package services

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"time"

	"github.com/golang-jwt/jwt/v4"
	"gorm.io/gorm"

	"oidc-oauth2-server/models"
)

type OAuthService struct {
	db         *gorm.DB
	keyManager *KeyManager
	tokenTTL   time.Duration
}

type AuthorizeRequest struct {
	ResponseType        string
	ClientID            string
	RedirectURI         string
	Scope               string
	State               string
	CodeChallenge       string
	CodeChallengeMethod string
	Nonce               string
}

type TokenRequest struct {
	GrantType    string
	Code         string
	RedirectURI  string
	ClientID     string
	ClientSecret string
	CodeVerifier string
}

type TokenResponse struct {
	AccessToken  string `json:"access_token"`
	TokenType    string `json:"token_type"`
	ExpiresIn    int    `json:"expires_in"`
	IDToken      string `json:"id_token,omitempty"`
	RefreshToken string `json:"refresh_token,omitempty"`
}

func NewOAuthService(db *gorm.DB) (*OAuthService, error) {
	keyManager, err := NewKeyManager()
	if err != nil {
		return nil, err
	}

	return &OAuthService{
		db:         db,
		keyManager: keyManager,
		tokenTTL:   time.Hour,
	}, nil
}

func (s *OAuthService) ValidateAuthorizeRequest(req *AuthorizeRequest) error {
	if req.ResponseType != "code" {
		return errors.New("unsupported response type")
	}

	client := &models.Client{}
	if err := s.db.First(client, "client_id = ?", req.ClientID).Error; err != nil {
		return errors.New("invalid client")
	}

	// 验证重定向 URI
	var redirectURIs []string
	if err := json.Unmarshal(client.RedirectURIs, &redirectURIs); err != nil {
		return errors.New("invalid redirect URIs format")
	}

	validRedirect := false
	for _, uri := range redirectURIs {
		if uri == req.RedirectURI {
			validRedirect = true
			break
		}
	}
	if !validRedirect {
		return errors.New("invalid redirect URI")
	}

	// 验证 PKCE
	if req.CodeChallenge != "" {
		if req.CodeChallengeMethod != "S256" && req.CodeChallengeMethod != "plain" {
			return errors.New("invalid code challenge method")
		}
		if len(req.CodeChallenge) < 43 || len(req.CodeChallenge) > 128 {
			return errors.New("invalid code challenge length")
		}
	}

	return nil
}

func (s *OAuthService) GenerateAuthorizationCode(userID uint, req *AuthorizeRequest) (*models.AuthorizationCode, error) {
	// 生成随机授权码
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return nil, err
	}
	code := base64.RawURLEncoding.EncodeToString(b)

	authCode := &models.AuthorizationCode{
		Code:                code,
		ClientID:            req.ClientID,
		RedirectURI:         req.RedirectURI,
		UserID:              userID,
		Scope:               req.Scope,
		ExpiresAt:           time.Now().Add(10 * time.Minute),
		Used:                false,
		CodeChallenge:       req.CodeChallenge,
		CodeChallengeMethod: req.CodeChallengeMethod,
		Nonce:               req.Nonce,
	}

	// 保存授权码到数据库
	if err := s.db.Create(authCode).Error; err != nil {
		return nil, err
	}

	return authCode, nil
}

func (s *OAuthService) ExchangeToken(req *TokenRequest) (*TokenResponse, error) {
	// 验证授权码
	authCode := &models.AuthorizationCode{}
	if err := s.db.Where("code = ? AND client_id = ? AND used = ?",
		req.Code, req.ClientID, false).First(authCode).Error; err != nil {
		return nil, errors.New("invalid authorization code")
	}

	// 验证授权码是否过期
	if time.Now().After(authCode.ExpiresAt) {
		return nil, errors.New("authorization code expired")
	}

	// 验证重定向 URI
	if authCode.RedirectURI != req.RedirectURI {
		return nil, errors.New("redirect URI mismatch")
	}

	// 验证 PKCE
	if authCode.CodeChallenge != "" {
		if req.CodeVerifier == "" {
			return nil, errors.New("code verifier required")
		}

		if err := validatePKCE(authCode.CodeChallenge, authCode.CodeChallengeMethod, req.CodeVerifier); err != nil {
			return nil, err
		}
	}

	// 验证客户端
	client := &models.Client{}
	if err := s.db.Where("client_id = ? AND client_secret = ?",
		req.ClientID, req.ClientSecret).First(client).Error; err != nil {
		return nil, errors.New("invalid client credentials")
	}

	// 获取用户信息
	user := &models.User{}
	if err := s.db.First(user, authCode.UserID).Error; err != nil {
		return nil, errors.New("user not found")
	}

	// 生成访问令牌
	accessToken, err := s.generateAccessToken(user, client, authCode.Scope)
	if err != nil {
		return nil, err
	}

	// 生成 ID 令牌
	idToken, err := s.generateIDToken(user, client, authCode.Scope, "")
	if err != nil {
		return nil, err
	}

	// 标记授权码为已使用
	authCode.Used = true
	s.db.Save(authCode)

	return &TokenResponse{
		AccessToken: accessToken,
		TokenType:   "Bearer",
		ExpiresIn:   int(s.tokenTTL.Seconds()),
		IDToken:     idToken,
	}, nil
}

func (s *OAuthService) generateAccessToken(user *models.User, client *models.Client, scope string) (string, error) {
	now := time.Now()
	claims := jwt.MapClaims{
		"sub":   user.ID,
		"exp":   now.Add(s.tokenTTL).Unix(),
		"iat":   now.Unix(),
		"iss":   client.ClientID,
		"scope": scope,
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	return token.SignedString(s.keyManager.GetPrivateKey())
}

func (s *OAuthService) generateIDToken(user *models.User, client *models.Client, scope string, nonce string) (string, error) {
	now := time.Now()
	claims := jwt.MapClaims{
		"iss":            client.ClientID,
		"sub":            fmt.Sprintf("%d", user.ID),
		"aud":            client.ClientID,
		"exp":            now.Add(s.tokenTTL).Unix(),
		"iat":            now.Unix(),
		"auth_time":      now.Unix(),
		"nonce":          nonce,
		"acr":            "1",
		"email":          user.Email,
		"email_verified": true,
		"name":           user.Username,
	}

	token := jwt.NewWithClaims(jwt.SigningMethodRS256, claims)
	token.Header["kid"] = s.keyManager.GetKID()

	return token.SignedString(s.keyManager.GetPrivateKey())
}

func validatePKCE(challenge, method, verifier string) error {
	if len(verifier) < 43 || len(verifier) > 128 {
		return errors.New("invalid code verifier length")
	}

	var computedChallenge string
	if method == "S256" {
		h := sha256.New()
		h.Write([]byte(verifier))
		computedChallenge = base64.RawURLEncoding.EncodeToString(h.Sum(nil))
	} else {
		computedChallenge = verifier
	}

	if computedChallenge != challenge {
		return errors.New("code verifier does not match challenge")
	}

	return nil
}

func (s *OAuthService) GetJWKS() (*JSONWebKeySet, error) {
	return s.keyManager.GetJWKS()
}

func (s *OAuthService) GetKeyManager() *KeyManager {
	return s.keyManager
}