package wechat

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

// Session is the jscode2session result.
type Session struct {
	OpenID     string
	UnionID    string
	SessionKey string
}

// Client exchanges a mini-program js_code for a session.
type Client interface {
	Code2Session(ctx context.Context, code string) (Session, error)
}

// APIClient calls api.weixin.qq.com.
type APIClient struct {
	AppID  string
	Secret string
	HTTP   *http.Client
}

type wxSessionResp struct {
	OpenID     string `json:"openid"`
	SessionKey string `json:"session_key"`
	UnionID    string `json:"unionid"`
	ErrCode    int    `json:"errcode"`
	ErrMsg     string `json:"errmsg"`
}

// Enabled reports whether WeChat credentials are configured.
func (c *APIClient) Enabled() bool {
	return c != nil && strings.TrimSpace(c.AppID) != "" && strings.TrimSpace(c.Secret) != ""
}

// Code2Session implements Client.
func (c *APIClient) Code2Session(ctx context.Context, code string) (Session, error) {
	if !c.Enabled() {
		return Session{}, errors.New("微信登录未配置")
	}
	code = strings.TrimSpace(code)
	if code == "" {
		return Session{}, errors.New("缺少微信登录码")
	}
	q := url.Values{}
	q.Set("appid", c.AppID)
	q.Set("secret", c.Secret)
	q.Set("js_code", code)
	q.Set("grant_type", "authorization_code")
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://api.weixin.qq.com/sns/jscode2session?"+q.Encode(), nil)
	if err != nil {
		return Session{}, err
	}
	cli := c.HTTP
	if cli == nil {
		cli = &http.Client{Timeout: 10 * time.Second}
	}
	resp, err := cli.Do(req)
	if err != nil {
		return Session{}, errors.New("微信服务暂不可用")
	}
	defer resp.Body.Close()
	var body wxSessionResp
	if err := json.NewDecoder(resp.Body).Decode(&body); err != nil {
		return Session{}, errors.New("微信服务暂不可用")
	}
	if body.ErrCode != 0 {
		return Session{}, fmt.Errorf("微信登录失败（%d）", body.ErrCode)
	}
	if body.OpenID == "" || body.SessionKey == "" {
		return Session{}, errors.New("微信登录失败")
	}
	return Session{OpenID: body.OpenID, UnionID: body.UnionID, SessionKey: body.SessionKey}, nil
}