package sharing

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"fmt"
	"io"
	"net/mail"
	"regexp"
	"strings"
)

const shareIDLength = 27

var (
	base62Alphabet = []byte("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
	shareIDPattern = regexp.MustCompile(`^[0-9A-Za-z]{27}$`)
	phonePattern   = regexp.MustCompile(`^\+?[0-9]{6,20}$`)
)

type secureCodec struct {
	aead cipher.AEAD
	rand io.Reader
}

func newSecureCodec(secret string) (*secureCodec, error) {
	secret = strings.TrimSpace(secret)
	if secret == "" {
		return nil, fmt.Errorf("%w: sharing encryption secret is required", ErrInvalidInput)
	}
	key := sha256.Sum256([]byte(secret))
	block, err := aes.NewCipher(key[:])
	if err != nil {
		return nil, err
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	return &secureCodec{aead: aead, rand: rand.Reader}, nil
}

func (c *secureCodec) newShareID() (string, error) {
	result := make([]byte, 0, shareIDLength)
	buffer := make([]byte, 64)
	for len(result) < shareIDLength {
		if _, err := io.ReadFull(c.rand, buffer); err != nil {
			return "", err
		}
		for _, value := range buffer {
			if value >= 248 {
				continue
			}
			result = append(result, base62Alphabet[int(value)%len(base62Alphabet)])
			if len(result) == shareIDLength {
				break
			}
		}
	}
	return string(result), nil
}

func (c *secureCodec) encrypt(value string) ([]byte, error) {
	nonce := make([]byte, c.aead.NonceSize())
	if _, err := io.ReadFull(c.rand, nonce); err != nil {
		return nil, err
	}
	return c.aead.Seal(nonce, nonce, []byte(value), nil), nil
}

func (c *secureCodec) decrypt(value []byte) (string, error) {
	if len(value) < c.aead.NonceSize() {
		return "", fmt.Errorf("%w: encrypted share value is invalid", ErrInvalidInput)
	}
	nonce := value[:c.aead.NonceSize()]
	plaintext, err := c.aead.Open(nil, nonce, value[c.aead.NonceSize():], nil)
	if err != nil {
		return "", err
	}
	return string(plaintext), nil
}

func hashValue(value string) []byte {
	digest := sha256.Sum256([]byte(value))
	return digest[:]
}

func hashID(value []byte) string {
	if len(value) > 16 {
		value = value[:16]
	}
	return hex.EncodeToString(value)
}

func hashesEqual(left []byte, right []byte) bool {
	return len(left) == len(right) && subtle.ConstantTimeCompare(left, right) == 1
}

func validShareID(value string) bool {
	return shareIDPattern.MatchString(value)
}

func normalizeIdentifier(value string) (string, string, error) {
	value = strings.TrimSpace(value)
	if value == "" {
		return "", "", fmt.Errorf("%w: email or phone is required", ErrInvalidInput)
	}
	if strings.Contains(value, "@") {
		address, err := mail.ParseAddress(value)
		if err != nil || !strings.EqualFold(strings.TrimSpace(address.Address), value) {
			return "", "", fmt.Errorf("%w: email is invalid", ErrInvalidInput)
		}
		return "email", strings.ToLower(address.Address), nil
	}
	phone := strings.NewReplacer(" ", "", "-", "", "(", "", ")", "").Replace(value)
	if !phonePattern.MatchString(phone) {
		return "", "", fmt.Errorf("%w: phone is invalid", ErrInvalidInput)
	}
	return "phone", phone, nil
}

func actorIdentifiers(actor Actor) []string {
	seen := make(map[string]struct{})
	appendIdentifier := func(values *[]string, value string) {
		kind, normalized, err := normalizeIdentifier(value)
		if err != nil || kind == "" {
			return
		}
		key := kind + ":" + normalized
		if _, ok := seen[key]; ok {
			return
		}
		seen[key] = struct{}{}
		*values = append(*values, key)
	}
	values := make([]string, 0, 3)
	appendIdentifier(&values, actor.Email)
	appendIdentifier(&values, actor.Phone)
	if strings.TrimSpace(actor.CountryCode) != "" && strings.TrimSpace(actor.Phone) != "" {
		countryCode := strings.TrimPrefix(strings.TrimSpace(actor.CountryCode), "+")
		phone := strings.TrimPrefix(strings.TrimSpace(actor.Phone), "+")
		appendIdentifier(&values, "+"+countryCode+phone)
	}
	return values
}

func ActorOwnsIdentifier(actor Actor, identifier string) bool {
	identifierType, normalized, err := normalizeIdentifier(identifier)
	if err != nil {
		return false
	}
	candidateHash := hashValue(identifierType + ":" + normalized)
	for _, actorIdentifier := range actorIdentifiers(actor) {
		if hashesEqual(candidateHash, hashValue(actorIdentifier)) {
			return true
		}
	}
	return false
}