Add backend foundation and config-driven workbench

backend/internal/platform/wechatmini/client.go

@@ -0,0 +1,120 @@
+package wechatmini
+
+import (
+	"context"
+	"crypto/sha1"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+type Client struct {
+	appID      string
+	appSecret  string
+	devPrefix  string
+	httpClient *http.Client
+}
+
+type Session struct {
+	AppID      string
+	OpenID     string
+	UnionID    string
+	SessionKey string
+}
+
+type code2SessionResponse struct {
+	OpenID     string `json:"openid"`
+	SessionKey string `json:"session_key"`
+	UnionID    string `json:"unionid"`
+	ErrCode    int    `json:"errcode"`
+	ErrMsg     string `json:"errmsg"`
+}
+
+func NewClient(appID, appSecret, devPrefix string) *Client {
+	return &Client{
+		appID:      appID,
+		appSecret:  appSecret,
+		devPrefix:  devPrefix,
+		httpClient: &http.Client{Timeout: 8 * time.Second},
+	}
+}
+
+func (c *Client) ExchangeCode(ctx context.Context, code string) (*Session, error) {
+	code = strings.TrimSpace(code)
+	if code == "" {
+		return nil, fmt.Errorf("wechat code is required")
+	}
+
+	if c.devPrefix != "" && strings.HasPrefix(code, c.devPrefix) {
+		suffix := strings.TrimPrefix(code, c.devPrefix)
+		if suffix == "" {
+			suffix = "default"
+		}
+		return &Session{
+			AppID:   fallbackString(c.appID, "dev-mini-app"),
+			OpenID:  "dev_openid_" + normalizeDevID(suffix),
+			UnionID: "",
+		}, nil
+	}
+
+	if c.appID == "" || c.appSecret == "" {
+		return nil, fmt.Errorf("wechat mini app credentials are not configured")
+	}
+
+	values := url.Values{}
+	values.Set("appid", c.appID)
+	values.Set("secret", c.appSecret)
+	values.Set("js_code", code)
+	values.Set("grant_type", "authorization_code")
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://api.weixin.qq.com/sns/jscode2session?"+values.Encode(), nil)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var parsed code2SessionResponse
+	if err := json.Unmarshal(body, &parsed); err != nil {
+		return nil, err
+	}
+	if parsed.ErrCode != 0 {
+		return nil, fmt.Errorf("wechat code2session failed: %d %s", parsed.ErrCode, parsed.ErrMsg)
+	}
+	if parsed.OpenID == "" {
+		return nil, fmt.Errorf("wechat code2session returned empty openid")
+	}
+
+	return &Session{
+		AppID:      c.appID,
+		OpenID:     parsed.OpenID,
+		UnionID:    parsed.UnionID,
+		SessionKey: parsed.SessionKey,
+	}, nil
+}
+
+func normalizeDevID(value string) string {
+	sum := sha1.Sum([]byte(value))
+	return hex.EncodeToString(sum[:])[:16]
+}
+
+func fallbackString(value, fallback string) string {
+	if value != "" {
+		return value
+	}
+	return fallback
+}