handle stock split

internal/filler.go

@@ -9,19 +9,27 @@ import (
 type Filler struct {
 	Record
 
-	filled decimal.Decimal
+	filled   decimal.Decimal
+	quantity decimal.Decimal
+	price    decimal.Decimal
 }
 
 func NewFiller(r Record) *Filler {
 	return &Filler{
-		Record: r,
+		Record:   r,
+		quantity: r.Quantity(),
+		price:    r.Price(),
 	}
 }
 
+func (f *Filler) Quantity() decimal.Decimal { return f.quantity }
+
+func (f *Filler) Price() decimal.Decimal { return f.price }
+
 // Fill accrues some quantity. Returns how mutch was accrued in the 1st return value and whether
 // it was filled or not on the 2nd return value.
 func (f *Filler) Fill(quantity decimal.Decimal) (decimal.Decimal, bool) {
-	unfilled := f.Record.Quantity().Sub(f.filled)
+	unfilled := f.quantity.Sub(f.filled)
 	delta := decimal.Min(unfilled, quantity)
 	f.filled = f.filled.Add(delta)
 	return delta, f.IsFilled()
@@ -29,7 +37,15 @@ func (f *Filler) Fill(quantity decimal.Decimal) (decimal.Decimal, bool) {
 
 // IsFilled returns true if the fill is equal to the record quantity.
 func (f *Filler) IsFilled() bool {
-	return f.filled.Equal(f.Quantity())
+	return f.filled.Equal(f.quantity)
+}
+
+// ApplySplit adjusts the lot for a stock split by the given ratio (newQty/oldQty).
+// The total cost basis is preserved: quantity scales up, price scales down proportionally.
+func (f *Filler) ApplySplit(ratio decimal.Decimal) {
+	f.quantity = f.quantity.Mul(ratio)
+	f.filled = f.filled.Mul(ratio)
+	f.price = f.price.Div(ratio)
 }
 
 type FillerQueue struct {
@@ -86,6 +102,16 @@ func (fq *FillerQueue) frontElement() *list.Element {
 	return fq.l.Front()
 }
 
+// AdjustForSplit applies a stock split ratio to all lots in the queue.
+func (fq *FillerQueue) AdjustForSplit(ratio decimal.Decimal) {
+	if fq == nil || fq.l == nil {
+		return
+	}
+	for e := fq.l.Front(); e != nil; e = e.Next() {
+		e.Value.(*Filler).ApplySplit(ratio)
+	}
+}
+
 // Len returns how many elements are currently on the queue
 func (fq *FillerQueue) Len() int {
 	if fq == nil || fq.l == nil {