package handlers

import (
	"encoding/base64"
	"errors"
	"platform/web/models"
	q "platform/web/queries"
	"platform/web/services"
	"strings"
	"time"

	"github.com/gofiber/fiber/v2"
	"golang.org/x/crypto/bcrypt"
	"gorm.io/gorm"
)

// region Token

type TokenReq struct {
	ClientID     string         `json:"client_id" form:"client_id"`
	ClientSecret string         `json:"client_secret" form:"client_secret"`
	GrantType    TokenGrantType `json:"grant_type" form:"grant_type"`
	Code         string         `json:"code" form:"code"`
	RedirectURI  string         `json:"redirect_uri" form:"redirect_uri"`
	CodeVerifier string         `json:"code_verifier" form:"code_verifier"`
	RefreshToken string         `json:"refresh_token" form:"refresh_token"`
	Scope        string         `json:"scope" form:"scope"`
}

type TokenResp struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token,omitempty"`
	TokenType    string `json:"token_type"`
	Scope        string `json:"scope,omitempty"`
	ExpiresIn    int    `json:"expires_in"`
}

type TokenErrResp struct {
	Error       string `json:"error"`
	Description string `json:"error_description,omitempty"`
}

type TokenGrantType string

const (
	AuthorizationCode = TokenGrantType("authorization_code")
	ClientCredentials = TokenGrantType("client_credentials")
	RefreshToken      = TokenGrantType("refresh_token")
)

// Token 处理 OAuth2.0 授权请求
func Token(c *fiber.Ctx) error {

	// 验证请求参数
	req := new(TokenReq)
	if err := c.BodyParser(req); err != nil {
		return sendError(c, services.ErrOauthInvalidRequest, "无法解析请求参数")
	}
	if req.GrantType == "" {
		return sendError(c, services.ErrOauthInvalidRequest, "缺少必要参数：grant_type")
	}

	// 基于授权类型处理请求
	switch req.GrantType {

	case AuthorizationCode:
		return authorizationCode(c, req)

	case ClientCredentials:
		return clientCredentials(c, req)

	case RefreshToken:
		return refreshToken(c, req)

	default:
		return sendError(c, services.ErrOauthUnsupportedGrantType)
	}
}

// 授权码
func authorizationCode(c *fiber.Ctx, req *TokenReq) error {
	if req.Code == "" {
		return sendError(c, services.ErrOauthInvalidRequest, "缺少必要参数：code")
	}

	client, err := protect(c, services.GrantTypeAuthorizationCode, req.ClientID, req.ClientSecret)
	if err != nil {
		return sendError(c, err)
	}

	token, err := services.Auth.OauthAuthorizationCode(c.Context(), client, req.Code, req.RedirectURI, req.CodeVerifier)
	if err != nil {
		return sendError(c, err.(services.AuthServiceOauthError))
	}

	return sendSuccess(c, token)
}

// 客户端凭证
func clientCredentials(c *fiber.Ctx, req *TokenReq) error {
	client, err := protect(c, services.GrantTypeClientCredentials, req.ClientID, req.ClientSecret)
	if err != nil {
		return sendError(c, err)
	}

	scope := strings.Split(req.Scope, ",")
	token, err := services.Auth.OauthClientCredentials(c.Context(), client, scope...)
	if err != nil {
		return sendError(c, err.(services.AuthServiceOauthError))
	}

	return sendSuccess(c, token)
}

// 刷新令牌
func refreshToken(c *fiber.Ctx, req *TokenReq) error {
	if req.RefreshToken == "" {
		return sendError(c, services.ErrOauthInvalidRequest, "缺少必要参数：refresh_token")
	}

	client, err := protect(c, services.GrantTypeRefreshToken, req.ClientID, req.ClientSecret)
	if err != nil {
		return sendError(c, err)
	}

	scope := strings.Split(req.Scope, ",")
	token, err := services.Auth.OauthRefreshToken(c.Context(), client, req.RefreshToken, scope)
	if err != nil {
		return sendError(c, err.(services.AuthServiceOauthError))
	}

	return sendSuccess(c, token)
}

// 检查客户端凭证
func protect(c *fiber.Ctx, grant services.GrantType, clientId, clientSecret string) (*models.Client, error) {
	header := c.Get("Authorization")
	if header != "" {
		basic := strings.TrimPrefix(header, "Basic ")
		if basic != "" {
			base, err := base64.URLEncoding.DecodeString(basic)
			if err != nil {
				return nil, err
			}
			parts := strings.SplitN(string(base), ":", 2)
			if len(parts) == 2 {
				clientId = parts[0]
				clientSecret = parts[1]
			}
		}
	}

	// 查找客户端
	if clientId == "" {
		return nil, services.ErrOauthInvalidRequest
	}
	client, err := q.Client.Where(q.Client.ClientID.Eq(clientId)).Take()
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil, services.ErrOauthInvalidClient
		}
		return nil, err
	}

	// 验证客户端状态
	if client.Status != 1 {
		return nil, services.ErrOauthUnauthorizedClient
	}

	// 验证授权类型
	switch grant {
	case services.GrantTypeAuthorizationCode:
		if !client.GrantCode {
			return nil, services.ErrOauthUnauthorizedClient
		}
	case services.GrantTypeClientCredentials:
		if !client.GrantClient || client.Spec != 0 {
			return nil, services.ErrOauthUnauthorizedClient
		}
	case services.GrantTypeRefreshToken:
		if !client.GrantRefresh {
			return nil, services.ErrOauthUnauthorizedClient
		}
	}

	// 如果客户端是 confidential，验证 client_secret，失败返回错误
	if client.Spec == 0 {
		if clientSecret == "" {
			return nil, services.ErrOauthInvalidRequest
		}
		if bcrypt.CompareHashAndPassword([]byte(client.ClientSecret), []byte(clientSecret)) != nil {
			return nil, services.ErrOauthInvalidClient
		}
	}

	return client, nil
}

// 发送成功响应
func sendSuccess(c *fiber.Ctx, details *services.TokenDetails) error {
	return c.JSON(TokenResp{
		AccessToken:  details.AccessToken,
		TokenType:    "Bearer",
		ExpiresIn:    int(time.Until(details.AccessTokenExpires).Seconds()),
		RefreshToken: details.RefreshToken,
	})
}

// 发送错误响应
func sendError(c *fiber.Ctx, err error, description ...string) error {
	var sErr services.AuthServiceOauthError
	if errors.As(err, &sErr) {
		status := fiber.StatusBadRequest
		var desc string
		switch {
		case errors.Is(sErr, services.ErrOauthInvalidRequest):
			desc = "无效的请求"
		case errors.Is(sErr, services.ErrOauthInvalidClient):
			status = fiber.StatusUnauthorized
			desc = "无效的客户端凭证"
		case errors.Is(sErr, services.ErrOauthInvalidGrant):
			desc = "无效的授权凭证"
		case errors.Is(sErr, services.ErrOauthInvalidScope):
			desc = "无效的授权范围"
		case errors.Is(sErr, services.ErrOauthUnauthorizedClient):
			desc = "未授权的客户端"
		case errors.Is(sErr, services.ErrOauthUnsupportedGrantType):
			desc = "不支持的授权类型"
		}
		if len(description) > 0 {
			desc = description[0]
		}

		return c.Status(status).JSON(TokenErrResp{
			Error:       string(sErr),
			Description: desc,
		})
	}

	return err
}

// endregion