package service

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"time"
)

const weChatCode2SessionURL = "https://api.weixin.qq.com/sns/jscode2session"

// WeChatClient 调用微信接口获取 session/openid。
type WeChatClient struct {
	appID     string
	appSecret string
	client    *http.Client
}

type WeChatSession struct {
	OpenID     string `json:"openid"`
	UnionID    string `json:"unionid"`
	SessionKey string `json:"session_key"`
}

type weChatSessionResponse struct {
	WeChatSession
	ErrCode int    `json:"errcode"`
	ErrMsg  string `json:"errmsg"`
}

// WeChatError 表示微信接口级错误。
type WeChatError struct {
	Code int
	Msg  string
}

func (e *WeChatError) Error() string {
	return fmt.Sprintf("wechat error: code=%d msg=%s", e.Code, e.Msg)
}

func NewWeChatClient(appID, appSecret string, client *http.Client) *WeChatClient {
	if client == nil {
		client = &http.Client{
			Timeout: 5 * time.Second,
		}
	}

	return &WeChatClient{
		appID:     appID,
		appSecret: appSecret,
		client:    client,
	}
}

func (c *WeChatClient) Code2Session(ctx context.Context, code string) (*WeChatSession, error) {
	query := url.Values{}
	query.Set("appid", c.appID)
	query.Set("secret", c.appSecret)
	query.Set("js_code", code)
	query.Set("grant_type", "authorization_code")

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, fmt.Sprintf("%s?%s", weChatCode2SessionURL, query.Encode()), nil)
	if err != nil {
		return nil, fmt.Errorf("build wechat request: %w", err)
	}

	resp, err := c.client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("call wechat api: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("wechat api unexpected status: %s", resp.Status)
	}

	var raw weChatSessionResponse
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, fmt.Errorf("decode wechat response: %w", err)
	}

	if raw.ErrCode != 0 {
		return nil, &WeChatError{Code: raw.ErrCode, Msg: raw.ErrMsg}
	}

	return &raw.WeChatSession, nil
}