//
// Copyright (C) 2024 veypi <i@veypi.com>
// 2025-07-24 15:27:31
// Distributed under terms of the MIT license.
//

package oauth

import (
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"github.com/veypi/OneAuth/cfg"
	"github.com/vyes-ai/vigo"
	"golang.org/x/crypto/bcrypt"
	"gorm.io/gorm"
	"time"
)

// TokenRequest 令牌请求参数
type TokenRequest struct {
	GrantType    string `form:"grant_type" binding:"required"`
	Code         string `form:"code"`
	RedirectURI  string `form:"redirect_uri"`
	ClientID     string `form:"client_id"`
	ClientSecret string `form:"client_secret"`
	RefreshToken string `form:"refresh_token"`
	CodeVerifier string `form:"code_verifier"`
	Username     string `form:"username"` // for password grant
	Password     string `form:"password"` // for password grant
	Scope        string `form:"scope"`    // for password grant
}

// TokenResponse 令牌响应
type TokenResponse struct {
	AccessToken  string `json:"access_token"`
	TokenType    string `json:"token_type"`
	ExpiresIn    int64  `json:"expires_in"`
	RefreshToken string `json:"refresh_token,omitempty"`
	Scope        string `json:"scope,omitempty"`
}

// handleToken 处理OAuth令牌请求
func handleToken(x *vigo.X) error {
	args := &TokenRequest{}
	if err := x.Parse(args); err != nil {
		return vigo.NewError("参数解析失败").WithError(err).WithCode(400)
	}

	db := cfg.DB()

	switch args.GrantType {
	case GrantTypeAuthorizationCode:
		return handleAuthorizationCodeGrant(db, x, args)
	case GrantTypeRefreshToken:
		return handleRefreshTokenGrant(db, x, args)
	case GrantTypePassword:
		return handlePasswordGrant(db, x, args)
	default:
		return vigo.NewError("不支持的授权类型").WithCode(400)
	}
}

// handleAuthorizationCodeGrant 处理授权码授权类型
func handleAuthorizationCodeGrant(db *gorm.DB, x *vigo.X, args *TokenRequest) error {
	// 1. 验证授权码
	var authCode OAuthAuthorizationCode
	if err := db.Where("code = ? AND used = ?", args.Code, false).First(&authCode).Error; err != nil {
		return vigo.NewError("无效的授权码").WithCode(400)
	}

	// 2. 检查授权码是否过期
	if authCode.IsExpired() {
		return vigo.NewError("授权码已过期").WithCode(400)
	}

	// 3. 验证客户端
	var client OAuthClient
	if err := db.Where("id = ? AND client_id = ?", authCode.ClientID, args.ClientID).First(&client).Error; err != nil {
		return vigo.NewError("无效的客户端").WithCode(400)
	}

	// 4. 验证客户端密钥（对于机密客户端）
	if !client.IsPublic && client.ClientSecret != args.ClientSecret {
		return vigo.NewError("无效的客户端凭据").WithCode(400)
	}

	// 5. 验证重定向URI
	if authCode.RedirectURI != args.RedirectURI {
		return vigo.NewError("重定向URI不匹配").WithCode(400)
	}

	// 6. 验证PKCE（如果使用）
	if authCode.CodeChallenge != "" {
		if err := validatePKCE(authCode.CodeChallenge, authCode.CodeChallengeMethod, args.CodeVerifier); err != nil {
			return vigo.NewError("PKCE验证失败").WithError(err).WithCode(400)
		}
	}

	// 7. 标记授权码为已使用
	if err := db.Model(&authCode).Update("used", true).Error; err != nil {
		return vigo.NewError("授权码更新失败").WithError(err).WithCode(500)
	}

	// 8. 生成访问令牌
	accessToken, err := generateAccessToken(db, &client, authCode.UserID, authCode.Scope)
	if err != nil {
		return vigo.NewError("访问令牌生成失败").WithError(err).WithCode(500)
	}

	// 9. 生成刷新令牌
	refreshToken, err := generateRefreshToken(db, accessToken, &client, authCode.UserID, authCode.Scope)
	if err != nil {
		return vigo.NewError("刷新令牌生成失败").WithError(err).WithCode(500)
	}

	return x.JSON(&TokenResponse{
		AccessToken:  accessToken.Token,
		TokenType:    TokenTypeBearer,
		ExpiresIn:    int64(DefaultAccessTokenExpiry.Seconds()),
		RefreshToken: refreshToken.Token,
		Scope:        authCode.Scope,
	})
}

// handleRefreshTokenGrant 处理刷新令牌授权类型
func handleRefreshTokenGrant(db *gorm.DB, x *vigo.X, args *TokenRequest) error {
	// 1. 验证刷新令牌
	var refreshToken OAuthRefreshToken
	if err := db.Where("token = ? AND revoked = ?", args.RefreshToken, false).First(&refreshToken).Error; err != nil {
		return vigo.NewError("无效的刷新令牌").WithCode(400)
	}

	// 2. 检查刷新令牌是否过期
	if refreshToken.IsExpired() {
		return vigo.NewError("刷新令牌已过期").WithCode(400)
	}

	// 3. 验证客户端
	var client OAuthClient
	if err := db.Where("id = ? AND client_id = ?", refreshToken.ClientID, args.ClientID).First(&client).Error; err != nil {
		return vigo.NewError("无效的客户端").WithCode(400)
	}

	// 4. 撤销旧的访问令牌
	if err := db.Model(&OAuthAccessToken{}).Where("id = ?", refreshToken.AccessTokenID).Update("revoked", true).Error; err != nil {
		return vigo.NewError("旧令牌撤销失败").WithError(err).WithCode(500)
	}

	// 5. 生成新的访问令牌
	accessToken, err := generateAccessToken(db, &client, refreshToken.UserID, refreshToken.Scope)
	if err != nil {
		return vigo.NewError("访问令牌生成失败").WithError(err).WithCode(500)
	}

	// 6. 更新刷新令牌关联
	if err := db.Model(&refreshToken).Update("access_token_id", accessToken.ID).Error; err != nil {
		return vigo.NewError("刷新令牌更新失败").WithError(err).WithCode(500)
	}

	return x.JSON(&TokenResponse{
		AccessToken:  accessToken.Token,
		TokenType:    TokenTypeBearer,
		ExpiresIn:    int64(DefaultAccessTokenExpiry.Seconds()),
		RefreshToken: refreshToken.Token,
		Scope:        refreshToken.Scope,
	})
}

// handlePasswordGrant 处理密码授权类型
func handlePasswordGrant(db *gorm.DB, x *vigo.X, args *TokenRequest) error {
	// 1. 验证必要参数
	if args.Username == "" || args.Password == "" {
		return vigo.NewError("用户名和密码不能为空").WithCode(400)
	}

	// 2. 验证客户端
	var client OAuthClient
	if err := db.Where("client_id = ?", args.ClientID).First(&client).Error; err != nil {
		return vigo.NewError("无效的客户端").WithCode(400)
	}

	// 3. 验证客户端密钥（对于机密客户端）
	if !client.IsPublic && client.ClientSecret != args.ClientSecret {
		return vigo.NewError("无效的客户端凭据").WithCode(400)
	}

	// 4. 验证用户凭据
	var user User
	if err := db.Where("username = ?", args.Username).First(&user).Error; err != nil {
		return vigo.NewError("用户名或密码错误").WithCode(400)
	}

	// 5. 验证密码
	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(args.Password)); err != nil {
		return vigo.NewError("用户名或密码错误").WithCode(400)
	}

	// 6. 处理权限范围
	scope := args.Scope
	if scope == "" {
		// scope = DefaultScope // 默认权限范围
	}

	// 7. 生成访问令牌
	accessToken, err := generateAccessToken(db, &client, user.ID, scope)
	if err != nil {
		return vigo.NewError("访问令牌生成失败").WithError(err).WithCode(500)
	}

	// 8. 生成刷新令牌
	refreshToken, err := generateRefreshToken(db, accessToken, &client, user.ID, scope)
	if err != nil {
		return vigo.NewError("刷新令牌生成失败").WithError(err).WithCode(500)
	}

	return x.JSON(&TokenResponse{
		AccessToken:  accessToken.Token,
		TokenType:    TokenTypeBearer,
		ExpiresIn:    int64(DefaultAccessTokenExpiry.Seconds()),
		RefreshToken: refreshToken.Token,
		Scope:        scope,
	})
}

// 辅助函数

func generateAccessToken(db *gorm.DB, client *OAuthClient, userID, scope string) (*OAuthAccessToken, error) {
	token, err := generateRandomString(64)
	if err != nil {
		return nil, err
	}

	accessToken := &OAuthAccessToken{
		Token:     token,
		ClientID:  client.ID,
		UserID:    userID,
		Scope:     scope,
		ExpiresAt: time.Now().Add(DefaultAccessTokenExpiry),
		Revoked:   false,
	}

	if err := db.Create(accessToken).Error; err != nil {
		return nil, err
	}

	return accessToken, nil
}

func generateRefreshToken(db *gorm.DB, accessToken *OAuthAccessToken, client *OAuthClient, userID, scope string) (*OAuthRefreshToken, error) {
	token, err := generateRandomString(64)
	if err != nil {
		return nil, err
	}

	refreshToken := &OAuthRefreshToken{
		Token:         token,
		AccessTokenID: accessToken.ID,
		ClientID:      client.ID,
		UserID:        userID,
		Scope:         scope,
		ExpiresAt:     time.Now().Add(DefaultRefreshTokenExpiry),
		Revoked:       false,
	}

	if err := db.Create(refreshToken).Error; err != nil {
		return nil, err
	}

	return refreshToken, nil
}

func validatePKCE(codeChallenge, method, codeVerifier string) error {
	if codeVerifier == "" {
		return fmt.Errorf("code verifier required")
	}

	switch method {
	case CodeChallengeMethodPlain:
		if codeChallenge != codeVerifier {
			return fmt.Errorf("invalid code verifier")
		}
	case CodeChallengeMethodS256:
		h := sha256.Sum256([]byte(codeVerifier))
		expected := base64.RawURLEncoding.EncodeToString(h[:])
		if codeChallenge != expected {
			return fmt.Errorf("invalid code verifier")
		}
	default:
		return fmt.Errorf("unsupported code challenge method")
	}

	return nil
}