create BookEntries type and add methods

gemini.go

@@ -166,16 +166,6 @@ type TradeVolume struct {
 	SellTakerCount    float64 `json:"sell_taker_count"`
 }
 
-type Book struct {
-	Bids []BookEntry
-	Asks []BookEntry
-}
-
-type BookEntry struct {
-	Price  float64 `json:",string"`
-	Amount float64 `json:",string"`
-}
-
 type CurrentAuction struct {
 	ClosedUntil                  int64   `json:"closed_until_ms"`
 	LastAuctionEid               Id      `json:"last_auction_eid"`

order-book.go

@@ -0,0 +1,85 @@
+package gemini
+
+type Book struct {
+	Bids BookEntries
+	Asks BookEntries
+}
+
+type BookEntries []BookEntry
+
+type BookEntry struct {
+	Price  float64 `json:",string"`
+	Amount float64 `json:",string"`
+}
+
+func (b *BookEntries) Set(price, amount float64) {
+	pos := b.findByPrice(price)
+
+	if pos == -1 {
+		*b = append(*b, BookEntry{
+			Price:  price,
+			Amount: amount,
+		})
+	} else {
+		if amount == 0 {
+			*b = append((*b)[:pos], (*b)[pos+1:]...)
+		} else {
+			(*b)[pos].Amount = amount
+		}
+	}
+}
+
+func (b BookEntries) Lowest() BookEntry {
+
+	var lowest float64
+	var index int
+
+	if len(b) == 0 {
+		return BookEntry{}
+	}
+
+	for idx, entry := range b {
+		if idx == 0 {
+			lowest = entry.Price
+			continue
+		}
+		if entry.Price < lowest {
+			lowest = entry.Price
+			index = idx
+		}
+	}
+
+	return b[index]
+}
+
+func (b BookEntries) Highest() BookEntry {
+
+	var highest float64
+	var index int
+
+	if len(b) == 0 {
+		return BookEntry{}
+	}
+
+	for idx, entry := range b {
+		if idx == 0 {
+			highest = entry.Price
+			continue
+		}
+		if entry.Price > highest {
+			highest = entry.Price
+			index = idx
+		}
+	}
+
+	return b[index]
+}
+
+func (b BookEntries) findByPrice(price float64) int {
+	for idx, entry := range b {
+		if entry.Price == price {
+			return idx
+		}
+	}
+	return -1
+}