package service

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

const weChatCode2SessionURL = "https://api.weixin.qq.com/sns/jscode2session"
const weChatAccessTokenURL = "https://api.weixin.qq.com/cgi-bin/token"
const weChatGetWXACodeURL = "https://api.weixin.qq.com/wxa/getwxacode"

// 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"`
}

type weChatAccessTokenResponse struct {
	AccessToken string `json:"access_token"`
	ExpiresIn   int    `json:"expires_in"`
	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
}

func (c *WeChatClient) GetAccessToken(ctx context.Context) (string, error) {
	query := url.Values{}
	query.Set("grant_type", "client_credential")
	query.Set("appid", c.appID)
	query.Set("secret", c.appSecret)

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

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

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

	var raw weChatAccessTokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return "", fmt.Errorf("decode access token response: %w", err)
	}
	if raw.ErrCode != 0 {
		return "", &WeChatError{Code: raw.ErrCode, Msg: raw.ErrMsg}
	}
	if raw.AccessToken == "" {
		return "", fmt.Errorf("wechat access token missing")
	}
	return raw.AccessToken, nil
}

type getWXACodeRequest struct {
	Path      string `json:"path"`
	Width     int    `json:"width,omitempty"`
	AutoColor bool   `json:"auto_color"`
	IsHyaline bool   `json:"is_hyaline"`
}

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

func (c *WeChatClient) GetWXACode(ctx context.Context, path string, width int) ([]byte, error) {
	accessToken, err := c.GetAccessToken(ctx)
	if err != nil {
		return nil, err
	}

	body, err := json.Marshal(getWXACodeRequest{
		Path:      path,
		Width:     width,
		AutoColor: false,
		IsHyaline: true,
	})
	if err != nil {
		return nil, fmt.Errorf("marshal getwxacode request: %w", err)
	}

	req, err := http.NewRequestWithContext(
		ctx,
		http.MethodPost,
		fmt.Sprintf("%s?access_token=%s", weChatGetWXACodeURL, url.QueryEscape(accessToken)),
		bytes.NewReader(body),
	)
	if err != nil {
		return nil, fmt.Errorf("build getwxacode request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

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

	payload, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read getwxacode response: %w", err)
	}
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("wechat getwxacode api unexpected status: %s", resp.Status)
	}

	var apiErr weChatAPIErrorResponse
	if err := json.Unmarshal(payload, &apiErr); err == nil && apiErr.ErrCode != 0 {
		return nil, &WeChatError{Code: apiErr.ErrCode, Msg: apiErr.ErrMsg}
	}

	return payload, nil
}