// Package wechat 封装微信小程序相关调用（此处为 code2session 实现）。
package wechat

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"net/url"

	"portal-mini-go/internal/pkg/errors"
)

const code2SessionURL = "https://api.weixin.qq.com/sns/jscode2session"

// SessionInfo 是 code2session 返回的会话信息。
type SessionInfo struct {
	OpenID     string
	UnionID    string
	SessionKey string
}

// Client 微信调用客户端。凭证（appid/secret）由调用方按请求传入，
// 不再依赖静态配置，方便后台动态纳管多个小程序。
type Client struct {
	client *http.Client
}

func NewClient() *Client {
	return &Client{client: &http.Client{}}
}

// Code2Session 用 appID + secret + 登录 code 换取 openid / session_key。
func (c *Client) Code2Session(ctx context.Context, appID, secret, code string) (*SessionInfo, error) {
	q := url.Values{}
	q.Set("appid", appID)
	q.Set("secret", secret)
	q.Set("js_code", code)
	q.Set("grant_type", "authorization_code")

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, code2SessionURL+"?"+q.Encode(), nil)
	if err != nil {
		return nil, errors.Wrap(50000, "build wechat request", err)
	}

	resp, err := c.client.Do(req)
	if err != nil {
		return nil, errors.Wrap(50000, "call wechat code2session", err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, errors.Wrap(50000, "read wechat response", err)
	}

	var r struct {
		OpenID     string `json:"openid"`
		UnionID    string `json:"unionid"`
		SessionKey string `json:"session_key"`
		ErrCode    int    `json:"errcode"`
		ErrMsg     string `json:"errmsg"`
	}
	if err := json.Unmarshal(body, &r); err != nil {
		return nil, errors.Wrap(50000, "decode wechat response", err)
	}
	if r.ErrCode != 0 {
		slog.Warn("wechat code2session error", slog.Int("errcode", r.ErrCode), slog.String("errmsg", r.ErrMsg))
		return nil, errors.Wrap(50000, fmt.Sprintf("wechat code2session: %s", r.ErrMsg), nil)
	}

	return &SessionInfo{OpenID: r.OpenID, UnionID: r.UnionID, SessionKey: r.SessionKey}, nil
}