feature: Add median price

Author: metarsit

internal/route/ticker/handler.go

@@ -6,6 +6,7 @@ import (
 	"log/slog"
 	"math/big"
 	"net/http"
+	"sort"
 	"strings"
 
 	"github.com/gin-gonic/gin"
@@ -66,6 +67,8 @@ func (a *API) GetPrice(c *gin.Context) {
 	switch method {
 	case "average":
 		price, err = a.averagePrice(symbol, exchanges)
+	case "median":
+		price, err = a.medianPrice(symbol, exchanges)
 	default:
 		c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid method"})
 		return
@@ -109,3 +112,26 @@ func (a *API) averagePrice(symbol string, exchanges []string) (*big.Float, error
 
 	return average, nil
 }
+
+func (a *API) medianPrice(symbol string, exchanges []string) (*big.Float, error) {
+	prices := []*big.Float{}
+	for _, exchange := range exchanges {
+		ticker, err := a.store.Get(fmt.Sprintf("%s:%s", exchange, symbol))
+		if err != nil {
+			return nil, fmt.Errorf("ticker not found: %w", err)
+		}
+		prices = append(prices, ticker.Price)
+	}
+
+	sort.Slice(prices, func(i, j int) bool {
+		return prices[i].Cmp(prices[j]) < 0
+	})
+
+	mid := len(prices) / 2
+	if len(prices)%2 == 1 {
+		return prices[mid], nil
+	} else {
+		sum := new(big.Float).Add(prices[mid-1], prices[mid])
+		return new(big.Float).Quo(sum, big.NewFloat(2)), nil
+	}
+}

internal/route/ticker/handler_test.go

@@ -61,3 +61,74 @@ func TestAveragePrice(t *testing.T) {
 		assert.Nil(t, price)
 	})
 }
+
+func TestMedianPrice(t *testing.T) {
+	t.Run("BTCUSDT median price", func(t *testing.T) {
+		memory := storage.NewMemory[connector.TickerUpdate]()
+		api := &API{
+			store: memory,
+		}
+
+		api.store.Store("binance:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10000),
+		})
+		api.store.Store("okx:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10010),
+		})
+		api.store.Store("bybit:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10020),
+		})
+
+		price, err := api.medianPrice("BTCUSDT", []string{"binance", "okx", "bybit"})
+		assert.NoError(t, err)
+		assert.Equal(t, big.NewFloat(10010), price)
+	})
+
+	t.Run("BTCUSDT median price with even number of exchanges", func(t *testing.T) {
+		memory := storage.NewMemory[connector.TickerUpdate]()
+		api := &API{
+			store: memory,
+		}
+
+		api.store.Store("binance:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10000),
+		})
+		api.store.Store("okx:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10010),
+		})
+
+		price, err := api.medianPrice("BTCUSDT", []string{"binance", "okx"})
+		assert.NoError(t, err)
+		assert.Equal(t, big.NewFloat(10005), price)
+	})
+
+	t.Run("Exchange not found", func(t *testing.T) {
+		memory := storage.NewMemory[connector.TickerUpdate]()
+		api := &API{
+			store: memory,
+		}
+
+		api.store.Store("binance:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10000),
+		})
+
+		price, err := api.medianPrice("BTCUSDT", []string{"binance", "okx"})
+		assert.Error(t, err)
+		assert.Nil(t, price)
+	})
+
+	t.Run("Symbol not found", func(t *testing.T) {
+		memory := storage.NewMemory[connector.TickerUpdate]()
+		api := &API{
+			store: memory,
+		}
+
+		api.store.Store("binance:BTCUSDT", connector.TickerUpdate{
+			Price: big.NewFloat(10000),
+		})
+
+		price, err := api.medianPrice("ETHUSDT", []string{"binance"})
+		assert.Error(t, err)
+		assert.Nil(t, price)
+	})
+}