fix: BG paper trading API - tradeSide param, correct host, marginMode

exchange/bitget_trade.go

@@ -9,49 +9,71 @@ import (
 	"io"
 	"math"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 )
 
-// BitgetTrade handles order placement on Bitget.
+// BitgetTrade handles order placement on Bitget (live or paper).
 type BitgetTrade struct {
 	APIKey     string
 	APISecret  string
 	Passphrase string
 	client     *http.Client
+	paperMode  bool
 }
 
+// NewBitgetTrade creates a BitgetTrade. Paper mode is auto-detected
+// from the API key prefix: "bg_" → Bitget paper trading.
 func NewBitgetTrade(apiKey, apiSecret, passphrase string) *BitgetTrade {
 	return &BitgetTrade{
 		APIKey:     apiKey,
 		APISecret:  apiSecret,
 		Passphrase: passphrase,
 		client:     &http.Client{Timeout: 10 * time.Second},
+		paperMode:  strings.HasPrefix(apiKey, "bg_"),
 	}
 }
 
 // PlaceMarketOrder places a market order on Bitget.
 // side: "buy" or "sell"
-// symbol: "BTCUSDT" (we use UMCBL perpetual)
+// symbol: "BTCUSDT" (always without _UMCBL suffix — appended internally for live)
 // size: contract size in coin units (e.g. 0.001 for BTC)
-func (b *BitgetTrade) PlaceMarketOrder(side, symbol, size string) (string, error) {
+// tradeSide: "open" or "close" — only used in paper mode
+func (b *BitgetTrade) PlaceMarketOrder(side, symbol, size, tradeSide string) (string, error) {
 	ts := fmt.Sprintf("%d", time.Now().UnixMilli())
 	method := "POST"
-	requestPath := "/api/v2/mix/order/place"
+
+	var requestPath string
+	var host string
+	if b.paperMode {
+		requestPath = "/api/v2/mix/order/place-order"
+		host = "https://api.bitget.com"
+	} else {
+		requestPath = "/api/v2/mix/order/place"
+		host = "https://api.bitget.com"
+	}
 
 	body := map[string]interface{}{
-		"symbol":      symbol + "_UMCBL",
 		"marginCoin":  "USDT",
 		"side":        side,
 		"orderType":   "market",
-		"size":        size,
 		"timeInForce": "IOC", // immediate-or-cancel for market orders
 	}
+
+	if b.paperMode {
+		body["symbol"] = symbol
+		body["marginMode"] = "crossed"
+		body["tradeSide"] = tradeSide
+	} else {
+		body["symbol"] = symbol + "_UMCBL"
+	}
+
 	bodyJSON, _ := json.Marshal(body)
 
 	sign := b.sign(method, requestPath, ts, string(bodyJSON))
 
-	url := "https://api.bitget.com" + requestPath
+	url := host + requestPath
 	req, err := http.NewRequest(method, url, strings.NewReader(string(bodyJSON)))
 	if err != nil {
 		return "", fmt.Errorf("create request: %w", err)
@@ -61,6 +83,9 @@ func (b *BitgetTrade) PlaceMarketOrder(side, symbol, size string) (string, error
 	req.Header.Set("ACCESS-SIGN", sign)
 	req.Header.Set("ACCESS-TIMESTAMP", ts)
 	req.Header.Set("ACCESS-PASSPHRASE", b.Passphrase)
+	if b.paperMode {
+		req.Header.Set("paptrading", "1")
+	}
 
 	resp, err := b.client.Do(req)
 	if err != nil {
@@ -93,6 +118,66 @@ func (b *BitgetTrade) sign(method, requestPath, timestamp, body string) string {
 	return base64.StdEncoding.EncodeToString(mac.Sum(nil))
 }
 
+// GetBalance queries available balance.
+func (b *BitgetTrade) GetBalance() (float64, error) {
+	ts := fmt.Sprintf("%d", time.Now().UnixMilli())
+	method := "GET"
+
+	var host, requestPath string
+	if b.paperMode {
+		host = "https://api.bitget.com"
+		requestPath = "/api/v2/mix/account/accounts?productType=USDT-FUTURES"
+	} else {
+		host = "https://api.bitget.com"
+		requestPath = "/api/v2/mix/account/accounts?productType=UMCBL"
+	}
+
+	sign := b.sign(method, requestPath, ts, "")
+
+	url := host + requestPath
+	req, err := http.NewRequest(method, url, nil)
+	if err != nil {
+		return 0, fmt.Errorf("create request: %w", err)
+	}
+	req.Header.Set("ACCESS-KEY", b.APIKey)
+	req.Header.Set("ACCESS-SIGN", sign)
+	req.Header.Set("ACCESS-TIMESTAMP", ts)
+	req.Header.Set("ACCESS-PASSPHRASE", b.Passphrase)
+	if b.paperMode {
+		req.Header.Set("paptrading", "1")
+	}
+
+	resp, err := b.client.Do(req)
+	if err != nil {
+		return 0, fmt.Errorf("http request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	respBody, _ := io.ReadAll(resp.Body)
+
+	var result struct {
+		Code string `json:"code"`
+		Msg  string `json:"msg"`
+		Data []struct {
+			MarginCoin string `json:"marginCoin"`
+			Available  string `json:"available"`
+		} `json:"data"`
+	}
+	if err := json.Unmarshal(respBody, &result); err != nil {
+		return 0, fmt.Errorf("parse: %s", string(respBody))
+	}
+	if result.Code != "00000" {
+		return 0, fmt.Errorf("bitget error: %s - %s", result.Code, result.Msg)
+	}
+	for _, acct := range result.Data {
+		if acct.MarginCoin == "USDT" {
+			bal, _ := strconv.ParseFloat(acct.Available, 64)
+			return bal, nil
+		}
+	}
+	return 0, fmt.Errorf("no USDT margin account found")
+}
+
 // GetBitgetSize calculates the contract size for a given USD amount.
 // Returns size as a decimal string complying with Bitget's USDT-FUTURES precision.
 // Enforces the exchange's minimum: minTradeNum contracts AND $5 min notional.