exchange-monitor-go/exchange/bitget_trade.go

package exchange

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"strings"
	"time"
)

// BitgetTrade handles order placement on Bitget.
type BitgetTrade struct {
	APIKey     string
	APISecret  string
	Passphrase string
	client     *http.Client
}

func NewBitgetTrade(apiKey, apiSecret, passphrase string) *BitgetTrade {
	return &BitgetTrade{
		APIKey:     apiKey,
		APISecret:  apiSecret,
		Passphrase: passphrase,
		client:     &http.Client{Timeout: 10 * time.Second},
	}
}

// PlaceMarketOrder places a market order on Bitget.
// side: "buy" or "sell"
// symbol: "BTCUSDT" (we use UMCBL perpetual)
// size: contract size in coin units (e.g. 0.001 for BTC)
func (b *BitgetTrade) PlaceMarketOrder(side, symbol, size string) (string, error) {
	ts := fmt.Sprintf("%d", time.Now().UnixMilli())
	method := "POST"
	requestPath := "/api/v2/mix/order/place"

	body := map[string]interface{}{
		"symbol":      symbol + "_UMCBL",
		"marginCoin":  "USDT",
		"side":        side,
		"orderType":   "market",
		"size":        size,
		"timeInForce": "IOC", // immediate-or-cancel for market orders
	}
	bodyJSON, _ := json.Marshal(body)

	sign := b.sign(method, requestPath, ts, string(bodyJSON))

	url := "https://api.bitget.com" + requestPath
	req, err := http.NewRequest(method, url, strings.NewReader(string(bodyJSON)))
	if err != nil {
		return "", fmt.Errorf("create request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	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)

	resp, err := b.client.Do(req)
	if err != nil {
		return "", 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 {
			OrderID string `json:"orderId"`
		} `json:"data"`
	}
	if err := json.Unmarshal(respBody, &result); err != nil {
		return "", fmt.Errorf("parse response: %s", string(respBody))
	}
	if result.Code != "00000" {
		return "", fmt.Errorf("bitget error: %s - %s", result.Code, result.Msg)
	}
	return result.Data.OrderID, nil
}

func (b *BitgetTrade) sign(method, requestPath, timestamp, body string) string {
	raw := timestamp + method + requestPath + body
	mac := hmac.New(sha256.New, []byte(b.APISecret))
	mac.Write([]byte(raw))
	return base64.StdEncoding.EncodeToString(mac.Sum(nil))
}

// 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.
// Uses math.Floor to round DOWN to the nearest valid step (B#5: prevent rounding up).
func GetBitgetSize(symbol string, amountUSD, price float64) string {
	if amountUSD < 5 {
		amountUSD = 5 // Bitget minimum notional
	}
	sz := amountUSD / price // raw coin count

	switch symbol {
	case "DOGEUSDT":
		if sz < 1 {
			sz = 1
		}
		sz = math.Floor(sz) // step=1
		return fmt.Sprintf("%.0f", sz) // minTradeNum=1, sizeMultiplier=1
	case "LINKUSDT":
		if sz < 1 {
			sz = 1
		}
		sz = math.Floor(sz) // step=1
		return fmt.Sprintf("%.0f", sz) // minTradeNum=1, sizeMultiplier=1
	case "ONDOUSDT":
		sz = math.Floor(sz*10) / 10 // step=0.1
		if sz < 0.1 {
			sz = 0.1
		}
		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
	case "OPUSDT":
		sz = math.Floor(sz*10) / 10 // step=0.1
		if sz < 0.1 {
			sz = 0.1
		}
		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
	case "WIFUSDT":
		sz = math.Floor(sz*10) / 10 // step=0.1
		if sz < 0.1 {
			sz = 0.1
		}
		return fmt.Sprintf("%.1f", sz) // minTradeNum=0.1, sizeMultiplier=0.1
	case "ARBUSDT":
		sz = math.Floor(sz*100) / 100 // step=0.01
		if sz < 0.01 {
			sz = 0.01
		}
		return fmt.Sprintf("%.2f", sz) // minTradeNum=0.01, sizeMultiplier=0.01
	default:
		return fmt.Sprintf("%.4f", sz)
	}
}