sig_EdDSA_SHA512_Ed25519 = "SIGNATURE_TYPE=EdDSA_SHA512_Ed25519"
)

var letters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")

func RandString() string {
	n := 4
	b := make([]rune, n)
	for i := range b {
		b[i] = letters[rand.Intn(len(letters))]
	}
	log.WithField("randomString", string(b)).Debug("Generated random string")
	return string(b)
}

// Creates a new controller for the I2P routers SAM bridge.
func NewSAM(address string) (*SAM, error) {
	log.WithField("address", address).Debug("Creating new SAM instance")
	s := SAM{
		address:   address,
		version:   common.SAM31Version,
		formatter: common.NewSAMFormatter(common.SAM31Version.String),
	}
	// TODO: clean this up
	conn, err := net.Dial("tcp", address)
	if err != nil {
		log.WithError(err).Error("Failed to dial SAM address")
		return nil, fmt.Errorf("error dialing to address '%s': %w", address, err)
	}
	if _, err := conn.Write(s.SAMEmit.HelloBytes()); err != nil {
		log.WithError(err).Error("Failed to write hello message")
		conn.Close()
		return nil, fmt.Errorf("error writing to address '%s': %w", address, err)
	}
	/*buf := make([]byte, 256)
	n, err := conn.Read(buf)*/
	reader := bufio.NewReader(conn)
	response, err := reader.ReadString('\n')
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("error reading SAM response: %w", err)
	}
	buf := []byte(response)
	n := len(buf)
	if strings.Contains(string(buf[:n]), "HELLO REPLY RESULT=OK") {
		log.Debug("SAM hello successful")
		s.SAMEmit.I2PConfig.SetSAMAddress(address)
		s.conn = conn
		// s.Config.I2PConfig.DestinationKeys = nil
		s.SAMResolver, err = NewSAMResolver(&s)
		if err != nil {
			log.WithError(err).Error("Failed to create SAM resolver")
			return nil, fmt.Errorf("error creating resolver: %w", err)
		}
		return &s, nil
	} else if string(buf[:n]) == "HELLO REPLY RESULT=NOVERSION\n" {
		log.Error("SAM bridge does not support SAMv3")
		conn.Close()
		return nil, fmt.Errorf("That SAM bridge does not support SAMv3.")
	} else {
		log.WithField("response", string(buf[:n])).Error("Unexpected SAM response")
		conn.Close()
		return nil, fmt.Errorf(string(buf[:n]))
	}
}

func (sam *SAM) Keys() (k *i2pkeys.I2PKeys) {
	// TODO: copy them?
	log.Debug("Retrieving SAM keys")
	k = &sam.SAMEmit.I2PConfig.DestinationKeys
	return
}

// read public/private keys from an io.Reader
func (sam *SAM) ReadKeys(r io.Reader) (err error) {
	log.Debug("Reading keys from io.Reader")
	var keys i2pkeys.I2PKeys
	keys, err = i2pkeys.LoadKeysIncompat(r)
	if err == nil {
		log.Debug("Keys loaded successfully")
		sam.SAMEmit.I2PConfig.DestinationKeys = keys
	}
	log.WithError(err).Error("Failed to load keys")
	return
}

// if keyfile fname does not exist
func (sam *SAM) EnsureKeyfile(fname string) (keys i2pkeys.I2PKeys, err error) {
	log.WithError(err).Error("Failed to load keys")
	if fname == "" {
		// transient
		keys, err = sam.NewKeys()
		if err == nil {
			sam.SAMEmit.I2PConfig.DestinationKeys = keys
			log.WithFields(logrus.Fields{
				"keys": keys,
			}).Debug("Generated new transient keys")
		}
	} else {
		// persistent
		_, err = os.Stat(fname)
		if os.IsNotExist(err) {
			// make the keys
			keys, err = sam.NewKeys()
			if err == nil {
				sam.SAMEmit.I2PConfig.DestinationKeys = keys
				// save keys
				var f io.WriteCloser
				f, err = os.OpenFile(fname, os.O_WRONLY|os.O_CREATE, 0o600)
				if err == nil {
					err = i2pkeys.StoreKeysIncompat(keys, f)
					f.Close()
					log.Debug("Generated and saved new keys")
				}
			}
		} else if err == nil {
			// we haz key file
			var f *os.File
			f, err = os.Open(fname)
			if err == nil {
				keys, err = i2pkeys.LoadKeysIncompat(f)
				if err == nil {
					sam.SAMEmit.I2PConfig.DestinationKeys = keys
					log.Debug("Loaded existing keys from file")
				}
			}
		}
	}
	if err != nil {
		log.WithError(err).Error("Failed to ensure keyfile")
	}
	return
}

// Creates the I2P-equivalent of an IP address, that is unique and only the one
// who has the private keys can send messages from. The public keys are the I2P
// desination (the address) that anyone can send messages to.

// Add constant for recommended sig type
const (
	DEFAULT_SIG_TYPE = "SIGNATURE_TYPE=7" // EdDSA_SHA512_Ed25519
)

func (sam *SAM) NewKeys(sigType ...string) (i2pkeys.I2PKeys, error) {
	log.WithField("sigType", sigType).Debug("Generating new keys")
	if sigType == nil {
		sigType = []string{DEFAULT_SIG_TYPE}
	}
	scmsg := []byte(fmt.Sprintf("DEST GENERATE %s\n", sigType[0]))
	if _, err := sam.conn.Write(scmsg); err != nil {
		log.WithError(err).Error("Failed to write DEST GENERATE command")
		return i2pkeys.I2PKeys{}, fmt.Errorf("error with writing in SAM: %w", err)
	}
	buf := make([]byte, 8192)
	n, err := sam.conn.Read(buf)
	if err != nil {
		log.WithError(err).Error("Failed to read SAM response for key generation")
		return i2pkeys.I2PKeys{}, fmt.Errorf("error with reading in SAM: %w", err)
	}
	s := bufio.NewScanner(bytes.NewReader(buf[:n]))
	s.Split(bufio.ScanWords)

	var pub, priv string
	for s.Scan() {
		text := s.Text()
		if text == "DEST" {
			continue
		} else if text == "REPLY" {
			continue
		} else if strings.HasPrefix(text, "PUB=") {
			pub = text[4:]
		} else if strings.HasPrefix(text, "PRIV=") {
			priv = text[5:]
		} else {
			log.Error("Failed to parse keys from SAM response")
			return i2pkeys.I2PKeys{}, fmt.Errorf("Failed to parse keys.")
		}
	}
	log.Debug("Successfully generated new keys")
	return i2pkeys.NewKeys(i2pkeys.I2PAddr(pub), priv), nil
}

// Performs a lookup, probably this order: 1) routers known addresses, cached
// addresses, 3) by asking peers in the I2P network.
func (sam *SAM) Lookup(name string) (i2pkeys.I2PAddr, error) {
	log.WithField("name", name).Debug("Looking up address")
	return sam.SAMResolver.Resolve(name)
}

// Creates a new session with the style of either "STREAM", "DATAGRAM" or "RAW",
// for a new I2P tunnel with name id, using the cypher keys specified, with the
// I2CP/streaminglib-options as specified. Extra arguments can be specified by
// setting extra to something else than []string{}.
// This sam3 instance is now a session
func (sam *SAM) newGenericSession(style, id string, keys i2pkeys.I2PKeys, options, extras []string) (net.Conn, error) {
	log.WithFields(logrus.Fields{"style": style, "id": id}).Debug("Creating new generic session")
	return sam.newGenericSessionWithSignature(style, id, keys, Sig_NONE, options, extras)
}

func (sam *SAM) newGenericSessionWithSignature(style, id string, keys i2pkeys.I2PKeys, sigType string, options, extras []string) (net.Conn, error) {
	log.WithFields(logrus.Fields{"style": style, "id": id, "sigType": sigType}).Debug("Creating new generic session with signature")
	return sam.newGenericSessionWithSignatureAndPorts(style, id, "0", "0", keys, sigType, options, extras)
}

// Creates a new session with the style of either "STREAM", "DATAGRAM" or "RAW",
// for a new I2P tunnel with name id, using the cypher keys specified, with the
// I2CP/streaminglib-options as specified. Extra arguments can be specified by
// setting extra to something else than []string{}.
// This sam3 instance is now a session
func (sam *SAM) newGenericSessionWithSignatureAndPorts(style, id, from, to string, keys i2pkeys.I2PKeys, sigType string, options, extras []string) (net.Conn, error) {
	log.WithFields(logrus.Fields{"style": style, "id": id, "from": from, "to": to, "sigType": sigType}).Debug("Creating new generic session with signature and ports")

	optStr := GenerateOptionString(options)

	conn := sam.conn
	scmsg := []byte(fmt.Sprintf("SESSION CREATE STYLE=%s FROM_PORT=%s TO_PORT=%s ID=%s DESTINATION=%s %s %s\n", style, from, to, id, keys.String(), optStr, strings.Join(extras, " ")))
	if style == "PRIMARY" || style == "MASTER" {
		scmsg = []byte(fmt.Sprintf("SESSION CREATE STYLE=%s ID=%s DESTINATION=%s %s %s\n", style, id, keys.String(), optStr, strings.Join(extras, " ")))
	}

	log.WithField("message", string(scmsg)).Debug("Sending SESSION CREATE message", string(scmsg))

	for m, i := 0, 0; m != len(scmsg); i++ {
		if i == 15 {
			log.Error("Failed to write SESSION CREATE message after 15 attempts")
			conn.Close()
			return nil, fmt.Errorf("writing to SAM failed")
		}
		n, err := conn.Write(scmsg[m:])
		if err != nil {
			log.WithError(err).Error("Failed to write to SAM connection")
			conn.Close()
			return nil, fmt.Errorf("writing to connection failed: %w", err)
		}
		m += n
	}
	buf := make([]byte, 4096)
	n, err := conn.Read(buf)
	if err != nil {
		log.WithError(err).Error("Failed to read SAM response")
		conn.Close()
		return nil, fmt.Errorf("reading from connection failed: %w", err)
	}
	text := string(buf[:n])
	log.WithField("response", text).Debug("Received SAM response")
	if strings.HasPrefix(text, session_OK) {
		if keys.String() != text[len(session_OK):len(text)-1] {
			log.Error("SAM created a tunnel with different keys than requested")
			conn.Close()
			return nil, fmt.Errorf("SAMv3 created a tunnel with keys other than the ones we asked it for")
		}
		log.Debug("Successfully created new session")
		return conn, nil //&StreamSession{id, conn, keys, nil, sync.RWMutex{}, nil}, nil
	} else if text == session_DUPLICATE_ID {
		log.Error("Duplicate tunnel name")
		conn.Close()
		return nil, fmt.Errorf("Duplicate tunnel name")
	} else if text == session_DUPLICATE_DEST {
		log.Error("Duplicate destination")
		conn.Close()
		return nil, fmt.Errorf("Duplicate destination")
	} else if text == session_INVALID_KEY {
		log.Error("Invalid key for SAM session")
		conn.Close()
		return nil, fmt.Errorf("Invalid key - SAM session")
	} else if strings.HasPrefix(text, session_I2P_ERROR) {
		log.WithField("error", text[len(session_I2P_ERROR):]).Error("I2P error")
		conn.Close()
		return nil, fmt.Errorf("I2P error %s", text[len(session_I2P_ERROR):])
	} else {
		log.WithField("reply", text).Error("Unable to parse SAMv3 reply")
		conn.Close()
		return nil, fmt.Errorf("Unable to parse SAMv3 reply: %s", text)
	}
}

// Close this sam session
func (sam *SAM) Close() error {
	log.Debug("Closing SAM session")
	return sam.conn.Close()
}

// CloseNotify the socket with a QUIT message
func (sam *SAM) CloseNotify() error {
	log.Debug("Quitting SAM session")
	_, err := sam.conn.Write([]byte("QUIT\n"))
	if err != nil {
		return fmt.Errorf("close notification failed: %v", err)
	}
	return nil
}