package crypt

import (
	"bytes"
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"io"
	"strconv"
	"strings"

	"github.com/Snider/Core/pkg/core"
	"github.com/Snider/Core/pkg/crypt/lthn"
	"github.com/Snider/Core/pkg/crypt/openpgp"
)

// HandleIPCEvents processes IPC messages for the crypt service.
func (s *Service) HandleIPCEvents(c *core.Core, msg core.Message) error {
	switch msg.(type) {
	case core.ActionServiceStartup:
		// Crypt is stateless, no startup needed.
		return nil
	default:
		if c.App != nil && c.App.Logger != nil {
			c.App.Logger.Debug("Crypt: Unhandled message type", "type", fmt.Sprintf("%T", msg))
		}
	}
	return nil
}

// Options holds configuration for the crypt service.
type Options struct{}

// Service provides cryptographic functions to the application.
type Service struct {
	*core.Runtime[Options]
}

// HashType defines the supported hashing algorithms.
type HashType string

const (
	LTHN   HashType = "lthn"
	SHA512 HashType = "sha512"
	SHA256 HashType = "sha256"
	SHA1   HashType = "sha1"
	MD5    HashType = "md5"
)

// newCryptService contains the common logic for initializing a Service struct.
func newCryptService() (*Service, error) {
	return &Service{}, nil
}

// New is the constructor for static dependency injection.
// It creates a Service instance without initializing the core.Runtime field.
func New() (*Service, error) {
	return newCryptService()
}

// Register is the constructor for dynamic dependency injection (used with core.WithService).
// It creates a Service instance and initializes its core.Runtime field.
func Register(c *core.Core) (any, error) {
	s, err := newCryptService()
	if err != nil {
		return nil, err
	}
	s.Runtime = core.NewRuntime(c, Options{})
	return s, nil
}

// --- Hashing ---

// Hash computes a hash of the payload using the specified algorithm.
func (s *Service) Hash(lib HashType, payload string) string {
	switch lib {
	case LTHN:
		return lthn.Hash(payload)
	case SHA512:
		hash := sha512.Sum512([]byte(payload))
		return hex.EncodeToString(hash[:])
	case SHA1:
		hash := sha1.Sum([]byte(payload))
		return hex.EncodeToString(hash[:])
	case MD5:
		hash := md5.Sum([]byte(payload))
		return hex.EncodeToString(hash[:])
	case SHA256:
		fallthrough
	default:
		hash := sha256.Sum256([]byte(payload))
		return hex.EncodeToString(hash[:])
	}
}

// --- Checksums ---

// Luhn validates a number using the Luhn algorithm.
func (s *Service) Luhn(payload string) bool {
	payload = strings.ReplaceAll(payload, " ", "")
	sum := 0
	isSecond := false
	for i := len(payload) - 1; i >= 0; i-- {
		digit, err := strconv.Atoi(string(payload[i]))
		if err != nil {
			return false // Contains non-digit
		}

		if isSecond {
			digit = digit * 2
			if digit > 9 {
				digit = digit - 9
			}
		}

		sum += digit
		isSecond = !isSecond
	}
	return sum%10 == 0
}

// Fletcher16 computes the Fletcher-16 checksum.
func (s *Service) Fletcher16(payload string) uint16 {
	data := []byte(payload)
	var sum1, sum2 uint16
	for _, b := range data {
		sum1 = (sum1 + uint16(b)) % 255
		sum2 = (sum2 + sum1) % 255
	}
	return (sum2 << 8) | sum1
}

// Fletcher32 computes the Fletcher-32 checksum.
func (s *Service) Fletcher32(payload string) uint32 {
	data := []byte(payload)
	if len(data)%2 != 0 {
		data = append(data, 0)
	}

	var sum1, sum2 uint32
	for i := 0; i < len(data); i += 2 {
		val := binary.LittleEndian.Uint16(data[i : i+2])
		sum1 = (sum1 + uint32(val)) % 65535
		sum2 = (sum2 + sum1) % 65535
	}
	return (sum2 << 16) | sum1
}

// Fletcher64 computes the Fletcher-64 checksum.
func (s *Service) Fletcher64(payload string) uint64 {
	data := []byte(payload)
	if len(data)%4 != 0 {
		padding := 4 - (len(data) % 4)
		data = append(data, make([]byte, padding)...)
	}

	var sum1, sum2 uint64
	for i := 0; i < len(data); i += 4 {
		val := binary.LittleEndian.Uint32(data[i : i+4])
		sum1 = (sum1 + uint64(val)) % 4294967295
		sum2 = (sum2 + sum1) % 4294967295
	}
	return (sum2 << 32) | sum1
}

// --- PGP ---

// EncryptPGP encrypts data for a recipient, optionally signing it.
func (s *Service) EncryptPGP(writer io.Writer, recipientPath, data string, signerPath, signerPassphrase *string) (string, error) {
	var buf bytes.Buffer
	err := openpgp.EncryptPGP(&buf, recipientPath, data, signerPath, signerPassphrase)
	if err != nil {
		return "", err
	}

	// Copy the encrypted data to the original writer.
	if _, err := writer.Write(buf.Bytes()); err != nil {
		return "", err
	}

	return buf.String(), nil
}

// DecryptPGP decrypts a PGP message, optionally verifying the signature.
func (s *Service) DecryptPGP(recipientPath, message, passphrase string, signerPath *string) (string, error) {
	return openpgp.DecryptPGP(recipientPath, message, passphrase, signerPath)
}